Trichinella spiralis

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Trichinella spiralis (Owen, 1835) Railliet, 1896

(Figures 4-64 through 4-66)


ETYMOLOGY:Trichinella = hair like and spiralis for the spiral nature of the larval stage

SYNONYMS:Trichinaspiralis Owen, 1835

HISTORY: The worm was first recovered at necropsy from the tissues of an Italian male patient in England. In 1845, Herbst found larvae in the muscles of a cat. Leuckart, 1845 showed that when larvae were fed to cats, they developed to adults within the intestinal mucosa.

GEOGRAPHIC LOCATION: There are currently 5 recognized species of Trichinella (Pozio et al., 1992). Trichinellaspiralis is considered the domiesticated species that is found throughout the world in pigs and associated wildlife. Trichinellabritovi Pozio, La Rosa, Murrell, and Lichtenfels, 1992 is found in the Palearctic where it infects various mammalian hosts. Trichinellanativa Britov and Boev, 1972 is found in the Holarctic where it infects sylvatic mammals. Trichinellapseudospiralis Garkavi, 1972 is found throughout the world and used both avian and mammalian host; this species differs from the tohers in that the larvae do not develop surrounding nurse cells within muscle tissue. The fifth species, Trichinellanelsoni Britov and Boev, 1972 is restricted to equatorial Africa. All these species are capable of infecting cats, and in the wild cats can probably fall prey to any of these species when they capture and eat infected animals. Due to the fact that Trichinellapseudospiralis will infect either avian or mammalian hosts, it would seem that cats are liable to rather commonly become infected with this species when it is present in their environment.

Holzworth and Georgi (1974) give an excellent and complete summary of the reported cases of trichinosis in cats. More recently, infections have been reported from Chile (Bonilla-Zepeda, 1980; Alcaino et al, 1981), Egypt (Morsy et al., 1981), Finland (Hirvela Koski, 1985), Italy (Pozio et al, 1987), and China (He et al., 1995; Liu et al, 1997; Zhu et al., 1998).

LOCATION IN HOST: The larval stages are within muscle fibers where they tend to form cyst like sages called nurse cells. The adults occur within the small intestine of the host.

PARASITE IDENTIFICATION: The larvae in muscles when they have finished development to the infective stage are about 0.8 mm to 1 mm in length. The adults that are present in the intestine have lengths of 1.2 and 2.2. mm, respectively, for the males and females. All stages of these worms like those of Trichuris, the capillarids, and Anatrichosoma have a stichosome esophagus that is composed of a linear arrangement of cells with large nuclei. The male of Trichinella species do not have a spicule and the tale terminates with two lateral lobes that give it a characteristic appearance. The mature patent female of Trichinella can be recognized by the prelarvae that she contains. Each prelarva is about 100 µm long.

LIFE CYCLE: The life cycle is basically the same for all species of Trichinella. The host becomes infected when it eats meat containing infective muscle-stage larvae. The larvae are digested out of the muscle and development takes place within the mucosa of the small intestine (Fig. 4-64). The larvae rapidly undergo 4 molts to form adults which are present a little over one day after infection. The adults then mate, and beginning about six days after the infected meat was ingested, the females begin to deposit small larvae into the mucosa (Figs. 4-65 & 4-66). The females can produce larvae for anywhere from 4 to 16 weeks. Larvae enter the bloodstream and make their way to the muscles, and here, the larvae penetrate individual striated muscle fibers. In all cases but Trichinella pseudospiralis, the larvae become encapsulated in the muscle cell in a structure called a nurse cell (Figs. 4-75 and 4-68). Typically, the larvae have completed their development before the completion of nurse cell formation, which can take place anywhere from 16 to 60 days after initiation of infection depending on the species involved. Larvae within th etissues can remain viable for years, although calcification often begins after 6 to 9 months of infection. Cats serve as rather good hosts for Trichinellaspiralis, and can support relatively large numbers of muscle larvae per gram of muscle (C; Holzworth and Georgi, 1974).

CLINICAL PRESENTATION AND PATHOGENESIS: After experimental infections, cats show signs referable to muscle damage including lethargy, weakness, weight loss, and hypersalivation. Other signs may include diarrhea that may or may not include bloody feces. In other cases, cats have shown very little in the way of signs of infection, even though they have ultimately supported rather high loads of muscle larvae (about 300 larvae per gram of muscle). Akhmurtova (1987) experimentally infected cats with Trichinellaspiralis, Tichinellanativa, and Trichinellanelsoni, and found that Trichinellanativa caused the most serious inflammation of the muscle tissue, and that Trichinellanelsoni was the least pathogenic for cats.

Experimentally infected cats with Trichinellaspiralis do not develop significantly increased numbers of circulating eosinophils as have been reported in human cases (Fourestié et al., 1988). However, in a naturally-infected cat, the highest eosinophil count reported during a 5 month period the cat was followed was 22% of the total white cell count (Holzworth and Georgi, 1974).

In the one naturally acquired infection in a cat that was carefully followed (Holzworth and Georgi, 1974), the initial presentation was puddles of fresh gelatinous, bloody feces in the litter box. The bloody feaces was produced for about 6 days, and was found to contain large numbers of adult Trichinella. In this case, although a larva was recovered from the blood of the cat, there were no signs of myocardial involvement as observed by electrocardiac examination two weeks after the appearance of the first bloody stool. The cat developed a moderate eosinophilia. About 3 weeks after the initial bloody stool, the cat did appear to undergo an episode of disorientation based on unusual behavior, but the relationship of this sign to the underling trichinosis can only be conjectured.

TREATMENT: Cats treated with albendazole (50 mg/kg twice daily for 7 days) had reduced numbers of larvae in their muscles about one week after the administration of the last treatment. However, the number of larvae in the muscles was reduced to 0 in only one of 4 treated cats, and this number was based only on a single small biopsy specimen from each animal.

EPIZOOTIOLOGY: There is a great deal to be learned about the epizootiology of trichinosis in cats, expecially in light of the fact that several species are involved. There have been no serious surveys performed amongst urban or suburban cats in most developed nations in recent years, and their has been little done to identify the serological status of cats around the world.

HAZARDS TO OTHER ANIMALS: Cats probably pose no serious threat to other animals due to their probably seldom being eaten.

HAZARD TO HUMANS: Cats pose no threat to humans.

CONTROL/PREVENTION: Cats can be prevented from becoming infected only by keeping them from eating captured prey. In a case from the Altai region of Siberia, a man became ill after having eaten raw badger meat. The family cat that had been fed on left-overs and offal also became infected (Krainyaya et al., 1979).


Akhmurtova, T.L. 1987. Infective porcess in domestic cats infected with different specis of Trichinella. Izvest Akad Nauk Kazak SSR, Biol 2:41-45 [Russian]

Alcaino H.A., Gorman T.R., Santibanez M., Vilches G. 1981. Trichinellosis en gatos y perros del area metropolitana de Chile. Rev Iberica Parasitol 41:461-462.

Bonilla Zepeda C., 1980. Estudio de la fauna helmintologica del gato en la ciudad de Valdivia, Chile. Arch Med Vet 12:277.

Bowmn D.D., Darrigrand R.A., Frongillo M.K., Barr S.C., Flanders J.A., Carbone L.G. 1993. Treaatment of experimentally induced trichinosis in dogs and cats. AJVR 54:1303-1305.

Fourestié V, Bougnoux ME, Ancelle T. LianceM. Roudot Thoraval F., Naga H., Pairon Pennachioni M., Rauss A., Lejonc J.L. 1988. Randomized trial of albendazole versus tiabendazole plus flubendazole during an outbreak of human trichinellosis. P{Arasitol Res 75:36-41.

He ZP, chen PH, Xie Y, Lu SQ, Wang FY. 1995. Study on the genomic DNA of 7 isolaes of Trichinellaspiralis in China. Acta Parastiol Med Ent Sinica 2:218-222 [Chinese].

Hirvela Koski V., Aho M., Asplund K., Hatakka M., Hirn J. 1985. Trichinellaspiralis in wild animals, cats, mice, rats and farmed fur animals in Finland. Nord Vet 37:234-247.

Holzworth J., Georgi J.R. 1974. Trichinosis in a cat. JAVMA 165:186-191.

Krainyaya V.S., Gorbunov N.S., Ivanov A.S. 1979. A case of group human infection with a natural strain of Trichinella in the Altai. Med Parazit Parazit Bol 48: 87-88. [Russian].

Liu MY., Song MX., Yang RF., Chen PH., An CL., Liu ZS., Guo ZB,. Hou SL.,. Lu YX., Zhu XP. 1997. Identification of some Chinese isolates of Trichinella spiralis by RAPD. Chin J Vet Sci Technol 27: 18 20. [Chinese]

Morsy T.A., Sadek M.S.M., Abdel Hamid M.Y. 1981. Intestinal parasties of stray cats in Cairo, Egypt. J Egypt Soc Parasitol 11:331-345.

Pozio E., Rossi P., Amati M. 1987 Epidemiologie de la trichinellose en Italie: correlation entre le cycle sauvage et l'homme. Annal Parasitol Hum Comp 62: 456 461.

Pozio E, LA Rosa G., Murrell K.D., Lichtenfels J.R. 1992. Taxonomic revision of the genus Trichinella. J Parastiol 78:654-659.

Zhu XP., . Liu MY., Wang FY, Zhou L., Song MX. 1998. Identification of three isolates of Trichinella in China on the basis of restriction fragment length polymorphisms (RFLP) analysis. Acta Parasitol Med Ent Sinica. 5: 101 105. [Chinese]


Figure 4-64. Trichinellaspiralis. Free infective first-stage larva experimentally digested out of rat muscle by the use of artificial digestion fluid (infected muscle supplied by Dr. Judith Appleton).

Figure 4-65.Trichinellaspiralis. Histological section with adult worms in the intestinal mucosa of an experimentally infected rat seven days after infection (Tissue supplied by Dr. Judith Appleton). Note the section through a female filled with prelarvae.

Figure 4-66.Trichinellaspiralis. Histological section through the intestinal mucosa of an experimentally infected rat showing two transverse sections through an adult female (Tissue supplied by Dr. Judith Appleton).

Figure 4-67.Trichinellaspiralis. Histological section of a muscle biopsy from an experimentally infected cat.

Figure 4-68.Trichinellaspiralis. Histological section of a muscle biopsy from an experimentally infected cat. Note the thick nature of the enclosing capsule.

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