Can co-helminthic infections suppress immunity against COVID-19?Some parasites have the capacity to modulate the immune system to assure their longevity inside their hosts [20,21] . This process is chiefly observed in helminths across the three taxonomic categories

Intracellular parasites(1) Toxoplasma gondii is an intracellular sporozoa that can cause infection in any nucleated cell. Toxoplasmosis has been shown to induce massive necrosis and extensive pathology in the distal intestinal mucosa and villi in murine models. These pathological changes were attributed to bacterial dysbiosis besides immune factors such as the CD-4 T cells and interferon gamma (IFN-γ) cytokine [15] . Dysbiosis had been proposed to be dependent on the destabilization of the intestinal barrier either by the lytic replication of the parasite or from the toxic by-products of the host immune reactions, such as nitrogen intermediates or reactive oxygen species. For instance, production of IFN-γ during toxoplasmosis leads to loss of Paneth cells resulting in reduced levels of the antimicrobial peptides and dysbiosis [16,17] dominated chiefly by Enterobacteriaceae [14] . In fact, the induced IFN-γ/ signal transducer and activator of transcription-1/ inducible nitric oxide synthase (IFN-γ/STAT-1/i-NOS) axis, was described as crucial for parasite resistance [18] . It was assumed to provide a pool of nitrate that acts as a source for anaerobic respiration and promotes overgrowth of Enterobacteriaceae.Similarly, in experimentally induced colitis using dextran sulphate sodium (DSS), host-derived nitrate was found to directly promote the flush of Enterobacteriaceae bacteria in the colon [19] . This proves that local inflammation in the large intestine causes upgrade of the respiratory electron acceptors