Protozoan Pathogens of Domestic and Companion Animals

Abstract

Protozoa parasitize every species of animal that has been examined for them. Many are of economic importance in domestic animals and many species of wildlife have protozoan parasites that affect their health and serve to modulate populations. Companion animals such as dogs and cats also have parasitic protozoa that have detrimental effects on their health.

Keywords: protozoa; protist; parasite; amoeba; flagellate; apicomplexan; ciliate; trichomonad; coccidium

Figure 1.

Three Giardia types. (a) G. agilis from amphibia. (b) G. muris of rodents. (c, d and e) G. duodenalis: (c) ventral view of the trophozoite; (d) lateral view of the trophozoite; (e) cyst. AD, adhesive disk; AF, anterior flagellum; AXN, axoneme; CW, cyst wall; K, kinetosome; MB, median body, N, nucleus; PF, posterior flagellum; VF, ventral flagellum. Bar, 10 μm. Redrawn from Kulda and Nohynkova (1978) In: Meyer EA (ed.) Giardiasis. San Diego, CA: Academic Press.

Figure 2.

Trophozoite of Hexamita sp. Hexamita is bilaterally symmetrical, has eight flagella and two nuclei. The organisms are quite small, measuring 9 × 3 μm. They are transmitted from one host to the next in cyst form. AF, anterior flagella; N, nucleus; PF, posterior flagella. Bar, 10 μm. From Marquardt et al. (1999).

Figure 3.

Trichomonas gallinae, the cause of avian trichomonosis. Members of the genus Trichomonas have four anterior flagella and one flagellum that is attached to the body by an undulating membrane. There is a central stiffening rod, the axostyle, which extends beyond the posterior end of the body. A parabasal body arises near the basal bodies of the flagella; the parabasal body is the Golgi of other protozoa and metazoa. Trichomonads have a single nucleus and do not form cysts. AF, anterior flagella; AX, axostyle; N, nucleus; PB, parabasal body; UNM, undulating membrane and flagellum. Bar, 10 μm. From Stabler RM (1947) Journal of Parasitology33: 207–213.

Figure 4.

Histomonas meleagridis, the cause of blackhead in turkeys, as seen by light microscopy. H.meleagridis is a member of the order Trichomonadida, but has only remnants of the structures seen in others of the same order, such as Trichomonas gallinae (Figure ) or Tritrichomonas foetus (Figure ). In these organisms, the only identifying structures that can be seen are the flagella extending from the anterior ends of the organisms and the nuclei. There is wide variation in the size of individuals of H. meleagridis, ranging from 8 to 21 μm. AF, anterior flagella; N, nucleus. Bar, 10 μm. From Wenrich DH (1943) Journal of Morphology72: 279–303.

Figure 5.

Entamoeba invadens: (a) trophozoite and (b) cyst. The trophozoites of E. invadens average 16 μm and range from 9 to 38 μm. There is a single nucleus that is discoid, has small clumps of chromatin at its margin and a small central nucleolus. The amoebas move by forming pseudopodia, which are clear, broad extensions of the cytoplasm. CB, chromatid body; N, nucleus; NC, nucleolus; PS, pseudopod. Bar, 10 μm. Courtesy of W. C. Marquardt.

Figure 6.

Oocyst of Eimeria bovis of cattle. The oocyst has a double‐layered outer wall and four sporocysts, each of which contains two sporozoites, the infective stage. E. bovis oocysts average 20 × 28 μm and taper toward the micropylar end. IW, inner wall; MP, micropyle; PG, polar granules, OW, outer wall; RB, refractile body; SB, Steida body; SC, sporocyst; SR, sporocyst residuum. Bar, 10 μm. From Nyberg P and Hammond DM Journal of Parasitology51: 669–673.

Figure 7.

Balantidium coli: (a) trophozoite and (b) cyst. The trophozoites of B. coli average 45 × 60 μm and have an ovoid shape. They are uniformly ciliated and have a large macronucleus with a micronucleus located on its concave side. There is a cytostome (mouth) at the anterior end. Transmission from one host to the next is by the spherical cysts, which average 50 μm in diameter. C, cilia; CP, cytopyge or cell anus; CW, cyst wall; CY, cytostome or mouth; MA, macronucleus. MI, micronucleus. From Marquardt et al. (1999).

Figure 8.

Trophont of Ichthyophthirius multifiliis. This stage of the life cycle of I. multifiliis can reach a size of 1 mm. It has a single macronucleus and a micronucleus located on its concave side. The trophonts are uniformly ciliated and have a cytostome (mouth) at the anterior end. C, cilia; CY, cytostome or mouth; MA, macronucleus; MI, micronucleus. From Marquardt et al. (1999).

Figure 9.

Tritrichomonas foetus as seen by scanning electron microscopy (SEM). T. foetus averages 18 × 9 μm and has three flagella that extend from the anterior end and a flagellum that is attached to the body by an undulating membrane. A central stiffening rod (Figure ), the axostyle, extends beyond the posterior end of the body. Internal structures do not show in SEM. AF, anterior flagella; AX, axostyle; PF, posterior flagellum; UNM, undulating membrane. Original magnification × 1000. From Speer CA and White MW (1992) Large Animal Veterinarian46: 18–30.

Figure 10.

Sarcocystis hemionilatrantis from the mule deer, as seen in low power transmission electron microscopy. A sarcocyst lies within a muscle cell and has a wall formed by the muscle cell as well as one formed by the parasite itself. Sarcocysts range in size from perhaps 20 μm to 1 mm or longer. In this organism, there are partitions, or septa, that enclose tens to a hundred or more zoites. The zoites are elongate, indistinctly shown organisms that have a single nucleus. OW, outer wall; S, septa; Z, zoites. Original magnification × 5000. Courtesy of C. A. Speer.

Figure 11.

Babesiabigemina as seen by light microscopy in a red blood cell of an ox. The red blood cells of an ox vary in size, with the one shown being about 7 μm; the parasites are about 3 μm long. B. bigemina is usually seen in red blood cells as a pair of pear‐shaped organisms, each of which has a single nucleus. A single organism enters the cell, divides once and then the cell breaks down, releasing the organisms, which in turn invade other red blood cells. B, babesia; N, nucleus; RBC, red blood cell. Bar, 10 μm. Courtesy of W. C. Marquardt.

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Further Reading

Atkinson CT (1991) Vectors, epizootology, and pathogenicity of avian species of Haemoproteus (Haemosporina: Haemoproteidae). Bulletin of the Society of Vector Ecology 16: 109–126.

Corliss JO (1994) An interim utilitarian (‘user‐friendly’) hierarchical classification and characterization of the protists. Acta Protozoologica 33: 1–51.

Dubey JP, Speer CA and Fayer R (1989) Sarcocystosis of Animals and Man. Boca Raton, FL: CRC Press.

Dubey JP, Speer CA, and Fayer R (1990) Cryptosporidiosis of man and animals. Boca Raton, FL: CRC Press.

Garnham PCC (1966) Malarial Parasites and other Haemosporidia. Oxford: Blackwell.

Lee JJ, Hutner SH and Bovee EC (eds) (1985) An Illustrated Guide to the Protozoa. Lawrence, KS: Society of Protozoologists.

Levine ND (1988) The Protozoan Phylum Apicomplexa, 2 vols. Boca Raton, FL: CRC Press.

Long PL (ed.) (1990) Coccidiosis of Man and Domestic Animals. Boca Raton, FL: CRC Press.

Margulis L, Corliss JO, Melkonian M and Chapman DJ (1990) Handbook of Protoctista. Boston, MA: Jones and Bartlett.

Marquardt WC, Demaree RS and Grieve RB (1999) Parasitology and Vector Biology, 2nd edn. San Diego, CA: Academic Press.

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How to Cite close
Marquardt, William C, and Speer, CA(Apr 2001) Protozoan Pathogens of Domestic and Companion Animals. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001940]