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The Ecology of Parasitism
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
The tapeworm Taenia solium provides a good example of the operation of an encounter filter. People acquire the tapeworm by ingesting the poorly cooked flesh of infected pigs containing the tapeworm’s larvae. The adult tapeworm living in the human small intestine passes its eggs in the host’s feces which in endemic areas are deposited outdoors near the infected person’s dwelling. The tapeworm eggs along with the human feces are ingested by the neighborhood domestic pigs. The likelihood that a pig encounters and becomes infected by ingesting the eggs, which go on to develop into cysticerci larvae, is strongly influenced by how close the pig lives to the dwelling of a person harboring T. solium adult worms (Figure 6.7). Pigs lucky enough to live far from an infected person are much less likely to encounter the eggs of this parasite and to become infected. Understanding such encounters are relevant for control of T. solium which is notorious for causing cysticercosis with associated epilepsy-like seizures in infected people.
The Parasitic Protozoa and Helminth Worms
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
The adult worm, Diphyllobothrium latum, is about 3 to 10 meters in length. Unlike Taenia species, the gravid proglottids do not pass out in the feces intact, but generally disintegrate and release their eggs into the intestinal lumen. If the eggs gain access to fresh water, they hatch and release ciliated embryos that are ingested by copepods in which the larva encysts. If the infected copepods are ingested by a fish, the larvae penetrate the intestinal wall and enter various tissues. When infected fish are ingested by humans, the larvae are released from the tissues and adhere to the intestinal wall where they mature into adult worms. Infection in the human is usually limited to a single worm. The worm has an exceptional propensity to absorb vitamin Bl2 and thus competes with the host for this nutrient. When dietary factors limit the ingestion of this vitamin, this competition can result in anemia in the host, otherwise the infection may be entirely symptomless. There is not thought to be any immunity against this tapeworm.
Gastrointestinal Infections
Published in Miriam Orcutt, Clare Shortall, Sarah Walpole, Aula Abbara, Sylvia Garry, Rita Issa, Alimuddin Zumla, Ibrahim Abubakar, Handbook of Refugee Health, 2021
Echinococcus granulosus causes cystic echinococcus and E. multilocularis causes alveolar echinococcus. Cysts can occur anywhere, but the liver (around two-thirds) and lung (around one-quarter) are the most common sites. Cystic echinococcus can be asymptomatic, particularly in early disease, and can have a long latent period. Infection occurs by ingestion of parasite eggs after excretion by tapeworm-infected animals, for example, dogs (definitive host). It is present in the Middle East, South America, Eastern Mediterranean and sub-Saharan Africa, particularly among rural/farming communities. Diagnosis is based on serology and typical imaging appearances on ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI). The WHO classification grades cystic echinococcus from grade 1 to grade 5 based on size and type, for example active, degenerating and inactive. There is a risk of anaphylaxis or secondary echinococcosis if cysts rupture or spill. Treatment depends on staging and can include surgery (if complicated or size >10 cm with risk of rupture), with adjunctive drug therapy with albendazole (15 mg/kg orally twice daily; usual adult dose is 400 mg twice daily; liver function should be monitored.) Puncture Aspiration Injection Re-aspiration (PAIR) is an option for some cysts. For cystic echinococcus stages 4 and 5 (degenerated cysts and solid) or inoperable, monitoring with ultrasound every 6 months is recommended.
New insights on the Taenia solium tapeworm using molecular tools: age-based human definitive host prevalence and deliberation on parasite life span
Published in Pathogens and Global Health, 2022
Tiaoying Li, Xingwang Chen, Christine M. Budke, Yuangui Zhou, Mianchuan Duan, Celine Wang, Bo Zhong, Yang Liu, Jianying Luo, Wei He, Jingye Shang, Akira Ito
The possibility of reinfection is high in highly endemic areas, such as the village of Guni. However, it is not clear if repeated infections impact immunogenicity and worm expulsion. In the current study, all T. solium carriers reported segment expulsion for no longer than five years. Preliminary work done by our research group has shown similar findings in low endemic areas (prevalence less than 1%) of China (unpublished), suggesting that repeated infection likely has no or only a limited effect on parasite longevity. Moreover, new infections are likely deterred through concomitant immunity caused by infection with the same species of tapeworm. This hypothesis is supported by the observation of cases infected with multiple tapeworms of the same species that likely have the same source of infection based on worm morphology and size [32].
Diagnostic and management strategies of ocular cysticercosis: current perspectives
Published in Expert Review of Ophthalmology, 2020
Cystercosis is a cestode infection that is an important problem in tropical medicine [1–3]. This is a form of Taenia species infection. The human cysticercosis is an accidental dead ended infection caused by pork tapeworm (Taenia solium). The disease is caused by larval cysts of the tapeworm. The two main ways that the patients can acquire this infection are ingestion of tapeworm eggs through a fecal-oral transmission or autoinfection. Basically, human is a definitive host for adult parasite and pig plays role as an intermediate hosts harboring parasitic larva. Accidentally, human might act as an intermediate host and result in cysticercosis. The heteroinfection due to intake of contaminated food or water with the parasitic eggs, external autoinfection by ingestion ova of the existing parasite or internal autoinfection by retrograde peristalsis that pushes proglottids bearing eggs from intestine directly to stomach are the three ways that a human might become an intermediate host and further develops cysticercosis. The disease is strongly related to poor hygiene and common in areas with poor background sanitation.
Prevalence and risk factors for neurocysticercosis in children with a first-onset seizure in rural North India
Published in Paediatrics and International Child Health, 2020
Amit Kumar Mital, Priyanka Choudhary, R. B. Jain
Taenia solium infection is usually contracted by eating undercooked pork and intestinal infection is generally asymptomatic. Cysticercosis occurs through consuming food contaminated with faeces containing eggs of T. solium (the faeco-oral route) [4,5]. Once a human ingests food or water contaminated with the eggs and the larvae are released from the eggs, they invade the intestine, migrate through the bloodstream and encyst in organs such as subcutaneous tissue, muscle and brain (NCC). In the brain they form a fluid-filled cyst containing a single invaginated scolex. Local transmission of the disease is, however, only possible in the presence of an adult T. solium worm in the gut. The tapeworm carrier is the sole source of infection and is at risk of acquiring cysticercosis, probably through faecal-oral autoinfection. Carriers are most at risk and prone to high levels of heavy infection, leading to disseminated or encephalitic NCC [6,7]. NCC can also lead to complications such as hydrocephalus, cerebral oedema, cerebral infarction, spinal transverse myelitis and ocular NCC with retinal detachment [8].