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Of particular note in modern times is HIV, which is known to have infected several million humans globally, along with the influenza virus. Today, while many medical advances have been made to safeguard against infection by pathogens, through the use of vaccination, antibiotics, and fungicide, pathogens continue to threaten human life.
HIV is commonly transmitted via unprotected sexual activity, blood transfusions, hypodermic needles, and from mother to child. Upon acquisition of the virus, the virus replicates inside and kills T helper cells , which are required for almost all adaptive immune responses .
However, network analysis of a food web of coinfection in humans suggests that there is greater potential for interactions via shared food sources than via the immune system. [7] A globally common coinfection involves tuberculosis and HIV. In some countries, up to 80% of tuberculosis patients are also HIV-positive. [8]
Because of this adaptation to survive longer on solid surfaces, viruses now have a prolonged opportunities to infect humans. [2] Enteric viruses primarily infect the intestinal tract through ingestion of food and water contaminated with viruses of fecal origin. Some viruses can be transmitted through all three routes of transmission.
Transmission can also be indirect, via another organism, either a vector (e.g. a mosquito or fly) or an intermediate host (e.g. tapeworm in pigs can be transmitted to humans who ingest improperly cooked pork). Indirect transmission could involve zoonoses or, more typically, larger pathogens like macroparasites with more complex life cycles.
The human immunodeficiency viruses (HIV) are two species of Lentivirus (a subgroup of retrovirus) that infect humans.Over time, they cause acquired immunodeficiency syndrome (AIDS), [1] [2] a condition in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive. [3]
Cross-species transmission is the most significant cause of disease emergence in humans and other species. [citation needed] Wildlife zoonotic diseases of microbial origin are also the most common group of human emerging diseases, and CST between wildlife and livestock has appreciable economic impacts in agriculture by reducing livestock productivity and imposing export restrictions. [2]
Vehicle transmission, transmission by an inanimate reservoir (food, water, soil). [31] Vertical transmission, directly from the mother to an embryo, fetus or baby during pregnancy or childbirth. It can occur as a result of a pre-existing infection or one acquired during pregnancy. Iatrogenic transmission, due to medical procedures such as ...