A study recently published in PLOS Neglected Tropical Diseases has explored the association between the prevalence of pre-existing parasitic diseases and outcomes of coronavirus disease 2019 (COVID-19) on the national level. The study reveals that countries with a high malaria prevalence have a lower incidence of COVID-19.

Study: The notable global heterogeneity within the distribution of COVID-19 cases and the association with pre-existing parasitic diseases. Image Credit: nechaevkon/Shutterstock

Background

The COVID-19 pandemic brought on by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused unprecedented damage to the worldwide economy and healthcare system. Within the early phase of the pandemic, it was anticipated that low-to-middle-income countries would have the best impact due to poor health policies and a scarcity of resources and infrastructure.

In contrast to the predictions, a lower incidence and severity of COVID-19 has been observed in socioeconomically deprived countries like sub-Saharan Africa in comparison with that in economically wealthy and developed countries just like the USA and Europe. 

Several hypotheses have been recommend to clarify this noticeable difference in COVID-19 outcomes between countries. Several causative aspects have been identified, including socio-demographic and geographical aspects, the prevalence of comorbidities, climatic conditions, in addition to the potential of underreporting.

In the present study, scientists have investigated whether the prevalence of neglected tropical diseases can impact the outcomes of COVID-19. Neglected tropical diseases primarily include parasite infections which can be highly prevalent in socioeconomically deprived countries.

Study design

The scientists conducted an ecological study using publicly available country-level data to discover the association between parasitic disease prevalence and COVID-19 incidence rates. They considered various demographic, socioeconomic, and geographic confounding aspects and adjusted their effects on the possible association.   

Of varied human-infecting parasites, only Schistosoma spp., soil-transmitted helminthiases, and Plasmodium spp. were considered within the study.

Given the severity of COVID-19 in individuals with pre-existing health conditions, the prevalence and mortality rates of non-communicable diseases were considered predictive aspects.

Given the severity of COVID-19 in older people, the proportion of the population aged 65 years and above was considered a demographic factor.   

Regarding socioeconomic aspects, country-level healthcare infrastructure, income, and overall way of life were considered. Furthermore, the country-level population density, population density in urban regions, and average surface temperature were considered geographic aspects. 

Necessary observations

The epidemiological data obtained from 202 countries were analyzed within the study. Amongst these countries, the best incidence of COVID-19 was observed within the USA, followed by Europe, Southeast Asia, East Mediterranean, Western Pacific, and Africa.   

A heterogeneous distribution of parasitic diseases was also observed across the analyzed countries. Malaria had an endemic status mostly in countries of Africa and the Western Pacific. Interestingly, these countries were the least affected by the pandemic.

The assessment of the connection between one independent and one dependent variable revealed that countries with a high prevalence of parasitic diseases have a lower incidence of COVID-19.

Considering confounding aspects, countries with high tuberculosis prevalence, high surface temperature, or later onset of COVID-19 experienced a lower incidence of COVID-19. Furthermore, a positive association was observed between COVID-19 incidence and the proportion of aged people in a population, country-level income, healthcare infrastructure, proportion of individuals living in urban regions, non-communicable disease-related mortality rates, educational level, and COVID-19 vaccine coverage.

Considering parasitic diseases, a significantly lower incidence of COVID-19 was observed in countries with a high malaria prevalence. This association remained significant even after adjusting for confounding variables, country-level income, the proportion of aged people, and differences in COVID-19 duration within the multivariable evaluation that included data from 165 countries.

Study significance

The study establishes that the national malaria prevalence is a vital predictor of COVID-19 incidence rate. The study also finds a negative but non-significant association between the prevalence of schistosomiasis and soil-transmitted helminthiases and COVID-19 incidence. As mentioned by the scientists, further studies are required to determine the impact of those other neglected tropical diseases.

Overall, the study highlights the necessity for more research on the sub-national and individual levels to explore COVID-19 outcomes, particularly in malaria-endemic countries.