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What is it?

Cysticercosis in humans is caused by Taenia solium. T. solium is a two host tapeworm.  The adult form lives in the intestine of human beings (the definitive host) and measures several meters in length. Tapeworms (taenia) are made up of segments called proglottids.  The head end is attached to the host’s intestine and at the opposite end, its segments, called gravid proglottids, contain several thousands of microscopic eggs. Proglottids detach from the worm and are expelled with the stools (faeces) during defecation. T. solium then needs pigs (its intermediate host) to continue its development. Pigs are coprophagous animals, feeding naturally on stools (faeces). When T. solium eggs reach the pig’s intestine, they hatch and release a larva that crosses the intestinal wall, reaches the blood circulation and settles in striated muscular tissue. The larva then develops into a cyst measuring only a few mm in diameter called a cysticercus, which is infective to humans. Humans are infected with the tapeworm when they consume raw or undercooked pork meat containing cysticerci. In the human intestine, cysticerci then turn inside out (a process called evagination) and attach to the intestinal wall and start growing.  The presence of adult T. solium in human intestine (taeniosis) is not very pathogenic. People are most often unware that they have a tapeworm. Similarly, the presence of cysticerci (cysticercosis) in pigs is not considered to be pathogenic either. However, humans may also be infected by T. solium eggs subsequently producing cysticerci in human tissues. Cysticerci in the brain cause neurocysticercosis, a severe condition in humans. Human cysticercosis is not only found in tapeworm carriers. It is even sometimes recorded in Jewish and Muslim communities not consuming pork. In fact, tapeworm carriers are capable of contaminating the wider environment, including food, hands and various objects, with T. solium eggs.

T. solium used to be a cosmopolitan parasite found in most countries of the world. Following the industrialization of pork production in developed countries, pigs were rarely infected, virtually causing no human taenioses. However, the parasite remains widely prevalent in developing countries practicing extensive pig production. Human migration results in the wide dissemination of eggs by human carriers, causing human cysticercosis virtually anywhere in the world. Nevertheless, developing countries remain those mostly affected by human cysticercosis.

Other human tapeworms (including the beef tapeworm) do not cause cysticercosis in humans.

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How to recognize it

In humans, adult T. solium live in the intestine. They measure 2-3 m, sometimes even longer. Their scolex (head) is very small (0.6 – 2 mm) and bears 4 suckers and a double crown of hooks. Their body is made up of proglottids of different levels of maturity. The gravid proglottids (egg-carrying segments), which are expelled with stools, measure about 5 mm in width and 20 mm in length and may be observed moving in fresh stools (white in color). The tapeworm infection itself does usually not cause any symptoms. However, some people may have abdominal discomfort. Confirmatory diagnosis can be performed through the observation of proglottids or eggs in stools. The pork tapeworm cannot be differentiated from the beef tapeworm and other tapeworms by its appearance and structure, but tapeworms other than T. solium expulse their proglottids independently of defecations, which is often noticed by the infected individual. Molecular characterization may be used to confirm the species. Serological tests may be used to detect specific antigens in stools and specific antibodies in blood of the patients.

Symptoms caused by cysticercosis in humans depend on the localization of the cysticerci. Sub-cutaneous cysts may be observed but are benign. The presence of cysts in the brain is the cause of neurocysticercosis, a severe condition characterized by seizures, headaches and, less commonly, epilepsy, confusion, lack of attention, difficulty with balance and dementia. The disease can result in death. In some communities, patients are severely stigmatized: the mental symptoms are often mistaken for mental illness, spirit possession or witchcraft. Neurocysticercosis is confirmed through medical imaging (CT- or MRI-scan). Serological tests are available to detect specific antigens and antibodies but cannot replace neuroimaging.

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In pigs, cysticerci are more abundant in heavily irrigated striated muscles such as the heart, the tongue, masseters (the muscles of the jaws) and diaphragm pillars. No symptoms are seen in infected pigs, even when they are very heavily infected. However, in live pigs, it is possible to feel cysticerci in the tongue. Live and dead (calcified) cysticerci may be observed at autopsy. Serological assays detecting specific antigens and antibodies are available but mostly used for epidemiological studies.

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How to control it

The lifecycle of the parasite can be disrupted at each parasitic stage: eggs, cysticerci and tapeworm. The use of closed toilets or latrines and the confinement of pigs are likely to disrupt the cycle, as observed in industrialized countries. The cysticerci in pigs can be targeted through meat inspection, though this method lacks sensitivity. Pork meat should either be well frozen or, preferably, thoroughly cooked to destroy cysticerci. Finally, human beings carrying tapeworms contribute heavily to the spread of the parasite at the international level. The risk of contaminating confined pigs and initiating a new cycle in disease-free areas is extremely low but there is a high risk of contamination of human beings. Identification and treatment of T. solium carriers is therefore very important to prevent human cysticercosis, even in areas where toilets are used and pigs are confined.

Cysticercosis is theoretically eradicable.

The construction and use of latrines in rural areas of Africa have been encouraged to control the access of pigs to human stools. Sociological and psychological issues strongly influence whether or not people use latrines. Improved sanitation may help controlling other parasitic and bacterial diseases as well. Importantly, pigs should not have access to toilet outlets. Confining pigs is only necessary if infected human stools are accessible. Confined pigs need to be appropriately fed and watered, which is not a usual practice in communities where pig production is based on pigs foraging for food. Drinking water given to pigs should not be contaminated with T. solium eggs.

Porcine cysticercosis can be prevented using a recombinant vaccine. This vaccine seems to be very effective but is not commercially available. Pigs may be treated with anthelmintics, before they are slaughtered, to kill cysticerci.

Meat inspection has been widely practiced and advocated throughout the world. Unfortunately, meat inspectors have no access to pigs that are slaughtered out of abattoirs.  Also, it is difficult to detect pigs with low levels of infection (which can be very frequent). Infected carcasses do not necessarily need to be destroyed since freezing and cooking kill the cysticerci but this is often not possible in developing countries, given the lack of meat processing facilities.

Eating roasted pork served in bars and at ceremonies seems to be the main occasion at which Africans are exposed to undercooked pork. Communities need be made aware of the need to cook pork thoroughly before it is eaten by people.

Finally, human taeniosis can be treated using specific drugs.  This results in the tapeworm being expelled. Extreme care should be taken when whole tapeworms are expelled since they contain large numbers of infective eggs. Consequently, treatment against the tapeworm should be done under strict medical supervision.

The risk of transmission of cysticercosis to humans may be mitigated by improved hygiene: hand washing (particularly after defecation), management of toilet outlets, preventing  the contamination of surface and drinking water by eggs, not using human manure in vegetable gardens…

In humans, neurocysticercosis is treated with antiepileptic drugs. The destruction of cysticerci with anthelmintics is not recommended since the death of cysticerci tends to increase the severity of neurological symptoms.

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Cultural and geographical specificities

Pastoralist communities

Generally not applicable since pastoralist communities usually do not raise pigs.  Information materials can be found in section 3 below, on mixed farming communities.

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Communities in northern Africa and the Sahel region

Generally not applicable in these zones, since the population is predominantly Muslim and Muslim societies do not raise pigs.  For non-Muslim communities in the region see the section below on mixed farming communities.

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Mixed farming communities in more humid regions.

Industrialized pig production is not affected by T. solium. Free-range pigs in rural and peri-urban areas are the main concern. Integrated approaches promoting the use of latrines, the confinement of pigs, meat inspection and appropriate cooking of pork are recommended. Tapeworm carriers should be identified and treated. If people examine their own stools, it is possible to identify individuals who may be tapeworm carriers. Confirmatory diagnosis should be an easy procedure in health centres and patients should receive treatment under medical supervision to avoid a massive contamination of the environment (and people) when the worm is expelled. Finally, patients suffering from neurocysticercosis should receive adapted antiepileptic treatment until the cysticerci disappear naturally. Their communities should be sensitised on the cause and the treatment of the disease to avoid stigmatization of these patients.

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