Serologic responses of cats against experimental Sarcocystis neurona infections

Natural Occurring Muscular Sarcocysts in Urban Domestic Cats (Felis catus) Without Sarcocystis-Associated Disease

PURPOSE

Despite of classically acting as definitive hosts of different Sarcocystis species, domestic cats have been pointed out as possible intermediate hosts of S. neurona and S. felis. Nonetheless, details concerning natural sarcocyst development in cats without Sarcocystis-associated disease are scarce. This study aimed to characterize the natural occurrence of muscular sarcocysts in a random group of cats submitted for necropsy.

METHODS

One hundred cats necropsied at a Veterinary Pathology Service were included. Nine different muscular tissues from each cat were sampled for histological analysis and Polymerase Chain Reaction (PCR) using multispecies primers for Sarcocystis neurona, Neospora caninum and Toxoplasma gondii. PCR-positive cases were sequenced for genus and species identification. Epidemiologic data was also analyzed.

RESULTS

Tissue sarcocysts were identified in hematoxylin and eosin-stained slides from five cats, and S. neurona was the only confirmed species. Multifocal sarcocysts affecting two or more muscles were common among positive cats (4/5). Sarcocysts were identified within vastus lateralis (3/5), intercostal (3/5), subscapular (2/5) and diaphragm (2/5) sections. These cysts were always incidental necropsy findings. All sarcocyst-positive cats were from urban areas, among which two were feral and three were pets. Outdoor access was consistently reported. Two cats were positive for retrovirosis, and treatments with potentially immunosuppressive drugs were never stated.

CONCLUSIONS

This study describes the natural occurrence of S. neurona muscular sarcocysts in a random group of cats without Sarcocystis-associated disease. These findings reinforce the participation of feral and pet cats from urban areas as natural intermediate hosts of S. neurona.

An update on Sarcocystis neurona infections in animals and equine protozoal myeloencephalitis (EPM)

Equine protozoal myeloencephalitis (EPM) is a serious disease of horses, and its management continues to be a challenge for veterinarians. The protozoan Sarcocystis neurona is most commonly associated with EPM. S. neurona has emerged as a common cause of mortality in marine mammals, especially sea otters (Enhydra lutris). EPM-like illness has also been recorded in several other mammals, including domestic dogs and cats. This paper updates S. neurona and EPM information from the last 15 years on the advances regarding life cycle, molecular biology, epidemiology, clinical signs, diagnosis, treatment and control.

Sarcocystis sp. encephalomyelitis in a cat

A 5-month-old male neutered domestic shorthair cat was evaluated for spinal pain, ataxia, and anisocoria. Neuroanatomic localization indicated diffuse or multifocal central nervous system disease. On cerebrospinal fluid analysis, neutrophilic pleocytosis and intracellular protozoal merozoites were observed. The merozoites were oval, 2-4 microm in width and 4-6 microm in length, and had linear arrays of nuclear material concentrated at one pole. Serum was positive for Sarcocystis sp. antibodies and negative for Toxoplasma gondii antibodies. The organism was determined to be either Sarcocystis neurona or Sarcocystis dasypi based on sequence analysis of the internal transcribed spacer 1 ribosomal RNA genomic region. Clinical disease resolved following treatment with 3 different protocols for protozoal infection. This case is the first to demonstrate the antemortem diagnosis and survival of a domestic cat with Sarcocystis sp.-associated encephalomyelitis. Clinicians and cytopathologists should include Sarcocystis sp. as a differential for feline inflammatory central nervous system disease characterized by neutrophilic pleocytosis.

Epidemiology of Sarcocystis neurona infections in domestic cats (Felis domesticus) and its association with equine protozoal myeloencephalitis (EPM) case farms and feral cats from a mobile spay and neuter clinic

Equine protozoal myeloencephalitis (EPM) is a serious neurologic disease in the horse most commonly caused by Sarcocystis neurona. The domestic cat (Felis domesticus) is an intermediate host for S. neurona. In the present study, nine farms, known to have prior clinically diagnosed cases of EPM and a resident cat population were identified and sampled accordingly. In addition to the farm cats sampled, samples were also collected from a mobile spay and neuter clinic. Overall, serum samples were collected in 2001 from 310 cats, with samples including barn, feral and inside/outside cats. Of these 310 samples, 35 were from nine horse farms. Horse serum samples were also collected and traps were set for opossums at each of the farms. The S. neurona direct agglutination test (SAT) was used for both the horse and cat serum samples (1:25 dilution). Fourteen of 35 (40%) cats sampled from horse farms had circulating S. neurona agglutinating antibodies. Twenty-seven of the 275 (10%) cats from the spay/neuter clinic also had detectable S. neurona antibodies. Overall, 115 of 123 (93%) horses tested positive for anti-S. neurona antibodies, with each farm having greater than a 75% exposure rate among sampled horses. Twenty-one opossums were trapped on seven of the nine farms. Eleven opossums had Sarcocystis sp. sporocysts, six of them were identified as S. neurona sporocysts based on bioassays in gamma-interferon gene knockout mice with each opossum representing a different farm. Demonstration of S. neurona agglutinating antibodies in domestic and feral cats corroborates previous research demonstrating feral cats to be naturally infected, and also suggests that cats can be frequently infected with S. neurona and serve as one of several natural intermediate hosts for S. neurona.

Naturally occurring Sarcocystis infection in domestic cats (Felis catus)

Equine protozoal myeloencephalitis is an important neurological disease of horses in the United States. Consequently, there is an active research effort to identify hosts associated with the primary causative agent, Sarcocystis neurona. The purpose of this study was to determine whether the domestic cat (Felis catus) is a natural host for S. neurona. Muscle sections from 50 primarily free-roaming domestic cats were examined for the presence of sarcocysts. Serum from cats in this group and another group of 50 free-roaming cats were evaluated for the presence of S. neurona antibody. Sarcocysts were found in five of 50 (10%) cats, and S. neurona antibody in five of 100 (5%) cats. Morphological, molecular (including ribosomal RNA genes), and biological characterisation of these sarcocysts showed that they were not S. neurona or S. neurona-like. Sarcocysts found in the cats were identified morphologically as Sarcocystis felis, a common parasite of wild felids. The life cycle of S. felis is not known, and prior to this study, no molecular marker for S. felis existed. Although cats were found to be infected with S. felis sarcocysts, serological data provided evidence of possible infection with S. neurona as well. Further work is needed to determine the role of the domestic cat in the life cycle of S. neurona.