Trichostrongylus nematodes are intestinal (mainly) parasites of animals, primarily ruminant mammals, including domesticated mammals such as sheep, goats, and camels (but, e,g, T. tenuis parasitizes birds and T. retortaeformis infects rabbits; Hoste et al. 1998). Trichostrongylus vitrinus is a parasite of sheep and a major cause of ovine gastroenteritis worldwide (Temperley et al. 2009 and references therein). Several species of Trichostrongylus have been known to infect humans, including T. orientalis, T. colubriformis, T. vitrinus, and T. axei. A variety of Trichostrongylus species are found worldwide, but they are more common where livestock is raised. (Centers for Disease Control Parasites and Health website)
Trichostrongylus eggs are passed in the stool of the definitive host (usually an herbivorous mammal) and under favorable conditions (moisture, warmth, shade) larvae hatch within several days. The released rhabditiform larvae grow in the soil or on vegetation and after 5 to 10 days (and two molts) they become filariform (third-stage) larvae that are infective. Infection of the human host occurs upon ingestion of these filariform larvae. The larvae reach the small intestine, where they reside and mature into adults. (Centers for Disease Control Parasites and Health website) Adult worms inhabit the digestive tract of the definitive host and may occur as incidental infections in humans (e.g., Lattès er al. 2011, which describes several individuals in a family being infected by eating strawberries from a garden that had been fertilized with fresh, rather than dried, sheep manure from infected sheep).
Because Trichostrongylus infection of humans is uncommon (and often aymptomatic) and the worms may be difficult to identify, reported cases are rare. Eggs can be distinguished from those of Necator and Ancylostoma hookworms by the fact that they are longer and narrower. After 6 days of culture, T. colubriformis nematodes can be distinguished from similar stages in Strongyloides and Ancylostoma species by the bead-like swelling at the tip of the tail. In the absence of adult worms, which are rarely found in feces, sequencing of the ITS2 region is the most accurate method for specific identification of Trichostrongylus worms isolated from humans. (Lattès er al. 2011)
Trichostrongylus species are nematodes (round worms), which are ubiquitous among herbivores worldwide, including cattle, sheep, donkeys, goats, deer, and rabbits.[1][2][3] At least 10 Trichostrongylus species have been associated with human infections.[1] Infections occur via ingestion of infective larvae from contaminated vegetables or water.[1][3] Epidemiological studies indicate a worldwide distribution of Trichostrongylus infections in humans, with the highest prevalence rates observed in individuals from regions with poor sanitary conditions, in rural areas, or who are farmers / herders.[4][5] Human infections are most prevalent in the Middle East and Asia,[3] with a worldwide estimated prevalence of 5.5 million people.[1]
Eggs are passed through the feces of an infected definitive host, usually a mammalian herbivore including rabbits, sheep, cattle, and rodents.[6] Under certain environmental conditions, which include optimal temperature and humidity, larvae hatch from eggs after several days. Hatched rhabditiform larvae grow on vegetation or within soil. After 5 to 10 days, two molts (L1 & L2) have occurred and the parasite becomes a filariform (L3) larvae that is infectious. Infection in mammals occurs upon ingestion of infective filariform (L3) larvae. The larvae reaches the small intestine to reside and mature into adult worms within their definitive hosts. Infections in humans may occur as incidental infections.[7] Trichostrongylus consists of multiple species that relate to each of its host, when it comes to parasitic survival and infection. For example, Trichostrongylus affinis primarily infects cottontail rats, Trichostrongylus sigmodontis affects hispid cotton rat, and marsh rice rat, and Trichostrongylus retortaeformis primarily affects European rabbits (Oryctolagus cuniculus).
The majority of human infections are asymptomatic or associated with mild symptoms. Symptomatic individuals may experience abdominal pain, nausea, diarrhea, flatulence, dizziness, generalized fatigue, and malaise.[1][2][3] Eosinophilia is frequently observed.[1][2][3] Infections with a heavy worm burden can lead to anemia, cholecystitis, and emaciation.[1][3] Regarding Trichostrongylus retortaeformis, worm burden is affected parallel to host immune system and climate change.[8] Although immunity prevents any significant long-term net accumulation of T. retortaeformis in the rabbit population, its seasonal effect is to increase heterogeneity in infection and transmission between individuals by worsening the parasite burden in the juveniles exposed to climate warming.[9]
The adult worms live in the small intestine. The diagnosis is based on the observation of eggs in the stool. The eggs are 85–115 um, oval, elongated, and pointed at one or both ends.[3] Trichostrongylus eggs must be differentiated from hookworm eggs, which are smaller and do not have pointed ends.[1][3]
Since the use of herbivore manure as fertilizer is a common practice preceding infection, thorough cleaning and cooking of vegetables is required for prevention of infection.[1][3] Treatment with pyrantel pamoate is recommended as the first line drug.[10] Alternative agents include mebendazole and albendazole.[10] Successful treatment with ivermectin has also been reported.[2] Another way of avoiding these free-swimming stages of infective larvae, is to wear protective footwear when walking in areas of parasite prominence, and maintain general sanitary practices throughout the day.
Species:[11]
Trichostrongylus species are nematodes (round worms), which are ubiquitous among herbivores worldwide, including cattle, sheep, donkeys, goats, deer, and rabbits. At least 10 Trichostrongylus species have been associated with human infections. Infections occur via ingestion of infective larvae from contaminated vegetables or water. Epidemiological studies indicate a worldwide distribution of Trichostrongylus infections in humans, with the highest prevalence rates observed in individuals from regions with poor sanitary conditions, in rural areas, or who are farmers / herders. Human infections are most prevalent in the Middle East and Asia, with a worldwide estimated prevalence of 5.5 million people.
