Macroparasites

Macroparasites are multicellular parasites that are generally larger than microparasites and persist in a host for extended periods. They include helminths (worms such as nematodes, cestodes, and trematodes) and various arthropods that inhabit the host either internally or on its surface. Unlike most microparasites, macroparasites produce relatively few surviving offspring, so parasite populations within hosts are typically described by burden—the number of parasites per host—and by overall abundance, rather than simple prevalence alone.

Distinguishing features include long lifespan, complex life cycles often involving intermediate hosts, and chronic disease that may cause anemia, malnutrition, organ damage, or impaired growth. Macroparasites can be endoparasites residing in the gastrointestinal tract, liver, blood, lungs, or other tissues, or ectoparasites living on the skin or external surfaces.

Major groups include intestinal nematodes such as Ascaris lumbricoides and hookworms; cestodes such as Taenia spp.; trematodes such as Schistosoma spp.; and ectoparasites such as lice, ticks, mites, and fleas.

Transmission and life cycles: many are ingested as eggs or larvae in contaminated food or soil, some penetrate the skin, and others require intermediate hosts or vectors. Reproduction often occurs in the definitive host, with eggs or larvae released into the environment to continue transmission. Because of long lifespans and environmental stages, control focuses on sanitation and hygiene to reduce transmission, periodic deworming to lower worm burdens, snail or vector control, and protective measures against ectoparasites.

Impact and public health: macroparasite infections contribute to morbidity, particularly in children and low-resource settings, through anemia, growth retardation, malnutrition, abdominal pain, organ damage, and impaired cognitive development. The study of macroparasites informs surveillance, transmission modeling, and evaluation of control programs.