Recently, there have been an increasing number of cases of Powassan virus infections being documented in the northeastern and upper mid-western United States. What is this virus, how can you reduce your risk of acquiring it and what are the implications of the rising number of cases noted in the past 2-3 months?

Powassan virus, named after the town in Ontario where it claimed its first known victim in 1958, is a flavivirus that, similar to Lyme disease (which is caused by a bacteria rather than a virus), is transmitted from ticks to humans.  Unlike Lyme disease however, this virus has no known cure, and can produce life-threatening neurological symptoms that may be difficult to associate with the virus, given that many physicians are not as aware of this virus when compared to other infectious organisms.

The virus is found primarily in the northeastern U.S along with the upper midwestern states, especially near the Great Lakes. Infections tend to occur between mid-spring through the fall, when human-tick interactions are highest due to the relatively warmer weather. Anyone in theory can become infected—young or old, man or woman, and both immunocompetent or immunosuppressed patients. Once the virus is transmitted by a tick bite into the bloodstream, there is an incubation period ranging from 1 week to 1 month. At that point, the virus makes its way into the central nervous system, where it affects the brain, causing symptoms of fevers, headaches, confusion, altered mental status and seizures. Spinal inflammation can also occur, causing limb weakness and impaired reflexes. It can also affect the membranes surrounding the brain (known as the meninges), resulting in meningitis.  Although patients may not have any symptoms that result from infection, in those that do develop manifestations of the disease, symptoms can be life threatening in up to 15-20% of patients, and up to half of the remaining symptomatic patents can develop long-term neurological sequelae.

Diagnosis is achieved through serological testing (predominantly by detecting IgM antibodies) of the cerebrospinal fluid, however it should be noted that testing is not readily available and is usually has to be sent out in most institutions, which can delay the diagnosis. However, as mentioned above, there is no known treatment for this infection, and management often involves providing respiratory support and IV fluids, correcting electrolyte imbalances and close monitoring of vital signs while awaiting to see if the patient’s immune system can successfully clear the infection. Given the lack of effective treatment options and the fact that anyone can become infected, there is concern that rising rates of Powassan virus infection will become a serious challenge for physicians both in the inpatient and outpatient setting.

As mentioned in a previous post, the rise of many infections this year (Lyme disease, Erlichiosis, Anaplasmosis, Babesiosis, Powassan virus infection, etc.) appears to be due to the rising number of ticks being noted, both in endemic areas as well as locations that have not classically been considered endemic. This is due in part to a rise in the number of natural hosts (deer and mice) that carry these ticks, as well as the redistribution of these hosts into different habitats, which in turn is being influenced by human factors (urbanization, deforestation, global warming).

Prevention will be the single key factor in limiting the number of cases of Powassan virus infections, as well as other tick-borne infections this coming spring. When possible, avoid prolonged exposure to wooded areas as well as areas with long grasses, where ticks often hide. If you are out for extended periods of time in these areas, wear long sleeved clothing to minimize exposed skin that ticks can latch onto, and use tick-spray (Picaridin, DEET, Permethrin), which are often available over-the-counter.

Prior to taking a shower, be sure to scan for ticks on your body—they are often located in the armpits, groin or abdomen area. Be aware of how to properly remove ticks, and seek medical care if prolonged tick bite exposure has occurred in order to minimize the chances of any future complications as best as possible.

Most importantly, however, though the incidence of this infection may be increasing, the absolute number of cases is very very low.  The CDC statistics indicate that nationally,  between 2006-2015, there were no more than 12 cases per year.  Compared to other diseases (Lyme e.g.) this is a very rare infection.