Article Figures & Data
Figures
- FIG. 1.
Trichinella sp. life cycle. (A) Main sources of Trichinella sp. infections for humans (including pigs, horses, wild boars, dogs, walruses, foxes, and bears). (B) Trichinella sp. cycle in the host body. In the enteral phase, muscle tissues are digested in the stomach, and larvae are released (1); larvae penetrate the intestinal mucosa of the small intestine and reach the adult stage within 48 h p.i., and male and female mate (2); female worm releases newborn larvae in the lymphatic vessels (from the fifth day p.i. onwards; the length of newborn production, from 1 week to several weeks, is under the influence of host immunity) (3). In the parenteral phase, the newborn larvae reach the striated muscle and actively penetrate in the muscle cell (4); the larva grow to the infective stage in the nurse cell (the former muscle cell) (5); and, after a period of time (weeks, months, or years), a calcification process occurs (6). (Modified from www.iss.it/site/Trichinella/index.asp with permission of the publisher.)
- FIG. 2.
World map showing the distribution areas of Trichinella spiralis (Tsp), Trichinella pseudospiralis from north America (TpsN), T. pseudospiralis from Europe and Asia (TpsP), T. pseudospiralis from Tasmania (TpsA), Trichinella papuae (Tpa), and Trichinella zimbabwensis (Tzi). (Modified from www.iss.it/site/Trichinella/index.asp with permission of the publisher.)
- FIG. 3.
World map showing the distribution areas of Trichinella nativa (Tna), Trichinella britovi (Tb), Trichinella murrelli (Tm), Trichinella nelsoni (Tne), Trichinella genotype T6 (T6), Trichinella genotype T8 (T8), and Trichinella genotype T9 (T9). In some regions, the distribution areas of these encapsulated species and genotypes overlap between them. (Modified from www.iss.it/site/Trichinella/index.asp with permission of the publisher.)
- FIG. 4.
Histological section (hematoxylin-eosin staining) of a muscle biopsy from a patient involved in a trichinellosis outbreak (100). (A) Cellular infiltrates; (B) collagen capsule of a “nurse cell”; (C) intersected muscle larva. (Photograph courtesy of Dietrich-Bonhoeffer-Klinikum, Neubrandenburg, Germany.)
Tables
- TABLE 1.
Main epidemiological features of Trichinella species and genotypesa
Species or genotype Geographical distribution Host range Main source of infection of humans Resistance of larvae in frozen muscles Encapsulated T. spiralis Cosmopolitan Domestic and sylvatic mammals Domestic and sylvatic swine horses Yes in horse muscles T. nativa Arctic and subarctic areas of America, Asia, Europe Sylvatic carnivores Bears, walruses Yes in carnivore muscles Trichinella genotype T6 Canada, Alaska, Rocky Mountains, and Appalachian Mountains in the United States Sylvatic carnivores Carnivores Yes in carnivore muscles T. britovi Temperate areas of Europe and Asia, Northern and Western Africa Sylvatic mammals and seldomly domestic pigs Wild boars, domestic pigs horses, foxes, jackals Yes in carnivore and horse muscles Trichinella T8 South Africa and Namibia Sylvatic carnivores None documented No T. murrelli United States and Southern Canada Sylvatic carnivores Bears, horses No Trichinella genotype T9 Japan Sylvatic carnivores None documented No T. nelsoni Eastern-Southern Africa Sylvatic mammals Warthogs, bush pigs No Trichinella genotype T12 Argentina Cougars None documented Unknown Nonencapsulated T. pseudospiralis Cosmopolitan Sylvatic mammals and birds, domestic pigs Domestic and wild pigs No T. papuae Papua New Guinea, Thailand Wild pigs, saltwater crocodiles Wild pigs No T. zimbabwensis Zimbabwe, Mozambique, Ethiopia, South Africa Nile crocodiles, monitor lizards None documented No ↵ a Based on data from reference 125.
- TABLE 2.
Predilection sites for Trichinella larvae in different animal speciesa
Animal species Predilection sites Aim of examination Domestic swine Diaphragm, tongue, masseter Meat inspection (domestic animals) Horse Tongue, masseter Meat inspection (domestic animals) Wild boar Forearm, diaphragm, tongue Meat inspection (game) Bear Diaphragm, masseter, tongue Meat inspection (game) Walrus seal Tongue, diaphragm, flippers, masseter Meat inspection (game) Fox Diaphragm, forearm muscles, tongue Epidemiological studies (reservoir animals) Raccoon dog Diaphragm, forearm muscles, tongue Epidemiological studies (reservoir animals) ↵ a Based on data from references 49, 66, and 70.
- TABLE 3.
Relationship between time of seroconversion and infection dose (T. spiralis) in pig, horse, wild boar, and red foxes
Animal species Infection dose (no. of larvae/animal) No. of lpg Time of seroconversion p.i. (wk) Swine 100 1.62-6.50b 5-7 500 18.4-48.6b 4-5 1,000 26.3-90.6e 4-6 2,500 87.6-99.5b 4 8,000 12.1-81.4c 3 20,000 699.2-1103.5e 3-4 64,000 221.4-466.6c 2.5-3 Horse 1,000 0.10-0.26b 3-4 4,000 0.39-7.8b 3-7 5,000 0.02-8.9e 2-4.5 10,000 6.6-60.0b 3-4 40,000 484-1060d 2-3 Wild boar 10,000 43-100e 3-4 Red fox 10,000 7.7-202.7 3 a Data for pig based on references 46, 104, and 152; data for horse based on references 47 and 157; data for wild boar based on reference 67; and data for red foxes based on reference 91.
↵ b Mean of tongue.
↵ c Mean of tongue, masseter, diaphragm, intercostal, psoas, and rectus abdominis.
↵ d Mean of masseter.
↵ e Mean of diaphragm.
- TABLE 4.
Classification of different clinical forms of trichinellosis, in dependence of the severity of signs and larval densitya
Clinical form/outcome of infectionb Serology Presence of eosinophils (>500 eosinophils per mm3) Presence of main clinical signs (fever, edema, myalgia) Recovery after infection Hypoalbuminemia Complications Estimated no. of larvae/g muscle Hospitalization Putative fatality Asymptomatic + Transient − − − − <10 − − Abortive + + Transient (1-2 days) − − − > − − Mild + + + 3 wk − − > − − Pronounced + + ++ 6 wk +/− Rare > +/− − Severe + Sometimes absent +++ >6 mo + Frequent >100 + +/− ↵ a Modified from reference 73 with permission of the publisher, with additional data from reference 153.
↵ b The asymptomatic form of trichinellosis relates to a history of exposure, but signs and/or symptoms are lacking. The diagnosis of asymptomatic cases is usually based upon serological findings. In the abortive form, the clinical signs and symptoms are weakly expressed and last up to a few days; diagnosis should also be confirmed by serological testing. The mild form exhibits a low intensity of signs and/or symptoms. No complications are encountered, and serological testing is indispensable in establishing a diagnosis. The pronounced form is characterized by the appearance of the complete syndrome of significant intensity, but complications are rare, and if present, they are benign and vanish soon. The severe form is characterized by the development of the full syndrome of highly pronounced signs and symptoms with metabolic disturbances accompanied by circulatory and/or neurological complications.
- TABLE 5.
Differential diagnosis of trichinellosisa
Clinical finding Disease to be differentiated Protracted diarrhea Salmonellosis, shigellosis, and other viral, bacterial, or parasitic infections of the gastrointestinal tract High fever and myalgia Influenza virus infection Periorbital or facial edema with fever Glomerulonephritis, serum sickness, toxic-allergic reactions to drugs or allergens, polymyositis, periarteritis nodosa, dermatomyositis High fever and neurological symptoms without periorbital edema Typhoid fever Intense headaches, fever, nuchal pseudorigidity with blurred consciousness and drowsiness, irritability, and neurological symptoms Cerebrospinal meningitis, encephalitis, neuroinfections Intraconjunctival hemorrhages, intradermal petechiae, fever Leptospirosis, bacterial endocarditis, and typhus exanthematicus Eosinophilia combined with myalgia and an inflammatory response Eosinophilia-myalgia syndromes (e.g., toxic oil syndrome, trytophan intake, and eosinophilic fasciitis) Eosinophilia combined with fever Fasciolasis, toxocarosis, and invasive schistosomosis ↵ a Based on data from references 26 and 29.
- TABLE 6.
Case definition for human trichinellosis according to the European Center for Disease Controla
Criterion group Prerequisites and case classificationb Clinical At least three of the following six: fever, muscle soreness and pain, gastrointestinal symptoms, facial edema, eosinophilia, and subconjunctival, subungual, and retinal hemorrhages Laboratory At least one of the following two laboratory tests: demonstration of Trichinella larvae in tissue obtained by muscle biopsy and demonstration of Trichinella-specific antibody response by indirect immunofluorescence, ELISA, or Western blot (i.e., seroconversion) Epidemiological At least one of the following three: consumption of laboratory-confirmed parasitized meat, consumption of potentially parasitized products from a laboratory-confirmed infected animal, epidemiological link to a laboratory-confirmed human case by exposure to the same common source ↵ a Modified from reference 29 with permission of the publisher.
↵ b Case classification is as follows: possible case, not applicable; probable case, any person meeting the clinical criteria and with an epidemiological link; confirmed case, any person meeting the laboratory criteria and with clinical criteria within the past 2 months (to be reported to the European Union level).
- TABLE 7.
Algorithm for diagnosing acute trichinellosis in humansa
Group Symptom A Fever, eyelid and/or facial edema, myalgia B Diarrhea, neurological signs, cardiological signs, conjunctivitis, subungual hemorrhages, cutaneous rash C Eosinophilia (>1,000 eosinophils/ml) and/or increased total IgE levels, increased levels of muscular enzymes D Positive serology (with a highly specific test), seroconversion, positive muscular biopsy ↵ a Modified from reference 29 with permission of the publisher. The diagnosis is very unlikely with one symptom from group A or one from group B or C, suspected with one symptom from group A or two from group B and one from group C, probable with three symptoms from group A and one from group C, highly probable with three symptoms from group A and two from group C, and confirmed with three symptoms from group A, two from group C, and one from group D or any of group A or B, one from group C, and one from group D.
- TABLE 8.
Practical recommendations to handle clinical trichinellosis casesa
Severity code Recommendation for treatment Severe and moderately severe diseases Hospitalization is compulsory for severe forms and debatable for moderately severe forms Administration of anthelmintics (albendazole or mebendazole) Monitoring of the pharmacokinetics of anthelmintics (if possible) Administration of glucocorticosteroids (e.g., prednisolone), always with anthelmintics Compensation of fluid and electrolyte deficits Administration of pain killers Benign, abortive, and asymptomatic diseases Administration of anthelmintics (albendazole or mebendazole) Administration of nonsteroidal anti-inflammatory drugs if necessary ↵ a Modified from reference 29 with permission of the publisher.
