Outbreaks of clinical toxoplasmosis in humans: 50-years of personal experience, prospective, and lessons learned

Authors: Dubey, Jitender

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2021
Publication Date: 5/19/2021
Citation: Dubey, J.P. 2021. Outbreaks of clinical toxoplasmosis in humans: 50-years of personal experience, prospective, and lessons learnt . Parasites & Vectors. 14:263. https://doi.org/10.1186/s13071-021-04769-4.
DOI: https://doi.org/10.1186/s13071-021-04769-4

Interpretive Summary: Toxoplasmosis is a worldwide zoonosis. The USDA provided the veterinary, clinical, and public health communities an indispensable resource by disseminating up to date scientific information on toxoplasmosis and its prevention. Humans become infected mostly by ingesting food and water contaminated with oocysts or by eating infected under cooked meat. The infective dose and the incubation period of T. gondii infection are unknown because there are no human volunteer experiments. Here, I have critically reviewed outbreaks of clinical toxoplasmosis in humans. Fever, cervical lymphadenopathy, myalgia, and fatigue were the most important symptoms, and were not age dependent. The incubation period was 7-30 days. A genetic predisposition to cause eye disease is suspected for the parasites responsible for three outbreaks (in Brazil, Canada, and India). This information will be useful to parasitologists, biologists and public health workers. No experiments or surveys were performed since the redirection of USDA’s program on toxoplasmosis.

Technical Abstract: Toxoplasmosis has a wide range of clinical symptoms involving almost all organ systems. In most persons that acquire infection postnatally, symptoms (when present) are mild and simulate other ailments such as flu, Lyme disease, Q fever, hematological alterations, or mumps. It is likely that clinical disease is more common than reported. The ingestion of infected meat or food and water contaminated with oocysts are the two main modes of postnatal transmission of Toxoplasma gondii. The infective dose and the incubation period of T. gondii infection are unknown because there are no human volunteer experiments. Here, I have critically reviewed outbreaks of clinical toxoplasmosis in humans. There were no differences in types or severity of symptoms in meat versus oocyst-acquired infections. Fever, cervical lymphadenopathy, myalgia, and fatigue were the most important symptoms, and were not age-dependent. The incubation period was 7-30 days. A genetic predisposition to cause eye disease is suspected for the parasites responsible for three outbreaks (in Brazil, Canada, and India). Only a few T. gondii tissue cysts might suffice to cause infection, as indicated by outbreaks affecting some (but not all) individuals sharing a meal of infected meat.