Parasitic Co-Infections and COVID-19 Pathophysiology

Parasitic co-infections have emerged as an important modifier of COVID-19 clinical trajectories, particularly in regions where helminths and protozoa remain endemic. In many low- and middle-income countries, the prevalence of intestinal worms and other parasites correlates with a distinct immunological milieu that may attenuate the hyperinflammatory responses characteristic of severe SARS-CoV-2 infection. Mechanistically, chronic parasitic infections often drive a regulatory or T helper 2-biased immune state, promoting anti-inflammatory cytokine production and modulating ACE2 receptor expression on epithelial surfaces. Such immunomodulation may dampen the cytokine storm and reduce tissue damage in the respiratory tract, potentially translating into lower rates of critical illness and mortality. Conversely, alterations in immune homeostasis by parasites can also interfere with antiviral effector functions and vaccine responsiveness, underscoring a complex balance of risk and benefit. Understanding this duality is crucial for guiding therapeutic interventions, designing public health strategies in parasite-endemic settings and optimising vaccine deployment where co-infections are widespread.

Research from Nature Portfolio

A foundational analysis explored global patterns of latent toxoplasmosis prevalence alongside the initial spread and impact of COVID-19 across multiple countries. The study revealed a strong negative covariation between national rates of toxoplasmosis in pregnant women and the timing and early burden of SARS-CoV-2 cases. However, when adjusting for national wealth and spatial autocorrelation, the direct association diminished, indicating that socioeconomic factors and geographic clustering largely mediate the observed relationship. This work highlights the necessity of disentangling parasitic prevalence from broader demographic and economic determinants when assessing its influence on COVID-19 susceptibility and outcome.

Parasitic Co-Infections and COVID-19 Pathophysiology publication trend

The graph below shows the total number of articles in parasitic co-infections and covid-19 pathophysiology across all publications each year (not limited to Nature Index journals).

Technical terms

Co-infection: Simultaneous infection of a host by two or more pathogens.

Helminth: Parasitic worm, including nematodes and trematodes, often residing in the gastrointestinal tract.

Protozoa: Single-celled eukaryotic organisms that can cause chronic infections and immune modulation.

Cytokine storm: Excessive release of pro-inflammatory cytokines driving tissue damage in severe viral infections.

Immunomodulation: Adjustment of the immune response by internal or external factors, including parasites.

ACE2 receptor: Host cell surface protein used by SARS-CoV-2 for entry, also influenced by immune signalling dynamics.

References

1. Negative association between ascaris lumbricoides seropositivity and Covid-19 severity: insights from a study in Benin. Frontiers in Immunology (2023).
2. Antigens from the Helminth Fasciola hepatica Exert Antiviral Effects against SARS-CoV-2 In Vitro. International Journal of Molecular Sciences (2023).
3. Effect of co-infection with intestinal parasites on COVID-19 severity: A prospective observational cohort study. EClinicalMedicine (2021).
4. A negative covariation between toxoplasmosis and CoVID-19 with alternative interpretations. Scientific Reports (2020).
5. Immunomodulation of COVID‐19 severity by helminth co‐infection: Implications for COVID‐19 vaccine efficacy. Immunity Inflammation and Disease (2021).