Helminths

Helminths are parasitic worms that infect humans and other animals. They are multicellular, eukaryotic organisms and include three major groups: nematodes (roundworms), cestodes (tapeworms), and trematodes (flukes). Each group has distinct morphology and life cycles, but all rely on a host to reach reproductive maturity.

Life cycles typically involve environmental stages and one or more hosts. Transmission can occur by ingesting eggs or larvae in contaminated food or water, by skin contact with larvae in soil, or by consuming intermediate hosts. Many species release eggs or larvae into the environment through feces or urine, perpetuating transmission in areas with poor sanitation.

Infections with helminths can cause a range of clinical problems, from mild symptoms to severe disease. Light infections may be asymptomatic; heavier burdens can cause abdominal pain, diarrhea, anemia, malnutrition, growth delays in children, or organ damage depending on the species. Immune responses often include eosinophilia and a skewed Th2 response, and chronic infection can modulate host immunity.

Diagnosis relies on identification of eggs, larvae, or adult worms in stool, urine, or tissue samples, supplemented by serology and imaging in some cases. Treatments use specific anthelmintic drugs, such as albendazole or mebendazole for nematodes, praziquantel for trematodes and cestodes, and ivermectin for certain infections. Prevention emphasizes sanitation, safe water, proper hygiene, snail control for certain trematodes, vaccination where available, and targeted deworming programs in endemic regions.