Parasitic Diseases
Cestodiasis
Goats and sheep serve as intermediate hosts for the canid tapeworm Taenia multiceps. The cysts produced by the intermediate stage of the parasite are usually found in the brains of small ruminants and the resulting disease, coenurosis or gid, is discussed in detail in Chapter 5.
In goats more often than sheep, cysts may develop at sites outside the central nervous system, especially in the intermuscular fascia. Cases of goats affected in this way have been reported from the Sudan and India (Ramadan et al. 1973; Dey et al. 1988). Metacestodes in muscle connective tissue produce visible or palpable swellings in muscle masses, accompanied by discomfort, restricted gait, poor appetite, and general malaise. Cysts may number in the hundreds. They feel firm rather than fluctuant and may exceed 7 cm in diameter. They can be distributed all over the body, including the face, but are most common in the thighs and shoulders. Attempts to manage these cases by surgical removal of multiple cysts have not been particularly successful, but this may be due to the advanced debilitation of affected goats at the time of presentation. There is no other known effective therapy. A case in an 11-month-old goat reported from Iran was notable in that the animal had multiple, pronounced, subcutaneous cysts over the whole body as well as in the fasciae of the skele - tal muscles, in the thoracic cavity, and on the mesentery (Azizi et al. 2019).Muscle cysts may also occur in goats infected with metacestodes of Taenia ovis, though sheep are the principal intermediate host of this canid tapeworm. In the case of T. ovis, muscle is the primary site of metacestode formation, with cysts most commonly found in the heart, diaphragm, and masseter muscles. This canid tapeworm has a cosmopolitan distribution and is responsible for economic wastage through condemnation and trimming of small ruminant carcasses at slaughter.
Besnoitiosis
Caprine besnoitiosis, caused by the cyst-forming protozoal apicomplexan Besnoitia caprae, has been reported only from Kenya, Iran, and Nigeria and is considered endemic in the first two countries. Bovine besnoitiosis is more widespread in Africa, Asia, and southern Europe. Infection with the protozoan parasite Besnoitia in goats is most commonly recognized as a granular conjunctivitis, as discussed in Chapter 6. However, Besnoitia infection can be generalized, producing respiratory disease, orchitis, and dermatitis, as seen in goats in Iran (Bazargani et al. 1987). On postmortem examination, multiple small, white, gritty granules may be present in tissues of the musculoskeletal system, including ligaments, tendons, tendon sheaths, synovial membranes, and muscular connective tissue. These granules represent cysts containing large numbers of bradyzoites of Besnoitia. The subject of caprine besnoitio- sis has been reviewed (Oryan et al. 2014).
Sarcocystosis
Sarcosystosis, also known as sarcosporidiosis, is a protozoal infection. In goats, it is primarily a subclinical infection detected at slaughter, and only rarely has it been reported to cause clinical disease in goats under natural conditions. The life cycle of Sarcocystis spp. involves predatory canids as definitive hosts and various species of livestock as intermediate hosts. The role of the goat as an intermediate host has been described (Collins and Charleston 1979; Collins et al. 1980; Dubey et al. 1984). Sarcocystis spp. affecting goats include Sarcocystis capra- canis, with the dog, coyote, and fox as definitive hosts; Sarcocystis hircicanis, with the dog as definitive host; and Sarcocystis moulei, with the cat as definitive host. Muscle cysts containing host-specific Sarcocystis spp. have long been recognized in carcasses at slaughter plants and have been a cause of condemnation. Beyond that, the condition was thought to be incidental. Sarcocystosis in ruminants has been reviewed (Lindsay and Dubey 2020).
Experimental studies have indicated that Sarcocystis spp. may produce a variety of clinical signs, including anemia, fever, vasculitis, myositis, abortion, chronic wasting, and sudden death in ruminants. The experimental disease in goats, produced by challenge with S. capracanis, has been studied extensively (Collins et al. 1980; Dubey et al. 1981; Dubey 1981; Lopez-Rodriguez et al. 1986). It is hard to describe typical clinical signs in goats because the clinical response is clearly dose dependent, and a wide range of oral challenge doses of sporocysts have been used, from 4 ? 103, which produced no clinical signs (Gomes et al. 1992); to 7 ? 104, which produced anemia, loss of appetite, and fever (Ivanov 1998); to 5 ? 105, causing fever, loss of appetite, muscle tremors, and weakness (Dey et al. 1995). A dose of 1 ? 104 sporocysts produced abortion in pregnant does (Juyal et al. 1989). In general, the most consistent signs of experimental infection are fever, which is often biphasic, anemia, and loss of appetite. At necropsy, streaky hemorrhage of skeletal muscles and petechiation of lymph nodes and serosal surfaces of abdominal viscera are prominent signs. Liver, kidneys, and spleen may also be swollen and friable (Wadajkar et al. 1995).
Despite the evidence for clinical disease in experimental work, cases of naturally occurring clinical caprine sarco- cystosis have not been reported, save for one naturally occurring case of congenital sarcocystosis in a stillborn kid from a Saanen milking herd in Australia experiencing abortions (Mackie and Dubey 1996). Naturally occurring clinical disease has been confirmed in sheep. Sporozoan encephalomyelitis has been reported in the United Kingdom, affecting sheep under 1 year of age. Clinical signs included ataxia, generalized tremors, compulsive nibbling, and hindlimb paresis (Caldow et al. 2000; Sargison et al. 2000). Other manifestations in sheep without neurologic presentation include anemia, retarded growth, and reduced wool production.
There is also a reported case of congestive heart failure and vegetative endocarditis associated with sarcocystosis in a young ram (Scott and Sargison 2001). Anticoccidial drugs such as amprolium and salinomycin may be effective in sarcocystosis.Subclinical caprine infections with characteristic muscle cysts predominantly in esophagus, diaphragm, and heart, as well as other sites, are well documented around the world, usually from slaughterhouse surveys, as reported from Sri Lanka (Seneviratna et al. 1975), India (Chhabra and Mahajan 1978), New Zealand (Collins and Crawford 1978), Spain (Perez Garro et al. 1978), Brazil (Barci et al. 1983), Turkey (Saym and Ozer 1984), the United States (Dubey and Livingston 1986), China (Ming et al. 1996), and Malaysia (Latif et al. 2015). Prevalence of subclinical infections may be greater than some survey reports suggest. For example, a slaughterhouse survey from Iran detected grossly evident sarcocysts in 28 of 169 goats by visual inspection. However, when impression smears of target tissues were examined microscopically, 168/169 had Sarcocystis spp. present and 169/169 were positive when tissues were subjected to pepsin digestion, centrifuged, and examined microscopically (Shekarforoush et al. 2005). Control of sarcocystosis requires separating dogs and goats, restricting access of goat offal to dogs, cooking meat fed to dogs, and burying dead goats.