Note: Google’s Blogger Platform experienced a prolonged outage Thursday-Friday and so I’ve been unable to update this blog for a couple of days.
I’ll be on the road either later today or early tomorrow, and so it will be Sunday night or Monday morning before I’m back to my regular blogging schedule.
# 5554
Aedes albopictus (Asian Tiger) Mosquito
Dark blue: Native range
Dark green: introduced (as of December 2007)
In the UK (and much of Europe), Dengue, Chikungunya, Yellow Fever, and Malaria remain imported illnesses. These countries, while not mosquito-free, aren’t normally home to the species that readily transmit these serious tropical diseases.
But in recent years, one of these disease vectors – the Asian Tiger Mosquito - has made inroads into many temperate countries (including Italy, France, and the eastern half of the United States) increasing the likelihood of local transmission.
In fact, a Chikungunya outbreak occurred – in all places – Northern Italy in 2007.
I told the story in It's A Smaller World After All, but the crux of the matter being that a traveler, returning from India, brought the virus to Italy which led to more than 290 cases reported in the province of Ravenna, which is in northeast Italy.
The UK’s HPA has this to say about the introduction of the Asian Tiger Mosquito to Britain.
The Asian Tiger Mosquito (Aedes albopictus) has been identified by the Health Protection Agency as an insect that could potentially arrive in the UK. If this were to happen and if the mosquito became established, then it could cause a greater biting nuisance and may become involved in the transmission of disease.
To date there have been no confirmed reports of the mosquito in the UK and the public health risk remains low. Suspected sightings occur every summer, but thus far have always been identified as the endemic species Culiseta annulata.
In March of 2010 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 this to say 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].
In order for an epidemic of Chikungunya, Yellow Fever, Dengue, or Malaria to occur in a previously unaffected area you need a competent vector (the right species of mosquito), and you need the (usually repeated) introduction of the causative pathogen into the mosquito population.
As the above Eurosurveillance article points out - 1.2 million people who live in the UK visit the Indian subcontinent, with average stays of 29 days) and, after malaria, dengue infection is the second most frequent reason for hospitalisation after their return
These tropical viruses are continually being introduced back into the UK (and other countries), increasing the chances that at some point they could become transmitted to others by the local mosquito population.
Which brings us to a recent HPA (Health Protection Agency) report on the rapidly increasing number of imported Dengue cases into the UK.
Dengue fever cases double among UK travellers
11 May 2011
Reports of dengue fever, a mosquito-borne infection, have more than doubled in UK travellers from 166 reported cases in 2009 to 406 in 2010, according to new figures from the Health Protection Agency (HPA).
Dengue fever does not occur in the UK and the highest proportion of cases were associated with travel to India - 84 cases (21 per cent) and Thailand - 61 cases (15 per cent).
This increase in dengue reports is coupled with a 34 percent rise in the number of reported cases of chikungunya, another mosquito borne infection, which rose from 59 cases in 2009 to 79 in 2010. Nearly 50 per cent of these cases were associated with travel to India.
Both diseases are endemic in Asia and Africa and dengue is also common in many other parts of the world including South America, Central America and the Caribbean and the Western Pacific.
These imported cases aren’t just a concern for the UK, of course.
Last summer, the CDC has issued a Health Advisory via their HAN (Health Alert Network) primarily to inform health care providers of the possibility of seeing Dengue Fever in returning visitors from areas where the virus is being seen.
This is an official
CDC HEALTH ADVISORYDistributed via Health Alert Network
Sunday, July 25, 2010, 22:35 EDT (10:35 PM EDT)
CDCHAN-00315-2010-07-25-ADV-NIncreased Potential for Dengue Infection in Travelers Returning from International and Selected Domestic Areas
Summary
Dengue virus transmission has been increasing to epidemic levels in many parts of the tropics and subtropics. Travelers to these areas are at risk of acquiring dengue virus and developing dengue fever (DF) or the severe form of the disease, dengue hemorrhagic fever (DHF).
The return of locally acquired dengue fever to Florida in 2009 after a 6 decade absence was no doubt due to repeated introductions of the virus by travelers coming from countries where the virus is endemic.
You can find the CDC MMWR report on the reemergence of Dengue in Key West HERE.
In mid-June of 2010 the MMWR came out with a new report on Travel Associated Dengue in the United States between 2006 and 2008.
This surveillance pre-dates the Key West outbreak, and as the study reports, `Clinically recognized cases of travel-associated dengue likely underestimate the risk for importation because many dengue infections are asymptomatic or mildly symptomatic’.
The link is Travel-Associated Dengue Surveillance --- United States, 2006—2008.
The explosive growth of Dengue around the world is well illustrated by the following graph from the World Health Organization.
What this graph doesn’t indicate is another doubling of dengue cases has taken place over the past 5 years.
For now, major outbreaks of Dengue, Chikungunya, Malaria, or Yellow Fever remain unlikely in the United States and Europe.
Conditions that are conducive to these kinds of epidemics, however, continue to evolve; Dense urban populations, climate change, increased international travel, and the expanding range of mosquito vectors.
So the advice offered by this week’s HPA announcement by Dr Jane Jones, head of the HPA's travel and migrant health section, is worth taking to heart:
"These figures demonstrate that the importance of taking precautions to avoid mosquito bites extends to protecting against other infections, not just malaria. Unlike for malaria where drugs can be taken to prevent infection, there is no such option available to prevent either dengue or chikungunya.
Although the overall risk of contracting a mosquito-borne illness in the United States remains very small, scattered cases of Dengue (along with West Nile, EEE, SLEV, and other rare arboviral threats) are why Florida health departments continue to urge people to remember to follow the `5 D’s’:
Good advice in Florida, and anyplace else mosquitoes can be found.
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