Oxyuris, Trichostrongylus and Trichuris

Trichostrongylosis: a zoonotic disease of small ruminants

In the present world a significant threat to human health is posed by zoonotic diseases. Helminth parasites of ruminants are one of the most common zoonotic organisms on the planet. Among them, trichostrongylid nematodes of ruminants, found worldwide, parasitize humans in different parts of the world with varying rates of incidence, particularly among rural and tribal communities with poor hygiene, pastoral livelihood and poor access to health services. In the Trichostrongyloidea superfamily, Haemonchus contortus, Teladorsagia circumcincta, Marshallagia marshalli, Nematodirus abnormalis and Trichostrongylus spp. are zoonotic in nature. Species of the genus Trichostrongylus are the most prevalent gastrointestinal nematode parasites of ruminants that transmit to humans. This parasite is prevalent in pastoral communities around the world and causes gastrointestinal complications with hypereosinophilia which is typically treated with anthelmintic therapy. The scientific literature from 1938 to 2022 revealed the occasional incidence of trichostrongylosis throughout the world with abdominal complications and hypereosinophilia as the predominant manifestation in humans. The primary means of transmission of Trichostrongylus to humans was found to be close contact with small ruminants and food contaminated by their faeces. Studies revealed that conventional stool examination methods such as formalin-ethyl acetate concentration or Willi's technique combined with polymerase chain reaction-based approaches are important for the accurate diagnosis of human trichostrongylosis. This review further found that interleukin 33, immunoglobulin E, immunoglobulin G1, immunoglobulin G2, immunoglobulin M, histamine, leukotriene C4, 6-keto prostaglandin F_1α, and thromboxane B₂ are vital in the fight against Trichostrongylus infection with mast cells playing a key role. This review focuses on the prevalence, pathogenicity and immunological aspects of Trichostrongylus spp. in humans.

Whipworm and roundworm infections

Trichuriasis and ascariasis are neglected tropical diseases caused by the gastrointestinal dwelling nematodes Trichuris trichiura (a whipworm) and Ascaris lumbricoides (a roundworm), respectively. Both parasites are staggeringly prevalent, particularly in tropical and subtropical areas, and are associated with substantial morbidity. Infection is initiated by ingestion of infective eggs, which hatch in the intestine. Thereafter, T. trichiura larvae moult within intestinal epithelial cells, with adult worms embedded in a partially intracellular niche in the large intestine, whereas A. lumbricoides larvae penetrate the gut mucosa and migrate through the liver and lungs before returning to the lumen of the small intestine, where adult worms dwell. Both species elicit type 2 anti-parasite immunity. Diagnosis is typically based on clinical presentation (gastrointestinal symptoms and inflammation) and the detection of eggs or parasite DNA in the faeces. Prevention and treatment strategies rely on periodic mass drug administration (generally with albendazole or mebendazole) to at-risk populations and improvements in water, sanitation and hygiene. The effectiveness of drug treatment is very high for A. lumbricoides infections, whereas cure rates for T. trichiura infections are low. Novel anthelminthic drugs are needed, together with vaccine development and tools for diagnosis and assessment of parasite control in the field.

Clinical and haematological characteristics of human trichostrongyliasis

Trichostrongylus spp. are primarily parasites of ruminants, but humans can become infected as accidental hosts. Information about the clinical aspects of human trichostrongyliasis is limited. This study investigated the clinical and haematological characteristics of a large number of trichostrongyliasis patients. In the Fouman district of Guilan Province in northern Iran, during 2015-2016, 60 patients were identified as positive for Trichostrongylus spp., using stool examination methods. The clinical manifestations and demographic data of all patients were recorded and further analysed. Twenty-three patients (38.3%) were male and 37 (61.7%) were female. Among the individuals infected only with Trichostrongylus, only nine patients (16.4%) were asymptomatic. Forty-six patients (83.6%) presented with gastrointestinal (76.3%), pulmonary (30.9%) and cutaneous (12.7%) symptoms. No statistically significant relationship was found between clinical manifestations and sex or age groups. Ten patients (18.1%) revealed eosinophilia and five (9.1%) presented with hypochromic microcytic anaemia. The relationship between eosinophilia and age group, sex and clinical manifestations showed no statistical significance. Our study indicated that trichostrongyliasis may be a major parasitic aetiology for gastrointestinal symptoms and eosinophilia in rural residents of endemic areas.

Prevalence and clinical aspects of human Trichostrongylus colubriformis infection in Lao PDR

There have been few studies on human trichostrongyliasis in Southeast Asia, information on its clinical manifestations is also sparse. Trichostrongyliasis occurs predominantly in areas where poor hygiene is common especially where human/animal feces are used as a fertilizer, thereby contaminating vegetables and stream water. The intimate coexistence of domestic animals and humans explains the prevalence of Trichostrongylus infection in such areas. The goal of the current study was to determine the prevalence of trichostrongyliasis among villagers in Thakamrien village, Sonkon district, Savannakhet province, Laos, and to investigate potential relationships between clinical features, laboratory data, and severity of infection. Of 272 villagers examined, 160 (58.8%) were determined positive for helminthic infections by fecal examination, and 59 (36.9%) of these were infected with Trichostrongylus. Only 58 cases were in the inclusion criteria of the study and then underwent further assessment, including a questionnaire on personal behaviors, physical examination, and laboratory tests. Villagers in the trichostrongyliasis group were more likely than the control group to have consumed fresh vegetables, not washed their hands before meals or after using the toilet, and to have had close contact with herbivorous animals (goats and cows). Similarly, villagers in the trichostrongyliasis group were more likely than the control group to have a history of loose feces, rash, or abdominal pain; however, no obvious clinical symptoms were observed during physical examination of the trichostrongyliasis patients. The degree of infection was determined by both fecal egg counts and quantification of adult worms after deworming. Laboratory data were evaluated for any relationship with severity of infection. No significant differences were found in laboratory values between the trichostrongyliasis and control groups, with most values being within normal limits; however, both groups had high eosinophil counts. This study demonstrated that the useful clinical characteristics of trichostrongyliasis patients include history of loose feces, rashes, and abdominal pain, as well as in personal behaviors, such as the regular consumption of fresh vegetables, lack of hand washing, and close contact with cattle.

Characteristics and incidence of large eggs in Trichuris muris

The production of small numbers of large eggs among the standard-sized eggs of Trichuris trichiura is well known. Large eggs have also been observed in Trichuris muris, but they have not been studied previously. This paper compares the characteristics of the large eggs (LEs, ≥74.5 μm long) and standard-sized eggs (SEs, <74.5 μm long) in cultures of T. muris. Among 112,554 cultured eggs, LEs occurred at very low frequency (0.03 %, i.e., about three large eggs per 10(4) cultured eggs). Embryonated eggs represented 93.72 % of SEs, but only 25.00 % of LEs were embryonated. Embryonated LEs and SEs contained fully matured larvae. An atypical category of unembryonated egg, which contained an incompletely developed larva, an abnormal larva, or granular components, was common among the LEs. However, similar atypical unembryonated SEs were rarely observed. These observations suggest that the LEs that occur very infrequently in T. muris result from an abnormality of embryonation (larval development).

[Helminths and inflammatory bowel diseases]

The current etiologic model of inflammatory bowel diseases proposes a genetically predisposed host responding to a variety of environmental triggers by exhibiting an abnormal immune response to normal luminal flora. Crohn's disease is common in highly industrialized western countries where helminths are rare and uncommon in less developed areas of the world where most people carry worms. From this observation grew the hygiene hypothesis, which states that our failure to be exposed to previously common infectious agents alters the immune repertoire established in childhood. Helminths diminish immune responsiveness in naturally colonised humans and reduce inflammation in experimental colitis. Crohn's disease involves over reactive T-helper (Th1) pathways, and helminths blunt Th1 responses, inducing production of Th2 cytokines. Helminths also induce regulatory T cells to maintain host mucosal homeostasis. Thus, there is an immunological basis to expect that exposure to helminths such as Trichuris suis will prove beneficial in Crohn's disease. Exposure to helminths may be effective in treating inflammatory bowel diseases and was well tolerated, according to the results of few studies. Its long-term safety remains unknown.

Chemotherapy of enterobiasis (oxyuriasis)

Enterobius vermicularis (syn. Oxyurus vermicularis), also known as pinworm or seatworm, is the causative agent of human enterobiasis (oxyuriasis). The disease is more prevalent in temperate regions and is facilitated by factors such as overcrowding in schools and family groupings, as well as inadequate personal and community hygiene. Although the infection is more likely to occur in lower socioeconomic groups, enterobiasis has been reported to affect virtually every level of the general population and especially children. In the great majority of cases, enterobiasis is asymptomatic. One common symptom is intense pruritus ani that in some patients can lead to insomnia, restlessness and irritability. Scratching may cause skin irritation, and in more serious cases, eczematous dermatitis, haemorrhage or secondary bacterial infections. Ectopic migration of E. vermicularis often results in pinworm infestation of the female genital tract often causing granulomas of the uterus, ovary and the fallopian tubes and pelvic peritoneum. Anthelmintic therapies for enterobiasis are successful and include mebendazole, albendazole and pyrantel pamoate. Mass medication of affected groups reduced symptoms rapidly, progressively and in a cost-effective way.

Multiple infection with Plasmodium and helminths in communities of low and relatively high socio-economic status

A study was conducted in the city of Lubumbashi, Zaire: (1) to survey parasitic infections and clinical conditions in the local children and their mothers; (2) to identify combinations of parasites and clinical conditions that commonly occurred together in individuals; and (3) to determine whether single- and/or multiple-species infections were risk determinants of the observed clinical conditions. Overall, 1100 children and mothers from three subdivisions, two of low socio-economic status (LSES) and one of relatively high socio-economic status (HSES), provided stool and blood samples and were clinically examined. Plasmodium prevalence was higher in the two LSES subdivisions than in the HSES subdivision. Prevalence and intensity of Ascaris lumbricoides infection were low in the HSES subdivision and one of the two LSES subdivisions. In contrast, prevalence and intensity of Trichuris trichiura and of hookworms were similar in all subdivisions. Plasmodium and A. lumbricoides were the most frequently found single-species infections. The combination of A. lumbricoides and Plasmodium was the most frequent double-species infection and that of A. lumbricoides, Plasmodium and T. trichiura was the most frequent triple-species infection. Significant positive associations between parasite species were detected in the HSES subdivision, and in one of the two LSES subdivisions. Because the relationships were not consistently detected, it is hypothesized that the associations are determined by environmental conditions rather than synergy between the parasites in the host. The most commonly observed clinical conditions were abdominal pain, diarrhoea, fever, and low packed-cell volume (PCV). The occurrence of each was significantly lower in the HSES subdivision than in at least one of the two LSES subdivisions. Abdominal pain and low PCV were most common in individuals presenting with only a single clinical condition, and the combination of this symptom and sign was the most commonly observed pair of conditions. Abdominal pain, low PCV and diarrhoea was the most common combination in individuals with three clinical conditions. Logistic regression revealed that hookworm infection, T. trichiura infection, young age and residence in an LSES subdivision were determinants of diarrhoea. Trichuris trichiura infection, young age and living in an LSES subdivision were risk factors for abdominal pain. Plasmodium infection and young age were risk factors for fever. LSES was the only predictor of low PCV. Infection with A. lumbricoides did not enter any of the models. No significant interactions were detected among parasites, indicating that there was no synergism or antagonism among parasites in the induced disease.

Human trichostrongyliasis in Queensland

Trichostrongylus infection, an uncommonly reported zoonosis in Australia, is common in parts of the world where there is close human contact with herbivorous animals. We report 5 cases diagnosed in our laboratory since 1992. Over this period the laboratory has conducted over 46,000 parasitological examinations on feces. All 5 cases were investigated for fecal parasites following detection of a blood eosinophilia. Two of the 5 cases complained of mild abdominal discomfort and diarrhea. It is likely that all obtained their infection following ingestion of contaminated unwashed vegetables which had been fertilized with animal manure. Four of the cases acquired their infection in Queensland and the fifth may have become infected in rural Victoria. All were treated with pyrantel embonate with resolution of the eosinophilia. Follow up fecal specimens showed no parasites. Patients were instructed on the mode of transmission and advised to thoroughly wash any uncooked vegetables prior to ingestion. In our cases, goats and horses were possibly implicated. No published reports of Trichostrongylus spp. in humans in Australia have occurred since the 1930s and it may be more common in Australia than is recognized. The infection may be missed because patients are asymptomatic or have mild gastrointestinal symptoms or only a blood eosinophilia. Trichostrongylus eggs may also be mistaken for hookworm eggs. It is important therefore to distinguish these infections from hookworm infection as the modes of transmission, management and advice regarding prevention differ.

Tropical diseases in immigrants and internationally adopted children

Immigrants, particularly those from the developing world, make up a significant number of tropical disease cases seen in a temperate climate. Internationally adopted children are another group in which tropical and other infectious diseases must be considered. The differential diagnoses of various syndromes in these populations in relation to relatively more common tropical diseases are reviewed.

Enterobiasis: a histopathological study of 259 patients

Enterobius worms or their eggs, or both, are present in preserved tissue sections or tissue specimens of 259 patients whose medical records are on file at the Armed Forces Institute of Pathology, Washington D.C., U.S.A. The most common site of infection (86.5%) was found to be the lumen of the appendix, where the worms provoke no reaction. Of the 259 patients 11 (4.2%) had worms and/or eggs in granulomas of the abdominal and pelvic peritoneum, and an equal number had granulomas on the peritoneum of the salphinx or on the surface of the ovary. There were also ectopic worms and/or eggs in granulomas on the peritoneum of the small and large intestines (2.7%). These Enterobius granulomas form around degenerating adult worms, around discrete eggs, around clusters of eggs, and, we believe, also around the tracks of migrating worms. Three patients (1.2%) had worms in perianal abscesses. A necrotic granuloma, removed from the lung of one patient, surrounded a degenerating adult worm. This suggests that the worm, carried to the lung as an embolus, impacted in a pulmonary arteriole. A stool specimen of one patient contains eggs of Enterobius, and that of another patient contains an adult Enterobius. This is the largest recorded histopathological study of enterobiasis in man.

Prevalence, incidence, intensity and associated morbidity of intestinal helminths in south Thailand

Intensive surveys for Ascaris lumbricoides, Trichuris trichiura and hookworm were carried out in two villages in Phang Nga Province, southern Thailand, in order to measure prevalence, estimate incidence and determine the relation between intensity of infection and morbidity before and after chemotherapy. The study populations were a small upland village community (Nai Tone) and a grade school in a small coastal village (Boh Saen). About half of the Nai Tone villagers were given a broad spectrum antihelminthic (albendazole), and the Boh Saen students were all treated successively with three drugs: piperazine citrate to treat for Ascaris, pyrantel pamoate to treat for hookworm, and mebendazole to treat for Trichuris. Stool examinations were made using the quick Kato smear technique, questionnaires were administered concerning a variety of possible symptoms, and anthropometric and blood biochemical parameters were measured both before and after treatment. The prevalence of Ascaris was 31.0 and 22.6%, hookworm was 89.1 and 88.0% and Trichuris was 59.7 and 77.8% in the Nai Tone and Boh Saen study populations, respectively. Average intensity of Ascaris was highest in the 0-9 year age class (greater than 32,000 epg) in Nai Tone Village. Hookworm intensity of infection was higher in males than in females in all age classes, and in Nai Tone Village at least 25% of males and 20% of females had 8000 or more epg of faeces. Trichuris intensity of infection was highest between 5 and 10 years of age in both populations. The only signs or symptoms showing a significant (P less than 0.05) difference between high and low classes of intensity of infection and a significant improvement (P less than 0.01) after drug treatment, were headache and flatulance in the case of hookworm infection in Boh Saen School. The presence of multiple infections made testing of hypotheses concerning particular parasite species difficult.

Benzimidazoles in the treatment of trichuriasis: a review

Treatment of severe symptomatic trichuriasis observed with heavy worm burdens is not satisfactory with recommended doses of mebendazole, flubendazole and albendazole. Higher doses of anthelmintics for longer periods of treatment generally improve the cure rates but treatment of such associated symptoms as diarrhoea is recommended before starting anthelmintic therapy. Such severe cases of trichuriasis should be considered separately; they do not represent the majority of cases infected by this parasite, which usually respond to benzimidazoles.