West Nile virus may not be a death sentence for crows. In a new study from the College of Veterinary Medicine, wildlife experts describe the successful treatment and release of five American crows infected with the deadly disease – the first crows to survive the West Nile virus.
“Their survival may indicate a change in the crows’ immunity or a shift in the behavior of the virus,” said Dr. Cynthia Hopf Dennis, clinical assistant professor at Janet L. Swanson Wildlife Hospital and first author on the research paper.
the paperPublished May 2 in the Journal of Avian Medicine and Surgery, details the crows’ survival and potential adaptation to the virus. The authors tracked the crows’ immune response while they were in the hospital, and found that the birds excreted the virus in respiratory secretions for at least 93 days after they were infected.
The researchers said this is an important finding that shows they can pass it on to others and test it via this method for 13 weeks after infection.
“It’s an interesting interaction that we know happens uniquely in different species. I think there are more around the country surviving,” said Hopf Dennis. It adapts to the species it has encountered over the past 20 years.”
The first known cases of West Nile virus in the United States were discovered in 1999, when an outbreak in New York City caused a 45% decrease in regional American crows. Since the initial spread of the virus, its severity has fluctuated across North America due to many vector, host, and environmental factors that are still not fully understood.
Transmitted by mosquitoes, West Nile virus can infect more than 250 bird species, but is most deadly to scavengers and birds of prey. These groups include American crows, bluebirds, crows, eagles, hawks, and owls.
The virus causes severe dehydration, acid-base and electrolyte imbalances, cellular injury, multiorgan inflammation, and necrosis. Affected birds may appear fluffy, weak, and unable to fly. Infection usually occurs during the spring, summer, and early fall, when mosquitoes are most prevalent.
West Nile virus is considered the most deadly of American crows, previously having a mortality rate of 100%. One contributing factor is the bird’s communal perching lifestyle. After a mosquito infects a crow, the crow excretes large amounts of virus in its faeces, which may affect bird-to-bird transmission of the virus during perching.
West Nile virus can infect mammals as well as birds, particularly horses and humans, which are endless hosts. Cases vary between people from year to year and can be fatal. In 2020, 33 of the 540 known West Nile virus infections died.
The study covers American crows admitted to the Janet L. Swanson Wildlife Hospital from 2013 to 20, when 32 Westerns were admitted to the hospital, 25 of which tested positive for West Nile virus. Of these twenty-five, the five American crows detailed in this study survived their release.
While there is no treatment or treatment prescribed for the birds suffering from West Nile virus, the five survivors at Cornell received supportive care, including fluid therapy, anti-inflammatory medications, vitamin B supplements, prophylactic antifungals, and antiparasitic medications. This is the gold standard approach for birds with the disease, although it may vary depending on hospital resources. The birds were tested regularly for the virus after infection, which was present in one bird as ‘suspect positive’ after 93 days.
“This 93-day period is a much longer shedding period than previously reported for American crows,” said Hopf Dennis. “More frequent testing would be useful in future cases to track how long birds shed West Nile virus.”
Although there is a vaccine for captive birds, the level of immunity varies between species, and broad vaccination of wild birds is not possible. “The most important protection for them would be any maternal immunity that the crows could pass on to their offspring,” said Hopf Dennis. “I hope that when we bring the crows back into the wild after treatment and rehabilitation, they will be able to contribute to a larger population that is able to survive the virus and provide a certain level of protection for their offspring.”
The study’s co-authors are Dr. Elizabeth Bunting, Professor of Practice in the Department of Public Health and Ecosystem Health. Dr.. Sarah Childs-Sanford, DVM ’99, assistant professor in the department of animal medicine and chief of department at Janet L. Swanson Wildlife Hospital; and Ann Clark, Bartle Professor in the Department of Biological Sciences at Binghamton University.
Hopf Dennis said, “For wildlife rehabilitators and other vets who have experienced the 100% mortality historically for West Nile virus-infected crows, this study reminds us that they deserve treatment, they can survive until they are released — and they can thrive in wild even after injury.”
Melanie Grever Cordova is the assistant director of communications for the College of Veterinary Medicine.