UPDATE:
Early in my book Natural Histories, I report on West Nile virus. In fact, I close the chickadee chapter by saying, “At this point, no one knows what the long-term affect of West Nile virus will be on chickadees or other birds. Recent loses may just be a temporary blip on the radar. It may be commonplace for their population to fluctuate.”
I wrote that in 2003. Seven years later we can breathe a collective sigh of relief. The avian epidemic—it can also infect horses and humans—has slowly lost its punch.
The most recent issue of the Cornell Lab of Ornithology’s BirdScope reports that “West Nile virus hit American crows particularly hard. When the disease first appeared in New York City, in summer 1999, nearly 5,500 crows died in four months. Tests suggested the disease was 100 percent fatal to crows. Many other species, from jays and magpies to gulls and chickadees, also proved susceptible. Millions of birds died as West Nile swept across the continent in just five years.”
Ten years later: “In a new analysis of the virus’s effects on American crows, Cornell Lab researches learned that West Nile virus became less virulent as it raced westward across North America. They also found that crows in diverse habitats were less likely to come down with the disease than crows in species-poor areas.”
This suggests that habitats with a high bio-diversity are better able to mitigate the pathogen’s effects, diluting it so to speak.
Early in my book Natural Histories, I report on West Nile virus. In fact, I close the chickadee chapter by saying, “At this point, no one knows what the long-term affect of West Nile virus will be on chickadees or other birds. Recent loses may just be a temporary blip on the radar. It may be commonplace for their population to fluctuate.”
I wrote that in 2003. Seven years later we can breathe a collective sigh of relief. The avian epidemic—it can also infect horses and humans—has slowly lost its punch.
The most recent issue of the Cornell Lab of Ornithology’s BirdScope reports that “West Nile virus hit American crows particularly hard. When the disease first appeared in New York City, in summer 1999, nearly 5,500 crows died in four months. Tests suggested the disease was 100 percent fatal to crows. Many other species, from jays and magpies to gulls and chickadees, also proved susceptible. Millions of birds died as West Nile swept across the continent in just five years.”
Ten years later: “In a new analysis of the virus’s effects on American crows, Cornell Lab researches learned that West Nile virus became less virulent as it raced westward across North America. They also found that crows in diverse habitats were less likely to come down with the disease than crows in species-poor areas.”
This suggests that habitats with a high bio-diversity are better able to mitigate the pathogen’s effects, diluting it so to speak.
From the point of view of the virus—and admittedly, that's a narrow point of view—it's not advantageous if your host dies. Host dies, virus dies. It's counterproductive, particularly if the infected host dies so quickly that the pathogen has not had time to jump to a new one. It's better if the sickened carrier lives and moves about so that the virus can spread and spread and spread, to an increasing number of new hosts.
Crows breathe sigh of relief: their populations are
recovering from affects of West Nile virus.
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