Chikungunya Virus


Chikungunya: An exotic virus on the move

A tropical virus now endemic in a temperate climate, chikungunya is not usually a killer though it is very painfully unpleasant. The first cases on the European continent occurred in northeastern Italy in 2007.

Infectious diseases, do not respect borders. Their vectors and hosts can hop a ride on a plane or a boat, and arrive in the US unexpectedly. Some of them like it just fine over here, and have adapted very well. West Nile arrived in the US in New York in just 1999. It is now endemic, and is continuing its spreading throughout the Americas killing hundreds of millions of birds and more than a thousand humans as well.

There is a possibility that the same thing could happen in the United States, since the two mosquito species that can spread the virus are found in the Southeast, according to an official with the US Centers for Disease Control and Prevention (CDC). But he said the likelihood of that is "relatively low."

Chikungunya usually causes fever, headache, fatigue, nausea, vomiting, muscle and joint pain, and a rash, according to the CDC. The disease is not life-threatening. Symptoms typically last a few days to 2 weeks, but fatigue or joint pain sometimes lingers for weeks to months, the CDC says.

The name "chikungunya" is Swahili for "that which bends up," a reference to the stooped posture associated with joint pain. There is no vaccine or specific antiviral treatment for the illness, which is caused by a virus of the genus Alphavirus.

The report says A albopictus is found in several other European countries, including Albania, France, Belgium, Montenegro, Switzerland, Greece, Spain, Croatia, the Netherlands, Slovenia, Bosnia, Herzegovina, and possibly more, suggesting a potential for further spread of the disease.

"We don't even know why West Nile disease [another mosquito-borne viral illness] became endemic in North America but not in Europe, even though the virus and the vector are present on both continents," Evelyn Depoortere, an epidemiologist at the European Centre for Disease Prevention and Control in Stockholm, told Nature.

"For chikungunya to be transmitted in the US, you need to have a viremic person or mosquito introduction in an area where both susceptible persons and the predominant mosquito vector are present," Hayes said. "Both those conditions exist in the US, so I think the importation of chikungunya is a concern."

But the risk of indigenous transmission is "probably relatively low in the continental United States," mainly because of socioeconomic and lifestyle differences that tend to limit the spread of mosquito-borne viruses like chikungunya, dengue, and yellow fever, Hayes said. For example, air conditioning and window screens help protect people from heavy exposure to mosquitoes, he explained.

However, areas where dengue transmission already occurs or is possible may be more vulnerable to chikungunya, Hayes said. Such areas include parts of Florida and Texas, plus Puerto Rico and the US Virgin Islands.

"It's possible, if the virus should become endemic in, say, the southeastern US, that it could provide a locus for spread to other parts of the country, but I wouldn't think it would spread like West Nile virus," he said. Birds have helped spread West Nile across the continent since the disease emerged in New York City in 1999.

Here is a brief explanation for why the Aedes albopictus mosquito has now become a much better vector for the spread of the chikungunya virus. It wasn't always, but viruses evolve, and adapt. Here is what this "smart" virus did to ensure its own survival.

The rapid global movement of chikungunya virus appears to be a consequence of a change in its mosquito vector. Some time during 2005 a virus was selected with a single amino acid change in the envelope glycoprotein which allows efficient replication in Aedes albopictus ...This mosquito was never a good host for chikungunya virus, partly because it bites so many different animal species. The amino acid change enhances viral replication in the mosquito, leading to much times higher levels of virus in the salivary gland. Consequently the virus is more likely to be transmitted upon biting a new host.

To further complicate matters, not only is Aedes albopictus now a good host for chikungunya virus, but the mosquito is spreading across the globe from eastern Asia to Europe and the United States. The mosquito was first found in the New World in 1985 when it was isolated in Houston, Texas. It probably traveled there from northern Asia in ships carrying scrap tires. But there are at least five other reasons to worry about Aedes albopictus: the mosquito has also been found to carry eastern equine encephalitis, Keystone, Tensaw, Cache Valley, and Potosi viruses.

Supporting public health efforts in the developing world helps to protect all of us, but our own public health system needs attention, and support too. It is underfunded, and likely to be overlooked given how bad the economy is. Maybe, the Obama administration will do the right thing by it.

The chain of chikungunya fever outbreaks from Kenya to Italy reflects a convergence of factors including: rapid international transport, previous introduction of exotic mosquito species, inadequate mosquito control, and climatic conditions. Increasingly important in vector-borne disease emergence, these factors have facilitated other recent epidemics involving imported microbes and local vectors. For high-income countries, the increasing range of vector-borne diseases suggests two major implications: First is the need to maintain vector control capabilities, and second countries should recognize that public health system weaknesses in developing countries endanger all countries.


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Yes, if you asked me I would say West Nile got endemic here because we have tropical areas whereas Europe does not.

....West Nile arrived in the US in New York in just 1999. It is now endemic, and is continuing its spreading throughout the Americas killing hundreds of millions of birds and more than a thousand humans as well.

That's a lot of birds.

indigo girl

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Yes, if you asked me I would say West Nile got endemic here because we have tropical areas whereas Europe does not.

Can't say why Europe is not having the same problem. The conditions must not be as favorable there somehow. They have the chikungunya virus instead.

The timing of when humans in the urban northeast (not a tropical area by any means) are most likely to become infected with West Nile is during the late summer and fall. If robins are the preferred host, and they have already migrated south, who is left for the mosquitoes to snack on but Homo Sapiens? We are nice big, juicy targets as are horses also. They too are very susceptible to this virus.

...Culex pipiens, the dominant enzootic (bird-to-bird) and bridge (bird-to-human) vector of WNV in urbanized areas in the northeast and north-central United States, shifted its feeding preferences from birds to humans by 7-fold during late summer and early fall, coinciding with the dispersal of its preferred host (American robins, Turdus migratorius) and the rise in human WNV infections. We also show that feeding shifts in Cx. tarsalis amplify human WNV epidemics in Colorado and California and occur during periods of robin dispersal and migration. Our results provide a direct explanation for the timing and intensity of human WNV epidemics. Shifts in feeding from competent avian hosts early in an epidemic to incompetent humans after mosquito infection prevalences are high result in synergistic effects that greatly amplify the number of human infections of this and other pathogens. Our results underscore the dramatic effects of vector behavior in driving the transmission of zoonotic pathogens to humans.

But, this study suggests something different is happening in southern California. Bird migration there does not seem to be a factor leading to human cases.

...a strong positive relationship exists between West Nile virus-positive mosquitoes, wild birds, and humans within any single month; in other words, as soon as mosquitoes become infected with West Nile virus, bird and human host populations are immediately at risk. In fact, of all variables examined, these mosquito pools are the best predictors of West Nile virus in humans for a given month. This is a very different result compared to previous studies that suggested that humans and other mammals were not necessarily at risk until later summer months as birds left for migration (Figure 2). In terms of bird species at risk, the impact of West Nile virus on avian populations in this area is still being investigated, but many species in Orange County have been found to carry high prevalence of West Nile virus (Figure 3).

While several environmental variables were investigated, it was precipitation in the previous winter months that best predicted the numbers of West Nile virus positives in the following summer. It is hypothesized that a rainy winter may facilitate the extent to which mosquitoes may survive and reproduce; more mosquitoes may lead to higher West Nile virus prevalence in the following summer months.

Spatial analyses have revealed that much of the valley area in Orange County may serve as good places for West Nile virus to persist. This is in part due to the fact that these valleys (primarily the Santa Ana and Saddleback Valleys) are consistently warm, highly urbanized (with ample man-made water sources such as canals, drainage, and ponds), and highly populated with both primary (bird) and secondary (humans) populations. Recently, Kern County, California has attributed its spike in West Nile virus cases to foreclosed homes that have left abandoned and unchlorinated swimming pools. These artificial pools may act as excellent breeding grounds for mosquitoes.

It is even present in Canada which is rather chilly in the winter, but this virus seems to have no problem wintering over, and reappearing the next year with the mosquitoes.

In September 2008, the Public Health Agency of Canada said the number of human cases to that point in the year totalled 29, with 13 cases reported in Manitoba and 12 in Saskatchewan.

There were 2,215 human cases of West Nile virus in 2007. More than half were in Saskatchewan.

Human to human transmission of West Nile can occur:

Person-to-person transmission has also been documented in 2002 through:

? Blood transfusion and organ donation

? Breast milk

? Pregnancy (mother to child prior to birth)

? Infection in 2 laboratory technicians through the skin from needle stick or scalpel

cut while working with infected birds

indigo girl

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French Riviera sees new case of chikungunya virus

AFP: French Riviera sees new case of chikungunya virus

I was not aware that this was a problem outside of Italy.

French health authorities have asked doctors on the Riviera to be on the alert after a second case was detected in the region this weekend of the mosquito-borne chikungunya virus.

Two 12-year girls in the town of Frejus have caught the virus that causes fever, headaches and arthritic-type symptoms that leave victims stooped, officials said Sunday.

They noted that both cases were "native," meaning that the victims had not travelled to the parts of eastern Africa, southeast Asia or the Indian subcontinent were the virus is widespread.

(hat tip crofsblog)

indigo girl

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First Cases of Chikungunya Virus in the Western Hemisphere Occur in Brazil

This is strange. One country, but three cases, and none of them connected. All cases were acquired abroad...Surely there are more cases in the west that we just have not heard about.

Now, if these people were bitten by the local mosquitoes once they got home, we might be seeing more cases. I wonder how good the Brazilians are about mosquito control. Just because no further cases have turned up yet does not mean that some of the local mosquitoes are not now carrying this virus.

Brazil reports first 3 Chikungunya cases

Brazil Wednesday reported first three cases of Chikungunya, a viral disease spread by mosquitoes that causes fever and severe joint pain.

The infected included one man from Rio de Janeiro and another from Sao Paulo who recently traveled to Indonesia. The third was a Sao Paulo woman recently returned from a trip to India, the Health Ministry said. All of them received treatment and have recovered.

So far there is no evidence of Chikungunya transmission in the country,the ministry said in an online statement.

(hat tip crofsblog)

indigo girl

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Just a thought, since I have been looking at dengue cases occurring in India in December, and mosquito eggs do survive the winter.

It took just one infected person in Ravena, Italy which has a temperate climate, to allow the virus to become endemic to that area, spread over the alps to Switzerland, and now there are cases on the French Riviera.

The Brazilians are congratulating themselves that there has been no further spread of Chikungunya virus despite having 3 separate incidents of unconnected cases infected abroad who were then diagnosed on returning to Brazil. If I was a gambler, I would bet on the the possibility of locally acquired cases in the not too distant future.

indigo girl

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India: Chikungunya Eye Infections

Conjunctivis from a mosquito borne disease? Apparently, this not a new symptom.

Indian doctors are warning Chikungunya patients who experience ocular problems (photophobia, pain, swelling, blurred vision) to seek out an ophthalmologist immediately.

First described in 1955 in Tanganyika, it was only sporadically seen over the years in eastern and central Africa. That is, until 2005, when Chikungunya made a jump to the Indian Ocean island of Réunion.

In the five years since that time, Chik has migrated to India, Indonesia, and much of south east Asia. It has even been imported into Italy.

Many infectious disease specialists have expressed concerns that Florida - which has recently seen a return of Dengue fever after more than 5 decades - could one day face the establishment of chikungunya as well.

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