Because of concerns over West Nile virus and now the rapidly occurring Chikungunya virus in the US, many customers want to know more about them. How are they transmitted and can animals become infected too? Epidemiologists who study the presence and progression of infectious diseases in populations often talk about hosts, reservoirs and vectors when discussing these questions.
Humans are hosts for West Nile virus. As hosts, mosquitoes bite us for their blood meal and we can become infected. Our status as a host has nothing to do with being a reservoir or vector, only that we can become infected with the virus because of being a target for the mosquito’s meal.
A vector for a virus can be a species that can transmit a disease to another species, directly or indirectly. For example, mosquitoes are a vector for West Nile virus. A mosquito’s bite may transmit the disease directly to another species, like birds or humans. Although mosquitoes are a vector for West Nile virus, humans are not. We cannot directly pass on West Nile to someone else.
Birds are a vector and reservoir for West Nile virus because they can pass on the virus on to uninfected mosquitoes that bite them. An uninfected mosquito that bites a bird with a high enough level of the virus in their blood can transmit the virus to the mosquito. The disease can then be passed back and forth between these two species. A study on PubMed.gov titled Birds, Migration and Emerging Zoonoses: West Nile… found, “The initial spread of WNV in the U.S. along the eastern seaboard coincided with a major bird migration corridor.” Humans are not a vector of West Nile because we cannot infect any uninfected mosquitoes that bite us, nor pass it onto other humans.
The Chikungunya virus is another frequently discussed mosquito borne infection. Our role in the transmission of the Chikungunya virus is like birds in their transmission of the West Nile virus. Our ability to infect previously uninfected mosquitoes is highest during the first 3-7 days we experience the most severe symptoms of Chikungunya. Since we can transmit the virus to mosquitoes, this makes us a reservoir for the virus exactly as birds are for West Nile virus.
The ability of humans to serve as a vector and reservoir for the Chikungunya virus is the reason for the increase in the number of Chikungunya cases in the Caribbean. The number went from 1 in December 2013 to more than 100,000 seven months later. During this same period, the number of Chikungunya cases in the US increased mostly from travelers returning from the Caribbean.
Only in the US territories of Puerto Rico and the US Virgin Islands have humans infected mosquitoes with the Chikungunya virus. No reported cases of local transmission of the disease have occurred so far on our mainland. CDC scientists believe we will eventually have small isolated outbreaks here in the US. Cases have been reported in over 29 states in 2014 but none involved local transmission of the disease. In order to lower your risk of contracting any mosquito borne disease, consider a proven and effective barrier treatment for your yard that will eliminate both mosquitoes and ticks. Reducing your exposure to these insects will also dramatically reduce the risk of their disease for both your family and yourself.