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EID Journal:Vector-Borne Infections

 

 

 

# 5491

 

 

The May issue of the CDC’s  EID JOURNAL will focus on vector borne diseases, and yesterday four ahead-of-print articles appeared including:

 

Vector-borne Infections 
R. Rosenberg and C.B. Beard

Babesiosis in Lower Hudson Valley, New York, USA
J.T. Joseph et al.

Evidence of Tungiasis in Pre-Hispanic America
V. Maco et al.

Upward Trend in Dengue Incidence among Hospitalized Patients, United States

J.A. Streit et al.

 

As a Lymie (I was infected in the mid-1990s but not diagnosed until 2000) - and a native of our national mosquito preserve known as Florida - I understandably have a strong and abiding interest in vector borne diseases.

 

This morning, a look at the article Vector-borne Infections by Ronald Rosenberg and C. Ben Beard.  In four short pages we get a nice overview of the topic, and some of the reasons why vector-borne illnesses are a growing concern.

 

The authors cite three primary reasons why these diseases are such prominent contributors to emerging diseases.

 

First, with the exception of fungi, practically all major classes of pathogens have evolved ways of being transmitted by blood feeding Arthopods: Viruses (Dengue, WNV), Bacteria (Lyme), Protozoas (Malaria), and helminths (river blindness).

 

Second, vectors bridge barriers that would normally prevent direct contact between humans and other species that serve as reservoirs for these zoonotic infections. 

 

Humans, for example, would normally have little contact with the rodents that naturally harbor B. burgdorferi (Lyme), but ticks serve as a bridge, transmitting the infection from these hosts to humans.

 

Third, these vectors don’t just serve as a simple vehicle for transmission.  They can actually help the pathogens they carry to evolve or mutate.


The authors explain:

 

Usually, the pathogen must move from the gut to the feeding apparatus to be transmitted. Mechanisms range from the relatively simple, as with the plague bacillus, Yersinia pestis, to the elaborately intricate, as with parasites in the genera Plasmodium and Leishmania.

 

In these examples, the pathogen replicates in some fashion, which makes it dependent on an invertebrate host physiology much different from what it will encounter in its various vertebrate hosts.

 

As a consequence, epidemic emergence can result from enhanced transmission independent of increased pathogenicity to humans. This is especially true of the arthropod-borne viruses (arboviruses) that infect humans, all of which are RNA viruses and have high potential mutability.

 

 

A classic example can be found in the recent explosion of Chikungunya across the Indian Ocean, a disease that  prior to 2005 was largely confined to small outbreaks in Africa.

 

Normally transmitted by the A. aegypti mosquito, a single-nucleotide polymorphism (SNP) evolved in the virus that enabled it to replicate efficiently in the more common Aedes albopictus mosquito. As a result, more than 2 million new infections from Chikungunya have occurred over the past 5 years.

 

Over the last decade the public’s awareness of vector-borne illnesses has increased with the introduction of West Nile Virus to the United States, the return of Dengue Fever to Florida after an absence of 60 years, and the growing number of Lyme Cases (MMWR Est. 20,000) each year.

 

The explosive growth of Dengue around the world is well illustrated by the following graph from the World Health Organization.

 

Average annual number of dengue cases reported to the World Health Organization - has steadily increased since the 1950s, with 908 cases average reported between 1950 and 1959 and 968,564 cases average reported annually between 2000 and 2007.

What this graph doesn’t indicate is another doubling of dengue cases has taken place over the past 5 years.  Once an obscure tropical disease, Dengue now poses a threat to parts of the United States and Europe.

 

 

Dengue, Malaria, EEE, West Nile Virus, Chikungunya, Lyme, Yellow Fever, Anaplasmosis, Ehrlichiosis, dozens of types of Encephalitis, Tularemia, Plague . . .  the list of vector-borne diseases is large and growing.

 

Two divisions of the CDC  focus on zoonotic and vector-borne diseases.  Both offer informative web pages.

 

Division of Vector-Borne Diseaes (DVBD)

 

 

National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)

 

 

A few of my previous blogs on vector borne diseases includes:

 

Lancet: Progress Towards A Dengue Vaccine
Florida: Locally Acquired Malaria Case Suspected
ASTMH: Dengue and Insect-Borne EIDs In The US
MMWR: Dengue Epidemic In Puerto Rico
MMWR: Dengue Fever In Key West
Eastern Equine Encephalitis (EEE)

 

Related Post:

CDC
EID
Vector Borne Diseases

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