Trichostrongyles are parasitic roundworms, or nematodes, that commonly infect herbivores, including livestock such as cattle, sheep, goats, and horses. They are a widespread concern in animal agriculture, causing significant health problems and economic losses. While primarily affecting animals, some Trichostrongylus species can also infect humans, though human infections are typically mild.
Understanding Trichostrongyles
Trichostrongyles are roundworms characterized by their slender, hair-like appearance. Common species include Trichostrongylus axei, Trichostrongylus colubriformis, and Trichostrongylus vitrinus in domestic animals. They generally reside in the host’s gastrointestinal tract. For instance, Trichostrongylus axei primarily inhabits the stomach (abomasum), while other species establish themselves in the small intestine.
The life cycle of Trichostrongyles is direct, without an intermediate host. Eggs are shed in the feces of an infected animal onto pasture. Under favorable conditions (moisture, warmth), larvae hatch from these eggs within several days.
Larvae develop through two molts on vegetation or in soil, becoming infective third-stage (L3) larvae in 5 to 10 days. Animals become infected by ingesting these L3 larvae while grazing on contaminated pastures. Once ingested, larvae migrate to their specific gastrointestinal location, maturing into adult worms and completing the cycle.
Impact on Animal Health
Infections with Trichostrongyles can lead to various health effects in animals. Common clinical signs include weight loss, reduced appetite, and diarrhea, sometimes appearing dark or tarry. Animals may also exhibit anemia, poor growth, or reduced productivity. In severe cases, especially in young animals, infections can be fatal.
Symptoms stem from damage the worms inflict on the gastrointestinal lining. For instance, Trichostrongylus axei damages the stomach lining, while other species harm the small intestine. This damage leads to inflammation (enteritis or gastritis), impaired digestion, and malabsorption of nutrients, contributing to weight loss and poor growth. Blood loss from worm feeding can result in anemia.
Species like T. orientalis, T. colubriformis, and T. axei can infect humans. Human infections are often asymptomatic or cause mild gastrointestinal issues like abdominal pain, nausea, and fatigue; heavy worm burdens can lead to anemia and emaciation.
Controlling and Preventing Infections
Diagnosis of Trichostrongyle infections involves examining fecal samples for parasite eggs. Microscopic identification of eggs is the primary method; concentration or flotation procedures are often recommended to improve detection, especially in light infections. Differentiating Trichostrongyle eggs from hookworm eggs is also important, as they can appear similar but differ in size and shape.
Treatment for Trichostrongyle infections relies on anthelmintic medications, or dewormers. Effective anthelmintics include albendazole, mebendazole, and ivermectin. Proper dosage and strategic rotation of drug classes are important to manage resistance, as widespread anthelmintic resistance, particularly in Trichostrongylus colubriformis, has been observed.
Prevention strategies focus on reducing exposure to infective larvae on pastures. Rotational grazing, moving animals between pastures to allow larval populations to decrease, is a common practice. Avoiding overgrazing also helps reduce infective larval density in pastures. Maintaining good hygiene in animal living areas and providing adequate nutrition supports animal health and resilience against infections. For new animals, quarantine and testing prevent parasite introduction into a herd.