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201.15.14 ARBO viruses West Nile fever Chances are, you will never get this illness even though the pathogen and host are found in Wisconsin. It’s never been clear how the West Nile virus got to the U.S. 1999. Up until that point, it had been considered a bird problem that was limited to Africa and Asia. The vector belongs to a very common and large genus of mosquitos – Culex. There have been at least 30 different species now found to carry the disease. Birds are the primary hosts with Humans and horses as poor secondary hosts. West Nile virus The virus was first discovered in Uganda in 1937 and rarely became a problem in the Human population. It may well be that the disease is so mild in most Humans, it was never considered a problem. The most susceptible birds to acquire the disease are members of the corvid family including crows, jays, magpies and nutcrackers. Pathogen West Nile virus belongs to the same viral family as yellow fever. It is an RNA virus. The image on the right is an electron micrograph of the virus in bird cells. Life cycle The virus is primarily spread by a mosquito bite, but it can be transmitted by an infected female mosquito to her eggs. It can also be transmitted by blood transfusions between Humans, by breast feeding, organ transplantation and by transplacental transmission meaning that an infected mother can transmit it to her fetus. Human symptoms Fortunately, most of show no symptoms and if problems do appear, they occur in older adults. Mild symptoms include, fever, headache, body aches, skin rashes and swollen lymph glands. Severe symptoms are high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Human symptoms If severe symptoms occur, they can last for several months or longer and may display severe neurological problems that are polio-like. Of those showing severe symptoms, the fatality rate is approximately 7%. Several hundred confirmed cases of the disease have been reported in Wisconsin since 2004. WNV invasion of the U.S.This image shows the rapid spread of the disease in the U.S. While the spread of the disease was towards the west, the outbreaks are a little less clear to understand. Areas in the bird flyways, west coast and through Nebraska, South and North Dakota, consistently retain west Nile virus activity, but the year outbreak patterns are unclear. It could be that rainfall and water for migratory fowl dictates the degree of the outbreaks. Compare the last image to this image for 2015. Note how the outbreak has lessened through the central flyways. Encephalitis Encephalitis is an inflammation of the brain brought about by a number of different causes. ARBO viruses have as one of their Human symptoms, encephalitis thus, the name was attached to some of the viruses. Most of these viruses are localized to certain geographical regions. One that can be a problem in the Midwest is La Crosse encephalitis. Its victims are primarily children between the ages of 7 to 14. La Crosse encephalitis – vector The regional vector for this disease is Aedes triseriatus, aka the tree hole mosquito. It is also known to some as the unofficial state bird of Wisconsin. It breeds in tires, cans, bottles and tree holes – hence the name. It prefers dark shady forests and can be quite aggressive in daytime biting. Prime breeding spot Around human habitation, the prime breeding spot is old tires and especially old tire dumps. An outbreak of La Crosse encephalitis in Grant County, WI was traced to old tires dumped near a school bus stop. Six children who boarded the bus at the same stop came down with the disease. Unfortunately, the disease can cause significant and permanent mental problems. Distribution of La Crosse encephalitis cases Geographical distribution of La Crosse places a bulls-eye on Wisconsin. There have been better than 500 case in the last 50 years. Zika virus A disease that has been in the news lately is Zika fever caused by the Zika virus. It was first reported in the Zika forest of Uganda in 1947. It belongs to the same group of viruses that cause dengue, yellow fever and West Nile fever. The disease remained relatively isolated in Africa until about 2017 when it appeared in the South Pacific. It made its appearance it in North and South America in 2015. Vectors We have met one of the vectors several times, Aedes aegypti but a more recent addition to the U.S. is Aedes albopictus. Albopictus is an invasive species, first observe in Houston, Texas in ashipment of used tires. Since 1983 when it first appeared, the mosquito has spread northward. Since 1983 when it first appeared, the mosquito has spread northward. Both species are capable of transmitting Zika virus. Hosts Humans and monkeys are known hosts although it is thought that domestic sheep, goats, horses, cows, ducks, rodents, bats and orangutans can harbor the disease. Whether they can pass the virus is unclear. Pathogen The pathogen is an RNA virus not unlike that for the yellow fever and West Nile viruses. The image on the left shows an artist's conception of the viral surface, with its hemagglutinins, and its neuraminidase. The image on the right shows an electronic micrograph of the virus in human cells. Zika symptoms Curiously and unfortunately only about 1 in 4 people display symptoms of infection. Unfortunate, because it makes pinpointing outbreaks more difficult for epidemiologists. For those who catch the disease, it doesn’t last long. Some of the symptoms are redness in the eyes, a fever, aching joints, headaches and a skin rash. Range of microcephaly The lack of symptoms has another larger problem. Women who become pregnant and have a viral infection run a serious risk of having children with severe neural issues. This image shows the difference between a normal child and children suffering the birth defect of microcephaly. The disease is strongly linked to brain and neural development. Children suffering from the disease have and will face serious mental challenges for the rest of their lives. Zika distribution 2016 We know the disease is fairly wide-spread in South America and in the Caribbean. But until recently, U.S. officials were cautiously optimistic that it would not be established here. This image shows the number of cases in the U.S. These are cases from people who have traveled to areas infected with Zika and contracted the disease.

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UW-Madison ENTOM 201 - ARBO Viruses

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