List of parasites of the marsh rice rat

A variety of parasites have been recorded from the marsh rice rat ("Oryzomys palustris"), a semiaquatic rodent found in the eastern and southern United States, north to New Jersey and Kansas and south to Florida and Texas, and in Tamaulipas, far northeastern Mexico. Some of these parasites are endoparasites, internal parasites, while others are ectoparasites, external parasites.
Parasitologist John Kinsella compared the endoparasites of marsh rice rats in a saltwater marsh at Cedar Key and a freshwater marsh at Paynes Prairie, both in Florida, in a 1988 study. He found a total of 45 species, a number unequaled in rodents. This may be related to the diverse habitats the rice rat uses and to its omnivorous diet; it eats a variety of animals which may serve as intermediate hosts of various parasites. The endoparasites in the saltwater marsh were dominated by trematodes (flukes), and those of the freshwater marsh by nematodes (roundworms). Endoparasites were found in the gastric mucosa (which lines the stomach), the cavity of the stomach, the small intestine, the cecum, the large intestine, the pancreatic duct, the bile ducts, the mucus of the liver, the pulmonary arteries, the abdominal cavity, and the pleural cavity. While the marsh rice rat harbors a number of host-specific species, such as the nematode "Aonchotheca forresteri", other parasite species, such as the lone star tick "(pictured)", are shared with other mammals. Compared to the hispid cotton rat ("Sigmodon hispidus"), Florida marsh rice rats usually harbor fewer individual ectoparasites of each species. "Borrelia", the bacterium that causes Lyme disease, has been identified in some ticks that infect the marsh rice rat and it has been identified as a possible natural reservoir for "Borrelia".
Ectoparasites.
Acari.
The Acari include the mites and ticks. Many are parasites of other animals. One study in South Carolina failed to find ticks on marsh rice rats living in marshes, which are an unsuitable habitat for the parasites.
Anoplura.
Sucking lice (Anoplura) are a diverse group infecting placental mammals. Species found on marsh rice rats include three of the common genus "Hoplopleura" and "Polyplax spinulosa", which more usually infects black and brown rats.
Siphonaptera.
Fleas (Siphonaptera) are common parasites of vertebrates, mainly mammals. Several species of fleas have been found on the marsh rice rat.
Endoparasites.
Unless otherwise specified, all information in this section is from Kinsella (1988, table 1).
Nematoda.
Nematodes are among the largest animal phyla and include at least 12,000 known species that are parasites of vertebrates. In Kinsella's 1988 study in Florida, species diversity was higher in the saltwater marsh (Cedar Key) than the freshwater marsh (Paynes Prairie), but nematodes at Paynes Prairie occurred more commonly and made up the bulk of the parasites found in rice rats there.
Cestoda.
Four tapeworms are known from the marsh rice rat, all in Florida, but three of those are usually found in other species and only rarely in the rice rat.
Digenea.
Flukes (Trematoda) from the subclass Digenea are common parasites of small mammals with complex life cycles. In his 1988 study, Kinsella found an unprecedented 21 species of trematodes in Florida marsh rice rats. The intermediate hosts of these trematodes include a variety of invertebrates, fish, and amphibians, which are eaten by the marsh rice rat. Trematodes were generally more common at the Cedar Key saltwater marsh than at the freshwater marsh in Paynes Prairie.
Pentastomida.
Pentastomida is an enigmatic group of parasites that may be related to maxillopod crustaceans. One species, "Porocephalus crotali", is known from the marsh rice rat. It infects various mammals in the southeastern United States, which serve as intermediate hosts; snakes which eat those mammals are the definitive hosts.
Apicomplexa.
Apicomplexa is a major group of unicellular eukaryotes that encompasses several important parasites, including the malaria parasite "Plasmodium". Three species are known from the marsh rice rat, all of which belong to the Eimerina clade. Two are in the genus "Eimeria", members of which cause the economically significant disease coccidiosis in poultry. The third is a member of "Isospora", which includes species that are pathogenic in humans and pigs.