Host Range

The species C. neoformans has been reported in a large variety of birds and mammals, including companion animals (pets) and domestic and free-range animals, worldwide. The species C.

12.6.1 Cryptococcosis in Invertebrates

Several nonmammalian models have been reported to allow the analysis of crypto- coccal pathogenesis through survival and cryptococcal growth assays in inverte­brates (Tenor et al. 2015), including the amoeba Acanthamoeba castellanii (Steenbergen et al. 2001; Malliaris et al. 2004), the nematode Caenorhabditis elegans (Mylonakis et al. 2002), the wax moth Galleria mellonella (Mylonakis et al. 2005), and the fruit fly Drosophila melanogaster (Apidianakis et al. 2004). These invertebrate models allow rapid analysis of cryptococcal virulence determinants and host genetics to various degrees (Desalermos et al. 2015).

12.6.2 Cryptococcosis in Cold-Blooded Vertebrates

12.6.2.1 Fishes

Zebra fish (Danio rerio) has been used as a visually and genetically accessible vertebrate model system to investigate cryptococcal pathogenesis and host-fungus interactions.

12.6.2.2 Amphibians

A case of pulmonary cryptococcosis caused by C. neoformans has been reported from Portugal in a free-living adult female toad (Bufo bufo). The animal was apparently healthy and was killed by a vehicle (Seixas et al. 2008). The causative agent was confirmed by immunohistochemistry, using the monoclonal antibody anti­C. neoformans, and by a PCR-based method using C. neoformans-specific primers.

12.6.2.3 Reptiles

Compared with mammals, cryptococcal infections are rarely seen in reptiles. Crypto­coccosis has been described in few cases of reptiles, including lizards and snakes (Spickler 2013). An eastern water skink (Eulamprus quoyii) was found to be infected with C. neoformans, resulting in a subcutaneous lesion (Hough 1998). Systemic cryptococcosis has also been reported in a common anaconda (Eunectes murinus), with C. neoformans as the etiologic agent (McNamara et al. 1994).

12.6.3 Diseases in Warm-Blooded Vertebrates

12.6.3.1 Birds

Excrement of avian species, especially from Columbiformes birds, provides the required nutrients for Cryptococcus to proliferate (Emmons 1955). The species C. neoformans temporarily colonizes the intestinal tract of some avian species following ingestion and has been detected in the guano or cloacae of swans, raptors, rheas, chickens, and starlings, as well as some Psittaciformes and Passeriformes birds (Sorrell et al. 1996; Cafarchia et al. 2006; Tsiodras et al. 2000). The cloacae of four migratory birds of the species Anas crecca, Anas platyrhynchos, and Fulica atra were also found to be positive for C.

Despite the very high degree of exposure of pigeons to massive quantities of C. neoformans, cryptococcosis seems to be very rare in poultry and pigeons. Cryptococcus species accounted for localized and disseminated infections of the upper respiratory tract of immunocompetent captive parrots of widely differing ages living in Australia, which resulted in signs of mycotic rhinitis or the involvement of structures contiguous with the nasal cavity, such as the beak, sinuses, choana, retrobulbar space, and palate (Malik et al. 2003). Cryptococcal rhinitis caused by C. gattii was also identified in the African grey parrot (Refai et al. 2014). Several cases of cryptococcosis have been reported in captive North Island brown kiwis (Apteryx australis mantelli) in Australia and in New Zealand (Hill et al. 1995; Malik et al. 2003); these birds are unusual in that they have a lower core body temperature than other avian species. Psittacines are occasionally infected by C. neoformans var. grubii or C. gattii (Cafarchia et al. 2006; Refai et al. 2014); e.g., C. gattii infection has been described in the pink-fronted cockatoo (Lester et al. 2004; Spickler 2013).

Clinical and laboratory findings have demonstrated minimally invasive subcuta­neous disease in an Australian racing pigeon caused by C. neoformans var. grubii (Malik et al. 2003). In contrast, pigeons and other birds studied principally in America and Europe display a different pattern of disease, more suggestive of opportunistic infection of immunodeficient hosts.

12.6.3.2 Marsupials

Overall, cryptococcosis is the second most common infectious disease of koalas (Phascolarctos cinereus) after chlamydiosis. However, it appears more frequently than chlamydiosis in captive populations owing to border security and quarantine measures. Cryptococcus spp. can be cultured from the mucosal surface of the nasal cavity or the skin of most healthy koalas, i.e., animals without any evidence of tissue invasion or disease.

12.6.3.3 Dogs

In dogs, cryptococcosis typically begins in the nasal cavity (Fig. 12.2), overtly or covertly, gradually affecting the CNS, ocular structures (especially the retinae and optic nerves), lymph nodes, digestive system, bones, and other organs (Duncan et al. 2006). Dogs may present with signs of disease in the upper and/or lower respiratory tract and with subcutaneous granulomata and lesions reflecting disseminated disease (Fig. 12.3). CNS and ocular involvement is most common, however, and is associated with high mortality rate (Castella et al. 2008; de Abreu et al. 2017).

Cryptococcal infection of the upper respiratory tract was reported in 57 dogs residing in Western Australia (McGill et al. 2009), and the predominant etiological agent was found to be the VGII genotype of C. gattii, whereas molecular genotyping suggested that C. gattii infections in domestic animals on the eastern seaboard of Australia are less common than C. neoformans infections and mainly due to the VGI genotype. Lester et al. (2004) also detected cryptococcosis in 15 dogs from British Columbia, Canada, which were initially from Vancouver Island.

Fig. 12.2 Photograph of a young adult German shepherd dog with localized cryptococcosis of the nasal cavity with involvement of the nasal planum. This case was successfully treated with intralesional amphotericin B and oral fluconazole. Photo courtesy of Steve Metcalfe

Fig. 12.3 Intestinal cryptococcomas (arrow) in a dog from Perth, Western Australia, due to C. gattii VGII infection. An ultrasound image showing the lesion is shown as an insert on the top right of the photograph. Images courtesy of Anna Tebb

cases of cryptococcal rhinitis, meningitis, disseminated cryptococcosis, and the CNS disease have been identified in dogs (Bowles and Fry 2009; Bryan et al. 2011; Trivedi et al. 2011).

Disseminated cryptococcosis is reported to be more common in dogs than in cats (Spickler 2013). However, subclinical infection and asymptomatic colonization of the sinonasal cavity by C. gattii have also been observed in dogs exposed to environments with high loads of C. gattii (Duncan et al. 2005). Dogs do not show any sex-related predisposition for cryptococcosis. American Cocker Spaniels, Labrador Retrievers, Doberman Pinschers, and Great Danes were overrepresented compared with other dog breeds, perhaps for genetic reasons or because of their tendency to be exposed to the great outdoors.

12.6.3.4 Cats

Feline cryptococcosis can be either focal or disseminated, and it mostly begins as mycotic rhinitis following asymptomatic colonization of the nasal cavity (Malik et al. 2003). Cryptococcosis represents the most common systemic mycosis of cats (Sorrell 2001; Duncan et al. 2006; McGill et al. 2009). Cats with cryptococcosis are most often brought to a veterinarian because of single or multiple, slowly enlarging cutaneous masses or ulcerative lesions (frequently located on the head in locations adjacent or contiguous with the sinonasal cavity or its draining lymph nodes) (Fig. 12.4).

Fig. 12.4 Photograph of a cat with disseminated cryptococcosis. The presence of numerous cutaneous masses of different sizes is usually referable to hematogenous dissemination in a cat with immunodeficiency, e.g., due to long-standing feline immunodeficiency virus (FIV) infection. Note that some of the masses have ulcerated. Similar lesions were present over the entire integument of this patient

infection commences in the back of the nasal cavity, neurological signs can develop. In some cats with nasal cavity involvement, fleshy masses protrude from the nostril, or gross deformation of the nasal planum or bridge of the nose is apparent. Cats with cutaneous lesions or nasal cavity involvement often feel otherwise well but can be lethargic and lack appetite. Fever is uncommon and typically low-grade. Lower respiratory tract signs such as tachypnea are unusual but can occur as a result of cryptococcomas, pleural effusion, or severe mediastinal lymphadenomegaly. Neuro­logical signs vary depending on the location of lesions in and around the CNS but include obtundation, abnormal behavior, ataxia, apparent blindness (typically peripheral, with widely dilated pupils that fail to respond to light), placing deficits, tremors, circling, head tilt, nystagmus, spinal pain, and/or focal or generalized seizures. Optic neuritis and chorioretinitis develop in as many as one-third of affected cats and almost always indicate CNS involvement (Malik et al. 2006b). Other reported signs include peripheral lymphadenomegaly (unassociated with skin lesions and often asymmetrical), lameness due to osteomyelitis or cryptococcal arthritis, and swollen digits. Rarely, the involvement of the abdominal lymph nodes, kidneys, spleen, liver, thyroid, and salivary glands occurs in cats (Sykes and Malik 2014).

No significant age- or sex-related propensity of the disease has been reported (Kerl 2003), although males might be affected slightly more often than females (Gerds-Grogan and Dayrell-Hart 1997). Among cats, Ragdoll and Birman breeds were found to be overrepresented (Refai et al. 2014), and this is most likely attributable to a breed-related defect in innate or cell-mediated immunity.

12.6.3.5 OtherCarnivores

C. neoformans has been recovered from the brain of wild foxes (Vulpes vulpes) (Staib et al. 1985; Weller et al. 1985). Two cases of pulmonary cryptococcosis and extensive meningoencephalomyelitis have been documented in captive cheetahs (Acinonyx jubatus) the causal organism being C. gattii (Bolton et al. 1999). Pulmo­nary cryptococcosis and cryptococcal meningoencephalomyelitis have also been described in a king cheetah (A. jubatus) (Berry et al. 1997). Millward and Williams (2005) also reported a case of C. neoformans infection in a wild free-ranging cheetah. It is well known that cheetahs have suffered an evolutionary genetic bottleneck, and the marked overrepresentation of cases compared to other large felids (lions, tigers, leopards) is akin to the overrepresentation of specific breeds of cat referred to earlier.

Cryptococcosis has also been diagnosed in seven domestic ferrets (Mustela putorius furo) (five from Australia and two from western Vancouver Island) displaying a wide range of clinical signs (Malik et al. 2002). Cryptococcal rhinitis; lymphadenopathy and respiratory signs; localized masses on the nose, spine, or digits; gastrointestinal and neurological signs; pneumonia; meningitis; and disseminated disease were documented in the affected ferrets. C. gattii VGII mole­cular type accounted for the Australian ferrets. The first case of ferret cryptococcosis in the USA was documented in 2006; cytological examination and culture of an enlarged mandibular lymph node revealed C. neoformans var. grubii (serotype A) (Hanley et al. 2006). In Spain, a domestic ferret presenting with lymphadenopathy and acute bilateral blindness was found to be infected with C. gattii (Morera et al. 2011).

12.6.3.6 Rodents

Clinical presentations, similar to those in other species, have been found in various rodents. In 1922, Sangiorgi reported for the first time the presence of Cryptococcus spp. in a rat (Rattus norvegicus). Subsequently, Cryptococcus spp. have been isolated from both mice and rats (Emmons et al. 1947). The isolation of C. neoformans from the striped grass mouse (Lemniscomys barbarus) has also been reported (Bauwens et al. 2004); subsequently, C. neoformans var. grubii was recovered from apparently healthy greater bandicoot rats (Bandicota indica) and house mice (Mus musculus castaneus) (Singh et al. 2007, 2017). The yeast was also isolated from fecal samples of striped grass mice, bandicoot rats, and house mice. Of note, experimental rodent models such as mouse (Mus musculus) (Fig. 12.5), rat (Rattus rattus), and guinea pig (Cavia porcellus) have been used extensively in cryptococcal pathogenesis research and mammalian host responses to Cryptococcus (Sabiiti et al. 2012).

12.6.3.7 Ruminants

Cases of meningoencephalitis, mastitis, and pulmonary disease have been reported in goats (Stilwell and Pissarra 2014), while in sheep, cryptococcal infection has been shown to manifest as mastitis or rhinitis (Lemos et al. 2007). Only mastitis has been documented in water buffaloes (Spickler 2013). Clinical manifestations of crypto­coccosis in camelids include the involvement of the lower respiratory tract and CNS

Fig. 12.5 Photographof multiple pulmonary cryptococcosis in mouse experimentally inoculated with C. gattii via intranasal instillation

disease, as well as widely disseminated infections (Bildfell et al. 2002; Goodchild et al. 1996). In 1953, an outbreak of bovine cryptococcosis was reported (Simos et al. 1953). Pulmonary infections, CNS involvement, and mastitis have been observed in cattle infected with Cryptococcus spp. Cryptococcosis has additionally been recorded in an elk (Cervus canadensis), in which the diencephalon, mesen­cephalon, and brain stem were found to be affected (Refai et al. 2014). Crypto­coccosis caused by C. gattii was reported in a white-tailed deer (Odocoileus virginianus) with nasopulmonary, lymph node, and CNS involvement (Overy et al. 2016). C. gattii has also been isolated from a black male alpaca in South American (Goodchild et al. 1996).

12.6.3.8 Equids

Riley et al. (1992) described the clinical and laboratory findings of cryptococcosis in seven horses from Australia (Riley et al. 1992). Most horses in this report had been exposed to areas where Eucalyptus camaldulensis, or the closely related Eucalyptus rudis, were growing. The species C. gattii was recovered from two of the horses. In pulmonary cryptococcosis, the lesions were either diffuse and multiple, with bilat­eral lung involvement, or localized mainly to the dorsocaudal region of one lung. The cases of widely disseminated cryptococcosis were associated with hemato­genous spread of the fungus most likely after primary gastrointestinal infection and dissemination from abdominal lymph nodes. The localized form of the disease was associated with the inhalation of C. gattii VGIIb (Riley et al. 1992).

Studies on animals in Vancouver Island revealed C. gattii in the nasal passage of horses (Duncan et al. 2011). Although upper respiratory tract infection is the common manifestation of cryptococcosis in horses in many regions, other clinical signs, such as meningitis, pneumonia, osteomyelitis, endometritis, and mycotic placentitis, have also been documented (Refai et al. 2014). Another case of crypto­coccosis in the form of cutaneous lesions was observed in a donkey (Refai et al. 2014).

12.6.3.9 MarineMammals

Cryptococcosis has also been identified in an increasing number of marine mammal species on southwestern Vancouver Island, including Pacific white-sided dolphins (Lagenorhynchus obliquidens) and both harbor and Dall's porpoises (Phocoena phocoena and Phocoenoides dalli~) (Bartlett et al. 2012; Stephen et al. 2002). C. gattii VGIIa has been documented in a harbor seal (Phoca vitulina) pup and in an unrelated adult (Rosenberg et al. 2016). Both animals showed generalized weakness, dehydration, respiratory compromise, minimally responsive mentation, and suboptimal body condition. Necropsy and histopathology findings showed generalized lymphadenopathy, bronchopneumonia, and meningoencephalitis with intralesional yeast and fungemia. Clinical cases of cryptococcosis have also been reported in a 7-year-old Atlantic bottlenose dolphin (Tursiops truncatus), a female Pacific white-sided dolphin (L. obliquidens), and a striped dolphin (Stenella coeruleoalba) kept in captivity (Migaki and Jones 1983; Nick Gales et al. 1985; Miller et al. 2002; Kidd et al. 2004). Rosenberg et al. (2016) recovered C. gattii VGIIa in a harbor seal juvenile pup and an adult. C. albidus, a traditionally nonpathogenic species, was recovered from a juvenile California sea lion (Zalophus californianus) (McLeland et al. 2012).

12.6.3.10 Nonhuman Primates and Other Mammals

Pulmonary cryptococcosis has been observed in a rhesus monkey (Macaca mulatta) (Pal et al. 1984). Multiple cryptococcosis were identified in the brain and heart of a 23-year-old captive-bred red-tailed guenon (Cercopithecus ascanius) (Helke et al. 2006). Cryptococcosis involving the respiratory tract and CNS was diagnosed in an Allen's swamp monkey (Allenopithecus nigroviridis), purple-faced leaf monkey (Presbytis senex), lion-tailed macaque (Macaca silenus), proboscis monkey (Nasalis larvatus) (Griner 1983; Barrie and Stadler 1995), tree shrews (Tupaia tana and Tupaia minor), and elephant shrews (Macroscelides proboscideus) (Tell et al. 1997).

12.7