Dear Colleagues,
For all the same reasons as for the emergence of new diseases and the spread of others we're well familiar with - people traveling more frequently, farther, and faster than in the past, people living in densely populated areas without clean running water, and people living in areas that encroach on the natural habitats of wild animals - the potential for human exposure to infectious diseases borne by arthropod vectors is greater than ever.
Vector-borne diseases account for more than 17% of all infectious diseases, causing more than 1 million deaths annually. While mosquitoes have been getting even more attention than usual lately, ticks are excellent disease transmitters, too. With over 800 identified species of ticks that can be encountered on every continent carrying bacteria, viruses, and protozoa, ticks place second only to mosquitoes as vectors of human disease. And while the impact of tick-borne disease pales in comparison with the millions infected with mosquito-borne pathogens, it is important to public health that we remain conscious of the growing threat.
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Powassan virus (POWV), identified in 1958, is a case in point. It remains rare, although a lineage of POWV, Deer tick virus, appears to be increasing in prevalence. A flavivirus related to Tick-borne encephalitis virus (TBEV), POWV can attack the nervous system, causing both encephalitis and meningitis. Symptoms range widely. Most infections appear not to cause serious illness, but among those with serious neurological disease, fatalities are reported in approximately 10 percent of cases; and more than 50 percent of survivors suffer significant long-term neurological effects.
Powassan virus infection is difficult to diagnose and is complicated by co-morbidity with other increasingly prevalent tick-borne diseases (including Lyme, Anaplasmosis, and Babesiosis), the pathogens for which are transmitted by the same Ixodes scapularis tick. There is no treatment other than supportive care for tick-borne viral infections and, with the low number of affected persons, there is little likelihood of a Powassan-specific vaccine being developed. Therefore, it is important that research be conducted to determine the level of cross protection against POWV afforded by TBE vaccination. This vaccine has been used very successfully in Europe against TBEV. It was noted by a ProMED subscriber that European vaccines protect against all TBE viral strains and show about 80% cross protection against Omsk Hemorrhagic fever, also related to POWV. These results suggest that the vaccine might also confer some immunity against POWV.
New tick-associated viruses continue to emerge, such as Heartland virus, likely transmitted by Amblyomma americanum, (the same tick species that vectors the bacteria leading to Ehrlichiosis), and is in the same family as Severe fever with thrombocytopenia virus recently reported in China. New Borrelia species are also suspected to cause disease, such as B. mayonii andB. miyamotoi. Other tick-borne diseases that must be kept in mind and complicate diagnosis of patients presenting with history of a tick bite include Rocky Mountain spotted fever, Southern tick associated rash illness, Colorado tick fever, Tularemia, and more.
As always, sharing information is the strongest defense against infectious disease. ProMED-mail keeps the international infectious disease community up-to-date, every day. With staff locate around the world and active readers in over 200 countries, ProMED is how we stay informed. ProMED-mail feeds our curiosity and our need to know. If ProMED-mail satisfies your need for current information, knowledgeable commentary, and connection with your community, please show that you are part of that community, please give what you can afford, but please give!
Best regards,
Laura D Kramer, PhD, FASTMH
ProMED-mail Viral Diseases Moderator
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