The geographical distributions of the Trichinella species/genotypes have recently been described by Pozio (2000). All species/genotypes seem to have individual ecological niches for which they are adapted (Kapel, 2000). Thus, T. spiralis is found primarily in the domestic habitat in which environmental stress is limited and the high reproductive capacity has a selective advantage. For the sylvatic species/genotypes, tolerance to high and low temperatures and decomposition of host tissue might be more important than the reproductive capacity (Kapel, 2000).
Trichinella spiralis: Temperate regions in Europe, Asia, New Zealand, North and South America.
Trichinella nativa: Arctic and subarctic areas of the Holarctic region. The isotherm –5°C in January appears to be the southern limit of its geographical distribution (see Pozio et al., 1996, 1998).
Trichinella britovi: Temperate areas of the Palearctic region (Europe, Asia). The January isotherm –6°C appears to be the northern limit of its distribution (see Pozio et al., 1996, 1998).
Trichinella nelsoni: Africa south of Sahara.
Trichinella murrelli: Temperate areas of North America.
Trichinella pseudospiralis: This species has been sporadically detected in Europe, Asia, North America, and in the Australian region, however, due to the lack of muscle capsules, the larvae are very difficult to detect by trichinoscopy and this may, in part, explain the low numbers of records.
Trichinella papuae: This species has been recovered very recently in Papua New Guinea and the geographical distribution has yet to be determined.
Trichinella T6: Temperate regions of North America, but too little data are available for defining the exact distribution.
Trichinella T8: T8 has only been detected in South Africa and Namibia, and the geographical distribution has yet to be determined.
Trichinella T9: T9 has only been detected in Japan, and the geographical distribution has yet to be determined.
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
The various species/genotypes of Trichinella are morphologically very similar. This is the main reason why the 10 species/genotypes have been recognized only very recently (see Murrell, 2000).
The males are 1-2 mm and the females 1-4 mm. The body is slender and the oesophageal region is not very much longer than the posterior part of the worm. The male has no spicules but a pair of lateral flaps. The muscle larvae measure 0.6-1.4 mm. See table in Murrell et al. (2000).
Trichinella rarely cause clinical infections in pigs or other domestic animals, however, due to the zoonotic behaviour and the serious or even fatal course of Trichinella infections in man, the most important economical losses are caused by the intensive Trichinella preventive programmes and routine meat inspections (see Pozio, 2000).
The detection of Trichinella infections in food animals has recently been reviewed by Nöckler et al. (2000). They also discussed important issues like sample size and sample location. The most simple method is trichinoscopy, which is direct microscopy of small muscle samples pressed between two glass plates (see Roepstorff and Nansen, 1998). This method is rather insensitive, has difficulties in recovering larvae of non-encapsulated species, and is time-consuming. Digestion with pepsin-HCl (see Roepstorff and Nansen, 1998; Nöckler et al., 2000) of pooled samples, is better but still rather time-consuming. Serodiagnostic methods (such as ELISA) have been developed, and are discussed by Nöckler et al. (2000).
Infection of domestic pigs with Trichinella spp. may be due to ingestion of raw or inadequately cooked flesh (culinary waste) containing infective trichinae or accidental ingestion of infected rodents, such as rats (see Gajadhar and Gamble, 2000). Control of trichinellosis by inspection and farm management, the use of computerized databases in Trichinella control and international recommendations on control have been reviewed by Knapen (2000), Polley et al. (2000), and Gamble et al. (2000), respectively.
Gajadhar AA; Gamble HR, 2000. Historical perspectives and current global challenges of Trichinella and trichinellosis. Veterinary Parasitology, 93:183-189.
Gamble HR et al., 2000. International Commission on Trichinellosis: recommendations on methods for the control of Trichinella in domestic and wild animals intended for human consumption. Veterinary Parasitology, 93:393-408.
Kapel CMO, 2000. Host diversity and biological characteristics of the Trichinella genotypes and their effect on transmission. Veterinary Parasitology, 93:263-278.
Pozio E; La Rosa G; Amati M, 1994. Factors influencing the resistance of Trichinella muscle larvae to freezing. In: Campbell WC, Pozio E, Bruschi F, eds. Trichinellosis. Rome, Italy: Instituto Superiore di Sanita Press, 173-178.
Pozio E; La Rosa G; Yamaguchi T; Saito S, 1996. Trichinella britovi from Japan. Journal of Parasitology, 82:847-849.