Introduction
Ticks are the most prevalent carriers of human pathogens leading to increased public health burdens worldwide. Tick-borne pathogens include bacteria and viruses (e.g., tick-borne encephalitis and Powassan). Further, ticks are the causative agents of Lyme disease, spotted fever rickettsiosis, and human anaplasmosis. Tick-borne diseases are increasing due to the geographical expansion of their vectors.
Powassan Virus (POWV) is an emerging viral infection that can cause nervous system disorders, such as encephalitis (brain inflammation). Although it is a rare illness, the number of reported cases has increased worldwide. Among patients with symptoms, the death rate is about 15 percent. Therefore, clinicians must be able to identify patients who present with geographic risk factors and encephalitis.
What Is the Pathophysiology of Powassan?
The initial stages of the POWV disease result from the virus in the blood circulation that develops due to an infected tick bite. Animal studies show that infection can occur 15 minutes after tick attachment. Further, human studies have established that infection can occur within three hours of tick attachment. One must note that POWV is transmitted to humans faster than other tick-borne diseases.
After primary infection, patients develop self-limited flu-like symptoms. Subsequently, some patients develop neurologic manifestations (encephalitis or meningoencephalitis) days or weeks after the initial symptoms.
Although the virus can not spread directly from human to human, it can pass to another person through blood transfusion. Therefore, a person with diagnosed POWV disease is advised not to donate blood or bone marrow for three months.
POWV can be spread by three types of ticks: Ixodes cookei (groundhog tick), Ixodes marxi (squirrel tick), and Ixodes scapularis (black-legged or deer tick). These are found in tree-covered areas and spread the infection to humans by biting them. They attach in non-prominent body areas, such as the groin, armpits, and scalp.
What Are Clinical Manifestations of Powassan Virus Disease?
POWV causes clinical disease in more than 10,000 to 20,000 people in Europe and Asia yearly. Moreover, an increase has been noted in Europe as a consequence of climate and socioeconomic changes. The incidence (new cases) depends on vaccination among residents in the affected areas.
Most people infected by POWV may sometimes show mild symptoms. The initial symptoms appear one to four weeks after the infection. These include:
-
Headache.
-
Nausea.
-
Vomiting.
-
Generalized weakness.
-
Speech difficulties.
-
Confusion.
-
Seizures.
-
Loss of coordination.
Patients with severe disease have a prolonged fever, confusion, decreased consciousness, and seizures. Also, they can develop ophthalmoplegia (eye muscle weakness) and nystagmus (rapid and uncontrolled eye movements). However, paralysis is less frequently associated with human POWV infection.
How Is Powassan Diagnosed?
The patient evaluation with suspected POWV infection should focus on the presence or absence of neurologic symptoms. It is because those who present with flu-like symptoms do not benefit from disease-specific investigations. Therefore, POWV testing should be done in patients with geographic exposure and encephalitis. Brain imaging, serum testing, and lumbar puncture are prominent aspects of the diagnostic approach. Cerebrospinal fluid (CSF) analysis shows lymphocyte increase, elevated protein, and glucose. Other laboratory findings in the peripheral blood include decreased platelet count, decreased lymphocyte count, and raised inflammatory markers.
A confirmatory diagnosis can be made by polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay. Serologic tests (measure blood antibodies) are the gold standard for confirming meningitis.
What Are the Complications of Powassan?
The most common complications include persistent headaches, memory impairment, loss of balance, tremors (shaky movements), weakness, and encephalopathy (brain disorders). In severe cases of POWV disease, about 50 percent of patients develop encephalitis, meningitis (inflammation of the membrane and the fluid covering the brain and spinal cord), cerebral edema (swelling of the brain because of fluid build-up around the brain, and coma. Many patients can have long-term effects such as loss of muscle mass, strength, and memory.
How Is Powassan Treated?
No medicine or vaccine is available for POWV disease. Hence, the treatments are based on symptomatic and preventive relief. In case of a severe infection, the patient should be hospitalized to support breathing. Further, general supportive treatment must be given with intravenous fluids and antipyretics. Critical care doctors must provide treatment to prevent cerebral edema as the death rate is high. Several studies have proposed high-dose corticosteroids use or intravenous immunoglobulin (IVIG). However, no data supports improved clinical outcomes with either agent. Also, data on specific antivirals against POW is limited. Therefore, there are no antiviral agents with known efficacy against POWV.
How to Prevent the Risk of Powassan?
Since no vaccine is currently available to treat Powassan, it is best to prevent the disease by reducing exposure to ticks. Hence, tick education and prevention are central to avoiding infection.
Counseling patients living in endemic areas is recommended for both primary and secondary prevention. Patients should be mindful of ticks when walking in wooded, grassy, or leaf-littered areas. It must be kept in mind during spring, summer, and fall when ticks are most active.
Also, when working outdoors, patients should cover their arms and legs with light-covered clothing to prevent exposure and identify potential ticks. Furthermore, tucking clothes into socks and pants can reduce tick access to exposed skin. Patients should also apply chemical repellents such as permethrin to clothing.
Tick checks should be diligently performed to identify any potential exposures. It further warrants prompt tick removal. However, it may not be a reliable prevention method due to the short attachment time needed for POWV transmission.
Vigilance for unexplained fevers or flu-like symptoms can help in early detection, which helps in early treatment and optimal outcomes. Finally, environmental controls such as keeping the grass mowed short, brush and leaf litter away, children far from forested areas, and removing stacks of wood from houses and off the ground can prevent exposure to ticks.
Conclusion
Tick populations are increasing with expansion in their geographic range. Ticks can transmit bacterial, parasitic, and viral pathogens and can simultaneously carry more than one agent. An interprofessional team is essential in POWV encephalitis management. The team should involve infectious disease specialists, neurologists, and critical care clinicians. Further, patients may also require physical and occupational therapists to improve short or long-term neurologic sequelae. Regional public health authorities should be notified of the cases as POWV infection can be reported. Moreover, quick reporting can identify and mitigate community outbreaks.
