TRICHINELLOSIS. By: Christi Smykal

Transcription

1 TRICHINELLOSIS By: Christi Smykal Trichinellosis : Etiological agent: Trichinellosis is caused by a parasitic roundworm known as trichinella (7). Trichinella spiralis are found to be the causative agents of human trichinellosis (3). TAXONOMIC CLASSIFICATION: Kingdom: Animalia Phylum: Nematoda Class: Adenophorea Order: Trichocephalida Family: Trichinellidae Genus: TRICHINELLA Railliet 1895 Species: Trichinella britovi Trichinella murrelli Trichinella nativa Trichinella nelsoni Trichinella papuae Trichinella pseudospiralis Trichinella spiralis Trichinella zimbabwensis Reference (7) DISEASE TRANSMISSION: Trichinosis is caused by eating raw or undercooked pork and wild game infected with the larvae of a parasitic worm. The larvae is from the roundworm trichinella spiralis (4). Trichinellosis cannot be spread to others. Eating raw or undercooked meat that is infected with the trichinella worms is the only way to become infected. RESERVOIRS: Main sources/hosts of Trichinella sp. infections for humans includes pigs, horses, wild boars, dogs, walruses, foxes, and bears (3). Seals are another host that can be infected with trichinella spp (8). Foxes, wolves, and bears have the highest infection rates, but small mammals, such as skunks, raccoons, and rats, provide the highest risk to infecting the domestic pig. In horses, natural infections are rare; however, infected horses from Mexico and Romania have been identified (6). SPECIFIC CHARACTERISTICS:

2 Trichinella is the genus of parasitic roundworms of the phylum Nematoda that cause trichinosis (also known as trichinellosis). Trichinella is known as the smallest human nematode parasite, yet it is also the largest of all intracellular parasites (6). When a human or animal eats meat that contains infective Trichinella cysts, the acid in the stomach dissolves the hard covering of the cyst and releases the worms. The worms pass into the small intestine and, in 1-2 days, become mature. After mating, adult females lay eggs. Newborn larvae migrate directly into predominantly lymphatic and blood vessels of the host. This allows them to be transported to predilection sites (highly oxygenated muscles), where they penetrate. Eggs develop into immature worms, travel through the arteries, and are transported to muscles. Within the muscles, the worms curl into a ball and encyst (become enclosed in a capsule). The incubation period ranges from 1-2 days (enteral phase) to 2 to 8 weeks (parenteral phase) or more, depending on the infectious dose and possibly the species of parasite (2). The life cycle repeats when meat containing these encysted worms is consumed by another human or animal (8). The host immune response leads to expulsion of the adult worms after several weeks; the larvae, once in the striated muscle cells, can persist for months or years, although clinical signs and symptoms typically wane after several months (2). In wild animals, Trichinella infection rates vary from region to region and seem to increase in colder climates (6). TESTS FOR IDENTIFICATION: There are multiple different ways to diagnose the presence of trichinella infection in animals. These include direct methods (muscle biopsy of postmortem carcasses), molecular techniques, and/or serology tests (presence of anti-trichinella antibodies). Diagnosing humans is understandably different methods. Often, mild cases of trichinellosis are never specifically diagnosed and are assumed to be the flu or other common illnesses (8). There are no accurate tests for the early phase of infection of the intestines (4). The diagnosis of trichinellosis should be based on three main criteria : clinical findings (recognition of the signs and symptoms of trichinellosis); laboratory findings (nonspecific laboratory parameters (eosinophilia and muscle enzymes), antibody detection, and/or detection of larvae in a muscle biopsy); and epidemiological investigation (identification of source and origin of infection and outbreak studies) (3). SIGNS AND SYMPTOMS OF DISEASE: Symptoms of trichinellosis may range from very mild to severe and relate to the number of infectious worms consumed in meat. In severe cases, death can occur (8). Signs/symptoms of trichinellosis are generally characterized by two different phases. The initial phase (intestinal) - consists of abdominal discomfort, diarrhea, and nausea that begins 1-2 days after ingestion (4). These earlier signs of trichinellosis - correspond to the new larvae migration through the body and can persist days to weeks. ). In addition to physical damage to affected tissues, larval penetration and tissue migration causes an immune-mediated inflammatory reaction and stimulates the development of eosinophilia (2).

3 The second phase (muscle) consists of muscle aches, itching, fever, chills, and joint pains that begin about two to eight weeks after ingestion (4). More severe manifestations include myocarditis, encephalitis, and thromboembolic disease (2). In addition, there can be "splinter" hemorrhages under fingernails and eye inflammation (conjunctivitis) (4). HISTORICAL INFORMATION: The genus was first recognized in a larval form in The L1 larvae live in a modified skeletal muscle cell. The adult worms occupy a membrane-bound portion of columnar epithelium, living as intramulticellular parasites. Infections with this genus have been reported from more than 150 different naturally or experimentally infected hosts. It has been shown to have a worldwide distribution in domestic and/or sylvatic animals (6). In the United States, trichinellosis cases are reported to CDC much less commonly now than in the past (7). During the late 1940s, when the U.S. Public Health Service began counting cases of trichinellosis, 400 cases in the United States were recorded each year on average. During , 20 cases were reported to CDC each year on average. The overall number of cases reported has decreased because of improved pig-raising practices in the pork industry, commercial and home freezing of pork, and public awareness of the danger of eating raw or undercooked meat products. The number of cases associated with raw or undercooked wild game meats has remained relatively constant over time (Figure 2). Over the past 40 years, few cases of trichinellosis have been reported in the United States, and the risk of trichinellosis from commercially raised and properly prepared pork is very low. However, eating undercooked wild game, particularly bear meat, puts one at risk for acquiring this disease (7). Reference for graph (7)

4 VIRULENCE FACTORS: The virulent nature of T. spiralis can be attributed to the capsule that surrounds the larvae during transmission as well as the high number of larvae a female produces in the intestine. The capsule is a distinguishing feature used to distinguish the two clades within the genus Trichinella. The capsule is believed to be an adaptive advantage of the pathogenic worm, allowing survival in high temperatures up to 70 degrees Celsius. The capsule also protects the nematode from freezing temperatures for extended time periods as well. Additional benefits of capsule include the ability to survive in dead and decaying animals for periods as long as four months (9). The exact mechanism used to construct the nurse cell continues to remain a mystery. CONTROL/TREATMENT: Trichinosis treatment focuses on reducing inflammation, and corticosteroids are usually administered. This treatment often leads to complete recovery, but muscle pain and weakness may persist (6). Prompt treatment with anti-parasitic drugs can help prevent the progression of trichinellosis by killing the adult worms and so preventing further release of larvae. Once the larvae have become established in skeletal muscle cells, usually by 3 to 4 weeks post infection, treatment may not completely eliminate the infection and associated symptoms. Treatment with either mebendazole or albendazole is recommended. If treatment is not initiated within the first several days of infection, more prolonged or repeated courses of treatment may be necessary. Both drugs are considered relatively safe but have been associated with side effects including bone marrow suppression. Patients on longer courses of therapy should be monitored by serial complete blood counts to detect any adverse effects promptly and discontinue treatment. In addition to anti-parasitic medication, treatment with steroids is sometimes required in more severe cases (2). PREVENTION: The prevention of trichinellosis in humans is based on three main approaches (3). These include the education of the consumer about the risk of consumption of raw or semi-raw meat and meat products from both domestic (e.g., pigs, horses) and sylvatic (e.g., wild boars, bears, walruses) animals that can be carriers of Trichinella parasites if they are not properly tested for Trichinella larvae upon meat inspection. Proper handling of meats is encouraged to prevent trichinellosis and many other infections. Some helpful tips are: - Wash your hands with warm water and soap after handling raw meat (1). - Freeze pork less than 6 inches thick for 20 days at 5 F (-15 C) to kill any worms (1). - Understanding that freezing wild game meats, unlike freezing pork products, may not effectively kill all worms because some worm species that infect wild game animals are freeze-resistant. - Clean meat grinders thoroughly after each use (1). Making sure that farming of pigs (the most important source of Trichinella infection for humans) in modern, industrialized, indoor pigsties, is under strict veterinary control and uses certified feedstuff.

5 And maintining control of all susceptible animals (both domestic and sylvatic) by a standardized artificial digestion method at slaughtering or after hunting. REPORTING CURRENT OUTBREAKS LOCALLY: Confirmed trichinellosis cases is a notifiable condition, that should be reported to your local or regional health departments. In Texas, confirmed cases should be reported within one week (5). In the United States, cases are rare associated with pork products because Centers of Disease Control and Prevention has warned people about the dangerous effects of eating pork if not cooked thoroughly. For people who have had recurring trichinellosis, there is certain criteria to distinguish a new case from an existing case. Serial or subsequent cases of trichinellosis experienced by one individual should only be counted if there is an additional epidemiologically compatible exposure. Because the duration of antibodies to Trichinella spp. is not known, mere presence of antibodies without a clinically-compatible illness AND an epidemiologically compatible exposure may not indicate a new infection especially among persons with frequent consumption of wild game that is known to harbor the parasite (9). Case classification can fall into three categories: SUSPECTED - No clinically compatible illness it should be reported as suspect if the person shared an epidemiologically implicated meal, or ate an epidemiologically implicated meat product, and has a positive serologic test for trichinellosis (and no known prior history of Trichinella infection) (9). PROBABLE - A clinically compatible illness in a person who shared an epidemiologically implicated meal or ate an epidemiologically implicated meat product. And/or a clinically compatible illness in a person who consumed a meat product in which the parasite was demonstrated (9). CONFIRMED - A clinically compatible illness that is laboratory confirmed in the patient (9). GLOBAL OUTBREAKS/TRENDS: Due to political and economic changes, recent increases in prevalence and incidence have been observed in many former eastern European countries. Such increases have been related mainly to a reduced efficacy of the veterinary control on susceptible production animals. This represents a serious problem for the meat trade within the European Union and for the exportation of pork outside European Union countries. As a consequence of the emerging European problem, the European Union and some associated non-european Union member countries implemented a Trichinella monitoring program for pigs, horses, wild boar, and other wildlife species. The European Commission has implemented a new regulation, regulation no. 2075/2005, laying down specific rules for the official controls of Trichinella in meat in order to improve food safety for European consumers (3). In the United States, a pilot program for Trichinella-free pig production has been developed. The described Trichinella certification mechanism allows the establishment of a process for ensuring the Trichinella safety of swine and, ultimately, food products derived from swine at the production level (3).

6 REFERENCES: 1) Parasites - Trichinellosis (also known as Trichinosis). (2017, July 05). Retrieved March 12, 2018, from 2) Parasites - Trichinellosis (also known as Trichinosis). (2018, January 09). Retrieved March 12, 2018, from 3) Home - PMC - NCBI. (n.d.). Retrieved March 12, 2018, from 4) Davis, C. P. (n.d.). What Is Trichinosis? Symptoms, Treatment, Causes & Complications. Retrieved March 12, 2018, from 5) Reporting Communicable Disease in Travis County. (n.d.). Retrieved March 12, 2018, from E29E8BDA93B0368E7&rd=1&h=8-ca3483X56pgv6If6a- _qvce3f_ccvbl6l1n5qgqbm&v=1&r=https%3a%2f%2fwww.austintexas.gov%2fsites%2fdefault %2ffiles%2ffiles%2fHealth%2fEpidemiology%2fReporting_Package_July_2014.pdf&p=DevEx, ) From Wikipedia, the free encyclopedia - PSSurvival.com. (n.d.). Retrieved March 12, 2018, from C432E036CE5&rd=1&h=0EFD4CtbStJSEhhNMSr6mCGscKndz1otXlwcMwaRzk&v=1&r=http%3a%2f%2fwww.pssurvival.com%2fPS%2fParasites%2fRou ndworm_trichinella-2017.pdf&p=devex, ) Epidemiology & Risk Factors. (2012, August 08). Retrieved March 12, 2018, from 8) Trichinellosis FAQs. (2012, August 08). Retrieved March 12, 2018, from 9) Trichinellosis / Trichinosis (Trichinella spp.)2014 Case Definition. (n.d.). Retrieved March 14, 2018, from