Estimates of the total number of protozoan species present in the Australian vertebrate fauna range from 1306 to 3194 species (Adlard and O'Donoghue, 1998). So far only
Australian mammal fauna that has been investigated (Adlard and O'Donoghue, 1998). This dearth of information on Australian protozoa is due not only to a lack of investigation, but also to a lack of distinguishing morphological characteristics and the availability of appropriate tools for studying them (Monis, 1999; McManus and Bowles, 1996). As such, surveys of the protozoan parasites of feral cats in Australia are few.
2.4.5.1 Isospora felis and I. rivolta
The coccidian parasites Isospora felis and I. rivolta were the most common protozoan parasites detected in feral cats for this study. At least one of these two parasite species was present in cats from all except two sample regions throughout Western Australia: the Bungle Bungles and the Cocos Islands. Whilst the absence of I. felis and I. rivolta
in cats from the Bungle Bungles may be due to the small sample size (n = 4), the lack of any protozoan parasites from the Cocos Islands cannot be explained. The introduction of cats to this island environment may have resulted in a protozoan-free population, though this is unlikely.
Like most coccidian parasites, the life cycle of I. felis and I. rivolta is typically direct, although rodents have been shown to act as paratenic hosts for both these species (Dubey and Frenkel, 1972b; Frenkel and Dubey, 1972). However, it is unclear whether cats are infected more commonly by oocysts or by the ingestion of paratenic hosts (Bowman et al., 2002). The prevalence of coccidian parasites in cats appears to be at
Collins et al. (1983) found only four of 71 cats examined from Sydney to be infected with enteric protozoa, whist Coman et al. (1981b) detected I. rivolta in 3% and I. felis in 4% of feral cats from Victoria and western New South Wales. Likewise, Gregory and Munday (1976) found I. rivolta in 5.4% and I. felis in 12.7% of feral cats from Tasmania. This is not unusual as I. felis is reported to occur more frequently in cats than I. rivolta (Prescott, 1984), although the overall prevalence of I. rivolta (16.9%) was higher than I. felis (4.5%) in the present study. This difference in prevalence of I. rivolta and I. felis in feral cats from Western Australia may be due to a climatic influence, as I. rivolta was most prevalent in cats collected from drier regions.
2.4.5.2 Sarcocystis
The life cycle of Sarcocystis is indirect and requires two hosts, a herbivorous and/or omnivorous intermediate host and a predatory or scavenging definitive host (Buxton, 1998; Savini et al., 1992a). Sarcocystis causes disease in the intermediate host and appears to have little or no pathogenicity in the definitive host carnivores (Prescott, 1984). Whilst cats are known to harbour two species of Sarcocystis infectious to sheep (Savini et al., 1993), dogs, dingoes and red foxes are more often responsible for the transmission of Sarcocystis to both sheep and cattle (Savini et al., 1993, 1992b).
Studies on Sarcocystis infections in Australia have predominantly been concerned with those species infecting sheep and cattle due to their potential economic impact, however
Sarcocystis spp. have been shown to occur in numerous species of Australian wildlife (Munday and Mason, 1980; Munday et al., 1980; Munday et al., 1979; Munday et al., 1978). Despite these investigations, the cat has only been identified as a definitive host for Sarcocystis in rabbits (Munday et al., 1980).
A survey of protozoan parasites in feral cats from Victoria and western New South Wales failed to detect Sarcocystis in any of the 300 cats examined (Coman et al., 1981b). Additionally, a survey by Gregory and Munday (1976) of feral cats from Tasmania found Sarcocystis in only one of 55 cats examined and tentatively attributed the presence of this infection to the possible scavenging of dead sheep or offal. The occurrence of Sarcocystis in feral cats from Western Australia was similarly uncommon with an overall prevalence of only 2.1%, with a single case of Sarcocystis detected from Shark Bay, the Gibson Desert and Lake Argyle, whilst five cats from Mount Keith were infected.
Savini et al. (1992a) reported a low prevalence (9%) of Sarcocystis infections in cattle from arid regions of Western Australia, and concluded that aridity coupled with low densities of both definitive and intermediate hosts are the factors most likely to limit the prevalence of Sarcocystis in an area. However, the results from the present study seem to show a preference for Sarcocystis infections in cats from dryer areas, which may reflect a seasonal or opportunistic infection source for these areas.
2.4.5.3 Toxoplasma gondii
None of the 379 cats examined in this study were found to be shedding Toxoplasma gondii oocysts in their faeces. Cats collected for this study were predominantly adults
2.4.5.4 Giardia
Species of the flagellated protozoan Giardia inhabit the intestinal tracts of virtually all classes of vertebrates, however G. duodenalis is the only recognised species to occur in most mammals (O'Handley et al., 2000; Thompson et al., 2000b; Thompson et al., 1998; Thompson et al., 1993b). A single Giardia infection was detected in a cat from the Dragon Rocks Nature Reserve. Molecular analysis of the purified oocysts revealed the isolate to be G. duodenalis of the genotype belonging to the zoonotic genetic Assemblage A, which is most commonly found in humans. This finding is further discussed in Chapter 4.
2.4.5.5 Cryptosporidium
Cryptosporidium was found in a total of four cats, however the oocysts were in poor condition and speciation was not possible. Further attempts to purify and characterise the parasite using molecular procedures proved unsuccessful. The poor quality of the oocysts may have been due to the preservative they were stored in or an effect of passing through the feline digestive tract if the oocysts originated from an infection source other than the cat. Given the wide host range and zoonotic potential of this parasite (Nizeyi et al., 1999; Graczyk et al., 1998; Olson et al., 1997b), it is impossible to determine if the Cryptosporidium detected in these cats were due to active infections or passive transfer without applying the proper diagnostic techniques.
2.4.5.6 Eimeria
often at high levels, is considered to originate from ingested prey infected with Eimeria. This is supported by the damaged condition of most Eimeria oocysts detected, which indicated that they were merely being passed through the cat intestine and did not represent an active infection. These artefact infections are believed to be a result of cat depredation of lizards and rodents with prevalence levels generally indicating the importance of these animals in the diet of feral cats.