The Risks Of Chikungunya Outbreaks In The United States

 

Credit Wikipedia

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Chikungunya, up until about a decade ago, was a little known mosquito-borne disease first described in Tanganyika in the early 1950s. For the next five decades it was sporadically seen across eastern and central Africa.

 

That is, until 2005, when Chikungunya made a surprise jump to the Indian Ocean island of Réunion. There, it infected nearly 1/3rd of the island’s 770,000 residents (see 2006 EID article Chikungunya Disease Outbreak, Reunion Island) in just a matter of months.

 

Chikungunya typically produces a fever, severe muscle and joint pain, and headaches. The symptoms usually go away after a few weeks, but some patients can sustain permanent disability, and some deaths have been reported.

 

In the eight years since that  jump, `Chik’ has spread further across the Indian Ocean, Southeast Asia, and even briefly into northern Italy.

 

While the virus isn't normally found in Europe, the vector, the Aedes mosquito, is.  All it took was one infected traveler to arrive infected with the virus to start the chain of transmission.

 

 

I told the story several years ago in It's A Smaller World After All, but the short version is that a traveler, returning from India, brought the virus to Italy in 2007 which led to more than 290 cases reported in the province of Ravenna, which is in northeast Italy.

 

The concern is that the same sort of introduction could happen elsewhere in Europe, or here in the United States, just as we saw with West Nile Virus in 1999 (see DVBID: Final West Nile Report For 2012) and with Dengue Fever in 2010 (see MMWR: Dengue Fever In Key West)

 

The two primary mosquito vectors of Chikungunya are the Aedes aegypti and Aedes albopictus (cite WHO FAQ) both of which can be found across many regions of the Americas.

Aedes albopictus (Asian Tiger) Mosquito - Wikipedia

Dark blue: Native range
Dark green: introduced (as of December 2007)

 

The risk is considered great enough that early last year, the CDC and PAHO (Pan American Health Organization) put together a 161-page guide on preparing for the arrival of Chikungunya to the Americas (see Preparedness and Response for Chikungunya Virus Introduction in the Americas).

 

All of which serves as prelude to a report that appeared last month in PloS Neglected Tropical Diseases called:

 

Modeling Dynamic Introduction of Chikungunya Virus in the United States

Abstract (reparagraphed for readability)

Chikungunya is a mosquito-borne viral infection of humans that previously was confined to regions in central Africa. However, during this century, the virus has shown surprising potential for geographic expansion as it invaded other countries including more temperate regions.

 

With no vaccine and no specific treatment, the main control strategy for Chikungunya remains preventive control of mosquito populations. In consideration for the risk of Chikungunya introduction to the US, we developed a model for disease introduction based on virus introduction by one individual. Our study combines a climate-based mosquito population dynamics stochastic model with an epidemiological model to identify temporal windows that have epidemic risk. We ran this model with temperature data from different locations to study the geographic sensitivity of epidemic potential.

 

We found that in locations with marked seasonal variation in temperature there also was a season of epidemic risk matching the period of the year in which mosquito populations survive and grow. In these locations controlling mosquito population sizes might be an efficient strategy.

 

But, in other locations where the temperature supports mosquito development all year the epidemic risk is high and (practically) constant. In these locations, mosquito population control alone might not be an efficient disease control strategy and other approaches should be implemented to complement it.

 

Our results strongly suggest that, in the event of an introduction and establishment of Chikungunya in the US, endemic and epidemic regions would emerge initially, primarily defined by environmental factors controlling annual mosquito population cycles. These regions should be identified to plan different intervention measures.

In addition, reducing vector: human ratios can lower the probability and magnitude of outbreaks for regions with strong seasonal temperature patterns. This is the first model to consider Chikungunya risk in the US and can be applied to other vector borne diseases.

(Continue . . . )

 

More background on this modeling study is available from the Cornell University Press Office.

 

 

Chances seen rising for chikungunya outbreaks in NYC, Atlanta, Miami

ITHACA, N.Y. – Global travel and climate warming could be creating the right conditions for outbreaks of a new virus in this country, according to a new Cornell University computer model.

 

The model predicts that outbreaks of chikungunya, a painful virus transported by travelers and spread by the invasive Asian tiger mosquito, could occur in 2013 in New York City during August and September, in Atlanta from June through September, and year-round in Miami. The probability of a disease outbreak is correlated with temperature, as warmer weather allows the Asian tiger mosquito to breed faster and grow in numbers, according to the study published in the November issue of PLOS Neglected Tropical Diseases.

 

According to the simulation, there is a high probability of a chikungunya outbreak if a single infected person arrives in New York in July or August and is bitten by an Asian tiger mosquito. The risks are the same, but with wider time frames, for transmission in Atlanta and Miami, according to the paper.

 

Asian tiger mosquitoes were introduced to the United States in Texas in the 1980s; they are established up the East Coast into New Jersey and are rising in numbers in New York City. The aggressive mosquito outcompetes local varieties and transmits more than 20 pathogens, including chikungunya and dengue, said Laura Harrington, associate professor of entomology and the study’s senior author.

 

“The virus is moving in people, and resident mosquito populations are picking it up,” Harrington said.

 

The model estimates that with typical regional temperatures, a chikungunya outbreak in New York would infect about one in 5,000 people, said Diego Ruiz-Moreno, a postdoctoral associate and the paper’s lead author

 

“However, this number would increase drastically as temperatures rise due to climate change,” Ruiz-Moreno said.

(Continue . . . )

 

While this study focused on Chikungunya, much the same could be said about the potential for seeing Dengue, Malaria, or even Yellow Fever making inroads in the United States and Europe. 

 

In March of 2010 the journal  Eurosurveillance carried a series of articles on vector borne diseases and their potential to impact those living in Europe. One of the articles, Yellow fever and dengue: a threat to Europe? by P. Reiter, had these sobering comments about the future of vector-borne illnesses in Europe.

 

The history of dengue and yellow fever in Europe is evidence that conditions are already suitable for transmission. The establishment of Ae. albopictus has made this possible, and the possibility will increase as the species expands northwards, or if Ae. aegypti is re-established.

 

The epidemic of chikungunya in northern Italy in 2007 [8,49] confirms that Ae. albopictus is capable of supporting epidemic transmission, although laboratory studies indicate that the strain of virus involved was particularly adapted to this species [50,51].

 

Nevertheless, it is not unreasonable to assume that climatic conditions that permit malaria transmission will also support transmission of yellow fever and dengue, in which case transmission could extend into northern Europe [52].

 

Reason enough that if you live in - or are visiting  - a mosquito prone area, to remember to follow the `5 D’s’  (courtesy Florida Department of Health).

 

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DVBID: Final West Nile Report For 2012

 

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While final numbers won’t be available until the spring, 2012 looks like it will go down as one of the most active West Nile Fever seasons since the virus arrived in North America in 1999.

 

The CDC’s  DVBID has released their final tally of cases for 2012 on their West Nile Update Page.  They summarize the season thusly:

 

2012 West Nile virus update: December 11

This will be the last update for 2012 until final data are available in the spring of 2013.

As of December 11, 2012, 48 states have reported West Nile virus infections in people, birds, or mosquitoes. A total of 5,387 cases of West Nile virus disease in people, including 243 deaths, have been reported to CDC. Of these, 2,734 (51%) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 2,653 (49%) were classified as non-neuroinvasive disease.

 

The 5,387 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the second week in December since 2003. Eighty percent of the cases have been reported from 13 states (Texas, California, Louisiana, Illinois, Mississippi, South Dakota, Michigan, Oklahoma, Nebraska, Colorado, Arizona, Ohio, and New York) and a third of all cases have been reported from Texas.

 

Neuroinvasive cases (which present with meningitis, encephalitis, or flaccid Paralysis) are severe enough that they result in hospitalization and diagnosis, and so they are considered the best indicator of the scope of each year’s epidemic.

 

Mild cases – called West Nile Fever – often go undiagnosed, with probably only 2%-3% being identified.

 

Meaning that with more than 2,600 mild cases reported, the true incidence was probably in excess of 100,000 infections.

Hardest hit this year was Texas, with more than 1,700 cases and 76 deaths. Far behind, but in second place, was California with 461 cases and 16 deaths. 

 

Nevertheless, the highest incidence of neuroinvasive disease occurred along the Gulf Coast and into the upper Mid West.

 

 

Earlier this year the CDC indicated they would be taking a look at this year’s WNV season to see if any changes have occurred in the virus to account for this sudden spike in activity. 

 

While West Nile season has passed for most of the country, there are still a few areas where mosquitoes are still active.  So, if you live in, or are visiting one of these areas, the advice by many health departments to follow the `5 D’s’ remains intact. 

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Dengue Update: Puerto Rico, Florida & The Americas

 

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While not reaching the levels we saw during their 2010 Dengue epidemic, Puerto Rico is once again seeing epidemic levels of the mosquito-borne virus, as evidenced by this latest chart from the CDC.  

 

As indicated by the red line, the number of cases over the past couple of weeks has been climbing like a homesick angel. 

 

Health Secretary Lorenzo Gonzalez of the Puerto Rico Health Department declared a Dengue epidemic on the island (PDF Link – in Spanish) in early October after six people died or the disease, two of them children.

 

This week, Florida also reported its third locally acquired Dengue case (see Another Central Florida dengue case confirmed) of 2012. This latest case was identified in Osceola County, and a fourth suspected case is being investigated.

 

While once a serious problem in Florida, through aggressive mosquito control efforts during the 1940s Dengue and Malaria were both eliminated from the Sunshine State – and remained so for nearly a half century.

 

In 2009 – for the first time in more than 50 years – we started to see a small number of locally acquired Dengue cases showing up in Key West (see MMWR: Dengue Fever In Key West), and in 2010 they totaled 65 cases in Key West and 1 each in Broward and Miami-Dade County.

 

The number of cases dropped in 2011, and have been low once again in 2012.

 

The concern is - with millions of visitors arriving each year, many from regions where these diseases are endemic – there are plenty of opportunities to re-introduce the virus.

 

The CDC’s MMWR in a report in May of 2010 on Locally Acquired Dengue in Key West, had this to say:

 

Cases of dengue in returning U.S. travelers have increased steadily during the past 20 years (8). Dengue is now the leading cause of acute febrile illness in U.S. travelers returning from the Caribbean, South America, and Asia (9).

 

Many of these travelers are still viremic upon return to the United States and potentially capable of introducing dengue virus into a community with competent mosquito vectors.

 

In truth, it may take many such introductions of Dengue or Malaria to an area before the right combination of weather, insect vectors, and ongoing transmission occur to enable it to get a foothold in a community.

 

But Florida’s latest Arbovirus Surveillance report lists more than 90 cases of Imported Dengue this year:

 

Ninety-four cases of dengue with onset in 2012 have been reported in individuals with travel history to a dengue endemic country in the two weeks prior to onset. Countries of origin were Brazil, Colombia, Cuba (21), Dominican Republic (9), Ecuador (4), El Salvador (2), Ghana, Guyana (2), Haiti (14), Honduras, India, Jamaica (17), Mexico (2), Nicaragua, Panama, Philippines, Puerto Rico (6), South Africa, Sri Lanka, St. Vincent, Suriname, Trinidad (4), and Turks & Caicos.

Counties reporting cases were Brevard (3), Broward (17), Collier, Duval (2), Hillsborough (4), Lee (2), Marion, Miami-Dade (36), Orange (12), Palm Beach (6), Pinellas (2), Polk, Sarasota (2), Seminole (3), and Volusia (2). Nine of the cases were reported in non-Florida residents.

 

The state has also reported more than 50 cases of Imported Malaria, although no locally acquired cases have been reported.

 

Fifty-three imported cases of malaria with onset in 2012 have been reported.  Countries of origin were: Afghanistan (2), Cameroon, Central African Republic, Colombia, Costa Rica, Ethiopia, Ghana (5), Guyana (2), Haiti (9), Honduras (3), India, Ivory Coast (3), Kenya, Liberia (2), Nigeria (8), Pakistan, Peru, Sierra Leone (2), South Africa, Sub Saharan Africa, Sudan, Togo, Uganda, Zambia, and multiple African countries (2).

Counties reporting cases were: Alachua, Brevard, Broward (8), Charlotte, Duval (6), Hillsborough (6), Lake (2), Leon, Manatee, Marion, Martin, Miami-Dade (7), Orange (5), Osceola (2), Palm Beach (4), Pinellas (3), Polk, Seminole, and Volusia. Five of the cases were reported in non-Florida residents.

 

A broader perspective comes from PAHO, who's Oct 31st update shows nearly 1 million cases of Dengue in the Americas this year.

 

An interactive map view of Dengue activity in the Americas, and around the world, can be seen via the CDC-Healthmap collaborative DengueMap.

 

 

Although the overall risk of contracting a mosquito-borne illness in Florida or Puerto Rico remains very small, reports of Dengue (along with West Nile, EEE, SLEV, and other rare arboviral threats) are reason enough that health departments continue to urge people to remember to follow the `5 D’s’:

 

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A Disease Detective Story: Figuring Out Where EEE Spends The Winter

 

 

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While West Nile Virus infections are far more common (see DVBID: West Nile Infections Continue Record Pace), the Eastern Equine Encephalitis (EEE) virus elicits considerable concern because of its high fatality rate (30%+) and the large number of survivors who suffer ongoing neurological impairment.

 

Most years, only about 6 cases (range: 3—21) of human EEE are reported in the United States.

 

But this year – just as we’ve seen with WNV – is an unusually active year, and thus far the USGS is reporting 12 cases of EEE.

 

 

Given the devastating effects of infection in humans, and the fact that there is no vaccine available for humans to prevent it, learning about the ecology of the EEE virus is of particular importance.

 

We know that the natural hosts for the EEE virus are songbirds, which can become infected usually without suffering ill effect. The primary vector that spreads the virus among birds is the female Culiseta melanura mosquito (males don’t bite).

 

 

After an infected mosquito feeds on a bird, the bird becomes infected and the virus begins reproducing. After a few days - and for only a few days - the bird’s bloodstream amplifies the virus enough to infect subsequent mosquitoes that feed on it.

 

Culiseta melanura, however, isn’t usually attracted to bite humans.

 

So it requires a secondary type of mosquito - one that isn’t quite as picky a feeder - such as the Aedes albopictus or  Coquillettidia perturbans  `salt and pepper’ mosquito, to bite an infected bird in order to move it into the equine or human population.

 

The Transmission cycle is illustrated by the following graphic from the CDC.

 

Humans and horses don’t develop a high enough viral EEE titer in their bloodstream to pass on the virus if they are subsequently bitten by a mosquito, so they are considered to be `dead-end hosts’.

 

This explains the transmission cycle of the virus, but for one rather conspicuous hole in the equation.

 

Since birds are only viremic for a few days after being bitten, and since mosquitoes die out for several months during the winter  . . . . how does the virus manage to return each spring and summer?

 

For years scientists have suspected there had to be another host in the wild that could provide the EEE virus a safe place to overwinter.

 

But it would have to be one that could carry a high enough viral titer throughout the winter in order to reseed the virus in mosquito populations the following spring.

 

All of which brings us to some fascinating research that points to snakes – cottonmouths and copperheads, in particular – as being the winter residence of the EEE virus. 

 

Cottonmouth – Credit Wikipedia

 

This new study, which appears in the American Journal of Tropical Medicine and Hygiene, provides strong support for the idea that hibernating snakes serve as a bridge for the EEE virus to make it from one year to the next.

 

Detection of Eastern Equine Encephalomyelitis Virus RNA in North American Snakes

Andrea M. Bingham, Sean P. Graham, Nathan D. Burkett-Cadena, Gregory S. White, and Thomas R. Unnasch 

ABSTRACT

The role of non-avian vertebrates in the ecology of eastern equine encephalomyelitis virus (EEEV) is
unresolved, but mounting evidence supports a potential role for snakes in the EEEV transmission cycle, especially as over-wintering hosts.

 

To determine rates of exposure and infection, we examined serum samples from wild snakes at a focus of EEEV in Alabama for viral RNA using quantitative reverse transcription polymerase chain reaction.

 

Two species of vipers, the copperhead (Agkistrodon contortrix) and the cottonmouth (Agkistrodon piscivorus), were found to be positive for EEEV RNA by using this assay. Prevalence of EEEV RNA was more frequent in seropositive snakes than seronegative snakes. Positivity for the quantitative reverse transcription polymerase chain reaction in cottonmouths peaked in April and September. Body size and sex ratios were not significantly different between infected and uninfected snakes.

 

These results support the hypothesis that snakes are involved in the ecology of EEEV in North America, possibly as over-wintering hosts for the virus.

(Continue . . . )

 

The entire article is available online, and is a fascinating disease detective story . . . well worth reading in its entirety.

 

While probably not the preferred target for hungry mosquitoes - during the early spring and late fall when other blood meal sources may be in short supply - mosquitoes do feed on snakes.

 

They bite – not through their tough skin – but through the soft membranes around the snake’s eyes.  

 

Beyond discovering antibodies to the EEE virus in 35% of the cottonmouths sampled, the also found a number of snakes positive (via qRT-PCR) for the EEE virus.

 

This, they believe, is the first time that the active EEE virus has been documented in wild-caught snakes.

 

Previous tests had showed that snakes experimentally infected with the EEE virus remain viremic only for 7 to 10 days before they clear the infection – not enough time for the virus to overwinter.  

 

But now it appears that when a snake hibernates, it can carry the virus over the winter, and can likely reintroduce it to mosquitoes the following spring.

 

All of which introduces an interesting notion regarding control of the virus. Normally spraying for mosquitoes doesn’t begin until EEE starts showing up in mosquito surveillance traps, horses, or worse . . . humans.

If spraying were conducted during the early spring in swampy areas where mosquitoes and snakes are likely to meet - it might be possible to interrupt this annual cycle - and thus thwart the virus’s reintroduction to the mosquito and bird population.

 

 

As the abstract states, this study supports the hypothesis that snakes are the `bridge’ host for the EEE virus, but there is still more research needed. 

 

For more on this story Maggie Fox of NBC News has a good report, along with some comments from the lead author of the study; Dr. Thomas Unnasch of the University of South Florida.

 

Snakes may harbor deadly virus

 

And for more on the EEE virus, you may wish to revisit some of these earlier blogs.

 

MMWR: Arboviral Disease Surveillance – 2010

ASTMH: Dengue and Insect-Borne EIDs In The US

Eastern Equine Encephalitis (EEE)

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DVBID: West Nile Infections Continue Record Pace

Credit DVBID

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The DVBID (Division of Vector Borne Infectious Diseases) has updated their West Nile numbers as reported to them through October 2nd, and as expected the number of new cases, and deaths, continues to rise.

 

2012 West Nile virus update: October 2

As of October 2, 2012, 48 states have reported West Nile virus infections in people, birds, or mosquitoes. A total of 3,969 cases of West Nile virus disease in people, including 163 deaths, have been reported to CDC. Of these, 2,010 (51%) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 1,959 (49%) were classified as non-neuroinvasive disease.

 

The 3,969 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the first week in October since 2003. Almost 70 percent of the cases have been reported from eight states (Texas, California, Louisiana, Mississippi, South Dakota, Michigan, Oklahoma, and Illinois) and a third of all cases have been reported from Texas.

 

The record pace continues, and we can expect – given incubation period of 2 or 3 weeks, and since some people may succumb only after weeks of illness – that we will see these numbers continue to rise for the next couple of months.

 

 

The incidence level of the more serious neuroinvasive form of West Nile disease – which can produce encephalitis, meningitis, and/or acute flaccid paralysis – is illustrated by the following chart. 

 

 

Although the peak period of transmission for WNV may have passed, infected mosquitoes are still out there and are still biting and infecting people.

 

So we still need to heed the advice of our local health departments to  follow the `5 D’s’ of mosquito protection:

 

And finally, to find out about the West Nile threat in your area, you can visit the DVBID website below:

Links to State and Local Government West Nile Virus Web Sites

 

Click on a state to link directly to their West Nile virus Web page.

See list below for additional city-level and main State Health Department Web sites.

»» Read More

Miami Reports Locally Acquired Dengue Case

 

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News this afternoon from the Miami-Dade Health Department on the detection of 2012’s first locally acquired case of Dengue fever in the state of Florida.

First some excerpts from the press release, and then I’ll return with more.

 

September 27, 2012

First Locally Acquired Case of Dengue Fever in Miami-Dade County

(Miami, FL – September 27, 2012) – Miami-Dade County Health Department officials received confirmation of the first locally acquired case of Dengue Fever in Miami-Dade County.

 

The individual was diagnosed with Dengue Fever based on symptoms and confirmed by laboratory tests. The individual fully recovered from this illness.

 

Dengue Fever is a viral disease transmitted by a type of mosquito common to the southeastern United States and the tropics. It is not spread from person to person. The symptoms of Dengue Fever include, fever (over 101 degrees Fahrenheit), severe headache, severe pain behind the eyes, muscle, joint and bone pain, rash, loss of appetite, nausea and vomiting. There is no specific medication or vaccine for Dengue Fever. If you are experiencing symptoms consistent with Dengue Fever, please call your healthcare provider to see if you need to be seen.

(Continue . . . )

 

When Dengue fever returned to the state of Florida in 2009 - after an absence of 70 years - (see Dengue Resurfaces In Key West), it wasn’t an entirely unexpected event.

 

The virus was likely reintroduced to the area by an infected traveler or visitor who was bitten by a local mosquito, and that mosquito went on to bite others.

 

Like many viral infections (influenza, West Nile, etc), not everyone who is infected experiences symptoms. And with Dengue, it is often the second or third infection (there are 4 sub-types) that proves the most serious.

 

The 2010 MMWR report  Locally Acquired Dengue --- Key West, Florida, 2009—2010 described South Florida’s vulnerability this way:

 

The environmental and social conditions for dengue transmission have long been present in south Florida: the potential for introduction of virus from returning travelers and visitors, the abundant presence of a competent mosquito vector, a largely nonimmune population, and sufficient opportunity for mosquitoes to bite humans.

 

There were 28 cases reported in 2009, and the state of Florida’s Weekly Data for Arbovirus Surveillance lists 63 locally-acquired cases in Key West, one in Broward County, and one in Miami-Dade County for 2010.

The following year, 2011, saw a significant reduction in cases with just three locally acquired in Miami-Dade County, two in Palm Beach County, and one each in Martin and Hillsborough counties.

 

While the most recent state surveillance report shows 67 cases of imported dengue in individuals with recent travel history to dengue endemic regions, today’s announcement is the first locally acquired case of the year.

 

In order to spread, Dengue requires the right mosquito vector.  And the two species best suited to transmit the virus are the Aedes aegypti and Aedes albopictus mosquitoes, which also can spread such diseases as West Nile, Malaria, Yellow Fever, and Chikungunya.

 

Map showing the distribution of dengue fever (red) and the distribution of the Aedes aegypti mosquito (cyan)  in the world, as of 2006. – Credit Agricultural Research Service of the US Department of Agriculture.

 

Map showing the native habitat (blue) and recent spread (green) of the Aedes albopictus mosquito. --Credit Wikipedia

 

According to a 2009 report, as many as 28 states in the US have at least one of the these mosquito vectors, a factoid that has some epidemiologists worried that Dengue, Chikungunya, and Malaria could one day become threats in the United States.

 

With only one locally-acquired dengue case in Florida this year, it’s pretty obvious the virus has not managed to get a solid foothold in the state. Each year, however - more travelers arrive carrying the virus - and that gives the virus another opportunity to take up residence.

 

Right now, Dengue is a minor threat in Florida, but when you add Dengue to the other mosquito-borne illnesses (EEE, WNV, SLEV) it just makes sense to do whatever you can to limit your exposure.

Which is why the State Health Department urges residents and visitors to follow the `5 D’s’:

 

 

For an extensive list of my blogs on Dengue and Mosquito Borne Diseases you can select the DENGUE Quick Search here,  or on my sidebar.

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DVBID Update On West Nile Virus

 

Source DVBID

 

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While the big infectious disease news this week has been the novel coronavirus that has killed one Saudi, and seriously sickened a Qatari man, there are other infectious disease threats we follow, including West Nile Disease.

 

The DVBID has updated their West Nile website, and while the number of new infections is beginning to decline, 13 additional deaths have been reported via ArboNet in the last week.

 

 

2012 West Nile virus update: September 25

As of September 25, 2012, 48 states have reported West Nile virus infections in people, birds, or mosquitoes. A total of 3,545 cases of West Nile virus disease in people, including 147 deaths, have been reported to CDC. Of these, 1,816 (51%) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 1,729 (49%) were classified as non-neuroinvasive disease.

 

The 3,545 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the last week in September since 2003. Seventy percent of the cases have been reported from eight states (Texas, Mississippi, South Dakota, Michigan, California, Louisiana, Oklahoma, and Illinois) and 38 percent of all cases have been reported from Texas.

 

It should be noted that the latest numbers reported via ArboNet may lag behind the most recent totals being reported by each state.  

 

Case in point: Texas,  which is shown to have  1345 cases and 52 deaths in today’s report, is reporting somewhat higher numbers on their website:

 

The incidence level of the more serious neuroinvasive form of West Nile disease – which can produce encephalitis, meningitis, and/or acute flaccid paralysis – is illustrated by the following chart. 

 

 

 

Although the peak period of transmission for WNV may have passed, infected mosquitoes are still out there and are still biting and infecting people.

 

So we still need to heed the advice of our local health departments to  follow the `5 D’s’ of mosquito protection:

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CDC West Nile Update

 

Credit DVBID

 

 

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I was away from my desk yesterday for the CDC’s  teleconference update on West Nile activity across the nation, but Lisa Schnirring for CIDRAP News  has an excellent overview.   

 

West Nile virus cases continue record pace

Lisa Schnirring Staff Writer

Sep 5, 2012 (CIDRAP News) – The number of West Nile virus cases in the United States this year has jumped by about 25% in the past week, and though new reports are still coming in at a record pace, Texas—the hardest hit state—is seeing some promising signs that interventions such as aerial spraying are working.

(Continue . . .)

 

The transcript of this teleconference and an audio file is now available on the CDC Newsroom webpage.

 

Texas, which has been particularly hard hit this year, has now reported 40 deaths, and a record 495 neuroinvasive cases this year.

 

Neuroinvasive cases (which present with meningitis, encephalitis, or flaccid Paralysis) are severe enough that they result in hospitalization and diagnosis, and so they are considered a better indicator of the scope of each year’s epidemic.

 

Mild cases – called West Nile Fever – often go undiagnosed, with probably only 2%-3% being identified.

 

As you can see from the chart below, while 44 states have reported human infections with the West Nile Virus this year, it is the middle of the country that is being hardest hit by neuroinvasive WNV.

 

Credit DVBID

 

Vector-borne illnesses like West Nile Virus, EEE (Eastern Equine Encephalitis), Dengue, Lyme Disease, Babesia, Powassan Virus, and even the newly reported Heartland Virus (see also Maryn McKenna’s report) are becoming increasingly common across the United States.

 

Many scientists believe that as climate change occurs, we will see more of these mosquito, flea, tick, and biting fly transmitted diseases here, and in the European Union.

 

To give you an idea how quickly a new, vector-borne disease like West Nile can spread, the WNV only arrived in the United States twelve years ago and in a few short few years had invaded all 48 contiguous states.

 

From the USGS Factsheet on West Nile Virus

 

Prevention is the key.

 

West Nile Virus is now endemic across most of the United States and the prudent move is to take the recommended precautions against mosquito bites.

 

 

 

And ticks, which can also easily transmit diseases, require preventative measures as well.

(Credit CDC)

 

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CDC Telebriefing on West Nile Virus

 

 

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A public health situation we’ve been following here for the past several weeks (see here, here, here, and here) was the subject of a CDC telebriefing today; the unusually high incidence of West Nile infections across the country, but most noticeably in Texas.

 

According to the CDC’s Dr. Lyle R. Petersen, director of the DVBID at the CDC, 2012 may be on track to be the worst yet in the 13 year history of the virus in the United States.

 

Yesterday, the CDC’s DVBID division updated their numbers through August 21st, indicating:

 

2012 West Nile virus update: as of August 21

Thus far in 2012, 47 states have reported West Nile virus infections in people, birds, or mosquitoes. A total of 1118 cases of West Nile virus disease in people, including 41 deaths, have been reported to CDC. Of these, 629 (56%) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 489 (44%) were classified as non-neuroinvasive disease.

 

The 1118 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the third week in August since West Nile virus was first detected in the United States in 1999. Approximately 75 percent of the cases have been reported from 5 states (Texas, Mississippi, Louisiana, South Dakota, and Oklahoma) and almost half of all cases have been reported from Texas.

 

 

Of the 1118 cases, nearly half (n=537) are from Texas, and 26 deaths so far this year have been recorded in the Lone Star State. Hard hit Dallas county reported their 11th fatality yesterday.

 

Elsewhere across the nation, 38 other states have reported West Nile infections in humans, and deaths have been reported across 16 states.

 

Of note, Louisiana has reported 6 fatalities and Oklahoma has reported 3.

 

Today’s telebriefing featured Lyle R. Petersen, M.D. and the transcript should be posted on the CDC’s media site tonight or tomorrow (now available at this link).

 

Lisa Schnirring writing for CIDRAP NEWS has an excellent summary of today’s briefing:

 

CDC reports surge in US West Nile virus activity

Lisa Schnirring Staff Writer

Aug 22, 2012 (CIDRAP News) – The United States is experiencing a dramatic rise in the cases of West Nile virus (WNV) infections over the past month, with record-setting numbers expected over the next several weeks and the US Centers for Disease Control and Prevention (CDC) warning people to take key preventive steps.

 

So far, 38 states have reported human cases, but the epicenter is Texas, which has reported half of the WNV infections. The CDC said so far it has received reports of 1,118 cases, including 629 people with the neuroinvasive form of the disease. Nationally, 41 deaths have been reported.

(Continue . . .)

 

 

 

Given that the WNV season doesn’t usually peak until mid-August, and it can take 2 to 3 weeks for symptoms to develop, many more cases are expected over the next few months.

 

While 80% of those infected don’t show symptoms, last week WEBMD carried a report (see New West Nile Threat: Kidney Disease) about research conducted by Baylor University West Nile expert Kristy O. Murray, PhD, DVM.

 

Dr. Murray’s research (see Persistent Infection with West Nile Virus Years after Initial Infection) suggests long-term sequelae may develop among a significant percentage of those who are infected with the West Nile Virus – even among those infected asymptomatically.

 

Dr. Murray was awarded an NIH grant in 2011 to study the effects of chronic WNV infection on the kidneys and central nervous system.

 

Reason enough to take seriously the recommendations from health departments across the nation that urge people to follow the `5 D’s’ of mosquito protection:

To find out about the West Nile threat in your area, you can visit the DVBID website below:

Links to State and Local Government West Nile Virus Web Sites

 

And as a final note, the CDC recently updated their information on mosquito repellants.

Updated Information regarding Insect Repellents

»» Read More

EEE: Eastern Equine Encephalitis

 

# 6501

 

While West Nile Virus is making headlines in Texas and across much of the nation, another mosquito-borne virus – EEE (Eastern Equine Encephalitis) – has the attention of Massachusetts health officials.

 

On Thursday, the Massachusetts Department of Health & Human Services released the following alert:

 

State Health Officials Raise EEE Threat Level in Two Communities after Detection of EEE-Positive Mosquitoes

New Bedford and Westborough raised to High; ground spraying to be enhanced

BOSTON — Thursday, August 16, 2012 – The Massachusetts Department of Public Health (DPH) today announced the detection of mammal-biting mosquitoes infected with Eastern Equine Encephalitis (EEE) in New Bedford and Westborough. As a result, health officials have raised the EEE threat level to “High” in these two communities and recommend that outdoor evening events are curtailed there for the remainder of the summer. Ground-based spraying by mosquito control projects is ongoing in both New Bedford and Westborough and will be enhanced.

(Continue. . . )

 

 

So far, only one human case of EEE has been detected in Massachusetts this year, and that one is believed to have been acquired out of state. This risk of seeing additional cases, however, is deemed high in communities where human-biting mosquitoes are found to carry the virus.

 

Although far less common than West Nile Virus, EEE is of concern because it has a high fatality rate (35%), and among the survivors, a large number suffer ongoing neurological problems.

 

Over the past decade there have been an average of about 7 cases (not deaths) of `Triple E’ in the United States each year (range range: 3—21), which makes EEE an exceedingly rare disease in humans.

 

But given its severity (and the co-circulation of other mosquito borne diseases like West Nile, La Cross Virus, & SLEV), it makes sense to take steps to protect against mosquito bites – even if your local officials have not issued a warning.

 

The Florida Department of Health’s advice to protect  against mosquito borne diseases is that people should practice the "5 D's"

Don't go outdoors at DUSK and DAWN when mosquitoes are most active.

DRESS so your skin is covered with clothing

Apply mosquito repellent containing DEET to bare skin and clothing. 

Other effective repellents include picaridin, oil of lemon eucalyptus, and IR3535

Empty containers and DRAIN standing water around your home where mosquitoes can lay eggs.

 

 

While the number of yearly cases is low, the distribution of EEE in the United States far ranging.

 

The natural host for the EEE virus are songbirds, which can become infected usually without suffering ill effect.  The virus is spread among these birds by the blood feeding of female mosquitoes (males don’t bite).

 

After an infected mosquito feeds on a bird, the bird becomes infected and the virus begins reproducing. After a few days, and for only a few days, the bird’s bloodstream amplifies the virus enough to infect subsequent mosquitoes that feed on it.

 

Culiseta melanura, which means "curly black hairs", is the species of swamp mosquito that serves as the primary vector for this virus among birds.

 

Culiseta melanura, however, isn’t usually attracted to humans.

 

So it generally requires a secondary type of mosquito - one that isn’t quite as picky a feeder - such as the Aedes albopictus or  Coquillettidia perturbans  `salt and pepper’ mosquito, to bite an infected bird in order to move it into the equine or human population.

 

The Transmission cycle is illustrated by the following graphic from the CDC.

 

Humans and horses don’t develop a high enough viral EEE titer in their bloodstream to pass on the virus if they are subsequently bitten by a mosquito, so they are considered to be `dead-end hosts’.

 

 

As there is no vaccine against EEE, the best tactic is prevention, and high in that category is the use of mosquito repellants.

 

To help you with choosing the right repellant the EPA has developed an interactive insect repellant search engine that will that will allow you to input your needs and it will spit out the best repellants to use.

 

(click image to go to search engine)

 

 

For more on Arboviruses in the United States you may wish to revisit this blog from last year:

 

MMWR: Arboviral Disease Surveillance – 2010

»» Read More

Dallas West Nile Update

 

 

# 6483

 

While we await today’s MMWR and a briefing this afternoon from the CDC on the H3N2v outbreak in Ohio and Indiana, we’ve three more West Nile Virus (WNV) deaths to report in Dallas County, Texas this week (see Ninth West Nile Virus Related Death in Dallas County August 8, 2012). 

 

Nationally, as of August 7th, 253 neuroinvasive cases of WNV have been reported to ArboNET, along with 137 non-neuroinvasive WNV infections. 

 

Of those, roughly half have been reported out of the state of Texas (see CHART).

 

 

It is estimated that only about 20% of the people who are infected with WNV develop symptoms, and the vast majority of those only experience a mild flu-like illness. Accordingly, mild, asymptomatic, or non-neuroinvasive infections are likely vastly undercounted.

 

The more severe `neuroinvasive’ form of WNV can produce symptoms that include headache, stiff neck, confusion, coma, convulsions, and even paralysis.

 

According to the CDC’s  WEST NILE SYMPTOMS Q&A page.

 

It is estimated that approximately 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease. Serious illness can occur in people of any age, however people over age 50 and some immunocompromised persons (for example, transplant patients) are at the highest risk for getting severely ill when infected with WNV.

<SNIP>

When someone is infected with West Nile virus (WNV) they will typically have one of three outcomes: No symptoms (most likely), West Nile fever (WNF in about 20% of people) or severe West Nile disease, such as meningitis or encephalitis (less than 1% of those who get infected).

If you develop a high fever with severe headache, consult your health care provider.

 

While many are concerned this week over an emerging swine flu virus, so far we are not aware of any deaths or serious illness from that flu strain.

 

The same, sadly, cannot be said about mosquito borne illnesses this summer. 

 

Reason enough for health departments across the nation to urge people to follow the `5 D’s’ of mosquito protection:

To find out about the West Nile threat in your area, you can visit the DVBID website below:

 

Links to State and Local Government West Nile Virus Web Sites

Click on a state to link directly to their West Nile virus Web page.

See list below for additional city-level and main State Health Department Web sites.

»» Read More

Update & Video On The Texas West Nile Outbreak

 

 
Map credit – DVBID

 

# 6476

 

 

A week ago, in Texas: West Nile Cases Rising I wrote about the high number of West Nile infections being reported in, and around, Dallas County Texas.  At the time, the DCHHS was reporting three local fatalities from WNV neuroinvasive disease (WNND).

 

That number has now doubled to six fatalities, according to this press release from the Dallas County Health Department. WNV related deaths have also been reported in Travis County (1) and McLennan County (1).

 

To put this into some kind of perspective, in previous years the entire state of Texas reported:

• 2 West Nile human fatalities in 2011
• 7 West Nile human fatalities in 2010
• 9 West Nile human fatalities in 2009
• 1 West Nile human fatalities in 2008
• 17 West Nile human fatalities in 2007

 

The latest edition of West Nile Watch indicates 115 human infections in Dallas County Alone – an increase of roughly 40% over last week’s total. Zachary Thompson -director of Dallas County Health and Human Services – is quoted on the department’s website about the seriousness of this outbreak:

 

 

Last week Baylor Health Care System sponsored a webinar called West Nile in North Texas: What you need to know, and that video is available on Youtube.  Participating in this 23 minute program were:

 

• Janet St. James, local Medical reporter with WFAA-TV, Channel 8
• William Sutker, M.D., chief of infectious disease, Baylor University Medical Center at Dallas
• Charles Perkins, D.O., medical director, Dallas County Department of Health and Human Services
• Roger Khetan, M.D., Internal Medicine physician on the medical staff at Baylor University Medical Center at Dallas

 

 

While Northern Texas, Oklahoma, and Mississippi are currently reporting the most West Nile Virus activity, the CDC noted last week that 42 states across the nation have reported WNV activity this year.

 

West Nile virus disease cases up this year

 

Take steps to protect yourself and your family

The Centers for Disease Control and Prevention is urging people to take steps to prevent West Nile virus infections.  Outbreaks of West Nile virus disease occur each summer in the United States.  This year, some areas of the country are experiencing earlier and greater activity.

 

Thus far in 2012, 42 states have reported West Nile virus infections in people, birds, or mosquitoes. A total of 241 cases of West Nile virus disease, including four deaths, have been reported to CDC. This is the highest number of cases reported through the end of July since 2004. Almost 80 percent of the cases have been reported from three states, Texas, Mississippi, and Oklahoma.

 

West Nile virus is transmitted to people by infected mosquitoes.  In the United States, most people are infected from June through September, and the number of these infections usually peaks in mid-August.  Seasonal outbreaks often occur in local areas that can vary from year to year.  Many factors impact when and where outbreaks occur, such as weather, numbers of mosquitoes that spread the virus, and human behavior.

 

“It is not clear why we are seeing more activity than in recent years,” said Marc Fischer, M.D., M.P.H., medical epidemiologist with CDC’s Arboviral Diseases Branch.  “Regardless of the reasons for the increase, people should be aware of the West Nile virus activity in their area and take action to protect themselves and their family.”

 

The best way to prevent West Nile virus disease is to avoid mosquito bites:

• Use insect repellents when you go outdoors. 
• Wear long sleeves and pants during dawn and dusk.
• Install or repair screens on windows and doors.  Use air conditioning, if you have it.
• Empty standing water from items outside your home such as flowerpots, buckets, and kiddie pools.

(Continue . . .)

 

To find out about the West Nile threat in your area, you can visit the DVBID website below:

Links to State and Local Government West Nile Virus Web Sites

 

Click on a state to link directly to their West Nile virus Web page.

See list below for additional city-level and main State Health Department Web sites.

»» Read More