Rare deer tick virus identified as cause of death
The death of a man in New York State is a fresh reminder for Islanders and visitors to continue to be vigilant when in areas where contact with deer ticks is possible and to take precautions against the possibility of infection.
A May 15 report in The New England Journal of Medicine (NEJM) confirmed that the 62-year-old man died from a rare deer tick virus. It is the first definitive case describing fatal deer tick virus encephalitis (inflammation of the brain) in humans, according to Norma P. Tavakoli, lead author of the study.
Cases of infection are rare, and some people may contract the virus with no outward signs of ill health. But since diagnostic testing for the virus is not routine, there may be instances that will be missed, according to public health officials.
"In certain locations of the northeastern and north central United States, the prevalence of deer tick virus in adult deer ticks is high, but human infection has not been reported previously," said the study. "This could indicate that the virus does not easily infect humans or that it is not particularly pathogenic."
The victim, a native of Putnam County in New York State, owned horses and spent time outdoors in a wooded area. He was admitted to a hospital in late spring of last year complaining of fatigue, fever, rash, and muscle weakness.
Although the man did not report a tick bite, the study said, transmission likely came from a deer tick in its nymphal, or juvenile, stage. Because nymphal deer ticks are tiny, it is not uncommon for their bites to remain undetected, said the study.
The man's medical history included leukemia, which may have contributed to a weakened immune system. He died 17 days after he was admitted to the hospital.
Deer tick virus is closely related to a number of other tick-borne viruses that include Powassan virus, which can also cause encephalitis. Both are part of a family of viruses that include West Nile virus, St. Louis encephalitis virus, dengue and yellow fever, all of which are transmitted by mosquitoes, according to a report provided by the U.S. Department of Health and Human Services.
Prevention remains the best strategy, said the NEJM study.
Martha's Vineyard and Nantucket are considered hot spots for tick-borne illnesses. As a result, Island physicians are generally well versed in the symptoms associated with a variety of diseases.
The ticks most people are likely to pull off their pant legs after a spring walk in the woods are the adult dog, or wood, tick which can carry Rocky Mountain spotted fever, a rare occurrence on the Vineyard. Dog ticks are also known to spread tularemia, sometimes called rabbit fever, a potentially fatal disease caused by the Francisella tularensis bacterium.
The smaller deer tick, which is responsible for infecting humans with Lyme disease, the most publicized of tick-borne illnesses, is less prevalent. Deer ticks are also capable of transmitting a malaria-like disease called babesiosis, and ehrlichiosis (HGE), a disease related to Rocky Mountain spotted fever.
Sam Telford, associate professor of infectious diseases at the Tufts University School of Veterinary Medicine and a well-known tick researcher, has been studying deer ticks for many years on Nantucket and Martha's Vineyard.
Mr. Telford responded to a series of questions about the NEJM report and the virus in an email to The Times.
Mr. Telford said he discovered the virus in 1997 but could not find evidence that it was a threat to people and moved on to other problems. "I knew about the NEJM report over a year ago and we have been gearing up to get back to work on deer tick virus," said Mr. Telford.
Mr. Telford said the virus is definitely on Martha's Vineyard. "We found it easily in deer ticks back in the late 90s and last year as well when we resumed looking for it," he said.
Mr. Telford said fewer than one percent of ticks carry the virus, as opposed to Lyme (about a 50 percent infection rate), and babesiosis or ehrlichiosis (about 5 percent for either).
Mr. Telford said it is likely that there is a lot of under-diagnosis. "We don't know what the clinical spectrum of disease is," he said. "Perhaps in many it is just fever and stiff neck and muscle aches that goes away after a couple of weeks."
Mr. Telford recalled that in 1994 Dr. Bill Tsikitas, a specialist in infectious diseases who has since left the Island, diagnosed a severe case of encephalitis in an Island woman in her early 40s as "severe Lyme meningitis." Dr. Tsikitas wisely sent the woman to Mass General Hospital, said Mr. Telford, where she at first rapidly deteriorated but then slowly recovered over a period of six months.
Mr. Telford spoke to the woman in an effort to try to discover where she might have picked up the tick. "At the time her disease was considered to be due to Powassan virus, which is the parent virus of deer tick virus," he said. "Powassan was described in the early 1960s in Canada and is considered the most dangerous of the North American arthropod-transmitted viruses."
Powassan is known to be maintained in nature by ticks that are carried by woodchucks, raccoons, and skunks. "The skunks and raccoons on Martha's Vineyard definitely have the right ticks, but we have yet to find bonafide Powassan virus," said Mr. Telford. "So, we wonder if that 1994 case was actually deer tick virus."
Mr. Telford said that based on his most recent Vineyard observations the number of deer and dog ticks is about normal for this time of the year. He has already found tularemia in ticks on the Vineyard and expects cases of infection have already occurred but have not yet been confirmed by the state Department of Public Health.
Ticks feed on blood, and deer, as large animals, host great numbers of ticks. Mr. Telford said that the number of deer in a community has a direct correlation to the number of ticks. He said reports by Island hunters of fewer animals would take some time to translate into fewer ticks.
"Even if there are fewer deer, even greatly reduced deer numbers won't translate to any relief right away, given the two or more years life cycle of the tick," said Mr. Telford. "I would expect that if deer are on the decline on Martha's Vineyard, the areas where deer are typically not commonly seen anyway would be the first sites to show any reduction in ticks."
