Trichinosis (or trichinellosis) is a complex disease about which little is known. It is caused by eight different species of round worm in the genus Trichinella. These parasites can be found in animals on all continents but Antarctica. Artic bears harbor a species of Trichinella that is resistant to freezing for reasons yet to be discovered. Recently a species of Trichinella has been discovered in East African reptiles, notably crocodiles. Carnivorous animals and humans acquire these nematodes (flat worms) by eating raw or undercooked meat and meat products of other animals, particularly pigs, horses, and wild game. The most reliable method of prevention is to cook meat thoroughly before eating.
Once consumed from the diet, the worms migrate from the intestines to the muscles. Symptoms are usually so mild that the diagnosis is missed, but they can include stomach upset, diarrhea, constipation, eyelid swelling, and fever. Muscle pain due to the inflammation caused by chemicals the worms secrete can appear as early as one to two days after ingestion of contaminated meat. Later symptoms appear within two to eight weeks, when the worms have migrated into the muscles. Breathing may be difficult if the diaphragm muscle is involved. The heart, brain, eyes, and lungs may be involved in more serious infections. Most symptoms disappear within three months, but vague muscle pains may last for longer periods of time. Severe infections may cause death.
The interaction of the Trichinella organism and its infected host is highly complex. The worm secretes a variety of chemicals that induce changes in the host cells. Some of these changes allow the worm to migrate from the gut to the muscles. Other chemicals cause the muscle cells to produce a capsule around the worm. Still others cause an inflammatory reaction in muscles. Discovering these chemicals will help researchers in understanding disease mechanisms in other infections as well.
According to the World Health Organization, the global prevalence of trichinosis is about 10 million infected individuals. Most of these are in the developing world where meat inspection and controls are absent and cooking practices are less standardized. In the United States, there has been an average of 12 cases per year. Despite a century of veterinary public health efforts to control and eradicate it, however, trichinosis has experienced a dramatic re-emergence worldwide over the past 10 to 20 years. The reasons for this re-emergence are diverse and include human interference with ecosystems, war and political turmoil, rapidly changing food distribution and marketing systems, and rising affluence in developing countries.
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Researchers hope that further understanding of the molecular basis of Trichinella infection will lead to development of new drugs, including drugs that will treat the muscle phase, but nothing has yet appeared. Molecular biology may also uncover new tools to identify patients who have the disease. These will take the form of more specific and easier-to-use laboratory tests for molecules unique to the Trichinella species or to the body's immune reaction to the infection.
On a less technologic basis, researchers also seek to identify social and economic trends that spread the disease, such as increasing affluence in developing countries that allows people to consume more meat products.
Future research will proceed along current directions, which include identifying the chemicals secreted by Trichinella and how they affect host tissues, identifying target molecules in Trichinella that may be susceptible to pharmaceutical interventions, and seeking ways to interrupt the worm's life cycle in host animals before they enter the food chain. Efforts are currently in progress to map the entire genome (all the genes) of Trichinella species as a database from which to explore its functions.
Transcriptomics, proteomics, and genomics are new techniques in molecular biology whereby the precise nature of genes, enzymes, and other molecules in cells are identified and their actions are better understood. Every infectious organism is in some way unique in how it damages its host and causes disease and currently, little is known about the mechanics of infection. Future research aims to develop new diagnostic tools to gain a better understanding in this area.