Reverse zoonosis

A reverse zoonosis, also known as a zooanthroponosis (Greek "animal", "man", ''"''disease") or anthroponosis, is a pathogen reservoired in humans that is capable of being transmitted to non-human animals.

Terminology

Anthroponosis refers to pathogens sourced from humans and can include human to non-human animal transmission but also human to human transmission. The term zoonosis technically refers to disease transferred between any animal and another animal, human or non-human, without discretion, and also been defined as disease transmitted from animals to humans ''and vice versa''. Yet because of human-centered medical biases, zoonosis tends to be used in the same manner as anthropozoonosis which specifically refers to pathogens reservoired in non-human animals that are transmissible to humans.

Additional confusion due to frequency of scientists using "anthropozoonosis" and "zooanthroponosis" interchangeably was resolved during a 1967 Joint Food and Agriculture and World Health Organization committee meeting that recommended the use of "zoonosis" to describe the bidirectional interchange of infectious pathogens between animals and humans.

Furthermore, because humans are rarely in direct contact with wild animals and introduce pathogens through "soft contact", the term "sapronotic agents" must be introduced. Sapronoses (Greek "decaying") refers to human diseases that harbor the capacity to grow and replicate (not just survive or contaminate) in abiotic environments such as soil, water, decaying plants, animal corpses, excreta, and other substrata. Additionally, sapro-zoonoses can be characterized as having both a live host and a non-animal developmental site of organic matter, soil, or plants. Obligate intracellular parasites that cannot replicate outside of cells and are entirely reproductively reliant on entering the cell to use intracellular resources such as viruses, rickettsiae, chlamydiae, and Cryptosporidium parvum cannot be sapronotic agents.

Etymological pitfalls

Categorizing of disease into epidemiologic classes by the infection's supposed source or the direction of transmission raises a number of contradictions that could be resolved by the use of cyclical models. See the following scenarios:

''Zoonosis'' vs ''reverse zoonosis'' vs ''anthroponosis''

In the case of diseases transferred from arthropod vectors such as urban yellow fever, dengue, epidemic typhus, tickborne relapsing fever, zika fever, and malaria, the differentiation between terms becomes ever more hazy. For example, a human infected with malaria is bitten by a mosquito that is subsequently infected as well. This is a case of reverse zoonosis (human to animal). However, the newly infected mosquito then infects another human. This could be a case of zoonosis (animal to human) if the mosquito is considered the original source, or anthroponosis (human to human) if the human is considered the original source. If this infected mosquito instead infected a non-human primate, it could be considered a case of reverse zoonosis/zooanthroponosis (human to animal) if the human is considered the primary source, or simply zoonosis (animal to animal) if the mosquito is considered the primary source.

''Zoonosis'' vs ''anthroponosis''

Similarly, HIV originating in simians (crossover due to humans consuming wild chimpanzee bushmeat) and influenza A viruses originating in avians (crossover due to an antigenic shift) could have initially been considered a zoonotic transference as the infections first came from vertebrate animals, but could currently be regarded as an anthroponosis because of its potential to transfer between human to human.

''Sapronosis'' vs ''sapro-zoonosis''

Typical examples of sapronotic agents are fungal such as coccidioidomycosis, histoplasmosis, aspergillosis, cryptococcosis, ''Microsporum gypseum''. Some can be bacterial from the sporulating clostridium and bacillus to ''Rhodococcus equi, Burkholderia pseudomallei, Listeria'', ''Erysipelothrix'', ''Yersinia pseudotuberculosis,'' legionellosis, Pontiac fever, ''and'' nontuberculous mycobacterioses. Other sapronotic agents are amebic as in primary amebic meningoencephalitis. Yet again, difficulties in classification arise in the case of sporulating bacteria whose infectious spores are only produced after a significant period of inactive vegetative growth within an abiotic environment, yet this is still considered a case of sapronoses. However, cases of zoo-sapronoses involving ''Listeria'', ''Erysipelothrix'', ''Yersinia pseudotuberculosis'', ''Burkholderia pseudomallei'', and ''Rhodococcus equi'' can be transferred by an animal or an abiotic substrate but usually occur via a fecal-oral route between humans and other animals.

Cases with modes of transmission

Arthropod vectors

Malaria

Malaria involves the cyclical infection of animals (human and non-human) and mosquitoes from the genus Anopheles with a number of Plasmodium species. The Plasmodium parasite is transferred to the mosquito as it feeds on the blood of the infected animal whereupon it begins a sporogenic cycle in the gut of the mosquito that will infect another animal at the next blood meal. There does not seem to be any deleterious effects to the mosquito as a result of the parasitic infection. The Plasmodium brasilianum parasite normally found in primates is morphologically similar to the malarial inducing Plasmodium malariae that is more commonly found in humans and it is contested as to whether the two are actually different species. Nevertheless, 12 reports of malaria in the remotely located indigenous Yanomami communities of the Venezuelan Amazon arose where it was surprisingly found to be caused by a strain of P. brasilianum with 100% identical to sequences found in Alouatta seniculus monkeys. This suggests a definite zoonosis and high possibility of spillback back into non-human primate bands as reverse zoonoses.

African sleeping sickness

''Trypanosoma brucei gambiense (T. b. gambiense) is a species of'' African trypanosomes which are protozoan hemoflagellate