Dr. Mike Cranfield was well known as a dedicated veterinarian at the Maryland Zoo and a wildlife conservationist with a longtime focus on gorillas. The retiree died after being infected with West Nile virus from a mosquito bite, the zoo reported this week.

Although deaths from the virus are uncommon, and Cranfield likely was infected while traveling, public health officials in Maryland had already been out in some neighborhoods warning people to take precautions. A growing number of people across the U.S. have been infected with West Nile this year.

“Our protocol — when there is a case of mosquito-borne illness, like West Nile virus, in Baltimore — is to conduct canvassing in neighborhoods where there may be a risk of local transmission to educate residents on mosquito control best practices,” said Yianni Varonis, a spokesman for the city health department.

The state has a surveillance system to look for West Nile infections in people, animals and mosquitoes because there are cases every year. This year in Maryland, there have been two cases suspected in people and 54 positive tests among groups of mosquitoes.

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Most people with West Nile have no symptoms. About 20% of people develop headaches, fever, aches and nausea. Fewer than 1% develop potentially deadly neurological damage.

On the heels of a case of locally acquired malaria in Maryland, the first in four decades, local officials and infectious disease experts caution people to take mosquito-borne diseases seriously. The resident of the Washington, D.C., suburbs has been released from the hospital.

The officials say measures include draining even small amounts of standing water that serve as mosquito breeding grounds, using repellent and covering up in the late summer and fall when mosquitoes are most active.

“We have West Nile every year, and now we have to worry about the occasional case of malaria, and there are tick-borne diseases like Lyme. So overall we should be aware of these things and take precautions,” said Dr. Meghan Davis, an associate professor of environmental health and engineering in the Johns Hopkins Bloomberg School of Public Health.

“I don’t think the status quo is the message we want to be sending,” she said. “We always want people to strive to do better.”

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West Nile virus cases trending up

Davis said, with the mosquito season still underway, it’s tough to know how bad this year will be for West Nile specifically, but cases are trending up in some places. This year, cases are higher than usual in the Western and mountain states.

In all, there have been 455 cases of West Nile this year in 36 states as of Aug. 29, federal figures show. There are normally more than 2,000 by the end of the busy fall season.

There also were cases of locally acquired malaria in Texas and Florida, in addition to Maryland.

Weather and climate suggest there could be more cases of mosquito-borne illness. Surges in the short term will depend on rainfall because wet weather can increase mosquito breeding ground, Davis said. In the long term, climate change will have an impact because increasing temperatures can quicken the mosquito life cycle.

A recent report from the U.S. Centers for Disease Control and Prevention found that West Nile is on the rise and is now the nation’s leading cause of arboviral disease, which is an infection from a bite from a mosquito or tick.

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State and local agriculture and health officials continue to tackle the issue with sprays to control mosquito populations, and Baltimore City and Anne Arundel County health departments are among those that have said they are canvassing to offer residents guidance.

State health officials said the department participates in the #fightthebite campaign on social media, which shares tips to prevent mosquito bites.

“The Maryland Department of Health is always concerned about the impact of West Nile virus and other reportable diseases,” said David McCallister, a department spokesman, in an email. “The department is mandated to track and provide updates to the public on the diseases’ spread so that they can protect themselves and seek treatment when necessary.”

The threat from West Nile and malaria infection, the CDC says, is when patients develop meningitis and encephalitis, inflammation of the tissues surrounding the brain and spinal cord or inflammation of the brain.

Malaria symptoms can be similar to those of West Nile. Though malaria is a big killer of children, particularly in Africa, cases in the United States are rarely severe or deadly. There are about 2,000 cases reported nationally a year, but most are travelers from other countries.

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A zoo vet’s legacy

Zoo officials said Cranfield, the veterinarian, felt ill a day after leaving Canada, where the 71-year-old had just bought a cottage on a river.

Officials described him as a great wildlife champion. He came to the zoo in 1982 as chief veterinarian and later became director of animal health, research and conservation, responsible for the care of the zoo’s more than 1,500 animals.

In 1998, he became executive director of the Mountain Gorilla Veterinary Project, a nonprofit group that worked to save the lives of critically endangered gorillas living in Rwanda, Uganda and the Democratic Republic of the Congo. It also worked to save endangered eastern lowland gorillas in the Congo.

The program was based at the Maryland Zoo until 2009, when it partnered with the Wildlife Health Center at the University of California Davis School of Veterinary Medicine and was renamed Gorilla Doctors.

Although Cranfield retired from the Maryland Zoo in 2019, he returned occasionally to help care for the animals.

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The announcement from the zoo said, “Mike leaves behind a legacy of contributions to global wildlife conservation and veterinary medicine along with hundreds, if not thousands, of people and animals he touched through his work.”


Meredith Cohn is a health and medicine reporter for The Baltimore Banner, covering the latest research, public health developments and other news. She has been covering the beat in Baltimore for more than two decades.

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