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201 15 8 Bacterial diseases transmitted by insects As we discussed earlier bacteria are a very diverse group of microorganisms that are for the most part free living and do not require a host for replication Bacteria have both a cell membrane and a cell wall but have no well defined nucleus There are a number of bacterial pathogens transmitted by insects but we will focus on just one that is endemic to our region Lyme disease A disease that hits close to home is Lyme disease Lyme disease is transmitted by a tick rather than an insect but ticks and insects are arthropods It has infected more than 35 000 Wisconsinites since 1980 and the numbers keep climbing It s estimated about 330 000 people in the U S are infected each year The disease is named after Old Lyme CT where the pathogen was first discovered in US Lyme distribution in the U S There are two very active areas of Lyme disease centered in the North East and in the upper Midwest Wisconsin appears to be the western epicenter of the disease Vector The vector is the deer tick The vector is much smaller than the typical dog tick or wood tick which doesn t carry the disease Once again ticks are not insects Lyme disease The pathogen is named Borellia burgdorferi after the fellow who discovered it Willi Burgdorfer The image on the right shows the pathogen It is a close cousin to the spirochete bacterium that cause some sexually transmitted diseases The hosts for this pathogen are Humans and small rodents Life cycle of the deer tick Tick eggs hatch into free living larvae about a month after being laid During the first summer the larva feeds once on the blood of a host and then enters a resting stage coincident with the onset of winter The following spring the larva molts and enters the nymphal cycle stage Notice that the larva has 6 legs while the nymph and adult stages have 8 legs At the end of summer the nymph molts to an adult Adults mate during late summer and the male dies The female still on the host then deposits her eggs and dies during the second spring Unfed and fed ticks Immature ticks attach themselves to a host and feed for 3 to 4 days They can engorge to the point of being quite large Tick infestation The infestations can become quite bad if not taken care of Ticks feed on a number of species and the deer tick will even feed on lizards in California Tick mouthparts When a tick attaches to its host it does so in a very stealthy manner You rarely feel it attach The image on the left shows the tick from the back side The mouthparts are partially hidden The image on the right shows the mouthparts from the underside The working end of the tick is called the hypostome It s hollow and allows host blood to flow up the tube The nasty recurved barbs let the tick remain attached until it s finished feeding Symptoms of Lyme disease Clinically Lyme disease can be broken down into three stages Stage 1 is characterized by a rash called erythema chronicum migrans Often the rash is accompanied by extreme fatigue fever chills headache and backache In about 70 of the cases the rash looks like a bull s eye but not always Not all bites lead to bull s eye rash Not all tick bites result in bull s eye rashes This image shows the types that might be expected however some individuals are asymptomatic showing no rash Symptoms of Lyme disease With early detection and treatment stage 2 is infrequent If the disease progresses this far it is marked by neurological complications and muscular pain Symptoms of Lyme disease The neurological response is a partial paralysis of the facial muscles giving rise to the syndrome Bell s Palsy Approximately 5 of the patients develop cardiac complications within 3 to 6 weeks Symptoms of Lyme disease Stage 3 of Lyme disease is characterized by arthritis similar to rheumatoid arthritis The onset of arthritis can occur within two months to two years after the rash If left untreated the disease can be fatal Symptoms of Lyme disease This image presents the potential effects of Lyme disease Note the variability in response Often symptoms are ascribed to other events and the disease is allowed to continue until it becomes serious Treatment of Lyme disease Antibiotics have been very successful in treating the disease IF the immune system is not compromised If you are an outdoor person and you suspect that you may have been bitten see your health care provider immediately The treatment with antibiotics is quite effective Emerging tick transmitted Ticks carry other diseases besides Lyme The diseases shown here combined with a new type of Lyme is appearing on epidemiologist s radar Preventive measures If you like the outdoors and plan to be in the field a lot during the heavy tick months of May and June then take precautions The ticks roost in the higher under story and wait for anything warm blooded to pass They launch from the high perch and jump with their front legs spread out to catch the passing host This cartoon provides excellent tips to prevent Lyme disease Important rules of tick removal There is a myth that has persisted among the outdoor folks that a hot match touched to the abdomen of the tick will cause it to withdraw from the skin This in fact would be the worst thing you could do The shock to the tick will cause it to regurgitate much quicker and increase your chances of getting the disease Do not use a hot match to remove a tick from the skin Tick removal It takes 24 48 hours after attachment before spirochetes move out of the midgut into the salivary glands If ticks are removed in that time the possibility of getting Lyme disease is reduced Tick removal The appropriate way to remove the tick is to use a pair of long nosed forceps Grab the tick s hypstome as close to the skin as possible Pull the tick straight out don t twist it The image on the right shows the forceps just before they are pushed under the tick Another equally effective tool Ticked Off can be purchased at a pet store The spoon is pushed under the tick and the mouthparts are guided into the slot With one rapid motion the tick can be leveraged off the skin Once the tick is removed try to detach the remaining mouthparts that remain embedded in the skin

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UW-Madison ENTOM 201 - Bacterial Diseases Transmitted by Insects

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