Thursday

Epilepsy, brain cysts and tapeworms

Ten pigs went to market, some pigs stayed at home, all pigs ate human faeces... and so a deadly tale begins.

Poor sanitation, poor hygiene practices, poor pig husbandry and poor meat inspection all fuel a vicious cycle that is destroying lives and livelihoods in many developing countries.

A potentially deadly parasite, Taenia solium, known as the pork tapeworm, is being transmitted from pigs to people, people to pigs and from people to people.

Cysticercosis has been dubbed one of the neglected diseases of neglected populations. It is considered by the World Health Organization to be one of the few potentially eradicable diseases, yet it is now an emerging disease of eastern and southern Africa.

Awareness and training activities are being organised in eastern and southern Africa to help combat the parasite that causes intestinal taeniasis in humans, cysticercosis in pigs and humans, and the potentially deadly human disease neurocysticercosis, which is the formation of (T. solium) cysts in the brain.

Neurocysticercosis affects millions of people in Africa and other developing countries in Asia and Latin America. It is rarely found in industrialized countries or in countries where pork is not consumed for religious or cultural reasons.

However, even in these countries more cases are being seen due to immigration, increased travel and importation of domestic workers from endemic countries.

It is a disease associated with poverty and underdevelopment, and is endemic in many developing countries where raising pigs and eating pork are popular.

Neurocysticercosis infection may remain non-symptomatic for years before manifesting as seizures, severe headaches or other neurological problems. It is also a major cause of acquired epilepsy in developing countries. It affects agility, concentration and in severe cases can result in death.

The true extent of the problem is not known because tapeworm carriers often do not know that they are carrying the parasite. It can lie in the human gut for years without causing any symptoms.

Major advances are being made in the diagnosis and treatment of people and pigs infected with pork tapeworm, but these diagnostic tools and medical treatments are not yet widely available in many endemic countries. A vaccine to prevent pigs from contracting the disease is also being developed.

Since the mid 1990s, more and more people in rural areas in eastern and southern Africa are keeping pigs, fuelled in part by a significant increase in the consumption of pork in both rural and urban areas. To poor smallholders in these regions, pigs represent a new opportunity in livestock keeping worth exploiting.

In Africa cattle are highly prized, but they can be problematic – protecting them from disease and theft requires constant vigilance and sometimes round-the-clock surveillance.

Pigs, however, are comparatively easy to manage, and are therefore becoming increasingly popular and important, especially in rural smallholder communities.

Pigs, like so many livestock, can serve as a 'mobile bank', with one adult pig fetching upwards of US$100 at markets in this region. Many farmers will keep between one to three pigs and sell an adult pig at the beginning of the school year to provide for school fees.

However, the increasing number of pigs being kept in eastern and southern Africa is raising its own set of problems, with a vicious cycle of infection and reinfection.

This is not just a problem for rural areas, where most pigs are kept, but it is also a problem for urban areas where infected pork can be consumed, and where human carriers of the parasite can infect other people.

Most worrying is the fact that people do not have to eat pork or keep pigs to become infected with cysticercosis. They can be exposed to the eggs from a human tapeworm carrier.

Disease and poverty go hand in hand. Poor sanitation and poor hygiene practices all increase the risk of contracting diseases.

In many developing countries, particularly in rural areas, human waste is generally disposed off in a pit or out in the fields, or in some cases it is simply thrown into the garden.

In many poor areas, livestock keeping is rudimentary and pigs, like many livestock, wander about freely. When the livestock keepers and family members go out to the fields to defecate, their pigs will follow.

Pigs like to eat human faeces and will trail out to where people have defecated to eat the stool. If these people are carriers of the tapeworm they will produce thousands of highly contagious eggs in their stool.

These eggs are hardy and may survive more than eight months in the environment, particularly in tropical conditions; the climate in Africa is ideal for the parasite to thrive. This presents a health hazard not only for pigs, but also for people.

If pigs ingest the eggs, they develop into the immature larval form of the parasite (cysticercosis) that can result in the formation of hundreds to thousands of cysts in the muscles of the animal.

In areas where meat inspection and control is lacking, infected pigs are often slaughtered and the pork sold for human consumption.

Eating infected raw or undercooked pork can cause people to become infected with the adult tapeworm form of the parasite (taeniasis). The parasite will remain in their gut, but eggs of the tapeworm will be expelled through their faeces.

This does not, however, cause neurocysticercosis, which requires transfer of the contagious eggs from the infected person’s faeces to the same or another person.

If humans come into contact with infected human stool and accidentally ingest the eggs, the eggs develop into the larval form of the tapeworm, which targets the muscles, the eyes and most commonly the brain (neurocysticercosis), manifesting as cysts.

This may occur through direct contact with a tapeworm carrier’s infested stool, by putting contaminated fingers in the mouth, or through ingestion of water or foods that have become contaminated with the infected faeces.

Pig traders have become aware of the heightened problem of cysticercosis in pigs. Many were finding that when the pigs they had purchased were slaughtered and inspected, they had cysts and were therefore condemned.

As a result, some pig traders have become extremely vigilant and now routinely carry out checks on pigs before purchase. Examining the underside of the pig’s tongue is a quick, easy and cheap way of checking for positive signs of infection, but may only detect about 50 per cent of the pigs infected.

Visual observation of the pork meat can also be used to determine the presence or absence of the parasite.

However, in areas where livestock and meat inspection are not so vigilant, infected pigs can be slaughtered and sold for human consumption.

The increasing consumption of pork in urban areas means that infected pigs can be transported into densely populated areas, where the infected pork finds its way into human diets. These unwitting consumers then become carriers of the parasite.

In poor rural communities where people are carriers of the intestinal tapeworm and pigs are allowed to roam and consume human faeces, it is likely that pigs will become infected with the parasite.

For these poor livestock keepers, their losses are threefold – they lose the income they expected to receive from the sale of their pigs; they and their families lose a valuable protein source when the pig carcasses are condemned, thus increasing the likelihood of family malnutrition; and their own health and productivity are at risk from cysticercosis infection. There is also the risk of tapeworm carriers transmitting the parasite to other people.

Cysticercosis can be prevented by interrupting the life cycle of the parasite at one or more points. Good pig husbandry, including preventing pigs access to human faeces, is one way to break the cycle.

Total confinement of pigs is a possibility but only sustainable if integrated with other management practices such as housing and feeding with locally available materials and feedstuffs.

Strict meat inspection and control also helps to break the cycle, preventing infected meat from being consumed by people.

Good hygiene practices and thorough cooking of pork can prevent people getting infected, or reinfecting themselves and/or infecting others.

These measures require education and training of all involved, including pig keepers and their families, pig traders, meat sellers, and the general public – whether they eat pork or not.

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