West Nile and Zika

Robin in Holly

Robin in Holly

Joe LaManna was last night’s speaker at Science on Tap. Dr. LaManna is an ornithologist who is studying at Washington University the long term effects of the West Nile virus on US bird populations. While, his talk was about West Nile, he began with a discussion of the Zika virus. Both viruses are of the Flavivirus genus and both viruses have in recent years emigrated from the Old world to the New, 1999 for West Nile and 2014 for Zika. While humans are the primary host for Zika, birds are the main hosts for West Nile. Mosquitoes are the vector for both diseases. The Asian tiger mosquito spreads West Nile in Saint Louis, while the Aedes Aegypti mosquito is spreading Zika across the Americas. Both mosquitoes are members of the Culex genus and also look enough alike that they are difficult to tell apart. LaManna referred to Aedes Aegypti as the Norway rat of mosquitoes, because like that rat, it has adapted well to living with humans. He offered one bit of solace for Saint Louisans, Aedes Aegypti is a tropical mosquito and as such will not likely range any further north in the US than the Gulf coast.

West Nile entered the US through NYC, most likely carried by a sick bird imported as part of the animal trade. In three years it had spread across the lower forty-eight states. While birds are the most affected by West Nile, humans are susceptible too. 80% of humans contract the disease without manifesting any symptoms. 20% of people have mild cold or flu-like symptoms and 1%, mainly the elderly becomes seriously ill and some die. There have been over 5,000 human deaths attributed to West Nile in the US, with half of them coming from eastern Texas. LaManna even supposed that Alexander the Great might have died from West Nile. Outside Babylon, a flock of ravens fought in the sky above him and then fell dead at Alexander’s feet. He became ill and died in Babylon soon afterwards.

When West Nile swept across America bird populations crashed, but scientific studies showed that these populations soon recovered. I can still remember the disappearances of the crows and their subsequent recovery. LaManna contends that this is not the full story. For some bird species this is what occurred, but for more species the detrimental effects of West Nile continues to this day. Those initial bird population studies used a technique called the point-count survey. Simply put, experts go to a point in the woods and count the birds there. Then they come back the next year and repeat the process. While this system is accurate at counting bird populations, it doesn’t account for the disease’s enduring effects. Subsequent counts can include individuals that weren’t in the previous ones. Reproduction and migration can recoup losses from West Nile and skew these surveys.

LaManna recommends using banding and recapture as a more accurate means to count birds. He piggybacked upon just such a nationwide survey that began well before the advent of West Nile. He concentrated on about fifty common species of small birds, like the pictured robin above, giving his research good sample sizes. His results showed that while a third of the species showed the predicted initial mortality and recovery, two-thirds of the species show persistent mortality due to West Nile.

While, LaManna’s talk was about West Nile the specter of Zika was always lurking and it resurfaced again during the Q&A session. A question was asked about Brazil’s current Zika epidemic and the associated occurrence of microcephaly in infants. Columbia is also enduring a Zika epidemic, but doesn’t seem to have the same number of microcephaly cases, LaManna’s response was “It sounds like we both heard the same NPR article this morning.” In today’s news three pregnant women in Florida have tested positive for Zika. LaManna hopes that some of the lessons learned dealing with West Nile can be applied to the looming Zika crisis.

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