are you like most humans?do you hate mosquitos? we talk about mosquitos a lot becausethey're terrible. they transmit malaria, west nile virus, and now the zika virus among many other pathogens. but what's so special about those diseases that we only get them from mosquito bites? why can't we get other diseases frommosquitoes? like if you have the flu and a mosquito bites you and then bites someone else, why don't they get the flu? well, the disease-causing organisms thatmosquitoes transmit to humans are actually special cases. they evolved toboth require an insect and a vertebrate
as a part of their life cycle. in fact,this requirement is so specific that each disease can only be carried byspecific genera or species of mosquito. for example, only mosquitoes of the genus aedes can carry the zika virus. but let's back up a little there are twomain types of mosquito-borne diseases in humans. malaria is caused by a single-celledprotozoan. most of the others are caused by viruses known as arthropod-borneviruses or arboviruses for short. arboviruses can infect both an arthropod - usually a mosquito or a tick - and a vertebrate - in this case, humans. typically, viruses latch on to host cells by
sticking to proteins on them calledreceptors. if a cell doesn't have the rightreceptor, the virus can't get in. and arboviruses recognize receptors on both insect and human cells. they can infect them both. so an arbovirus can jumpfrom mosquitoes to humans because it can use the receptors on insect cells to getfrom the mosquito's stomach to its salivary glands. from there, it canreplicate and infect the next human. by contrast, influenza viruses don't havethis ability because they can't recognize insect cell receptors. so it'sunlikely that it, or any regular old virus, could get from a mosquito'sstomach to a human. the malaria parasites'
process is even weirder. it can reproduce both sexually andasexually, but it needs a human and two mosquitoes to do it. first, immatureparasites enter the human body through the salivary glands of the mosquito. theymature in the liver and then hijack our red blood cells and divide. this is theasexual part of their life cycle. but some of these parasites - instead of justdividing - produce the precursors to sex cells, like the protozoan version ofsperm and eggs. those then get sucked up by anothermosquito. those proto-sex cells then mature and combine inside the second mosquito,which is the sexual reproduction part,
producing new parasites to infect thenext person. which, i gotta say, is a pretty slick system, but that does notchange how i feel about those protozoans or the mosquitoes they rode in on. thanks for watching and thanks especially to all of our patrons on patreon who keepthese answers coming. if you would like to submit questions tobe answered, or get some videos a few days early, you can go to patreon.com/scishow and if you just want to keep getting smarter with us you can go toyoutube.com/scishow and subscribe. viruses are master mutators and humansare master travelers, both of which could
help zika spread. some experts think zikacame to brazil around the time of the 2014 world cup among the thousands...
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