Трихинеллез: причины, симптомы и лечение

Parasitic disease due to invasion by Trichinella spp. the disease

Trichinosis is mainly spread when undercooked meat containing Trichinella cysts is eaten. Several species of Trichinella can cause disease, with T. spiralis being the most common. Infection is typically treated with antiparasitic medication such as albendazole or mebendazole. Without treatment, symptoms typically resolve within three months. The risk of death from infection is low.

The great majority of trichinosis infections have either minor or no symptoms and no complications. The two main phases for the infection are enteral (affecting the intestines) and parenteral (outside the intestines). The symptoms vary depending on the phase, species of Trichinella, quantity of encysted larvae ingested, age, sex, and host immunity.

The severity of symptoms caused by larval migration from the intestines depends on the number of larvae produced. As the larvae migrate through tissue and vessels, the body's inflammatory response results in edema, muscle pain, fever, and weakness. A classic sign of trichinosis is periorbital edema, swelling around the eyes, which may be caused by vasculitis. Splinter hemorrhage in the nails is also a common symptom. They may very rarely cause enough damage to produce serious neurological deficits (such as ataxia or respiratory paralysis) from worms entering the central nervous system (CNS), which is compromised by trichinosis in 10–24% of reported cases of cerebral venous sinus thrombosis, a very rare form of stroke (three or four cases per million annual incidence in adults). Trichinosis can be fatal depending on the severity of the infection; death can occur 4–6 weeks after the infection,

The classical agent is T. spiralis (found worldwide in many carnivorous and omnivorous animals, both domestic and sylvatic (wild), but seven primarily sylvatic species of Trichinella also are now recognized:

T. spiralis is most adapted to swine, most pathogenic in humans, and is cosmopolitan in distribution. T. britovi is the second most common species to infect humans; it is distributed throughout Europe, Asia, and northern and western Africa, usually in wild carnivores, crocodiles, birds, wild boar, and domesticated pigs. T. murrelli also infects humans, especially from black bear meat; it is distributed among wild carnivores in North America. T. nativa, which has a high resistance to freezing, is found in the Arctic and subarctic regions; reservoir hosts include polar bears, Arctic foxes, walruses, and other wild game. T. nelsoni, found in East African predators and scavengers, has been documented to cause a few human cases. T. papuae infects both mammals and reptiles, including crocodiles, humans, and wild and domestic pigs; this species, found in Papua New Guinea and Thailand, is also nonencapsulated. T. pseudospiralis infects birds and mammals, and has demonstrated infection in humans; it is a nonencapsulated species. T. zimbabwensis can infect mammals, and possibly humans; this nonencapsulated species was detected in crocodiles in Africa. The larvae then migrate to the small intestine, and burrow into the intestinal mucosa, where they molt four times before becoming adults.

Diagnosis of trichinosis is confirmed by a combination of exposure history, clinical diagnosis, and laboratory testing.

An epidemiological investigation can be done to determine a patient's exposure to raw infected meat. Often, an infection arises from home preparation of contaminated meat, in which case microscopy of the meat may be used to determine the infection. Exposure determination does not have to be directly from a laboratory confirmed infected animal. Indirect exposure criteria include the consumption of products from a laboratory confirmed infected animal, or sharing of a common exposure with a laboratory confirmed infected human.

Clinical presentation of the common trichinosis symptoms may also suggest infection. These symptoms include eye puffiness, splinter hemorrhage, nonspecific gastroenteritis, and muscle pain.

Public education about the dangers of consuming raw and undercooked meat, especially pork, may reduce infection rates. Hunters are also an at risk population due to their contact and consumption of wild game, including bear. As such, many states, such as New York, require the completion of a course in such matters before a hunting license can be obtained.

Testing methods are available for both individual carcasses and monitoring of the herds. Artificial digestion method is usually used for the testing of individual carcasses, while the testing for specific antibodies is usually used for herd monitoring. Nonetheless, allowing a margin of error for variation in internal temperature within a particular cut of pork, which may have bones that affect temperature uniformity, is prudent. In addition, kitchen thermometers have measurement error that must be considered. Pork may be cooked for significantly longer and at a higher uniform internal temperature than listed below to be safe. Internal Temperature Internal Temperature Minimum Time (°F) (°C) (minutes) 120 49 1260 122 50.0 570 124 51.1 270 126 52.2 120 128 53.4 60 130 54.5 30 132 55.6 15 134 56.7 6 136 57.8 3 138 58.9 2 140 60.0 1 142 61.1 1 144 62.2 Instant
However, under controlled commercial food processing conditions, some of these methods are considered effective by the USDA. The USDA Animal and Plant Health Inspection Service (APHIS) is responsible for the regulations concerning the importation of swine from foreign countries. The Foreign Origin Meat and Meat Products, Swine section covers swine meat (cooked, cured and dried, and fresh). APHIS developed the National Trichinae Certification Program; this is a voluntary "preharvest" program for U. S. swine producers "that will provide documentation of swine management practices" to reduce the incidence of Trichinella in swine. The CDC reports 0.013% of U. S. swine are infected with Trichinella. These drugs prevent newly hatched larvae from developing, but should not be given to pregnant women or children under two years of age.

After infection, steroids, such as prednisone, may be used to relieve muscle pain associated with larval migration.

Researchers trying to develop a vaccine for Trichinella have tried using either "larval extracts, excretory–secretory antigen, DNA, or recombinant antigen protein." Another study used extracts and excretory–secretory products from first stage larvae to produce an oral vaccine. To prevent gastric acids from dissolving the antigens before reaching the small intestine, scientists encapsulated the antigens in microcapsules. This vaccine significantly increased CD4+ cell levels, and increased antigen specific serum IgGq and IgA, resulting in a statistically significant reduction in the average number of adult worms in the small intestines of mice. The significance of this approach is that, if the white blood cells in the small intestine have been exposed to Trichinella antigens (through vaccination), when an individual does get infected, the immune system will respond to expel the worms from the small intestine fast enough to prevent the female worms from releasing their larvae. A DNA vaccine tested on mice "induced a muscle larva burden reduction in BALB/c mice by 29% in response to T. spiralis infection".

About 11 million humans are infected with Trichinella; T. spiralis is the species responsible for most of these infections. Infection was once very common, but this disease is now rare in the developed world, but two known outbreaks occurred in 2015. In the first outbreak, around 40 people were infected in Liguria, Italy, during a New Year's Eve celebration. The second outbreak in France was associated with pork sausages from Corsica, which were eaten raw, affecting 14 people in total. The incidence of trichinosis in the U. S. has decreased dramatically in the past century from an average of 400 cases per year mid 20th century down to an annual average of 20 cases per year (2008–10). China reports around 10,000 cases every year, so is the country with the highest number of cases.

The disappearance of the pathogen from domestic pigs has led to a relaxation of legislation and control efforts by veterinary public health systems. Trichinosis has lately been thought of as a re emerging zoonosis, supplemented by the increased distribution of meat products, political changes, a changing climate, and increasing sylvatic transmission. Major sociopolitical changes can produce conditions that favor the resurgence of Trichinella infections in swine and, consequently, in humans. For instance, "the overthrow of the social and political structures in the 1990s" in Romania led to an increase in the incidence rate of trichinosis.

As early as 1835, trichinosis was known to have been caused by a parasite, but the mechanism of infection was unclear at the time. A decade later, American scientist Joseph Leidy pinpointed undercooked meat as the primary vector for the parasite, and two decades afterwards, this hypothesis was fully accepted by the scientific community.

The circumstances surrounding the first observation and identification of T. spiralis are controversial, due to a lack of records. In 1835, James Paget, a first year medical student, first observed the larval form of T. spiralis, while witnessing an autopsy at St. Bartholomew’s Hospital in London. Paget took special interest in the presentation of muscle with white flecks, described as a "sandy diaphragm". Although Paget is most likely the first person to have noticed and recorded these findings, the parasite was named and published in a report by his professor, Richard Owen, who is now credited for the discovery of the T. spiralis larval form.

A series of experiments conducted between 1850 and 1870 by the German researchers Rudolf Virchow, Rudolf Leuckart, and Friedrich Albert von Zenker, which involved feeding infected meat to a dog and performing the subsequent necropsy, led to the discovery of the lifecycle of Trichinella. Through these experiments, Virchow was able to describe the development and infectivity of T. spiralis.

The International Commission on Trichinellosis (ICT) was formed in Budapest in 1958. Its mission is to exchange information on the epidemiology, biology, pathophysiology, immunology, and clinical aspects of trichinosis in humans and animals. Prevention is a primary goal. Since the creation of the ICT, its members (more than 110 from 46 countries) have regularly gathered and worked together during meetings held every four years: the International Conference on Trichinellosis.