by Gertrud U. Rey
On February 7, 2025, the world lost Dickson Despommier, a formidable parasitologist, gifted storyteller, and original co-host of the podcast This Week in Virology. Being a life-long learner, Dickson developed a keen interest in medical ecology, an interdisciplinary field that investigates how our ever-changing environment impacts human health. In his book “West Nile Story,” he describes the 1999 epidemic of West Nile virus in New York City, and he hypothesizes about the sequence of events that led to the appearance of the virus in the United States. In this post, I will summarize West Nile Story as a tribute to Dickson, who I had the privilege of meeting in person.
During the summer and fall of 1999, several thousand people in New York City came down with a mysterious illness that was characterized by fever, headache, and other flu-like symptoms. A few dozen affected people also developed encephalitis, a condition that ended up being fatal in seven of these individuals. Around the same time, countless dead crows materialized in parks across the city, and numerous exotic birds in the Bronx Zoo and a few horses on Long Island fell ill and died. The pathogenic cause was initially thought to be St. Louis encephalitis virus, a member of a group of mosquito-borne viruses that also includes Zika virus, dengue virus, yellow fever virus, and West Nile virus (WNV). However, a series of collaborations between scientists at the Bronx Zoo, the University of California at Irvine, and the CDC eventually led to the conclusion that the illnesses and deaths in humans, birds, and horses were actually caused by WNV. In particular, an analysis of the brain tissues of five of the deceased patients revealed the presence of a WNV RNA sequence that matched the WNV strain that had caused an epidemic on Israeli goose farms the year before. This was a surprising revelation, because until then, WNV was geographically limited to the Mediterranean countries, the Middle East, Africa, West Asia, and Australia.
WNV was originally isolated in 1937 from the blood of a febrile woman living in the West Nile region of Uganda. The virus typically cycles between mosquitoes and birds, but it can also be transmitted to humans, horses, and other animals through the bite of at least seven different species of mosquito. Although there is no clear evidence for how WNV was introduced into the United States, most theories involve the arrival of an infected bird, mosquito, or human from Africa or the Middle East. Because the WNV strain isolated in New York City in 1999 was the same as the one that circulated in Israel in 1998, Dickson suggested the following hypothetical scenario. A farm worker or visitor on a goose farm in Israel likely became infected with WNV, then traveled to New York City while still harboring virus in their bloodstream. Shortly upon arrival, this individual was bitten by a WNV-transmitting mosquito (possibly at the Bronx Zoo), which then transmitted the virus to others, thus initiating the epidemic in New York.
WNV outbreaks occur mostly during hot, dry weather, just like the weather conditions in New York City during the summer of 1999. Culex pipiens, the dominant mosquito vector for WNV, preferentially feeds on birds; however, when rainfall is limited, birds tend to migrate away in search of water. With fewer birds to feed on, Culex pipiens mosquitoes switch to humans and other organisms for their blood meals. The coincident rising energy costs during that summer caused many swimming pool owners to shut off their pool pumps, allowing the pools to become stagnant breeding ponds for Culex pipiens and other WNV-transmitting mosquitoes. This unfortunate combination of economic circumstances and environmental conditions could have easily allowed a single WNV-infected person to introduce the virus into New York City and allow it to gain a foothold in its new niche.
Dickson optimistically noted that the 1999 WNV epidemic “resulted in the establishment of lines of communication among groups that heretofore had never been in contact with one another,” and that “continuation of these interactions most likely will lead to a stronger surveillance system for all kinds of diseases, regardless of whether they affect humans and wildlife.” In line with this thinking, public health agencies across the world have gradually adopted a “One Health” approach to disease prevention, which aims to achieve optimal health outcomes by monitoring the interplay between humans, animals, and plants in their shared environment.
West Nile Story describes in detail the various ways in which mosquitoes impact our ecosystem, and it does not downplay their potential threat to humans. “Throughout our evolution, there has never been a more real and present danger to our extinction than that which emanates from the bite of an infected female mosquito. Attacks by saber toothed tigers, poisonous snakes, noxious insects, aggressive tribes of Neanderthals, droughts, floods, famines, volcanic eruptions, earthquakes, and other such hazards of our earliest days on this planet pale by comparison to the destruction wreaked upon our species by infections delivered to our bloodstream through her dainty, hypodermic needle-like mouth parts.” Malaria is a good example of such a destructive infection – it is one of the world’s most deadly infectious diseases, and it is caused by a parasite that happens to be transmitted by mosquitoes.
WNV is now well established across the United States, with more than 51,000 recorded cases since 1999; however, there are still no licensed vaccines that prevent WNV disease in humans. There are also no specific treatments, but supportive care can be used to alleviate symptoms and prevent complications. The most effective way to prevent infection is by preventing mosquito bites through the use of insect repellent and other strategies, which prevent many other infections as well.
Links related to Dickson Despommier:
Dickson’s websites: Trichinella.org; Thelivingriver.org; Fordhamopolis.com; Despommierphotoart
I’ve been following your blog for some time now, and I’m consistently blown away by the quality of your content. Your ability to tackle complex topics with ease is truly admirable.