Powassan Virus

What is Powassan Virus?

The Powassan virus, also known as POW, is a kind of virus that primarily affects people living in the Northeastern United States, Canada, and Russia. This virus belongs to the Flavivirus family and is spread to humans through the bites of various tick species. It was first identified as a harmful virus to humans in 1958 when it caused a child to pass away due to brain inflammation (encephalitis) in Powassan, Ontario.

The most serious effects of the Powassan virus involve the nervous system. The majority of people who seek medical help due to the Powassan virus have developed encephalitis or meningoencephalitis, a condition where both the brain and its surrounding tissue are inflamed. If the virus starts affecting the nervous system, there’s a 10 to 15 percent chance of dying. Although this kind of severe infection is still quite rare, there are more cases being reported across the US and Canada over the past ten years. This increase is likely due to better methods of testing for this virus and also due to its spread.

If a person is potentially at risk because of where they live or if they are showing symptoms of encephalitis or meningoencephalitis, they should be checked for the Powassan virus.

What Causes Powassan Virus?

The POW virus, or arbovirus, is part of the Flaviviridae family and is further classified under the Flavivirus genus. Viruses from this family are often transmitted via ticks or mosquitoes, with some examples including the viruses that cause Yellow fever, Japanese encephalitis, West Nile, Dengue, and Zika.

The POW virus specifically is characterized by having a single-strand of RNA. There are two key lineages or types of this virus, which can be differentiated through genomic sequencing. However, for most purposes, these two types are virtually the same as they react similarly to antibodies and display similar disease progression.

The primary way humans contract the POW virus is through tick bites, primarily from the deer tick or “Ixodes scapularis”. The same tick is also a carrier for other common diseases, including Lyme disease, Babesiosis, and Anaplasmosis. Although two other tick species – the groundhog tick and the squirrel tick – can carry the POW virus, they rarely bite humans.

Rodents and small mammals serve as the main carriers of the POW virus. Mice, groundhogs, voles, and squirrels are often found to have the virus. Larger animals like skunks, foxes, deer, and horses may also play a role in its spread.

Animals infected with the POW virus develop high levels of the virus in their blood, which can then be transmitted to ticks that feed on these animals. These ticks then pass on the virus to humans or other animals they bite. However, when humans get infected, the amount of virus in their blood doesn’t usually reach high enough levels to spread the disease further, which is why humans are often considered “dead-end hosts”.

Risk Factors and Frequency for Powassan Virus

The POW virus is not as common as other flavivirus infections, but cases have been increasing steadily, especially in certain areas. The majority of human infections have been found in Canada, Russia, and the United States. In the United States, the areas most affected are New England and the Great Lakes region, particularly Minnesota, Wisconsin, Massachusetts, and New York. In Canada, the most cases have occurred in Eastern Canada, especially Ontario and Quebec. Russia has also recorded cases, mainly in its Far East province of Primorsky Krai.

Most new cases appear from April to November, coinciding with when ticks are most active. However, infections can occur year-round during milder weather. Studies indicate that the POW virus has a wider distribution across Europe and North America than clinical case reports have previously suggested. This is shown by studies that detect antibodies, suggesting people have been infected with the virus, stretching from one side of North America to the other, and even reaching parts of northern Mexico.

Current studies have yet to fully explore the prevalence of the virus in areas where it is common. Older research suggests that between 1% to 6% of people in such areas have evidence of past infection. It is not clear whether the antibodies against the virus remain present throughout a person’s life after infection. The low number of clinical cases in relation to the number of people showing evidence of past infection suggests that many infections are mild and don’t cause serious illness.

Over the past ten years, there have been several outbreaks of the POW virus. For example, there was an outbreak involving severe illness in Maine and Vermont in 2001 after years without any cases, and similar outbreaks have occurred across New England and the Midwest. Between 2010 and 2019, the CDC reported 347 cases of POW virus infection in the US, of which 166 were severe. In 2019, the highest number of serious illnesses caused by the virus was reported, with a total of 39 cases, a 5-fold increase from 2015. It is clear that cases are increasing, but it is not yet understood what factors are driving the resurgence of POW virus.

Signs and Symptoms of Powassan Virus

Powassan (POW) virus infection frequently manifests as inflammation of the brain or meninges but often goes unnoticed due to the lack of symptoms. After exposure, it typically takes between 1 to 5 weeks for symptoms to show, starting with a non-specific illness that may include fever, muscle pain, tiredness, weakness, headache, and a sore throat. Other symptoms can include nausea, vomiting, or a measles-like rash. This initial phase lasts 1 to 3 days and is always followed by neurological symptoms, if they develop at all. These neurological symptoms may not surface until weeks or even months after the initial illness. It’s still unclear how frequently these symptoms progress to more severe neuroinvasive disease, or which risk factors contribute to worsened outcomes.

In severe cases, symptoms may extend to the central nervous system and could include prolonged fever, confusion, a decreased level of consciousness, and seizures. Some patients may also experience eye-related symptoms such as eye muscle weakness or uncontrolled eye movements. Varying degrees of paralysis have also been linked to POW virus infection, though less commonly. However, none of these symptoms are exclusive to POW virus infection and thus cannot be used to differentiate POW infection from conditions caused by other similar viruses, such as West Nile, Eastern Equine, La Crosse, or Saint Louis encephalitis virus.

Here’s a brief summary of the signs and symptoms of POW virus infection:

• Fever
• Muscle pain
• Tiredness
• Weakness
• Headache
• Sore throat
• Nausea
• Vomiting
• Measles-like rash (in some cases)
• Neurological symptoms (if they occur, weeks or months after initial illness)
• In severe cases, symptoms related to central nervous system such as prolonged fever, confusion, decreased consciousness, and seizures
• Eye-related symptoms or paralysis (less common)

Testing for Powassan Virus

If you or someone you know is suspected of having a Powassan (POW) virus infection, doctors focus on checking for neurological symptoms. People who only show non-specific symptoms like those associated with the flu usually don’t require specific testing for the virus. However, in cases where someone exposed to certain geographic areas presents symptoms like encephalitis or meningoencephalitis (conditions associated with brain inflammation), testing for POW virus should be considered.

For those with high suspicion of infection, a few key parts of the diagnostic approach include brain imaging, blood tests (serology), and a lumbar puncture. A lumbar puncture, often referred to as a spinal tap, is a procedure that can be used to collect a sample of cerebrospinal fluid (CSF). This is the fluid that surrounds the brain and spinal cord to protect them from injury. This test can indicate a type of white blood cell (lymphocyte) increase, elevated protein, and normal glucose levels. However, the results can also normally appear even if you have the POW virus.

Sometimes, the virus can cause other signs detectable by general laboratory tests, such as low platelet count (thrombocytopenia), decreased lymphocytes (lymphopenia), and increased inflammatory markers.

To confirm a diagnosis, a few methods can be used. These include PCR (direct virus amplification), detection of IgM antibodies in the blood through an enzyme immunoassay (EIA), or detection of these antibodies in the CSF using the same method. Antibodies are proteins produced by the immune system to block invaders like viruses. But, if the IgM antibodies test positive in the blood, a plaque neutralization assay should be carried out to confirm the results with increased accuracy. In many cases, antibody testing on the CSF is considered the gold standard for confirming if the disease has invaded your nervous system.

There’s also a critical need to assess patients for coinfection because of the geographic overlap of POW virus with other diseases transmitted by bugs like ticks or mosquitoes. Coinfections or simultaneous infections can increase the severity of the sickness and risk of death if they aren’t identified. Plus, they’re generally treatable. Some observational studies have shown that up to 10-30% of patients with confirmed POW virus encephalitis also had coinfection with viruses like Anaplasma phagocytophilum or Borrelia burgdorferi.

Treatment Options for Powassan Virus

At this time, there is no officially-approved medicine, vaccine, or specific treatment available to prevent or treat POW virus infection. Managing patients who contract this virus mostly revolves around providing care and relief, not eliminating the virus itself. Naturally, specialists in infectious disease should be closely involved in this care.

Providing patients with fluids through an IV, fever reducers, and intensive care if necessary can work effectively. Despite this, the fatality rate of those infected remains high. There have been some reports that suggest high-dose corticosteroids or intravenous immunoglobulin (IVIG), which is a treatment derived from the blood plasma of thousands of blood donors and used to strengthen the immune system, may be helpful. However, these suggestions are not backed by clinical studies, and these treatment options should be used with caution if considered.

In terms of antiviral drugs, those specific to the POW virus don’t have much data to support their usage. As of now, no antiviral medicines have been proven to be successful in treating the POW virus.

What else can Powassan Virus be?

When a doctor is trying to diagnose a POW virus infection, several other conditions need to be considered, as they often show similar symptoms. These conditions might be more likely depending on a patient’s location, immune system health, and other potential risk factors. This list includes the more common types of virus and tick-borne brain inflammation issues:

• West Nile virus (WNV)
• Herpes simplex virus (HSV-1 and HSV-2)
• Varicella-zoster virus (VZV)
• Cytomegalovirus (CMV)
• Epstein-Barr virus (EBV)
• Human Herpesvirus 6 (HHV-6)
• Lyme disease, known medically as Neuroborreliosis
• Anaplasmosis
• Ehrlichiosis
• Tick-borne relapsing fever
• Saint Louis encephalitis virus (SLEV)
• Eastern Equine Virus
• Tick-borne encephalitis virus (TBEV)
• Adenovirus
• Influenza A
• Enterovirus
• La Crosse virus
• Dengue fever
• Murray Valley encephalitis
• Japanese encephalitis
• Bacterial meningitis
• HIV
• Neurosyphilis
• Rabies

As the symptoms can be similar across these conditions, it’s important for the doctor to evaluate the patient’s history and possible exposure to specific risk factors.

What to expect with Powassan Virus

Most people who get infected with the POW virus don’t experience symptoms or have only mild symptoms, and their prognosis is generally very good. Many times, these symptomless infections go completely unnoticed. However, a small group of patients may experience a progression of the disease. This could lead to neuroinvasive disease, which usually appears as encephalitis or meningoencephalitis, both being serious inflammation conditions of the brain.

Unfortunately, among these cases where the virus affects the brain, the mortality rate is quite high. It’s estimated that about 10% to 15% of these patients may not survive the infection.

Possible Complications When Diagnosed with Powassan Virus

For patients who develop serious infections that affect the Central Nervous System (CNS) or brain, many can end up with long-term nerve-related disabilities. This applies especially to those who survive a disease that has spread to the CNS, where nearly 50% end up with some sort of lifelong neurological disability.

Previous studies have revealed a range of disability types, but the most prevalent ones include:

• Persistent headaches
• Memory problems
• Difficulty with balance and coordination (ataxia)
• Shaking or tremors
• Muscle weakness
• Brain disorders (encephalopathy)
• Paralysis or muscle weakness on one side of the body (hemiplegia)
• Long-lasting eye movement issues (persistent ophthalmoplegia)

Preventing Powassan Virus

Since there aren’t a lot of options for treating tick-borne diseases, the best way to avoid getting sick is by preventing tick bites. This is especially important for people who live in or visit areas where tick infestations are common. It’s recommended to stay aware of ticks when you’re walking in areas with lots of trees, grass, or leaves, and this includes your own backyard. Ticks are most active during the spring, summer, and fall, so be extra cautious during these seasons.

When you’re spending time outdoors, it’s a good idea to dress in light-colored clothes that cover your arms and legs, as this can both keep ticks from biting you and make it easier for you to spot any ticks that do get on you. Tucking your clothes into your socks and pants can also help keep ticks off of your skin. Using chemical repellents, like permethrin or DEET, can deter ticks even more. Once you come inside, it’s critical to check your body for ticks. It can be helpful to have someone else look over your body with you to ensure you haven’t missed any. If you find a tick, you should remove it as quickly as possible. However, the POW virus, a disease spread by ticks, can be transmitted quickly after a tick attaches, so just relying on finding and removing ticks may not be fully effective in preventing disease.