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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. Water virology started about half a century ago when scientists attempted to detect the polio virus in water samples. [3]
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]
Fecal–oral transmission is primarily considered as an indirect contact route through contaminated food or water. However, it can also operate through direct contact with feces or contaminated body parts, such as through anal sex. [19] [20] It can also operate through droplet or airborne transmission through the toilet plume from contaminated ...
HIV-1 is more virulent and more infective than HIV-2, [20] and is the cause of the majority of HIV infections globally. The lower infectivity of HIV-2, compared to HIV-1, implies that fewer of those exposed to HIV-2 will be infected per exposure. Due to its relatively poor capacity for transmission, HIV-2 is largely confined to West Africa. [21]
This specificity restricts the virus to a very limited type of cell. For example, the human immunodeficiency virus (HIV) infects only human T cells, because its surface protein, gp120, can only react with CD4 and other molecules on the T cell's surface. Plant viruses can only attach to plant cells and cannot infect animals.
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]
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 .
HIV is a retrovirus that primarily infects components of the human immune system such as CD4 + T cells, macrophages and dendritic cells. It directly and indirectly destroys CD4 + T cells. [88] HIV is a member of the genus Lentivirus, [89] part of the family Retroviridae. [90] Lentiviruses share many morphological and biological characteristics.