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The salivary glands of some tick species could become important research tools for studying the mode of transmission of tick viruses to mammals and for developing preventive medical countermeasures. The salivary glands of ticks usually block transmission, but a new study by scientists at the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health focuses on the role of salivary glands in the spread of flaviviruses from blacklegged ticks (Ixodes scapularis) to mammals. The new study, published in the journal mBio, advances the work of researchers published in 2017 who established tick organs in culture as a model for flavivirus infection.
Flaviviruses include dengue virus, Zika virus, West Nile virus, yellow fever virus, Powbadan virus and several other viruses. Powbadan is the only endemic tick-borne flavivirus in North America, where it is considered a re-emerging virus. In the United States, physicians have reported about 100 cases of illness in the last 10 years, half of them in 2016-17. Powbadan virus disease mainly affects the northeastern states and the Great Lakes region. Although diseases caused by the Powbadan virus are rare – most people with the Powbadan virus do not develop symptoms – the virus can be transmitted very quickly. In less than 15 minutes, an infected tick can transmit the virus to a person or other mammal on which it is feeding. Symptoms of Powbadan virus disease may include fever, headache, vomiting, weakness, confusion, loss of coordination, difficulty speaking and convulsions. If the virus infects the central nervous system, it can cause brain inflammation and meningitis. Long-term debilitating neurological problems, even death, can occur.
By examining the molecular interactions between blacklegged ticks and mammals, NIAID scientists have learned that flaviviruses breed at specific locations in tick salivary gland cultures. This could explain why the transmission of the virus occurs so quickly. They also noted that only certain types of salivary gland cells are infected and they have identified a tick-specific gene involved in the infection. Taken together, these results help identify the transmission pathways that could potentially be blocked by a countermeasure. The group is also evaluating how viruses develop in cultured midgut cells to help identify different viruses that can develop in blacklegged ticks.
Reference: J Grabowski et al. Dissect the biology of flaviviruses in salivary gland cultures of Ixodes scapularis fed and unfed (blacklegged tick). mBio DOI: 10.1188 / mBio.02628-18 (2019).
Source: National Institutes of Health (NIH)
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