This study suggested the possible defensive role of parasitic infections against COVID-19 since the incidence and severity of SARS-CoV-2 decreased in people with parasitic infections compared to those who had SARS-CoV-2 alone.

A cross-sectional study was performed to explore the function of  interferon gamma (IFN-γ) in terms of reduction in numbers and severity of COVID-19 patients in the parasitic infected regions.

A total of 375 COVID-19 infected individuals aged 18 to 69 years old were included. Complete examinations were performed, specifically focused on SARS-CoV-2 nucleic acid and Toxoplasma IgG and IgM antibody detection, stool test, and quantitative analysis of IFN-γ. 

More than half of the patients had chest manifestation either alone (54.7%) or along with gastrointestinal (GIT) manifestations (19.7%). However, 25.6% presented with GIT symptoms. About 72.8% of patients with mild and 20.7% with severe COVID-19 had parasitic infections. The most frequent parasitic infections among COVID-19 patients were Cryptosporidium, Blastocyst, Toxoplasma gondii, and Giardia.

The affirmative role of parasitic infections in the modulation of human immune response to coronavirus infection was very clear from the elevated level of IFN- γ in moderate cases versus declined levels in severe cases.