Sarcocystis neurona schizonts-associated encephalitis, chorioretinitis, and myositis in a two-month-old dog simulating toxoplasmosis, and presence of mature sarcocysts in muscles.

Sarcocystis neurona is an unusual species of the genus Sarcocystis. Opossums (Didelphis virginianus, D. albiventris) are the definitive hosts and several other species, including dogs, cats, marine mammals, and horses are intermediate or aberrant hosts. Sarcocysts are not known to form in aberrant hosts. Sarcocystis neurona causes fatal disease in horses (Equine Protozoal Myeloencephalitis, EPM). There are numerous reports of fatal EPM-like infections in other species, usually with central nervous system signs and associated with the schizont stage of S. neurona. Here, we report fatal disseminated S. neurona infection in a nine-week-old golden retriever dog from Mississippi, USA. Protozoal merozoites were identified in smears of the cerebrospinal fluid. Microscopically, lesions and protozoa were identified in eyes, tongue, heart, liver, intestines, nasal turbinates, skeletal muscle and brain, which reacted intensely with S. neurona polyclonal antibodies. Mature sarcocysts were seen in sections of muscles. These sarcocysts were ultrastructurally similar to those of S. neurona from experimentally infected animals. These data suggest that the dog is another intermediate host for S. neurona. Data suggest that the dog was transplacentally infected.

Establishment of Besnoitia darlingi from opossums (Didelphis virginiana) in experimental intermediate and definitive hosts, propagation in cell culture, and description of ultrastructural and genetic characteristics.

Besnoitia darlingi from naturally infected opossums (Didelphis virginiana) from Mississippi, USA, was propagated experimentally in mice, cats, and cell culture and was characterised according to ultrastructural, genetic, and life-history characteristics. Cats fed tissue cysts from opossums shed oocysts with a prepatent period of nine or 11 days. Oocysts, bradyzoites, or tachyzoites were infective to outbred and interferon-gamma gene knockout mice. Tachyzoites were successfully cultivated and maintained in vitro in bovine monocytes and African green monkey cells and revived after an 18-month storage in liquid nitrogen. Schizonts were seen in the small intestinal lamina propria of cats fed experimentally-infected mouse tissues. These schizonts measured up to 45 x 25 microm and contained many merozoites. A few schizonts were present in mesenteric lymph nodes and livers of cats fed tissue cysts. Ultrastructurally, tachyzoites and bradyzoites of B. darlingi were similar to other species of Besnoitia. A close relationship to B. besnoiti and an even closer relationship to B. jellisoni was indicated for B. darlingi on the basis of the small subunit and ITS-1 portions of nuclear ribosomal DNA.

Zonal dermal separation: a distinctive histopathological lesion associated with hyperelastosis cutis in a Quarter Horse.

This case report describes a distinctive deep cutaneous lesion in a 1-year-old Quarter Horse filly with hyperelastosis cutis. The horse had a typical clinical presentation of hyperelastic skin associated with a 6-month history of cutaneous wounds that developed following minor cutaneous trauma. Punch biopsies of skin from the affected horse were thinner than similar biopsies from an age- and breed-matched control. Significant microscopic lesions were not seen in cutaneous punch biopsies stained with haematoxylin and eosin and Masson's trichrome stains, but the ultrastructure of the dermis from the affected horse was characterized by variation in collagen fibre diameter and loose packing of collagen fibres within bundles. The horse was euthanized and necropsied, and full-thickness sections of skin were collected and examined microscopically. Affected skin was of normal thickness; however, the deep dermis contained a distinctive horizontal linear zone in which separation of collagen bundles resulted in the formation of large empty cleft-like spaces between the upper and lower regions of the deep dermis. We suggest the term 'zonal dermal separation' for this microscopic lesion. Incisional full-thickness skin biopsies should be taken in suspected cases of equine hyperelastosis cutis because punch biopsies may not obtain enough deep dermis to adequately represent pathological change in the skin of horses with this disorder.

Prevalence of Sarcocystis neurona sporocysts in opossums (Didelphis virginiana) from rural Mississippi.

Sarcocystis species sporocysts were found in intestinal scrapings from 24 of 72 opossums (Didelphis virginiana) from rural Mississippi. The number of sporocysts in each opossum varied from a few ( < 100000) to 187 million. Sporocysts from 24 opossums were bioassayed for Sarcocystis neurona infections by feeding to gamma-interferon knockout (KO) mice. S. neurona was detected in the brains of KO mice fed sporocysts from 19 opossums by immunohistochemical staining with anti-S. neurona specific polyclonal rabbit serum, and by in vitro culture from the brains of KO mice fed sporocysts. The isolates of S. neurona from opossums were designated SN16-OP to SN34-OP. Merozoites from 17 of 19 isolates tested at the 25/396 locus were identical to previously described S. neurona isolates from horses. The high prevalence of S. neurona sparocysts in D. virginiana suggests that this opossum constitutes an ample reservoir of infection in the southern United States.

Risk factors associated with the presence of Sarcocystis neurona sporocysts in opossums (Didelphis virginiana).

Sarcocystis neurona is the most important cause of equine protozoal myeloencephalitis (EPM) in horse in the Americas. The only known definitive host for this parasite in the United States is the opossum (Didelphis virginiana); however, despite the importance of the disease, the epidemiology of the parasite in the definitive host is poorly understood. To begin addressing these data gaps, potential risk factors were evaluated for their association with the presence of sporocysts of S. neurona in opossums live-trapped in March 1999 and November 1999 to May 2000. Sporocysts of S. neurona were found in 19 of the 72 animals examined. Potential risk factors evaluated were locality, trap date, age, gender, the presence of young in the pouch of females, and body condition score. Variables that were associated with the presence of S. neurona sporocysts were used in logistic regression analysis. Of the factors examined, season and body condition score were associated with increased odds of an animal harboring sporocysts.

Papillomatous pastern dermatitis with spirochetes and Pelodera strongyloides in a Tennessee Walking Horse.

Papillomatous digital dermatitis is a common disease in cattle. The pastern dermatitis observed in a horse shared many of the gross characteristics of papillomatous digital dermatitis in cattle. Lesions included a mixture of proliferative and erosive changes, with a verrucose appearance in some areas. Microscopic similarities included pseudoepitheliomatous and papillomatous epidermal hyperplasia with hyperkeratosis, spongiosis of the epidermis, and intraepidermal spirochetes. The horse was also concurrently infected with Pelodera strongyloides. Papillomatous digital dermatitis in cattle is associated with poor husbandry practices. The environment of the affected horse was heavily contaminated with urine, manure, and other organic debris. Verrucous pododermatitis of horses may be the same as or similar to bovine papillomatous digital dermatitis, and these conditions have similar etiologies.

Epitheliotropic T-cell gastrointestinal tract lymphosarcoma with metastases to lung and skeletal muscle in a cat.

An Abyssinian cat examined because of hypoproteinemia and weight loss was found to have epitheliotropic T-cell lymphosarcoma of the gastrointestinal tract. Neoplastic lymphocytes infiltrated the epithelium and lamina propria of the stomach, small intestine, and large intestine. Metastatic foci were found in the lungs and the musculature of the right hind limb. Chemotherapy resulted in transient shrinkage of the lung and limb masses; however, these masses grew to approximately their original size within 2 weeks after initiation of treatment, and the cat was euthanatized.

Encephalitozoon hellem in budgerigars (Melopsittacus undulatus).

Microsporidiosis with concurrent megabacteriosis in budgerigar (Melopsittacus undulatus) chicks contributed to significant economic floss in a commercial pet bird aviary in Mississippi. Three budgerigar chicks, 1-2 weeks old, from the aviary were necropsied. Microscopic lesions in the chicks consisted of heavy infection of enterocytes with microsporidia (2/3; autolysis precluded critical evaluation of the intestine of chick No. 2), multifocal hepatic necrosis and inflammation with intralesional microsporidia (1/3), spherical clusters of microsporidia in the hepatic sinusoids in the absence of inflammation (1/3), and gastric megabacteriosis (3/3). The ultrastructure of the microsporidian spores was consistent with an Encephalitozoon species. The polymerase chain reaction and Southern blot analysis were used to identify the microsporidian as Encephalitozoon hellem, an organism that has only been identified in humans. Encephalitozoon hellem causes keratoconjunctivitis and respiratory infections in humans with acquired immunodeficiency syndrome. This report presents the first confirmed case of microsporidiosis in budgerigars. The finding of E. hellem in pet birds may be important in elucidating the epidemiology of human infections with this organism.

Subclinical cyathostomiasis and unidentified helminthiasis in a juvenile emu (Dromaius novaehollandiae).

The nematode Cyathostoma variegatum (a lungworm) was present in the distal trachea and proximal bronchi of an 8-mo-old emu that was euthanatized after fracturing the left tibiotarsus. Clinical signs of infection were not present prior to euthanasia and abnormalities were not noted on gross or histologic examination of the respiratory tract. The absence of respiratory signs in this and other emus underscores the need for routine fecal examinations to interrupt the inadvertent spread of this potentially life-threatening parasite. In addition to the lungworms, large helminth eggs were present in renal and reproductive tissue. Egg morphology was suggestive of species of Deletrocephalus or Paradeletrocephalus. The mechanism by which these eggs became lodged in this ectopic site is unknown.

Isolation of Yersinia pseudotuberculosis and Listeria monocytogenes serotype 4 from a gray fox (Urocyon cinereoargenteus) with canine distemper.

In February 1993, clinical, pathological, and microbiological investigations were performed on an adult female gray fox (Urocyon cinereoargenteus) from northern Mississippi (USA). The fox had clinical signs consistent with canine distemper virus encephalitis. Eosinophilic inclusions characteristic of canine distemper virus were in the nuclei and cytoplasm of cerebral neurons and glial cells and in the cytoplasm of urinary, gastric, pancreatic and biliary epithelial cells. The liver contained multifocal microscopic nodular foci of granulomatous to pyogranulomatous inflammation and necrosis with large colonies of small Gram-negative coccobacilli. A low number of small Gram-positive bacilli were within viable-appearing Kupffer cells and hepatocytes. Yersinia pseudotuberculosis and Listeria monocytogenes serotype 4 were isolated from the liver and a mesenteric lymph node.

Caryospora-associated dermatitis in dogs.

Numerous developmental stages of Caryospora sp. were seen in skin and lymph node of a 2-mo-old-dog with severe pyogranulomatous dermatitis. Schizonts were up to 20 microns long and contained up to 25 merozoites. Gamonts, unsporulated oocytes, sporulated oocysts, and caryocysts were seen in macrophages, connective tissue cells, and in unidentifiable host cells. Caryocysts were up to 18 microns long, and had thin walls, and contained a host cell nucleus and 1-3 sporozoites. All developmental stages of the coccidium reacted positively with anti-Caryospora bigenetica serum when examined in an immunoperoxidase test.