Dengue, West Nile virus, yellow fever, Zika, and malaria: what do they all have in common? All five are diseases spread to humans by a mosquito bite (in the microbiology world, the first four are known as arthropod-borne viruses, or arborviruses for short). All five have been present here in the United States, and all five have the capacity to cause several public health issues, with disease symptoms ranging from small fever, to rashes, to serious disease, and death.
Zika is the new kid on the American block. Previously found only in Africa, it has been slowly spreading around the world, as diseases are not stopped by geopolitical borders. The most recent outbreak in South America has left doctors and epidemiologists mystified, as countless babies born to infected mothers are developing new and very serious complications, such as microcephaly and central nervous system damage. Sadly, as these infants represent the first generation to grow up with these Zika-related conditions, doctors don’t know what lies ahead for these children.
Zika isn’t the first disease to attack pregnant women. Malaria has a special affinity for the placenta, and up until large-scale eradication efforts, it was infecting people in the U.S., particularly in the South. We have mosquito-breeding-site elimination programs and (now largely-banned) insecticide programs to thank for the lack of domestic malaria here in the U.S. Yellow fever virus, after killing tens of thousands in the American South, was similarly eradicated here through destruction of habitats that can breed mosquitoes.
Dengue and West Nile are two arborviruses still found in the U.S., although there are infrequent outbreaks for two specific reasons. West Nile’s predominant victim is the corvid (black-birds and ravens are examples). Humans get infected by accident: a mosquito who likes to feed on both corvids and humans will take up infectious blood from the bird, the virus will infect the mosquito’s salivary glands, and when the mosquito bites the human, virus gets into the human’s bloodstream. West Nile killed 90 percent of the corvids in the U.S. — luckily, the mosquitoes no longer have enough opportunities to become infectious. Dengue, however, spreads infrequently through the U.S. because there is limited contact between the mosquitoes who have it, and the people who don’t. Limited mosquito contact may surprise some, but it’s a specific type of mosquito that typically spreads Dengue (Aedes aegypti), and its human-shy biter, usually kept at bay with air conditioning.
Will Zika be like Dengue, causing a few cases of mild illness and never gaining a foothold? Or will Zika be like yellow fever, harming many before we are able to eliminate it from our borders?
The answer will lie in the little critters at the heart of it: the humble mosquitoes. If we are lucky, the local mosquitoes will prove resistant to infection, and Zika will pop in and out of the country, usually travelling in the blood of a tourist. If we are unlucky, many of the local species will prove capable of both becoming infected, and passing it on. In this case, Zika will become firmly established, and we will once again need great efforts for eradication.
We can all get a head start by refusing to take the gamble. Be diligent about preventing mosquitoes from breeding in your house or garden. Spill out stagnant water, clean gutters to keep water flowing, and be cognizant that mosquitoes can breed in an area of still water as small and shallow as a yogurt pot. Not only will these actions reduce your contact with potentially infectious mosquitoes, it will make time spent in your garden more pleasant as well!
By Aimee Kopolow
Aimee Kopolow, Ph.D., lives in Kemp Mill, Maryland, and works in the DC area.