Scientists are learning more about COVID-19 each day. For instance, we now know that adults with specific underlying medical conditions such as obesity are at a higher risk for severe illness from SARS-CoV-2.
SARS-CoV-2 stands for severe acute respiratory syndrome coronavirus 2, which is the virus that causes the disease COVID-19. The disease has a broad range of severity and symptoms. Some underlying conditions that increase the risk of severe COVID-19 include obesity, cardiovascular disease, diabetes, and chronic lung disease.
Infectious diseases are very prevalent in low- to medium-income countries (LMICs). Approximately 2 billion people have some form of parasitic infection around the world. The effect of coinfection with parasites on symptoms of COVID-19 is unknown. However, some new research is providing insights into these issues.
In fact, research is being reported from Ethiopia, which investigates how a parasitic infestation impacts the prognosis of COVID-19. While the paper is still awaiting peer review, it indicates that intestinal parasitosis is protective against severe COVID-19.
The researchers conducted the study on more than 500 patients who had SARS-CoV-2. Around 63% were male. The study used the World Health Organization criteria to categorize the severity of the COVID-19 disease: asymptomatic, mild/moderate, severe, and critical.
Around 87% of the study participants had asymptomatic or mild/moderate disease. The median age was approximately 32 years, and patients with more severe symptoms were older. The researchers used a fresh stool examination to test for ova and parasites. More than 50% of the study participants tested positive for a parasite infection in the intestine. The intensity of infection was reported as eggs per gram of feces, based on which the participants were classified as light, moderate and heavy.
Of the 52% of participants who had one or more intestinal parasites, 25% had protozoal infestations, and 34% had helminthic infestations. Symptomatic COVID-19 was significantly more common in the proportion of patients without parasitic infestation.
- Proportion of parasites, protozoa and helminths among COVID-19 patients with asymptomatic, mild/moderate, severe and critical clinical presentation. P-values for trend (p=0.002,
- Proportion of parasites, protozoa and helminths among COVID-19 patients with asymptomatic, mild/moderate, severe and critical clinical presentation. P-values for trend (p=0.002, p=0.006 and p=0.196 for any parasite, helminth and protozoa, respectively).
Higher incidence of severe COVID-19
They found a negative correlation between a parasitic coinfection and the severity of COVID-19. A total of 8% of the 270 participants with an infestation developed severe symptoms of COVID-19 versus 20% of those without an intestinal parasitic infestation.
Approximately 370 participants had non-protozoal parasites versus 150 with protozoal infections. About 15% and 8% of patients in these two groups developed severe COVID-19. When it came to helminthic infection, there were 174 and 341 patients with and without pre-existing helminthiasis. Only 6% of the former developed severe COVID-19 compared to 17% of the latter.
After adjusting for the impact of age and comorbid conditions, the presence of any parasitic infestation resulted in a 60% decrease in the odds of severe COVID-19. For those with a protozoal or helminthic infestation, the adjusted odds of severe COVD-19 fell by 55% and 63%, respectively.
Parasitic infestations and SARS-CoV-2
LMICs have a considerable difference in standards of living and access to adequate healthcare. This impacted how the COVID-19 pandemic spread through their communities. It also means that many of their communities have higher rates of parasitic infections. These parasites include hookworm tapeworm, roundworm, and whipworm, among helminthic parasites, as well as protozoa such as Entamoeba, Giardia, Toxoplasma, and Cryptosporidium.
Scientists suggest that chronic parasitic infestations may act as an immunomodulatory agent impacting the host response to other infections and altering the outcomes. Thus, a preexisting parasite infection could alter the immune response to the SARS-C0V-2 virus.
Parasites that cause chronic infections enhance T helper cell responses and cause predominant regulatory (Treg) responses. This prompts a Th2-biased response, which compensates for the Th1 response that causes the severe inflammation resulting from COVID-19.
In addition, generalized immunomodulation may happen in the host’s gut microbiome due to chronic parasitic infections. Each factor may change the severity of the SARS-CoV-2 symptoms.
Other studies suggest a lower incidence of COVID-19 in areas with significant numbers of cases of malaria, schistosomiasis, and helminthiasis.
The implications of these findings
The presence of any parasitic co-infestation reduced the risk of severe COVID-19, while the presence of hypertension, chronic renal disease, and older age drove up the odds of severe disease. Even after these comorbidities were adjusted for, patients with parasitic infestation had significantly lower odds of severe COVID-19.
Another interesting tidbit from this study: COVID-19 patients with parasitic coinfections had dramatically lower risks of having a non-communicable disease. The risks of having NCDs were lowered by a respectable 48% and 74%, if the COVID-19 patient had parasites or helminths, respectively.
The researchers stated, “Our results suggest that co-infection with parasitic co-infection appears to be associated with reduced COVID-19 severity. The results suggest that parasite-driven immunomodulatory responses may mute hyper inflammation associated with severe COVID-19.”
This may explain why COVID-19 has a low fatality rate in LMICs. More studies are obviously necessary, but the findings should lead researchers to investigate how the gut microbiome impacts the risk of severity in COVID-19 symptoms. This in turn could lead to new preventative measures and therapies to suppress the pandemic.