Study finds deadly strain of encephalitis in Hudson Valley ticks

Above: The black-legged or deer tick, Ixodes scapularis. Photo by Scott Bauer of the USDA; published under Creative Commons license. Source:

In the Hudson Valley and across the nation, tick-borne disease is on the rise. The deer ticks common in the area are vectors for several diseases whose infection rates have ballooned over the last decade -- from Lyme disease, which infects several thousand New York State residents every year, to rarer ailments like babesiosis and anaplasmosis.

According to a new study, locals now have another tick-borne disease to worry about: A strain of a rare but deadly form of encephalitis known as Powassan virus. Named for the Canadian town where it was discovered in 1958, Powassan virus has historically been rare, with only a handful of cases reported in the United States each year. But the disease is life-threatening, and often leaves those who contract it with long-term neurological problems.

In recent years, the new study reports, 14 cases of Powassan virus have been confirmed in New York State, two of them fatal. Most of the cases were from Westchester, Dutchess and Putnam Counties. For the study, scientists from the state Department of Health, the Cary Institute of Ecosystem Studies in Millbrook, and SUNY Albany set out to figure out whether local tick populations were carrying the Powassan virus.

To measure the prevalence of the Powassan virus among Hudson Valley ticks, researchers collected 13,500 ticks of several species in Sullivan, Ulster, Orange, Rockland, Westchester, Dutchess and Putnam Counties, and tested them for viral RNA. The researchers also trapped mammals and birds and used blood tests to see if the animals had antibodies to the virus.

The study found that in the eastern Hudson Valley, in areas where humans have contracted Powassan virus, many local deer tick populations were infected with a strain of the virus. Infected ticks were found in Dutchess, Putnam, Westchester and Rockland Counties. The highest infection rate among ticks sampled in the study was in Putnam County, where researchers estimated that 3.84 percent of ticks were infected. (Click here for a table of results for each county sampled.)

No ticks infected with Powassan virus were found in Sullivan, Ulster or Orange Counties.

Much is still unknown about how the virus is spreading throughout local ecosystems, and whether local birds and mammals play a role in transmitting the virus to uninfected ticks. But the widespread infection of local deer ticks is a worrying sign. Another strain of Powassan virus has been associated mostly with the groundhog tick, Ixodes cookei, which is not as common in the Hudson Valley as the deer tick.

Another worrying trait of the virus: It can infect a host almost immediately after the bite of an infected deer tick. Scientists have found that unlike other tick-borne diseases, which typically require long attachment periods to be transmitted, Powassan virus can be transmitted from tick to host in just 15 minutes.

To prevent tick bites, the Centers for Disease Control recommend that people avoid walking through tall grass and brushy leaf litter if possible, use tick repellents containing DEET or permethrin to prevent bites, and check for ticks after returning from infested areas.

The full text of the recent Powassan virus study, published this week in the open-access journal Parasites and Vectors, is available to read online.

Hat tip to the Poughkeepsie Journal's John Ferro, who reported on the Parasites and Vectors study earlier this week.