Powassan virus

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at February 4, 2016
StartDiseasesPowassan virus

The Powassan virus, or POW virus, is a disease transmitted by ticks. It is relatively rare with only a handful of cases each year and many patients do not develop any symptoms or develop only minor symptoms. However, it can become serious, requiring hospitalization and causing long-term health consequences.


Definition & Facts

The POW virus is a virus that affects the nervous system. It has afflicted only 60 Americans in the last decade. The virus also has a narrow infection area that is concentrated heavily in the Great Lakes region with 22 of the 60 total cases occurring in Minnesota.

The Powassan virus belongs to the genus Flavivirus. It is related to other viruses transmitted by blood-sucking insects, including West Nile virus and tick-borne encephalitis. It is an RNA virus, meaning that is does not have DNA and codes its genetic material only on RNA.

Symptoms & Complaints

Many people infected with the POW virus display minor symptoms or no symptoms at all. Minor symptoms include vomiting, weakness, confusion, headache, and fever.

The POW virus affects the nervous system and can result in several neurological complications. The two most serious of these complications are encephalitis and meningitis. Both of these conditions can become life-threatening very rapidly, and if not treated quickly they may result in permanent brain damage.

Encephalitis is an inflammation of the brain usually caused by infection. This inflammation puts increased pressure on the brain and may lead to brain damage. Meningitis is inflammation of the membranes around the brain and spinal cord. Both of these conditions tend to display few symptoms and then suddenly become very serious. Both conditions require immediate hospitalization.

Although 90 percent of people with POW virus infection survive, about half of all survivors are left with long-term neurological problems including frequent headaches, memory loss and muscle atrophy. Loss of neurological function may also lead to sudden losses of coordination, seizures and difficulty speaking.


The Powassan virus can only be transmitted to humans through the bite of a few tick species, including the deer tick and blacklegged tick. Not all ticks carry the virus, but any of these tick species may potentially carry the virus. The virus cannot be transmitted from human to human or to other animals, so there is no risk of infection by being around or helping someone who is infected.

Tick bites can happen without warning, and most people do not feel tick bites at all. While it is possible to get a tick bite anywhere, ticks tend to bite in an area of the body that is dark and well-protected or shaded, like the armpit, in the belly button, around the ear and on the top of the head.

Diagnosis & Tests

Since the symptoms of Powassan virus are closely related to a variety of other diseases, diagnosis is usually based on a variety of risk factors taken together. The most common indicators are the patient's symptoms combined with the risk of exposure to tick bites. If a person suspects infection, it is important for him or her to inform the health care provider about any recent vacations or activities that would make someone susceptible to a tick bite, especially travel to regions where the virus is concentrated.

A lab test of serum or cerebrospinal fluid can be conducted to determine infection for sure. This test usually takes 4 to 14 days to process. It works by detecting virus-specific components and antibodies. In most cases, the test is not necessary and does not dramatically affect treatment.

Treatment & Therapy

The majority of infections do not require any treatment. Only when the disease displays life-threatening complications or symptoms of encephalitis or meningitis does it require hospitalization. There is no direct cure or treatment for the disease, such as an antiviral drug. Since the disease is a virus, no antibiotic will be effective either. There is also no vaccine available to prevent the disease.

Instead of direct treatment, healthcare providers will give the patient supportive therapy designed to keep them alive and healthy, allowing their immune system to fight off the infection. Supportive therapy includes bed rest, medications for pain, plenty of fluids and general comfort.

In the case of serious complications, such as encephalitis, specific treatments for those symptoms may be used, such as medications that reduce brain swelling. A person may also need intravenous fluids due to excessive vomiting. If complications begin to affect breathing, a person may also need respiratory support.

Lasting complications or neurological damage may require long-term therapy. This could include help with memory loss and coordination and other therapies designed to restore neurological function.

Prevention & Prophylaxis

The best way to prevent infection with the Powassan virus is to prevent the tick bite that transmits it. These preventative measures apply to all tick bites and related diseases, most notably Lyme disease.

It is important to limit outdoor activities in areas prone to the disease. This is especially true during the season with the highest tick population, usually in the fall. Ticks are most common in wooded areas, so it is important to exercise caution when camping and hiking.

Ticks can be repelled with insect repellents. Taking precautions to find ticks before they bite is important. Showering will help remove ticks from the body, and manual tick checks should be performed, especially on children and pets.