''Schistosoma malayensis'' is a schistosome

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

. It was first described in 1988 in Peninsular Malaysia and appears to be a zooenotic infection. The species is named after the country of

Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...

. The natural vertebrate host is van Müller's rat (''

Rattus muelleri ''Rattus'' is a genus of muroid rodents, all typically called rats. However, the term rat can also be applied to rodent species outside of this genus. Species and description The best-known ''Rattus'' species are the black rat (''R. rattus'' ...

''). The intermediate hosts are aquatic snails, ''Robertsiella kaporenisis''. Among ''Robertsiella kaporenisis'' are two other ''Roberstiella'' species. Among humans exposed to this parasite the lifetime incidence appears to be 5–10%.Sagin D.D., Ismail G., Fui J.N., Jok J.J. (2001) ''Schistosomiasis malayensis''-like infection among the Penan and other interior tribes (Orang Ulu) in upper Rejang River Basin Sarawak Malaysia. Southeast Asian J. Trop. Med. Public Health 32(1):27–32 The symptoms are unclear, because the symptoms have never been reported. The disease has been little studied and it is currently considered to be a relatively minor public health problem.

Taxonomy

''Schistosoma malayensis'' is a member of the ''japonicum''

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

along with ''Schistosoma japonicum'' and ''Schistosoma mekongi''. While the three species are grouped together because of their similarity, ''Schistosoma malayensis'' is more closely related to ''Schistosoma mekongi''.

Morphology

Size is the only morphological difference compared to its natural host possibly due to host-induced variation. The adult ''S. malayensis'' is typically smaller than ''S. mekongi'' and ''S. japonicum''. ''S. malayensis'' eggs have been found in liver granulomas, embedded within dense, fibrous tissue. The eggs of ''S. malayensis'' have a thin-walled, yellowish shell. The eggs contain

miracidia Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secr ...

and are approximately 50 μm long × 28 μm wide. The ova is not operculated and has no bipolar plugs and the thin covering was not striated.

Epidemiology

Serologic surveys for schistosomiasis due to ''S. malayensis'' indicate of 3.9% prevalence in rural populations. It was unsuccessful at adapting to human host. Infected rodents are often found near snail habitats. Infections in humans are unlikely and are considered rare. Humans are most likely to become infected while fishing or canoeing on small streams.

Intermediate host

Freshwater snails (''

Robertsiella ''Robertsiella'' is a genus of freshwater snails which have a gill and an operculum, gastropod mollusks or micromollusks in the family Pomatiopsidae. Distribution The distribution of ''Robertsiella'' includes Malaysia. Species Species wit ...

'' sp.) act as an intermediate host for ''S. malayensis'', that can infect humans and other mammals when cercaria are released from the snail and eventually get in contact with the definitive host. ''Robertsiella'' species are

Caenogastropoda Caenogastropoda is a taxonomic clade, a large diverse group which are mostly sea snails and other marine gastropod mollusks, but also includes some freshwater snails and some land snails. The clade is the most diverse and ecologically successfu ...

snails of the family

Pomatiopsidae Pomatiopsidae is a family of small, mainly freshwater snails, (some also occur in other habitats) that have gills and an operculum, aquatic gastropod mollusks in the superfamily Truncatelloidea (according to the taxonomy of the Gastropoda b ...

. This species is known to be located in limestone areas in the foothills of the mountain chains of Kedah and Perak States in West Malaysia.

Definitive host

The final or definitive mammalian hosts include ''Rattus muelleri'' and ''R. tiomanicus''. ''R. muelleri'' has been found in lowland secondary, and disturbed primary forests in wet conditions in Western Malaysia. ''R. muelleri'' is often found near river banks due to the species prioritization of crustaceans and mollusks over other food sources, such as insects. The predation of mollusks by ''R. muelleri'' allows ''S. malayensis'' a route into its definitive host. It is possible infected rodents defecate in bodies of water they hunt for prey in, maintaining a constant contamination with ''S. malayensis'' eggs and continuing the life cycle.

References

{{Taxonbar, from=Q7431530 Diplostomida Parasites of rodents Animals described in 1988