DEADLY DEER TICK VIRUS

                            DEADLY DEER TICK VIRUS

A new, potentially lethal tickborne threat known as Powassan or deer tick virus is emerging in New York's Hudson Valley, researchers reported.
In an extensive 5-year project that involved collecting nymphal and adult ticks from multiple locations in counties along the Hudson River, the virus was found in 58 tick pools, according to Laura D. Kramer, PhD, from the New York State Department of Health's Wadsworth Center Arbovirus Laboratories in Slingerlands, and colleagues.
Among the individual ticks, the infection rate ranged from 0.2 to six per 100, the researchers reported online in Parasites & Vectors.

"Doctors need to be aware of this pathogen when patients present with encephalitis or even severe fever, particularly if there has been a tick bite," Kramer said in an interview. "And for the general public, it's another reason that people need to protect themselves against ticks."
The culprit tick, Ixodes scapularis, is also the transmitter of Lyme disease, and the infecting vertebrate hosts in this study included opossums, skunks, and raccoons.
The deer tick virus was first identified in the brain tissue of a patient in Powassan, Ontario, who succumbed to encephalitis in 1958, and the first isolates from I. scapularis ticks in North America were detected in 1997.
Since that time, infected ticks increasingly have been found in numerous locations ranging from Connecticut to Wisconsin, and two variants of the virus have been recognized.
Seropositive individuals have been identified in Dutchess, Putnam, and Westchester counties, and also further afield in Albany and Suffolk counties.
The numbers are still low -- 10 to 12 cases per year -- but fatality rates ranging from 10% to 60% have been reported, and survivors can have debilitating neurologic sequelae.
In one recent case, a patient with serologically proven encephalitis died after 8 months of severe neurologic dysfunction (Clin Infect Dis 2013; 56: e40-7).
Because of the potential severity and the apparent recent increase in cases, particularly in the lower Hudson Valley, Kramer and her colleagues from the Department of Health partnered with the Cary Institute of Ecosystem Studies in Millbrook, N.Y., to estimate the extent of spread of the virus and to seek out its sources.
Between 2007 and 2012, they collected more than 13,500 ticks, with the most common being I. scapularis, or the black-legged tick.
"This is an aggressive human-biting tick," explained Richard S. Ostfeld, PhD, of the Cary Institute.
"The infection prevalence of about 1% to 6% among these ticks is low compared with Lyme disease, which often is found in 30% to 50% of ticks, but it's still alarmingly high, giving you a one in 20 chance that the tick biting you might be transmitting a deadly virus," Ostfeld told MedPage Today.
"But we're probably only seeing the most severe cases. There could be many milder cases of flu-like illness that resolve on their own," said co-author Alan P. Dupuis, PhD, of the Wadsworth Center.
In addition, unlike Lyme disease, which usually requires 24 to 48 hours of tick attachment for transmission of the pathogen Borrelia burgdorferi, Powassan virus can be transmitted in just 15 minutes.
"Doing a tick check immediately after returning from a tick habitat is very important," said Dupuis.
One possible reason for the apparent increase in cases in recent years has been improved diagnostic methods.

DEER TICK VIRUS

"After the emergence of West Nile virus, diagnosis of these encephalopathies caused by arboviruses improved tremendously," Kramer explained in an interview. But there also has been a major increase in tick populations, she noted.
The infected ticks have been found in greater densities in areas to the east of the Hudson River, in Westchester, Putnam, and Dutchess Counties, and thus far the river seems to be acting as a barrier to spread, according to Ostfeld.
But this geographic barrier has been breached by other tickborne diseases including Lyme disease, babesiosis, and anaplasmosis, he cautioned.
"Therefore, we might expect Powassan to move across the Hudson into western New York and potentially elsewhere in the Mid-Atlantic and New England regions like the other tickborne diseases," Ostfeld said.
Spread of the virus also may be enhanced through tick carriage by birds, the study suggested.
"For the first time in the U.S. we discovered neutralizing antibodies to Powassan virus in birds," said Dupuis.
"That has implications, with birds providing a vehicle for long-distance dispersal of infected ticks," he said in an interview.
More than 700 birds were tested in Dutchess and Putnam Counties, and the most common found to carry infected ticks were cardinals, catbirds, veeries, and Eastern towhees. Almost all the ticks carried by birds were I. scapularis, and antibody titers ranged from 1:20 to 1:80.
Much remains to be learned about the virus, its vectors, and its mode of transmission, the researchers noted. For instance, it has not been determined whether transmission occurs horizontally to ticks from vertebrate hosts, during co-feeding by multiple ticks, or transovarially, from parent to offspring.
"Results of this study emphasize a need for further investigation to determine risk of human exposure, demarcate the geographic range of [deer tick virus] in the Hudson Valley and across the range of I. scapularis, elucidate important vertebrate hosts, and evaluate/assess the role of alternative transmission cycles," Kramer and colleagues concluded in the article.