Cryptosporidium felis Iseki, 1979
ETYMOLOGY:Crypto (hidden) + sporidium (related to the spore-like oocyst stage) and felis for cat.
HISTORY: This species was described by Iseki in 1979, but it has taken some time for the separate disignation of the species in the cat to be generally accepted. At this time, it is considered by many that this is a valid species of Cryptosporidium.
GEOGRAPHIC DISTRIBUTION: It is believed that this species is worldwide in distribution. Thre have been reports specifically identifying this species from cats in Japan (Iseki, 1979) and Australia (Morgan et al., 1998; Sargent et al., 1998); . It has also been found in a calf in Poland (Bornay-Llinares et al., 1999).
LOCATION IN HOST: Mucosal cells of the small intestine. The stages are found throughout the small intestine, but the schizont and oocysts are more common in the posterior third of the intestine. The parasites tend to be found mainly at the tips of the intestinal villi and are never found in the crypts.
PARASITE IDENTIFICATION: The oocysts of Cryptosporidiumfelis differ from those of Cryptosporidiumparvum in that they are smaller. The oocysts of Cryptosporidiumfelis measure 4.3 μm in diameter (3.5 to 5.0 μm). Those of Cryptosporidiumparvum tend to have a mean diameter of 5.0 μm.
LIFE CYCLE: Cats are infected by the ingestion of an oocyst. Each oocyst contains four sporozoites. Upon stimulation of various aspects of the new host, the sporozoites excyst from the oocyst and penetrate cells of the mucosa. The sporozoites, like other coccidians, induce phagocytosis; however,, unlike with other coccidians, the small sporozoites appears to remain on the surface of the cell, that is, the cell membrane bulges out around the small parasite. Between the host cell and the vacuole containing the parasite developes a highly convoluted membrane like structure that is called the “feeding organelle” or “apical organelle.” Within the vacuole, the parasite undergoes schizogony to produce eight daughter merozoites. These then go onto infect other cells. The next phase of the infection is the development of sexual stages, macrogametocytes and microgametocytes. The microgametes are aflagellar, but are capable of movement and they will fuse with a macrogamete. After fusion, the macrogamete deposits an oocyst wall to become an oocyst. While still within the host, the oocyts undergoes a process of sporulation to produce oocysts that contain four infective sporozoites. Iseki (1979) described that these sporozoites were sometimes seen to be undergoing spontaneous excystation within the intestinal material he examined, and he felt that atuoinfection was a distinct possibility. In experimentally infected cats, the pretatent period was 5 to 6 days, and the patent period was 7 to 10 days.
CLINICAL PRESENTATION AND PATHOGENESIS:Cryptosporidiumfelis has not been reported to cause disease in cats, but it is very unclear as to whether cats are routinely infected with this species or with isolates of Cryptosporidiumparvum (See the next section on Cryptosporidiosis in cats).
Asahi et al. (1991) showed that experimentally infected cats shed oocysts for an extended period, up to three to five months. They held three of these cats for a year, and then initiated prednisolone inoculations. After about a week of prednisolone treatment, these cats again shed large numbers of oocyts in their feces. None of the cats developed significant diarrhea or weight loss during the infections even though they shed large numbers of oocyts.
TREATMENT: Cases known to be caused by Cryptosporidiumfelis have not been treated, and there have been no attempts to treat cats experimentally infected with this species.
EPIZOOTIOLOGY: The stage shed in the feces of cats is infective when passed in the feces. Thus, cats that are infected put other animals and their handlers at risk of infection. The fact that there have been numerous cases of zoonotic infections of Cryptosporidiumparvum amongst veterinary students who are working with neonatal calves or foals would indicate that it is highly likely that the oocysts can be spread to people who believe they are taking proper precautions.
HAZARD TO OTHER ANIMALS: Initially, it was felt that Cryptosporidiumfelis was fairly well restricted to the cat. Iseki (1979) tried to infect mice (3) and guinea pigs (3) with this parasite and was unsuccessful. Asahi et al. (1991) gave oocysts recovered from cats to mice, hydrocortisone treated mice, suckling mice, guinea pigs, and dogs; none of these animals developed infection. Similarly, Mtambo et al. (1996) were unable to infect suckling mice with oocysts isolated from a cat in Scotland. Recently, however, a calf in Poland was identified that had small oocysts in its feces that were identified via molecular typing to be Cryptosporidiumfelis (Bornay-Llinares et al., 1999)
HAZARD TO HUMANS: It is unclear what the role is between Cryptosporidiumfelis and human infections. There is a report that molecular sequencing identified oocysts with the Cryptosporidiumfelis genotype in the feces of HIV-infected patients (Pieniazek et al., 1999). This would indicate that cats infected with Cryptosporidiumfelis might pose a threat to humans, perhaps only immunocompromised humans.
CONTROL/PREVENTION: The oocyst is infective when passed, but it is killed by heating to over 60ºC. Thus, good hygiene, the routine washing of cages, and the washing of bedding in a regular washer and drier (or drying on a line on a good sunny day) will probably destroy oocysts.
Asahi H, Koyama T, Arai H, Funakoshi Y, Yamaura H, Shirasaka R, Okutomi K. 1991. Biological nature of Cryptosporidium sp. isolated from a cat. Parasitol Res 77:237-240.
Bornay-Llinares FJ, da Silva AJ, Moura IN, Myjak P, Pietkiewicz H, Kruminis-Lozowska W, Graczyk TK, Pieniazek NJ. Identification of Cryptosporidiumfelis in a cow by morphologic and molecular methods. Appl Environ Microbiol 65:1455-1458.
Iseki M. 1979. Cryptosporidiumfelis sp. n. (Protozoa: Eimeriorina) from the domestic cat. Jap J Parastiol 28:285-307.
Morgan UM, Sargent KD, Elliot A, Thompson RCA. 1998. Cryptosporidium in cats – additional evidence for C. felis. Vet J 156:159-161.
Mtambo MMA, Wright SE, Nash AS, Blewett DA. 1996. Infectivity of a Cryptosporidium species isolated from a domestic cat (Felisdomestica) in lambs and mice. Res Vet Sci 60:61-63.
Pienazek NJ, Bornay-Llinares FJ, Slemenda SB, da Silva AJ, Moura IN, Arrowood MJ, Ditrich O, Addiss DG. 1999. New Cryptosporidium genotypes in HIV-infected persons. Emerg Infect Dis 5:444-449.
Sargent KD, Morgan UM, Elliot A, Thompson RCA. 1998. Morphological and genetic characterization of Cryptosporidium oocysts from domestic cats. Vet Parasitol 77:221-227.