William J. A. Saville

A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM).

Equine protozoal myeloencephalitis (EPM) is a serious neurological disease of horses in the Americas. The protozoan most commonly associated with EPM is Sarcocystis neurona. The complete life cycle of S. neurona is unknown, including its natural intermediate host that harbors its sarcocyst. Opossums (Didelphis virginiana, Didelphis albiventris) are its definitive hosts. Horses are considered its aberrant hosts because only schizonts and merozoites (no sarcocysts) are found in horses. EPM-like disease occurs in a variety of mammals including cats, mink, raccoons, skunks, Pacific harbor seals, ponies, and Southern sea otters. Cats can act as an experimental intermediate host harboring the sarcocyst stage after ingesting sporocysts. This paper reviews information on the history, structure, life cycle, biology, pathogenesis, induction of disease in animals, clinical signs, diagnosis, pathology, epidemiology, and treatment of EPM caused by S. neurona.

COMPLETION OF THE LIFE CYCLE OF SARCOCYSTIS NEURONA

Sarcocystis neurona is the most important cause of a neurologic disease in horses, equine protozoal myeloencephalitis (EPM). The complete life cycle of S. neurona, including the description of sarcocysts and intermediate hosts, has not been completed until now. Opossums (Didelphis spp.) are definitive hosts, and horses and other mammals are aberrant hosts. In the present study, laboratory-raised domestic cats (Felis domesticus) were fed sporocysts from the intestine of a naturally infected opossum (Didelphis virginiana). Microscopic sarcocysts, with a maximum size of 700 × 50 µm, developed in the muscles of the cats. The DNA of bradyzoites released from sarcocysts was confirmed as S. neurona. Laboratory-raised opossums (D. virginiana) fed cat muscles containing the sarcocysts shed sporocysts in their feces. The sporocysts were ∼10–12 × 6.5–8.0 µm in size. Gamma interferon knockout mice fed sporocysts from experimentally infected opossums developed clinical sarcocystosis, and S. neurona was identified in their tissues using S. neurona-specific polyclonal rabbit serum. Two seronegative ponies fed sporocysts from an experimentally-infected opossum developed S. neurona-specific antibodies within 14 days.

Utilization of stress in the development of an equine model for equine protozoal myeloencephalitis.

Neurologic disease in horses caused by Sarcocystis neurona is difficult to diagnose, treat, or prevent, due to the lack of knowledge about the pathogenesis of the disease. This in turn is confounded by the lack of a reliable equine model of equine protozoal myeloencephalitis (EPM). Epidemiologic studies have implicated stress as a risk factor for this disease, thus, the role of transport stress was evaluated for incorporation into an equine model for EPM. Sporocysts from feral opossums were bioassayed in interferon-gamma gene knockout (KO) mice to determine minimum number of viable S. neurona sporocysts in the inoculum. A minimum of 80,000 viable S. neurona sporocysts were fed to each of the nine horses. A total of 12 S. neurona antibody negative horses were divided into four groups (1-4). Three horses (group 1) were fed sporocysts on the day of arrival at the study site, three horses were fed sporocysts 14 days after acclimatization (group 2), three horses were given sporocysts and dexamethasone 14 days after acclimatization (group 3) and three horses were controls (group 4). All horses fed sporocysts in the study developed antibodies to S. neurona in serum and cerebrospinal fluid (CSF) and developed clinical signs of neurologic disease. The most severe clinical signs were in horses in group 1 subjected to transport stress. The least severe neurologic signs were in horses treated with dexamethasone (group 3). Clinical signs improved in four horses from two treatment groups by the time of euthanasia (group 1, day 44; group 3, day 47). Post-mortem examinations, and tissues that were collected for light microscopy, immunohistochemistry, tissue cultures, and bioassay in KO mice, revealed no direct evidence of S. neurona infection. However, there were lesions compatible with S. neurona infection in horses. The results of this investigation suggest that stress can play a role in the pathogenesis of EPM. There is also evidence to suggest that horses in nature may clear the organism routinely, which may explain the relatively high number of normal horses with CSF antibodies to S. neurona compared to the prevalence of EPM.

The Global One Health Paradigm: Challenges and Opportunities for Tackling Infectious Diseases at the Human, Animal, and Environment Interface in Low- Resource Settings

Zoonotic infectious diseases have been an important concern to humankind for more than 10,000 years. Today, approximately 75% of newly emerging infectious diseases (EIDs) are zoonoses that result from various anthropogenic, genetic, ecologic, socioeconomic, and climatic factors. These interrelated driving forces make it difficult to predict and to prevent zoonotic EIDs. Although significant improvements in environmental and medical surveillance, clinical diagnostic methods, and medical practices have been achieved in the recent years, zoonotic EIDs remain a major global concern, and such threats are expanding, especially in less developed regions. The current Ebola epidemic in West Africa is an extreme stark reminder of the role animal reservoirs play in public health and reinforces the urgent need for globally operationalizing a One Health approach. The complex nature of zoonotic diseases and the limited resources in developing countries are a reminder that the need for implementation of Global One Health in low-resource settings is crucial. The Veterinary Public Health and Biotechnology (VPH-Biotec) Global Consortium launched the International Congress on Pathogens at the Human-Animal Interface (ICOPHAI) in order to address important challenges and needs for capacity building. The inaugural ICOPHAI (Addis Ababa, Ethiopia, 2011) and the second congress (Porto de Galinhas, Brazil, 2013) were unique opportunities to share and discuss issues related to zoonotic infectious diseases worldwide. In addition to strong scientific reports in eight thematic areas that necessitate One Health implementation, the congress identified four key capacity-building needs: (1) development of adequate science-based risk management policies, (2) skilled-personnel capacity building, (3) accredited veterinary and public health diagnostic laboratories with a shared database, and (4) improved use of existing natural resources and implementation. The aim of this review is to highlight advances in key zoonotic disease areas and the One Health capacity needs.

A REVIEW OF SOME OF THE HEALTH ISSUES OF CAPTIVE BLACK RHINOCEROSES (DICEROS BICORNIS)

Abstract In captivity, black rhinoceroses (Diceros bicornis) are beset by many disease syndromes not described in black rhinoceroses in the wild. Hemolytic anemia, hepatopathy, and ulcerative dermatopathy that lead to increased morbidity and mortality characterize these syndromes. It is uncertain whether these are separate disease syndromes with different etiologies or the same disease with different manifestations. This article offers a brief review of some of the health issues of concern for the captive black rhinoceros population and proposes some possible avenues of research for consideration.

In vivo effects of adjunctive tetracycline treatment on refractory corneal ulcers in dogs

OBJECTIVE To evaluate effect of adjunctive treatment with tetracycline analogues on time to complete corneal reepithelialization in dogs with nonhealing (ie, refractory) corneal ulcers. DESIGN Randomized controlled clinical trial. ANIMALS 89 dogs with refractory corneal ulcers. PROCEDURES Corneal ulcers were treated via debridement and grid keratotomy. Dogs were assigned to receive 1 of 3 treatment regimens for up to 6 weeks: doxycycline (5 mg/kg [2.27 mg/lb], PO, q 12 h) with topically applied ophthalmic ointment containing neomycin, polymyxin B, and bacitracin (ie, triple antibiotic ointment; q 8 h); cephalexin (22 mg/kg [10 mg/lb], PO, q 12 h) with topically applied oxytetracycline ophthalmic ointment (q 8 h); or a control treatment of cephalexin (22 mg/kg, PO, q 12 h) with topically applied triple antibiotic ointment (q 8 h). Healing was monitored via measurements of the wound with calipers and evaluation of photographs obtained every 2 weeks. Treatment effectiveness was evaluated by wound healing and decreased signs of pain. RESULTS The Boxer breed was overrepresented in all groups. At the 2-week time point, wound healing was significantly more common in small-breed dogs, compared with large-breed dogs. Dogs treated with oxytetracycline ophthalmic ointment had a significantly shorter healing time than did dogs receiving the control treatment. Corneal ulcers in dogs that received doxycycline PO healed more rapidly than did ulcers in dogs in the control treatment group; however, this difference was not significant. CONCLUSIONS AND CLINICAL RELEVANCE Topical tetracycline ophthalmic ointment was a safe, inexpensive, and effective adjunctive treatment for refractory corneal ulcers in dogs.

Risk factors associated with cataracts and lens luxations in captive pinnipeds in the United States and the Bahamas.

OBJECTIVE To determine risk factors for lens luxation and cataracts in captive pinnipeds in the United States and the Bahamas. DESIGN Cross-sectional study. ANIMALS 111 pinnipeds (99 California sea lions [Zalophus californianus], 10 harbor seals [Phoca vitulina], and 2 walruses [Odobenus rosmarus]) from 9 facilities. PROCEDURES Eyes of each pinniped were examined by a veterinary ophthalmologist for the presence of cataracts or lens luxations and photographed. Information detailing husbandry practices, history, and facilities was collected with a questionnaire, and descriptive statistical analyses were performed for continuous and categorical variables. Odds ratios and associated 95% confidence intervals were estimated from the final model. RESULTS Risk factors for lens luxation, cataracts, or both included age >or= 15 years, history of fighting, history of ocular disease, and insufficient access to shade. CONCLUSIONS AND CLINICAL RELEVANCE Diseases of the lens commonly affect captive pinnipeds. Access to UV-protective shade, early identification and medical management of ocular diseases, and prevention of fighting can limit the frequency or severity of lens-related disease in this population. An extended life span may result from captivity, but this also allows development of pathological changes associated with aging, including cataracts.

Tear production in normal juvenile dogs

OBJECTIVE To establish a baseline range or average for tear production in normal juvenile dogs and evaluate the effects of age, weight, and gender on Schirmer tear test (STT) in juvenile dogs. MATERIALS AND METHODS Healthy puppies of various breeds <6 months of age. STT1 and STT2 were performed in both eyes of each subject. Statistical analysis was performed using a backwards stepwise regression model with repeated measures. Using continuous variables of STT1 and STT2 as the dependent variables separately, the independent variables were age (days), eye (left or right), gender (male or female), ocular disease processes in eyes or not, and weight (kg). RESULTS Eighty-six eyes from 27 males and 16 females were included in this study. Ages ranged from 25 to 133 (mean ± SEM: 61.74 ± 24.15) days and weights ranged from 0.88 to 8.86 (3.27 ± 2.22) kg. STT1 results ranged from 0 to 26 (15.76 ± 5.79) mm/min. STT2 results ranged from 0 to 24 (8.79 ± 5.01) mm/min. Age, weight, and gender significantly affected STT1 results. Weight and gender significantly affected STT2 results. STT1 values increased by 0.15 mm/min for each 1 day increase in age and by 0.84 mm/min for each 1 kg increase in body weight. STT2 values increased by 0.57 mm/min for each 1 kg increase in body weight. CONCLUSIONS Age, weight, and gender significantly affect tear production in normal juvenile dogs. STT1 increases to adult values at approximately 9-10 weeks of age.

RISK FACTORS ASSOCIATED WITH A SKEWED NATAL SEX RATIO IN CAPTIVE BLACK RHINOCEROSES (DICEROS BICORNIS) IN THE UNITED STATES

Abstract The skew toward males in the sex ratio of calves is considered to be a problem for the captive population of black rhinoceroses (Diceros bicornis) in North America. This study used a retrospective case-control design to determine whether there was a predisposition toward birth of male calves over female calves and to examine risk factors associated with the occurrence of any detected skewed natal sex ratio in captive black rhinoceroses in the United States. The study population included captive female black rhinoceroses housed in the United States that had given birth to at least one calf of known sex. This study confirmed a skewing of the natal sex ratio toward male calves in the captive black rhinoceros population. The skewed ratio was found in calves born to wild-born dams, for which an increased time in captivity, irrespective of age, was associated with an increased likelihood of a male calf. Dams between 12 and 19 yr of age had a decreased likelihood of a male calf. The data also suggested a possible trend for the southern subspecies of black rhinoceros (Diceros bicornis minor) to be more likely to produce male calves than the eastern subspecies (Diceros bicornis michaeli). No associations were found with the sex of offspring in captive-born dams; however, this lack of association could be a result of low power in the study.

Early outbreak detection using an automated data feed of test orders from a veterinary diagnostic laboratory

Disease surveillance in animals remains inadequate to detect outbreaks resulting from novel pathogens and potential bioweapons. Mostly relying on confirmed diagnoses, another shortcoming of these systems is their ability to detect outbreaks in a timely manner. We investigated the feasibility of using veterinary laboratory test orders in a prospective system to detect outbreaks of disease earlier compared to traditional reporting methods. IDEXX Laboratories, Inc. automatically transferred daily records of laboratory test orders submitted from veterinary providers in Ohio via a secure file transfer protocol. Test products were classified to appropriate syndromic category using their unique identifying number. Counts of each category by county were analyzed to identify unexpected increases using a cumulative sums method. The results indicated that disease events can be detected through the prospective analysis of laboratory test orders and may provide indications of similar disease events in humans before traditional disease reporting.