Mosquito Borne Viruses

Transcription

1 Mosquito Borne Viruses

2 GENERAL DISEASES AND TRANSMISSION WEST NILE DENGUE FEVER ZIKA CHIKUGUNYA OTHER ARBOVIRUSES

3 Flooding tends to flush out both mosquito larvae & their predators from established mosquito breeding areas. Mosquitoes tend to recolonize faster than the predators dependent upon them, however, so following a flood a predictable pattern of heavy die-off of mosquitoes, followed by a spike in numbers, is commonly seen. The reasons for why mosquito populations rebound after storm or flood events vary with their genus specific breeding habits, summarized below. Anopheles spp. mosquitoes lay their eggs directly in clean, standing water; consequently existing larvae are washed away during floods & as floodwaters recede, leftover pools are used as breeding sites. Anopheles spp. mosquitoes will also lay their eggs in a wide range of environments (e.g., shady/sunny, flood pools, streams, irrigated lands, marshes, etc.), so events like hurricanes that cover a large area will yield massive breeding potential. It is predictably common to see spikes in Anopheles spp. Populations following hurricanes &/or flood events. In Texas, Anopheles spp. don t currently serve as disease vectors, so they are more of a nuisance concern than a public health threat following a storm. Aedes spp. mosquitoes lay eggs specifically in places that will be either subject to flooding (in the ground around streams for example) or in places affected by an increase in rainwater (like the sides of flower pots that will fill upon rainfall). Their eggs can sit for several months waiting for just such an event, thus heavy rains are an integral part of their reproductive strategy & a spike in Aedes spp. numbers can always be expected after a hurricane or excessive rains that lead to flooding. Aedes spp. are carriers of the Zika virus. Ochlerotatus spp. & Psorophora spp. are also flood-dependent breeders. West Nile virus & Lacrosse viruses are carried by some Ochlerotatus spp., but Psorophora spp. are nuisance mosquitoes only & are not vectors of human disease. Culex spp. require stagnant water specifically (i.e. the kind often found accumulated in old tires, bird-baths, rusty coffee cans in landfills, etc.). Since heavy rains will fill up such items, an inevitable increase in Culex spp. populations is to be expected following rainfall events. All mosquito species lifecycle times are dependent upon temperature; the warmer the temperature the faster they will reproduce. Although it varies by species & region, a good rule of thumb is that in a tropical environment you can expect a spike in adult mosquito numbers days following the end of heavy rainfall. Because Zika & WNV infection are currently the most commonly occurring arboviral infections in Texas, increases in the Culex spp. vector populations present the biggest public health concern. Post- hurricane/flood mosquito control strategies should focus on getting the public to dump out containers on their property that may have collected water. Larviciding is typically the best & most-efficient control strategy for adult mosquitoes, however during outbreaks of WNV or other arboviral diseases, adulticiding results in more rapid control of adult mosquito populations & thus more effectively decreases disease transmission. If no disease is present following an observed post-storm spike in mosquito numbers, then control methods will depend & focus on the particular need to control nuisance mosquito populations that may hinder recovery efforts.

4 Mosquito Cycle

5 West Nile and Dengue Fever In addition to malaria, mosquitoes carry the West Nile virus and Dengue fever. West Nile is a disease the insects pick up from infected birds. It affects the nervous system and, like malaria, can be very serious in people with lowered immune systems. The virus became prevalent for the first time in the eastern United States around 1999 [source: CDC]. As with malaria, the best way to avoid West Nile is to protect yourself from mosquitoes. Mosquitoes also carry dengue fever, which causes a rash and extreme muscle and joint pain. It can be fatal if not treated properly.

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9 ZIKA Zika virus disease (Zika) is a disease caused by the Zika virus, which is spread to people primarily through the bite of an infected Aedes species mosquito. The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild with symptoms lasting for several days to a week after being bitten by an infected mosquito. People usually don t get sick enough to go to the hospital, and they very rarely die of Zika. For this reason, many people might not realize they have been infected. However, Zika virus infection during pregnancy can cause a serious birth defect called microcephaly, as well as other severe fetal brain defects. Once a person has been infected, he or she is likely to be protected from future infections. 939 Confirmed Cases in U.S. Territories 591 Confirmed Cases in the USA 38 Confirmed Cases in Texas 1 from sexual transmission 1 Confirmed Pregnancy w/zika in Texas 12 Pregnancies with possible Zika in Texas

10 ZIKA Mosquito-borne flavivirus (ZIKA) 1947: First identified in Uganda 2007: First major outbreak in Yap (Micronesia) 2013: Outbreak in French Polynesia 2014: Cases in Pacific Islands 2015: Outbreak in Brazil 2016: In >20 countries in the Americas For soon to be mothers, the risk has a more severe outcome. If contracted while pregnant, fetuses can receive the virus in the womb which will cause adverse reactions, such as Microcephaly.

11 Preventive Measures