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Schistosoma hippopotami is a is a species of digenetic trematode, belonging to a group (genus) of blood flukes (Schistosoma). These parasites primarily infect hippopotamuses and have a more limited host range compared to other Schistosoma species. S. hippopotami is found in sub-Saharan Africa, where it primarily infects the blood vessels of hippopotamuses (Thurston, 1961).

Adults are found in the heart, aorta, and multiple veins and arteries of the hippopotamuses (Kruger et al., 1988).

S. hippopotami was found in hippopotamuses in the Queen Elizabeth National Park in Western Uganda along with S. edwardiense. These two species make up the S. hippopotami clade due to how these are the only two Schistosoma species that infect hippopotamuses. The understanding of the existence of this clade brings the thought that this clade could be basal to all African species of Schistosoma, plus several Asian species (Morgan et al, 2003).

Taxonomy
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Belong to the taxonomic group of S. mansoni

Part of the S. hippopotami clade, With S. edwardiense.

"The validity of S. hippopotami as a distinct species was called into question by Pitchford and Visser (1981) who considered it an aberrant form of S. mansoni or S. rodhaini. However, subsequent studies providing data from enzyme electrophoresis (Fripp, 1981), scanning electron microscopy (Kruger et al., 1988) and ITS2 rDNA sequence from a single male worm recovered from a hippo in Kruger National Park (Després et al., 1995) support the status of S. hippopotami as a distinct species." (Stanley et al., 2012)

Morphology and Identification
Unlike other trematodes, schistosomes are dioecious, often with a marked degree of dimorphism between male and female worms (Loker and Brant, 2006). The largest difference is that the males are significantly larger than the females and typically have a ventral groove, the gynaecophoric canal, which holds the longer and thinner female (Rollinson and Southgate, 1987). This process in which the adult male worm holds the adult female is called in copula and is when they are paired (Erasmus, 1987). Adult schistosomes all have a similar structure. They have a basic bilateral symmetry, oral and ventral suckers, a body covering of a syncytial tegument, a blind-ending digestive system consisting of mouth, esophagus and bifurcated caeca; the area between the tegument and alimentary canal filled with a loose network of mesoderm cells, and an excretory or osmoregulatory system based on flame cells. Adult worms tend to use globins from their hosts' hemoglobin for their own circulatory system. '''- WORK ON THIS! (maybe Microscopic Anatomy of Invertebrates)'''

"The normal oviposition sites and the mode of egress of eggs from the body are not known for this species. Although adult morphology might be somewhat plastic in response to different environmental conditions, males of S. hippopotami recovered from major arteries are stout, with extraordinarily large suckers. They have a well-de                                                                                                                                                                                                 veloped gynecophoric canal in which the female is held. Females are unusual for being shorter than the male, again suggesting that the unusual high blood velocity environment of this species has selected for divergent adult morphology. (Loker and Brant, 2006)

"The characters of S. hippopotami which most readily separate it from other species of Schistosoma are the shape of the eggs, the position of the ovary in the anterior third of the body, the oval shape of the ovary, and the paired intestinal caeca of the male, which do not reunite except for very short distances" (Thurston, 1961).

"Female. Shorter than the male. Ovary oval in shape, situated in the anterior third of the body. Egg with subterminal spine. A single egg in the uterus.

Male. Number of testes indistinct; about four. Intestinal caeca do not reunite to form a common caecum but anastomose for very short distances posteriorly." (Thurston, 1961)

Life Cycle
"The schistosome life cycle occurs in 2 hosts: snails and mammals. Either asexual or sexual reproduction occurs, depending on the type of host (Figure 1). Asexual reproduction occurs in freshwater snails. In the snail, this begins with the development of miracidia into a sporocyst. Sporocysts multiply and grow into cercariae. In the mammalian hosts, parasites grow to become mature, mate, and produce eggs.1, 8 Mammalian hosts include humans, mice, and dogs." (Newlan, 2019).

The snail host for S. hippopotami is assumed to be Biomphalaria due to how Biomphara is the snail host for S. edwardiense, the other Schistosoma S. hippopotami clade. However, the snail host for S. hippopotami is in fact unknown (Rollinson and Southgate, 1987).

"This species, together with S. edwardiense, is also unusual in only having been found in a single species of definitive host: the African hippopotamus (Hippopotamus amphibius)." (Stanley et al., 2012)

Geographic Distribution
S. hippopotami have been found in hippopotami in the Queen England National Park in Western Uganda and in hippopotami from the Letaba River in the Kruger National Park in South Africa (Kruger et al., 1988).

Diagnosis
"Adult schistosomes were encountered in the heart (especially in the right heart chambers), aorta, pulmonary arteries and veins, posterior vena cava and a number of veins draining into the posterior vena cava. Because of this unusual distribution of adults and low ovogenesis in females, these authors considered the hippopotamus to be an aberrant host for S. hippopotami. Thurston (1971) examined a further 31 hippopotami from Uganda and agreed that the hippopotamus appears to be an abnormal host." (Kruger et al., 1988)

"S. hippopotami, however, has been found in heart, aorta, pulmonary arteries and veins, posterior vena cava and a number of veins draining into the posterior vena cava (McCully, Van Niekerk & Kruger, 1965). The pathway of eggs to the exterior remains a mystery." (Després et al., 1995)

Unlike other Schistosoma species that infect humans and cause schistosomiasis, S. hippopotami infections in humans are extremely rare. The primary host for this parasite is the hippopotamus.