Sarcocystis spp. of New and Old World Camelids: Ancient Origin, Present Challenges

Abstract

Sarcocystis spp. are coccidian protozoans belonging to the Apicomplexa phylum. As with other members of this phylum, they are obligate intracellular parasites with complex cellular machinery for the invasion of host cells. Sarcocystis spp. display dixenous life cycles, involving a predator and a prey as definitive and intermediate hosts, respectively. Specifically, these parasites develop sarcocysts in the tissues of their intermediate hosts, ranging in size from microscopic to visible to the naked eye, depending on the species. When definitive hosts consume sarcocysts, infective forms are produced in the digestive system and discharged into the environment via feces. Consumption of oocyst-contaminated water and pasture by the intermediate host completes the parasitic cycle. More than 200 Sarcocystis spp. have been described to infect wildlife, domestic animals, and humans, some of which are of economic or public health importance. Interestingly, Old World camelids (dromedary, domestic Bactrian camel, and wild Bactrian camel) and New World or South American camelids (llama, alpaca, guanaco, and vicuña) can each be infected by two different Sarcocystis spp: Old World camelids by S. cameli (producing micro- and macroscopic cysts) and S. ippeni (microscopic cysts); and South American camelids by S. aucheniae (macroscopic cysts) and S. masoni (microscopic cysts). Large numbers of Old and New World camelids are bred for meat production, but the finding of macroscopic sarcocysts in carcasses significantly hampers meat commercialization. This review tries to compile the information that is currently accessible regarding the biology, epidemiology, phylogeny, and diagnosis of Sarcocystis spp. that infect Old and New World camelids. In addition, knowledge gaps will be identified to encourage research that will lead to the control of these parasites.

Keywords: Old World camels; Sarcocystis; South American camelids; sarcocysts.

Figure 3

Phylogenetic tree of Sarcocystis spp. cox-1 sequences. The evolutionary history was inferred by using the maximum likelihood method, applying the Kimura 2-parameter model [89]. The analysis involved 68 nucleotide sequences and comprised a total of 946 positions in the final dataset. Bootstrap values are shown close to the branches. Neospora caninum cox-1 gene sequence was used as the outgroup. The analysis was carried out using MEGA11 [90].

Figure 1

Life cycle of Sarcocystis. A typical life cycle of Sarcocystis species is shown, exemplified with a llama and a dog as intermediate and definitive hosts, respectively.

Figure 2

Morphology of sarcocysts and bradyzoites in S. aucheniae. (a,b) Macroscopic sarcocysts in llama (a) and alpaca (b) skeletal muscle; (c) hematoxylin eosin-dyed cross-section of alpaca skeletal muscle with two macroscopic sarcocysts, in which zoites are located to the periphery and the center is empty (100×); (d,e) details of hematoxylin eosin-dyed section of a macroscopic sarcocyst showing the morphology of the cell wall (d) and compartments with thousands of banana-shaped bradyzoites (e) (400×); (f) bradyzoites observed in a cyst stained with Giemsa (1000×). The photographs were obtained by S.N.W. and L.V.M.O.

Figure 4

Schematic representation of the evolutionary history of camelids and canids. The likely time period when the ancestor of camelid Sarcocystis spp. evolved is shown.