Powassan Virus: New Test Reveals Rare Tick-Borne Disease More Dangerous Than Lyme

In the US, ticks can spread several pathogens in one bite. A new test offers physicians the ability to identify what infections ticks are carrying and can detect if one of the pathogens could be the spreading Powassan virus.

Ixodes scapularis, better known as the black-legged tick or deer tick, is questing in the cover image above. It happens to be how ticks catch dinner. Holding onto the leaf with its third and fourth pair of legs, it moves its first pair of legs out in hopes of grabbing a passing human, or another animal, to get a blood meal. In recent years, Lyme disease, a tick-vectored bacterial infection, has steadily spread across the US.

Since researchers discovered Lyme disease in 1981, it has drawn considerable attention to tick-borne diseases that infect humans in the US. But it's not the only tick-borne disease out there.

The black-legged tick is a particularly dangerous tick. According to a study published in mSphere, researchers at the Center for Infection and Immunity at Columbia University's Mailman School of Public Heath report that I. scapularis can transmit multiple pathogens. These include Borrelia burgdorferi (which causes Lyme disease), Borrelia miyamotoi (a related bacterial infection that causes similar symptoms), Anaplasma phagocytophilum (which causes anaplasmosis), Babesia microti (which causes babesiosis), and the serious, potentially emerging Powassan virus (POWV).

The general geographic range of the black-legged tick, I. scapularis

POWV is commonly found in wildlife, but doctors first identified it in humans in Powassan, Ontario, in 1958. Although it is a virus, POWV is not communicable between humans. It is carried by the I. scapularis tick, and more than most tick-borne infections, POWV can be immediately serious. With Lyme disease, the longer a tick is attached to a human or animal, the more likely they are to be infected with the bacteria. The infected tick transmits POWV within minutes of attachment.

POWV causes neurological symptoms including swelling of the lining of the brain and spinal cord, leading to potentially fatal conditions like encephalitis and meningitis, both severe inflammatory infections.

While some persons infected with POWV have no symptoms, others suffer:

• confusion
• seizures
• headache
• muscle pain and fatigue

Because it is a virus, antibiotics are not an option. With no vaccine and no antivirals that work against the infection, the only treatment for POWV is medical support — and approximately 10% of victims die.

The Prevalence of Powassan Virus

Durland Fish, Professor Emeritus of Epidemiology of the Yale School of Public Health, said in a press release that POWV has the potential to spread in the US. While the infection is currently considered rare, Fish notes the virus used to be transmitted only by a tick that does not commonly feed on humans. In recent years, as their territories overlapped, the virus has spread to the black-legged tick, significantly raising the odds of human infection with POWV.

Powassan is spreading due to the expansion in the range of deer ticks. Because deer ticks can now transmit Powassan virus infection to humans, cases are being reported in areas where they have never occurred before. As the geographic range of Lyme disease expands, so will Powassan.

As the number of patients reporting Lyme disease increases, and the reports of complicated symptoms — including the mysterious "chronic Lyme disease" — persist, researchers are looking at the possibility that ticks are actually spreading co-infections with more than one pathogen.

For example, a third tick-borne disease, the treatable parasitic infection babesiosis, can be transmitted at the same time as Lyme disease or other tick-borne pathogens, causing a co-infection. A parasite that infects human blood cells, babesiosis often causes no symptoms but may eventually cause anemia, from the destruction of red blood cells.

A co-infection of babesiosis and Lyme could be passed on by only one vector event — like a tick bite. Co-infections usually cause more severe symptoms, and can be responsible for lasting illness and possible disability.

Taking Stock of Dangerous Tick Diseases

To better understand the types of pathogens carried by black-legged ticks, Columbia scientists analyzed 318 adult and nymph ticks collected at five sites in New York, and three sites in Connecticut, using a newly developed test designed to detect and identify multiple pathogens.

With the new DNA amplification process, the research group was able to test for five pathogens in each tick (for the presence of A. phagocytophilum, B. miyamotoi, B. burgdorferi, B. microti, and POWV), up from a limit of three with previous technology. The new test lowers diagnostic costs, includes pathogens considered rare (like POWV), and offers information about co-infections present in tick populations.

In both New York and Connecticut, the Lyme disease bacteria B. burgdorferi was the most commonly identified pathogen (21% of nymphs and 67% of adult ticks in New York infected), followed by B. microti (the bacteria that causes babesiosis), present in 17% of nymphs and 30% of adult ticks in New York. Co-infections were identified in 45% of adults and 11% of nymphs (the immature tick life stage). Specifically, POWV was present in 2% of adults.

Among other observations, the study authors wrote: "For POWV, improvement in surveillance is essential in light of the potential for POWV to result in life-threatening encephalitis."

Commenting on the importance of the DNA amplification technique for identifying co-infections and improving surveillance, W. Ian Lipkin, director of the Center for Infection and Immunity and professor of Epidemiology at the Mailman School, said in a press release, "This new test can strengthen surveillance for tick-borne illnesses which are underreported and growing rapidly."

While Lyme disease is serious, it can still be treated with antibiotics. Fish raised the specter of widespread tick-borne disease much worse than Lyme when he said that "Powassan could become epidemic like Lyme disease. Because it can be a serious disease causing fatalities and there is no treatment for it, Powassan has the potential to become a greater ... public health threat than Lyme disease."

You can avoid POWV using the same techniques used to avoid Lyme disease — including watching for ticks, wearing long pants and long-sleeves, and most importantly, using DEET when in tick territory.

By the side of a trail, in your yard, or in recreational areas, ticks are questing, waiting patiently for their next meal. Do what you can to make sure that meal isn't you.

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Cover image via Jim Gathany/CDC