There are plenty of good reasons to safeguard against tick bites, which can transmit babesiosis, anaplasmosis, tularemia, Rocky Mountain Spotted Fever, and, most commonly, Lyme disease. Researchers have now added another rare but potentially deadly disease to the list of tick-borne illnesses possible on Cape Cod.
Deer ticks infected with the Powassan virus were recently found at various sites around Cape Cod, including Brewster and Orleans. Though most who are exposed to the virus experience no symptoms, around 10 percent become severely ill or die.
“We're looking at this in the context of West Nile virus,” said Larry Dapsis, entomologist and deer tick project coordinator with the Cape Cod Cooperative Extension. Though that virus is transmitted by mosquitoes, it is genetically related to Powassan.
“We can consider the viruses kind of cousins to each other,” Deputy Massachusetts State Epidemiologist Catherine Brown said. In both cases, most people who are exposed show no symptoms at all. “Their immune system takes care of the disease,” she said.
“A lot of people can be exposed and be asymptomatic. But in rare instances when it goes a neuro-invasive route, that's when bad things happen,” Dapsis said. The virus can cause meningitis, the inflammation of the covering of the brain and spinal cord, and encephalitis, the inflammation of the brain itself.
“It can be serious, and it's fatal in about 10 percent of the cases,” he said. “And the people who survive this usually have long-term or permanent neurological damage.” Symptoms of the disease usually begin one week and one month after the bite of an infected tick, and can include fever and headache, vomiting, weakness and confusion, loss of coordination, speech difficulties and seizures.
There is no specific treatment for people infected with Powassan virus, aside from supportive care.
State officials have had reports of nine cases of the virus in Massachusetts residents since the beginning of 2013, prompting the Cape Cod Cooperative Extension and the Laboratory of Medical Zoology at Umass-Amherst to begin checking local ticks for the virus. At the six locations tested on Cape Cod, Powassan-infected ticks were discovered at four, with infection rates ranging from 2.5 percent to more than 10 percent.
“Geographic distribution is complete across the Cape,” Dapsis said. For that reason, researchers are starting to believe that the virus has been present in local ticks for some time, “and has flown under the medical radar screen,” he said. Researchers are applying for grant funds to extend their tick testing on the Cape.
Experts say there is another reason to be concerned about Powassan. Unlike the virus that causes Lyme disease, the Powassan virus can be transferred from the tick to its host almost immediately. With Lyme, the tick needs to be attached for many hours before transmission of the virus is likely.
“It's a game-changer because it resets our educational efforts,” Dapsis said. No longer is it adequate to check one's body for ticks at the end of the day. But Powassan underscores the need for many of the other methods of tick bite prevention.
“Powassan virus, like all other tick-borne diseases, is best prevented by avoiding tick bites,” Brown said. Regular tick checks are important, and people who have been outdoors in the woods or on the edges of yards should place their clothing in the dryer for 20 minutes. Exposed skin should be treated with Deet-based insect repellents or alternatives like picaridin.
“But permethrin-treated clothing is at the top of the list,” Dapsis said. “That is my ace card.” Ticks often die on contact with pants, socks and particularly footwear treated with permethrin, an insecticide and repellent that is 2,250 times more toxic to ticks than to humans. Officials say the chemical is safe enough for use even by infants, children and pregnant women because of its very low rate of skin absorption. While some outdoor retailers sell pre-treated clothing, people can treat their own clothes and the insecticide will remain effective through several washings.
While state public health laboratories in Massachusetts and some other states have the ability to provide screening tests for Powassan, routine tests are not available from commercial labs, Brown said.
Ticks can also be tested for the presence of Powassan; information is available at www.TickReport.com.
Given the difficulties in testing and the fact that the virus appears to be widespread on Cape Cod, “It is definitely possible that there are cases of Powassan virus that have gone undiagnosed,” Brown said. It is also possible that the percentage of asymptomatic patients is higher than currently expected.
“What we know is that Powassan remains rare at this point. However, the testing that was done on Cape Cod does indicate that, at least in some areas, there's a significant portion of ticks that are infected,” Brown said. But in terms of researchers' understanding of this virus, “it's early days,” she said.