Medical research in the 1980s suggested that a perceived lower level of parasitic infection in developed countries was contributing to a rise of inflammatory diseases and allergy. The ‘helminth hypothesis’ proposed that certain parasites suppressed inflammation in the body and that without them, it was suggested, humans were fated to chronic inflammatory conditions. Additional research soon challenged this notion.
While some worms can suppress inflammation – that they themselves also create – a parasitic infection will increase total and specific levels of IgE antibodies to a range of substances and toxins including those produced by the parasites. In fact, a 2018 case study suggested that helminth infections may be a more common cause of eczema than previously considered:
“Patients with ascaridiasis and high IgE levels may have allergy-like symptoms such as asthma, urticaria and atopic dermatitis.”
Intestinal helminths (visible to the eye) and protozoan parasites (visible under a microscope), are among the most prevalent infections in humans. There are two general categories of helminths: roundworms (ascaris, hookworms, trichinella, filarial, and eye worms) and flatworms (tapeworm, fluke). Helminths attach to the intestinal wall of their host where they lay eggs and feed on blood and tissue. Helminths are spread through contaminated water, food and soil. Pets, cats and dogs, are also a potential method of transmission.
There are thousands of types of protozoan parasites -- the most common are Giardia intestinalis, Entamoeba histolytica, Cyclospora cayetanenensis, and Cryptosporidium spp. Protozoan parasites are spread through contaminated food or water – to help prevent this, tap water is treated with chemical disinfectants such as chlorine, chloramine, or chlorine dioxide as well as ultraviolet light. Protozoans can spread through person-to-person contact or through the bite of a vector. Plasmodium parasites which cause malaria are spread through the bite of infected mosquitoes.
According to the National Institutes of Health, “neglected parasitic infections are not rare conditions in the US.”