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*Will Zika explode across the US as it did elsewhere?Housing in US better, so people if they choose can avoid contact with A. aegypti mosquitoesA. aegypti restricted to Florida and Gulf Coast (but A. albopictus could play a role), so vectorsnot wide-spread across the USCities here are less conducive to mosquito development, fewer larval habitatsEffective mosquito control efforts can be mobilized here.So a major Zika outbreak is unlikely in the US.But new viruses are lurking (as we all know now!!).Zoonotic virus diseases transmitted to humans by mosquitoesSpecies in the genus Culex are commonly involvedReservoirs typically birds, but sometimes small mammalsHumans are dead-end hosts**Eastern Equine Encephalitis (EEE)A bird disease that cycles through Culiseta melanura. That mosquito will not bite humans, butkeeps the virus cycling in nature. But other “bridge” mosquito vectors get infected from birdsand will bite people or horses (and emus!), making these dead-end hosts sick. (A mosquitocannot pick up virus from a dead-end host).EEE is mostly an issue with horses, human cases are rare (but if occur are very serious)EEE: 270 human cases 1964-2010, 21 cases in 2005Case fatality rate 35%; serious neurological impairment 35%No vaccine available*LAC is unique in that it is only mosquito-borne virus with vertical transmission (mother toeggs; this is common in ticks, but not insects).Vector: Ae. triseriatus, Reservoir: squirrels*SLE: Another bird disease with humans as a dead-end hostLast major epidemic outbreak 1975-1977: 2,500 cases in 35 states,Virtually no cases in last 20 years. But?????*West Nile Virus vectors: Culex quinquefasciatus (SE), pipiens (NE), tarsalis (West) are majorvectorsReservoir: birds (crows)Humans are dead-end hostWest Nile virusIntrinsic incubation (in people) period 5-15 daysOnly 1/500 to 1/1000 infections result in serious clinical symptomssymptoms of a severe infection may be marked by:high fever, severe headache, neck stiffness, stupor,disorientation, tremors, convulsions, muscle weakness,paralysis, and comaAlmost all original cases were in elderly patients withcompromised immune function, but more recentlyhealthy adults have been seriously impactedJapanese encephalitisLeading cause of encephalitis in Asia, 30-50,000 cases/yrCase-fatality rate 30% (range 0.3 to 60%)Serious neurologic disease 30%Symptoms: acute encephalitis, can progress to paralysis, seizures, coma, death; most infectshowever are subclinicalIncubation period 5-15 daysVector: Culex tritaeniorhynchus groupReservoirs: wild birds, domestic pigsGood news: an attenuated virus vaccine is available*Factors associated with Mosquito-related viral epidemic outbreaks:Large populations develop of non-immune (virus naïve) reservoir animals (e.g. humans or birds)Large populations of suitable-vector mosquitoes develop (from rainy years, more human createdlarval habitats)Virus is then introduced (which is hard to predict)So viral diseases tend to “erupt” and then subsequently decline, but then lurk in the backgroundThe “right” conditions for an outbreak tend to occur cyclically (e.g. every 15-20 years) andspottily (only in certain places)Calculating metrics of infectionDetermination of the infectionthreshold: titer of virus thatresults in at least 5% of themosquitoes infected (so need enough virus in blood for mosquitoes to get infected)Determination of theextrinsic incubationperiod (how long after ingesting virus does it take until the mosquito can transmit (around 12days in this study))Can mosquitoes transmit HIV?Studies show that HIV ingested by mosquitoes is simply digested, and the virus does not surviveto penetrate the gut wall, replicate, and migrate to the salivary glands (i.e., biologicaltransmission is not possible).HIV circulates at very low titers in the human bloodstream, and a mosquito has very little bloodon the outside of its mouthparts after feeding. So minimal chance of HIV being on proboscis.Mechanical transmission is very, very unlikely (studies estimate a 1:10,000,000 chance).A mosquito proboscis is not like a hypodermic needle. Blood is sucked up through one canal,and saliva delivered via another canal. Flow is unidirectional. A mosquito will not inject bloodfrom a previous meal into a second host, so can’t be transmitted that way.Under any realistic scenario that can be devised, the answer to the above question is NO. (Verylikely applies even more to COVID, which is not even blood

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GSU BIOL 1103K - Zika

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