Friday, March 12, 2010

The Threat Of Vector Borne Diseases



# 4424




Yellow fever, now pretty much relegated to Africa and parts of South America, was once the scourge of North America and was not unknown Europe, appearing in ports as far north as Ireland.   


Ian York over at the Mystery Rays blog has been doing a terrific job relating the history and science behind Yellow Jack Fever over the past few months, with recent entries that include:


Yellow fever, stasis, and diversification

The deadliest, most awe-inspiring of the plagues

The good old days


The maps in Ian’s blog The good old days  are particularly fascinating to me, as I live in a region that was once a haven for Yellow Fever.


A little over a year ago, in a blog entitled  Outnumbered By A Competent Vector  I outlined the rapid spread of West Nile via mosquitoes here in the United States, and reported that scientists were worried that Dengue and Chikungunya were also candidates to spread in North America.



From the USGS Factsheet on West Nile Virus


As you can see, the virus managed to spread rapidly in the first three years of introduction into the western hemisphere.   In 2002, however, the range of the virus virtually exploded.


Most people infected with WNV experience mild, or sub-clinical symptoms.  A small percentage develop WNV neuroinvasive disease (WNND), a form of encephalitis.   For every serious presentation, there are probably 100 mild, or asymptomatic cases.


Well, timing is everything.


As luck would have it, roughly six months later – for the first time in five decades – Dengue was reported as spreading in Florida, infecting at least 20 people in Key West.



Researchers monitoring Denge outbreak


University of Florida mosquito researchers have been watching with a wary eye as the dengue virus returns to the state after more than 50 years.


As of early February, 20 cases of locally transmitted dengue had been confirmed in Key West. Monroe County officials have issued a health alert and launched an education campaign urging residents to eliminate water sources in and around their homes where mosquitoes can breed.


"We haven't seen dengue in Florida in a long time, but this does give us evidence that we can have it again," said Roxanne Connelly , an associate professor of medical entomology with UF's Institute of Food and Agricultural Sciences .



Dengue, malaria, Chikungunya and Yellow Fever all have potential to re-emerge – at least in limited outbreaks - in places like the United States and Europe. In fact, Chikungunya showed up – in all places – Northern Italy a few years ago.  



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 in 2007 which led to more than 290 cases reported in the province of Ravenna, which is in northeast Italy. 



Eurosurveillance today has a series of articles on vector borne diseases and their potential to impact those living in Europe.  While they are all of interest, perhaps the biggest threat is addressed in:



Yellow fever and dengue: a threat to Europe?

P Reiter ()1

  1. Insects and Infectious Disease Unit, Institut Pasteur, Paris, France

Citation style for this article: Reiter P. Yellow fever and dengue: a threat to Europe?. Euro Surveill. 2010;15(10):pii=19509.

Date of submission: 06 May 2009

The introduction and rapidly expanding range of Aedes albopictus in Europe is an iconic example of the growing risk of the globalisation of vectors and vector-borne diseases. The history of yellow fever and dengue in temperate regions confirms that transmission of both diseases could recur, particularly if Ae. aegypti, a more effective vector, were to be re-introduced.  The article is a broad overview of the natural history and epidemiology of both diseases in the context of these risks.



While this is a long and informative article, I’ll skip to the chase, where the author sums up the threat of Yellow Fever and Dengue to Europe.   Much of what is said here applies equally as well to North America.



The future in Europe

Dengue is essentially an urban disease because of the urban ecology of its vectors and the behaviour of its hosts. Rapid urbanisation has made it an increasingly serious public health problem in the tropics [48]. Millions of people travel from the tropics to Europe and North America each year (for example, 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 [11,12].


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].



With budget cuts in public health departments around the country, including in mosquito control operations, our ability to prevent or deal with outbreaks of vector borne diseases grows weaker.  A risky strategy in a world with increasing globalization, travel, and urban sprawl.


Eurosurveillance has a number of other review articles on vector-borne diseases in the current issue, including:


West Nile virus in Europe: understanding the present to gauge the future

by P Reiter

The appearance of West Nile virus in New York in 1999 and the unprecedented panzootic that followed, have stimulated a major research effort in the western hemisphere and a new interest in the presenc(...)

Rift Valley fever - a threat for Europe?

by V Chevalier, M Pépin, L Plée, R Lancelot

Rift Valley fever (RVF) is a severe mosquito-borne disease affecting humans and domestic ruminants, caused by a Phlebovirus (Bunyaviridae). It is widespread in Africa and has recently spread to Yemen (...)

Leishmaniasis emergence in Europe

by PD Ready

Leishmaniasis emergence in Europe is reviewed, based on a search of literature up to and including 2009. Topics covered are the disease, its relevance, transmission and epidemiology, diagnostic method(...)

Arthropod-borne viruses transmitted by Phlebotomine sandflies in Europe: a review

by J Depaquit, M Grandadam, F Fouque, P Andry, C Peyrefitte

Phlebotomine sandflies are known to transmit leishmaniases, bacteria and viruses that affect humans and animals in many countries worldwide. These sandfly-borne viruses are mainly the Phlebovirus, the(...)