Differences in expression of uroplakin III, cytokeratin 7, and cyclooxygenase-2 in canine proliferative urothelial lesions of the urinary bladder.

The expression of immunohistochemical markers that have been used in diagnosis and/or prognostication of urothelial tumors in humans (uroplakin III [UPIII], cytokeratin 7 [CK7], cyclooxygenase-2 [COX-2], and activated caspase 3) was evaluated in a series of 99 canine proliferative urothelial lesions of the urinary bladder and compared to the lesion classification and grade as defined by the World Health Organization / International Society of Urologic Pathology consensus system. There were significant associations between tumor classification and overall UPIII pattern (P = 1.49 × 10(-18)), loss of UPIII (P = 1.27 × 10(-4)), overall CK7 pattern (P = 4.34 × 10(-18)), and COX-2 pattern (P = 8.12 × 10(-25)). In addition, there were significant associations between depth of neoplastic cell infiltration into the urinary bladder wall and overall UPIII pattern (P = 1.54 × 10(-14)), loss of UPIII (P = 2.07 × 10(-4)), overall CK7 pattern (P = 1.17 × 10(-13)), loss of CK7 expression (P = .0485), and COX-2 pattern (P = 8.23 × 10(-21)). There were no significant associations between tumor classification or infiltration and caspase 3 expression pattern.

Necrotizing and eosinophilic masticatory myositis in farmed mink: a preliminary description.

This report describes necrotizing and eosinophilic myositis affecting the masticatory muscles of a group of mink. Affected animals demonstrated sudden death with marked subcutaneous oedema over the dorsal head. The temporalis and masseter muscles were pale, swollen and friable. Histologic changes consisted of varying degrees of myodegeneration, myonecrosis and inflammation. Eosinophils were prominent in the inflammatory infiltrate. Similar to dogs, masticatory muscles in mink were found to contain unique type 2M fibres, suggesting a possible target for an immune response. Aerobic and anaerobic tissue cultures of the affected musculature revealed no significant pathogens. Histological and nutritional analyses were not typical of vitamin E/selenium deficiency. This case series supports the existence of a novel disease entity in mink with some features comparable with masticatory muscle myositis in dogs.

Performance of diagnostic tests for bovine tuberculosis in North American furbearers and implications for surveillance.

Risks of bovine tuberculosis (bTB) transmission from free-ranging wildlife to livestock remain a concern in the United States, in both known endemic areas and where spillover from recently-infected livestock herds occurs. Federal agriculture officials in the United States (US) have recommended surveillance of non-cervid furbearers to determine whether free-ranging wildlife in the vicinity of cattle herd breakdowns are bTB infected, yet the efficacy of common diagnostic tests in these species is largely unknown. We calculated the sensitivity, specificity, predictive values and positive likelihood ratios for bTB infection in carcasses of sixteen species of furbearers tested via: (i) the presence of gross lesions compatible with bTB; (ii) histopathology consistent with bTB; and (iii) the presence of acid-fast bacilli (AFB) on histopathology. The gold standard comparison test was mycobacterial culture of cranial ± visceral lymph nodes pooled for each animal. Forty-two animals distributed across six species cultured bTB positive from among 1522 furbearers tested over thirteen years. The sensitivity of all three tests was poor (10%, 22% and 24% for gross lesions, AFB and histopathology, respectively), while specificities (all ≥ 99%) and negative predictive values (all ≥ 97%) were high. Positive predictive values varied widely (31-75%). Likelihood ratios for culture positivity given a positive test result showed AFB on histopathology to be the most reliable test, and gross lesions the least, though confidence intervals were wide and overlapping. While non-cervid furbearers may prove useful in North American bTB surveillance, wildlife managers should be aware of factors that may abate their utility and complicate interpretation of surveillance.

Distribution of eastern equine encephalomyelitis viral protein and nucleic acid within central nervous tissue lesions in white-tailed deer (Odocoileus virginianus).

An outbreak of eastern equine encephalomyelitis (EEE) occurred in Michigan free-ranging white-tailed deer (Odocoileus virginianus) during late summer and fall of 2005. Brain tissue from 7 deer with EEE, as confirmed by reverse transcriptase polymerase chain reaction, was studied. Detailed microscopic examination, indirect immunohistochemistry (IHC), and in situ hybridization (ISH) were used to characterize the lesions and distribution of the EEE virus within the brain. The main lesion in all 7 deer was a polioencephalomyelitis with leptomeningitis, which was more prominent within the cerebral cortex, thalamus, hypothalamus, and brainstem. In 3 deer, multifocal microhemorrhages surrounded smaller vessels with or without perivascular cuffing, although vasculitis was not observed. Neuronal necrosis, associated with perineuronal satellitosis and neutrophilic neuronophagia, was most prominent in the thalamus and the brainstem. Positive IHC labeling was mainly observed in the perikaryon, axons, and dendrites of necrotic and intact neurons and, to a much lesser degree, in glial cells, a few neutrophils in the thalamus and the brainstem, and occasionally the cerebral cortex of the 7 deer. There was minimal IHC-based labeling in the cerebellum and hippocampus. ISH labeling was exclusively observed in the cytoplasm of neurons, with a distribution similar to IHC-positive neurons. Neurons positive by IHC and ISH were most prominent in the thalamus and brainstem. The neuropathology of EEE in deer is compared with other species. Based on our findings, EEE has to be considered a differential diagnosis for neurologic disease and meningoencephalitis in white-tailed deer.

Wildlife reservoirs of bovine tuberculosis worldwide: hosts, pathology, surveillance, and control.

Bovine tuberculosis due to Mycobacterium bovis is a zoonotic disease classically carried by cattle and spilling over into humans primarily by the ingestion of milk. However, in recent decades, there have been many endemic geographic localities where M. bovis has been detected infecting wildlife reservoirs, limiting the progress toward eradication of this disease from cattle. These include cervids in North America, badgers in Great Britain, feral pigs in Europe, brushtailed possums in New Zealand, and buffalo in South Africa. An overview of these wildlife hosts will provide insight into how these reservoirs maintain and spread the disease. In addition, the authors summarize the pathology, current ongoing methods for surveillance, and control. In many instances, it has proven to be more difficult to control or eradicate bovine tuberculosis in wild free-ranging species than in domesticated cattle. Furthermore, human influences have often contributed to the introduction and/or maintenance of the disease in wildlife species. Finally, some emerging themes regarding bovine tuberculosis establishment in wildlife hosts, as well as conclusions regarding management practices to assist in bovine tuberculosis control and eradication in wildlife, are offered.

Nested case-control study of feline calicivirus viruria, oral carriage, and serum neutralizing antibodies in cats with idiopathic cystitis.

BACKGROUND: The epidemiology of feline calicivirus (FCV) infection in cats with idiopathic cystitis (FIC) has not been investigated by contemporary molecular biologic methods. OBJECTIVES: To determine the prevalence of and evaluate risk factors for FCV viruria, oral carriage, and virus neutralizing (VN) antibodies in cats with and without FIC. ANIMALS: Cats with nonobstructive FIC (n = 47), obstructive FIC (n = 22), and FCV upper respiratory tract infection (URI; n = 25), and healthy client-owned (n = 18) and colony-housed (n = 24) cats. METHODS: Oropharyngeal secretions and urine were evaluated with a FCV p30 gene-based real-time reverse-transcriptase polymerase chain reaction (RT-PCR) assay. Serum VN antibody titers were determined by a modified microtiter assay. Associations of risk factors with log-transformed antibody titers were determined by multivariable generalized linear regression. RESULTS: FCV viruria was detected in 4 (6%) and 3 (12%) cats with FIC and URI, respectively. In 3 FIC cats, viruria was unassociated with detectable oral virus carriage. Oral FCV carriage was detected in 7 (10%) FIC cats. Median antibody titers were significantly higher in cats with obstructive FIC (1 :256), nonobstructive FIC (1:128), and URI (1:512) compared with healthy client-owned (1:16) and colony-housed (1:4) cats (P < .001). Other than disease, multivariate analysis did not identify any other explanatory variables for increased titers in cats with FIC or URI. CONCLUSIONS AND CLINICAL IMPORTANCE: FCV viruria was detected in cats with FIC and URI, however, its etiologic significance is uncertain. Serologic results suggest increased FCV exposure in FIC cats compared with controls. Further investigations are needed to clarify the potential role of FCV in FIC.

Proposal of a 2-tier histologic grading system for canine cutaneous mast cell tumors to more accurately predict biological behavior.

Currently, prognostic and therapeutic determinations for canine cutaneous mast cell tumors (MCTs) are primarily based on histologic grade. However, the use of different grading systems by veterinary pathologists and institutional modifications make the prognostic value of histologic grading highly questionable. To evaluate the consistency of microscopic grading among veterinary pathologists and the prognostic significance of the Patnaik grading system, 95 cutaneous MCTs from 95 dogs were graded in a blinded study by 28 veterinary pathologists from 16 institutions. Concordance among veterinary pathologists was 75% for the diagnosis of grade 3 MCTs and less than 64% for the diagnosis of grade 1 and 2 MCTs. To improve concordance among pathologists and to provide better prognostic significance, a 2-tier histologic grading system was devised. The diagnosis of high-grade MCTs is based on the presence of any one of the following criteria: at least 7 mitotic figures in 10 high-power fields (hpf); at least 3 multinucleated (3 or more nuclei) cells in 10 hpf; at least 3 bizarre nuclei in 10 hpf; karyomegaly (ie, nuclear diameters of at least 10% of neoplastic cells vary by at least two-fold). Fields with the highest mitotic activity or with the highest degree of anisokaryosis were selected to assess the different parameters. According to the novel grading system, high-grade MCTs were significantly associated with shorter time to metastasis or new tumor development, and with shorter survival time. The median survival time was less than 4 months for high-grade MCTs but more than 2 years for low-grade MCTs.

Congenital ureteral ectopia in continent and incontinent-related Entlebucher mountain dogs: 13 cases (2006-2009).

BACKGROUND: Ectopic ureters (EUs) associated with varying combinations of urinary incontinence, hydronephrosis, and urinary tract infection have been identified in related North American Entlebucher Mountain Dogs. OBJECTIVES: To characterize the disease phenotype in affected dogs and evaluate possible modes of inheritance. ANIMALS: Twenty client-owned Entlebucher Mountain Dogs. Nine dogs had clinical signs of urinary tract disease. METHODS: Prospective case series in which 17 dogs were evaluated with excretory urography, ultrasonography, and urethrocystoscopy. Three additional dogs were evaluated by necropsy alone. Clinical and pedigree histories from 165 North American Entlebuchers were compiled for analysis. RESULTS: Eleven female and 2 male dogs were found to have EUs. Six females and 1 male were continent. Bilateral intravesicular ectopic ureters (IVEUs) were identified in 9 dogs, bilateral extravesicular ectopic ureters (EVEUs) in 3 dogs, and 1 dog had IVEU and EVEU. Hydronephrosis was identified in 5 dogs, 3 of which had bilateral IVEUs. Two necropsied dogs had bilateral hydronephrosis with presumed ureterovesical junction obstruction associated with chronic granulation tissue or lymphoplasmacytic inflammation. Twenty-six dogs with EUs were identified in the pedigree. Because of incomplete penetrance, mode of inheritance could not be determined. CONCLUSIONS AND CLINICAL IMPORTANCE: Ureteral ectopia is common in North American Entlebucher Mountain Dogs and clinical signs alone could not reliably predict disease phenotype. EVEUs were associated with urinary incontinence and occasionally hydronephrosis. IVEUs were clinically silent or associated with hydronephrosis. Further analyses are necessary to confirm and characterize the hereditary nature of the disorder.

Malignant lymphoma in african lions (panthera leo).

Malignant lymphoma has become an increasingly recognized problem in African lions (Panthera leo). Eleven African lions (9 male and 2 female) with clinical signs and gross and microscopic lesions of malignant lymphoma were evaluated in this study. All animals were older adults, ranging in age from 14 to 19 years. Immunohistochemically, 10 of the 11 lions had T-cell lymphomas (CD3(+), CD79a(-)), and 1 lion was diagnosed with a B-cell lymphoma (CD3(-), CD79a(+)). The spleen appeared to be the primary site of neoplastic growth in all T-cell lymphomas, with involvement of the liver (6/11) and regional lymph nodes (5/11) also commonly observed. The B-cell lymphoma affected the peripheral lymph nodes, liver, and spleen. According to the current veterinary and human World Health Organization classification of hematopoietic neoplasms, T-cell lymphoma subtypes included peripheral T-cell lymphoma (4/11), precursor (acute) T-cell lymphoblastic lymphoma/leukemia (2/11), chronic T-cell lymphocytic lymphoma/leukemia (3/11), and T-zone lymphoma (1/11). The single B-cell lymphoma subtype was consistent with diffuse large B-cell lymphoma. Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) testing by immunohistochemistry on sections of malignant lymphoma was negative for all 11 lions. One lion was seropositive for FeLV. In contrast to domestic and exotic cats, in which B-cell lymphomas are more common than T-cell lymphomas, African lions in this study had malignant lymphomas that were primarily of T-cell origin. Neither FeLV nor FIV, important causes of malignant lymphoma in domestic cats, seems to be significant in the pathogenesis of malignant lymphoma in African lions.

Subgroup J avian leukosis virus-induced histiocytic sarcomatosis occurs only in persistently viremic but not immunotolerized meat-type chickens.

The role of subgroup J avian leukosis virus (ALV J) infection profile in the development of histiocytic sarcomatosis (HS) in chickens was evaluated using retrospective analysis of 2 experiments involving in ovo and at-hatch inoculation of commercial meat-type and ADOL line 0 chickens with 100 or 10,000 TCID(50) of various strains ALV J. HS was observed only in persistently viremic, meat-type chickens that were inoculated at hatch, but not in immunotolerized (persistently viremic, with no antibodies), in ovo inoculated chickens. However, the immunotolerized, in ovo inoculated chickens developed a high incidence of myeloid tumors. HS appeared to arise from the splenic ellipsoids and red pulp, and metastasized to liver, kidney, and other organs. The neoplastic cells were diffusely positive for ChL5, CD45, and MHC class II with multifocal infiltration of T and B lymphocytes. Expression of viral antigen gp85 within HS was very low compared with that noted in ALV J-induced myelocytomas. The above observations suggest that the mechanisms of oncogenesis of HS might be different from that of other ALV J-induced tumors.

Embryo toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin to the wood duck (Aix sponsa).

We examined the sensitivity of the wood duck (Aix sponsa) embryo to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) by injecting the toxicant into their eggs. Six groups of wood duck eggs (n = 35 to 211 per trial) were injected with 0 to 4600 pg TCDD/g egg between 2003 and 2005. Injections were made into yolk prior to incubation, and eggs were subsequently incubated and assessed weekly for mortality. Significant TCDD-induced mortality was not observed through day 25 (90% of incubation). Liver, heart, eye, and brain histology were generally unremarkable. Hepatic ethoxyresorufin-O-deethylase activity, a biomarker of dioxin-like compound exposure, was induced by 12-fold in the 4600 pg/g treatment relative to controls. The median lethal dose for chicken (Gallus domesticus) eggs we dosed identically to wood duck eggs was about 100 pg/g, similar to other assessments of chickens. Among dioxin-like compound embryo lethality data for 15 avian genera, the wood duck 4600 pg/g no-observed-effect level ranks near the middle. Because no higher doses were tested, wood ducks may be like other waterfowl (order Anseriformes), which are comparatively tolerant to embryo mortality from polychlorinated dibenzo-p-dioxins and dibenzofurans when exposed by egg injection.

Absence of Mycobacterium bovis infection in dogs and cats residing on infected cattle farms: Michigan, 2002.

A cross-sectional field study was performed to evaluate infection in dogs and cats living on farms with Mycobacterium bovis-infected cattle. The purpose was to determine pet infection status and assess their risk to farm families and/or tuberculosis-free livestock. Data and specimens were collected from 18 cats and five dogs from nine participating farms. ELISA testing for M. bovis and M. avium was conducted. Fifty-one biological samples were cultured; all were negative for M. bovis, although other Mycobacterium species were recovered. No radiographic, serological or skin test evidence of mycobacterial infection was found. These negative results may be due to the low level of M. bovis infection in the cattle and the limited duration of exposure of pets to infected cattle residing on the same farm. No evidence was found to indicate that pets residing on M. bovis-infected Michigan cattle farms pose a risk to humans or M. bovis-free livestock; however, precautionary advice for farm owners was provided.

Marek's disease virus-induced skin leukosis in scaleless chickens: tumor development in the absence of feather follicles.

Marek's disease virus (MDV) is an oncogenic cell-associated herpesvirus that causes T-cell lymphoma in chickens. Lymphoproliferative neoplasms in Marek's disease (MD) occur in various organs and tissues, including the viscera, peripheral nerves, skin, gonads, and musculatures. MDV is restrictively produced in the feather follicle epithelial (FFE) cells, and it gains access to the external environment via infected cells or as infectious enveloped cell-free virus particles. The goals of the present study were to 1) determine whether the MDV-induced skin lesions are neoplastic in nature or inflammatory reactions to viral infection, 2) determine whether physical presence of feather follicles (FF) is necessary for skin tumor development, and 3) study the role of skin epithelial cells not associated with feathers or FF in the replication and dissemination of infectious virus particles. Scaleless chickens that produce only a few scattered feathers and no sculate scales along the anterior metatarsi were used as a unique model to study the pathogenesis of dermal lesions. Histologic and immunohistochemical analysis revealed that the cutaneous lesions were tumorous as was manifested by massive accumulation of lymphoblasts and extensive activation of meq oncoprotein, the hallmark of MDV oncogenesis, within the skin lesions. Neoplastic cutaneous lesions in the scaleless chickens indicate that feather follicles are not necessary for skin tumor development. Finally, our preliminary data indicate that inoculation with supernatant fluid from homogenized and sonicated skin samples of MDV-infected scaleless chickens induces MD in susceptible birds, suggesting that skin epithelial cells not associated with FF also harbor infectious viral particles.

Classification of canine urinary bladder urothelial tumours based on the World Health Organization/International Society of Urological Pathology consensus classification.

One hundred canine urinary bladder urothelial (transitional cell) tumours, including roughly equal numbers of benign and malignant forms, were retrospectively categorized in accordance with the newly described human consensus classification of the World Health Organization/International Society of Urological Pathology (WHO/ISUP). The tumours were reviewed and classified by three veterinary pathologists from Michigan State University and two human pathologists from the Armed Forces Institute of Pathology (AFIP). The current human WHO/ISUP classification system was considered to be readily applicable to the dog. Canine tumours, however, differed from human tumours in that the great majority showed extensive glandular differentiation (or metaplasia) and hyperplastic lesions tended to be more florid than those seen in human beings. The various diagnoses and grades assigned to the tumours were highly consistent between all reviewing pathologists. This paper presents the salient features of the new WHO and ISUP consensus classification and provides illustrations of the various tumour types that were directly applicable to the dog.

Experimental inoculation of wild turkeys (Meleagris gallopavo) with Mycobacterium bovis.

Although avian species are known to be susceptible to infection with Mycobacterium spp. organisms, much remains unknown about the susceptibility of birds to infection with M. bovis. The objective of this current study was to determine if wild turkeys (Meleagris gallopavo) can be infected with M. bovis when inoculated by the oral or intratracheal route. Six turkeys were orally inoculated and another six were inoculated via the trachea with a high dose of M. bovis, 1 x 10(5) CFU/ml. Six turkeys were sham-inoculated controls. Two turkeys from each treatment group were sacrificed on days 30, 60, and 90 postinoculation. There were no gross or microscopic lesions consistent with mycobacteriosis in the 23 inoculated turkeys over the 90-day duration of this study. Fecal cultures were also consistently negative for M. bovis when sampled before inoculation and on days 1, 30, and 60 postinoculation. Two intratracheally inoculated turkeys were positive for M. bovis in visceral tissues at 30 days postinoculation. However, this finding was only indicative of passive persistence of mycobacteria in the tissues and not of infection, as there were no attendant lesions or clinical compromise to support infection. Thus, it can be concluded that young wild turkeys are resistant to infection with M. bovis and, therefore, pose minimal threat as reservoir or spillover hosts for this organism.

Resistance of Mallard ducks (Anas platyrhynchos) to experimental inoculation with Mycobacterium bovis.

The purpose of this study was to investigate whether mallard ducks (Anas platyrhynchos) are susceptible to infection with Mycobacterium bovis by either oral or intratracheal inoculation and to assess their potential role in the spread of bovine tuberculosis. Six ducks were orally inoculated with 1.0 x 10(5) colony-forming units of M. bovis, six ducks were intratracheally inoculated with the same dose, and six ducks served as sham-inoculated controls. The study length was 90 days postinoculation, with samples of two birds from each group necropsied at 30-day intervals. Both fecal and tissue samples were collected for mycobacterial culture. None of the inoculated ducks shed M. bovis in their feces at any culture point (days 1, 30, and 60) during the study. No evidence of illness or weight loss was present during the course of the study, and only one duck had M. bovis isolated from any tissue, although there were no associated microscopic lesions. Mallard ducks were highly resistant to infection with M. bovis following high-dose inoculation and did not shed the organism in their feces. This study was conducted using high-dose inoculation; therefore, it appears that ducks are unlikely to play any significant role in the transmission of M. bovis between infected and uninfected mammalian hosts.

Concurrent presence of Sarcocystis neurona sporocysts, Besnoitia darlingi tissue cysts, and Sarcocystis inghami sarcocysts in naturally infected opossums (Didelphis virginiana).

Opossums (Didelphis virginiana) are exposed to a wide range of coccidia through feeding on a variety of foods, including, but not limited to, carrion, insects, and nestling birds. Abundant D. virginiana populations in urban and suburban areas can be important reservoirs of parasitic infection because of their profuse and prolonged excretion of the sporocysts of several species of Sarcocystis, their omnivorous diet, and their relatively long life span. This report describes 2 adult female opossums found to be simultaneously infected with the tissue cysts of Besnoitia darlingi, sarcocysts of Sarcocystis inghami, as well as with the intestinal sporocysts of S. neurona. Cysts typical of B. darlingi based on gross, histological, and ultrastructural characteristics were disseminated throughout the visceral organs, musculature, ears, and skin. The S. neurona and B. darlingi infections were confirmed by comparative sequence analysis of polymerase chain reaction-amplified diagnostic genetic loci. Sarcocysts of S. inghami are also described. Such examples of multiple parasitic infections show that concurrent infections occur naturally. The propensity for species to coexist should be considered in the differential diagnosis of tissue cyst-forming coccidian protozoa and may have important epidemiological and evolutionary implications.

Efficacy of a commercial mycotoxin binder in alleviating effects of ochratoxin A, fumonisin B1, moniliformin and zearalenone in adult mink.

The addition of nutritionally inert adsorbents to mycotoxin-contaminated animal feed has been a popular approach to decreasing toxicity in animals and carryover of mycotoxins from contaminated feed to animal by-products. Some studies suggest that esterified glucomannan derived from the cell wall of Saccharomyces cerevisiae is effective in reducing the bioavailability of at least some of the mycotoxins occurring in contaminated feed. Because cereal grains are important components of ranch mink diets, mycotoxicoses in mink is a potential problem faced by mink ranchers. We conducted a series of studies to determine if inclusion of a commercially available esterified glucomannan in ranch mink feed was effective in alleviating clinical signs indicative of exposure to ochratoxin A, fumonisin B1, moniliformin or zearalenone in adult mink. In 4 separate trials, mink were fed diets that contained 2.5, 5 or 10 mg ochratoxin A/kg feed, 200 mg fumonisin B1/kg feed, 20 mg moniliformin/kg feed, or 30 mg zearalenone/kg feed with or without 2 g esterified glucomannan/kg feed. Male mink fed diets containing ochratoxin A had significantly decreased feed intake as well as renal lesions characteristic of exposure to that mycotoxin. Inclusion of the esterified glucomannan did not ameliorate these effects. Male mink exposed to fumonisin B1 had increased urinary sphinganine concentration, which was not significantly reduced by the mycotoxin adsorbent. Male mink that consumed monilformin-contaminated diets had characteristic ultrastructural changes in the heart that were not reduced in severity by the esterified glucomannan. Female mink exposed to zearalenone had increased uterine weight, which was not reversed by inclusion of commercial mycotoxin binder in the contaminated feed. The results of this study suggest that a commercial esterified glucomannan was generally ineffective in alleviating effects indicative of exposure to ochratoxin A, fumonisin B1, monilformin and zearalenone in mink.

West Nile virus infection in Eastern fox squirrels (Sciurus niger).

Since the initial outbreak of West Nile virus (WNV) in the northeastern United States in 1999, the virus has rapidly spread westward and southward across the USA, causing high mortality in crows as well as sporadic mortality in horses, humans, and a wide variety of birds. In 2002 the epidemic widened as hundreds of equine and human cases and sporadic cases in other mammalian species were reported. This is the first report of WNV infection in three Eastern fox squirrels (Sciurus niger). Neurologic signs included head tilt, uncoordinated movement, paralysis, and tremors. Gross lesions were absent. Microscopic lesions consisted of lymphoplasmacytic inflammation involving the brain, heart, kidney, and liver. Formalin-fixed tissues from the three squirrels were tested for WNV antigen by immunohistochemical staining and for WNV-specific RNA by reverse transcriptase-polymerase chain reaction (RT-PCR). The kidneys of all three squirrels stained positive with immunohistochemistry for WNV, whereas the brain and heart were positive in only one animal. Two of the three squirrels were positive for WNV by RT-PCR.

Clinical and pathologic features of West Nile virus infection in native North American owls (Family strigidae).

Since the initial report of West Nile virus in the northeastern United States in 1999, the virus has spread rapidly westward and southward across the country. In the summer of 2002, several midwestern states reported increased cases of neurologic disease and mortality associated with West Nile virus infection in various native North American owl species. This report summarizes the clinical and pathologic findings for 13 captive and free-ranging owls. Affected species were all in the family Strigidae and included seven snowy owls (Nyctea scandiaca), four great-horned owls (Bubo virginianus), a barred owl (Strix varia), and a short-eared owl (Asio flammeus). Neurologic signs identified included head tilt, uncoordinated flight, paralysis, tremors, and seizures. Owls that died were screened for flaviviral proteins by immunohistochemical staining of formalin-fixed tissues, followed by specific polymerase chain reaction assay to confirm West Nile virus with fresh tissues when available. Microscopic lesions were widespread, involving brain, heart, liver, kidney, and spleen, and were typically nonsuppurative with infiltration by predominantly lymphocytes and plasma cells. Lesions in owls were much more severe than those previously reported in corvids such as crows, which are considered highly susceptible to infection and are routinely used as sentinel species for monitoring for the presence and spread of West Nile virus. This report is the first detailed description of the pathology of West Nile virus infection in Strigiformes and indicates that this bird family is susceptible to natural infection with West Nile virus.