Borrelia burgdorferi infection is common in horses living in Lyme endemic areas and the geographic range for exposure is increasing. Morbidity after B. burgdorferi infection in horses is unknown. Documented, naturally occurring syndromes attributed to B. burgdorferi infection in horses include neuroborreliosis, uveitis, and cutaneous pseudolymphoma. Although other clinical signs such as lameness and stiffness are reported in horses, these are often not well documented. Diagnosis of Lyme disease is based on exposure to B. burgdorferi, cytology or histopathology of infected fluid or tissue and antigen detection. Treatment of Lyme disease in horses is similar to treatment of humans or small animals but treatment success might not be the same because of species differences in antimicrobial bioavailability and duration of infection before initiation of treatment. There are no approved equine label Lyme vaccines but there is strong evidence that proper vaccination could prevent infection in horses.

The objective of the current retrospective study was to describe naturally occurring type A botulism in horses in the United States. In the past 10 years, the Botulism Laboratory at the University of Pennsylvania's School of Veterinary Medicine has identified 3 isolated cases and 8 outbreaks of type A botulism in horses via samples positive for Clostridium botulinum type A toxin or spores using the mouse bioassay test. Additional information was obtained by review of submission forms and by telephone or email interviews. Almost all type A cases and outbreaks occurred in the western United States, with Oregon and Idaho overrepresented. Type A toxin was identified in only 1 outbreak; all other identified cases and outbreaks were positive for spores but not preformed toxin. Reported clinical signs included progressive muscle weakness, recumbency, decreased tail and/or tongue tone, dysphagia, respiratory distress, and death. Isolated cases involved foals ≤1 month of age; outbreaks involved horses ≥11 months. One hundred and nineteen horses were potentially exposed to the toxin source; 54 out of 119 showed signs of botulism, and 49 out of 54 affected horses were confirmed dead. The number of horses affected per outbreak ranged from 2 to 24. The source of infection was confirmed to be hay or silage in 6 out of 8 outbreaks and was unknown in 2 out of 8 outbreaks. The present report is the first description of outbreaks of type A botulism in horses and has important implications for prevention and treatment. Based on these findings, type A botulism should be considered in suspect cases of equine botulism in the western United States.

Background Recent research suggests that serum : CSF titer ratios could provide the most accurate antemortem diagnosis of equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona. Objectives The purpose of this study was to assess the utility of two commercially available tests, the indirect fluorescent antibody test (IFAT) and the surface antigen 2, 4/3 ELISA (SAG2, 4/3 ELISA), using archived paired serum and CSF samples. Animals Samples were obtained from 4 types of clinical patients. Confirmed positive cases (n = 9 horses; 11 sample sets) had neurologic deficits and postmortem lesions consistent with EPM. Confirmed negative cases (n = 28) had variable clinical signs and postmortem lesions consistent with another disease. Suspected positive cases (n = 6) had neurologic deficits consistent with EPM, marked improvement after treatment, and exclusion of other diseases. Suspected negative cases (n = 14) had variable signs with a strong presumptive diagnosis of another disease. Methods For each test, descriptive statistics were calculated using serum results alone, CSF results alone, and a serum : CSF titer ratio. Results Overall accuracy was highest for SAG2, 4/3 ELISA titer ratio at 0.97 (95% CI 0.88–0.99) with sensitivity = 0.88 (95% CI 0.66–0.97) and specificity = 1 (95% CI 0.92–1). IFAT CSF and titer ratio results also showed high accuracy at 0.88 (95% CI 0.77–0.94), but lower sensitivity = 0.65 (95% CI 0.41–0.83). Conclusions and Clinical Importance Using serum results alone was least accurate for both test types. The more accurate methods, such as the SAG2, 4/3 ELISA serum : CSF titer ratio, should be utilized.

Background: Prognosis associated with lymphoma in horses is poorly characterized, and treatment is often palliative. Long-term outcome after chemotherapy for horses with lymphoma is not well documented. Objective: To report long-term outcome of horses with lymphoma treated with chemotherapy. Animals: Fifteen equids. Methods: Retrospective case series. Medical record search and call for cases on the ACVIM listserv for horses treated with chemotherapy for lymphoma. Results: Fifteen cases with adequate data were identified. Complete remission was achieved in 5 horses (33.3%), partial response was achieved in 9 equids (60%), and stable disease was achieved in 1 horse. Overall response rate was 93.3% (14/15). Overall median survival time was 8 months (range, 1-46 months). Nine horses experienced a total of 14 adverse effects attributable to chemotherapy. Adverse effects were graded according to the Veterinary Cooperative Oncology Group common terminology criteria for adverse events grading system (grade 1 alopecia, n = 2; grade 1 neutropenia, n = 2; grade 1 lymphopenia, n = 3; grade 1 lethargy, n = 1; grade 2 neurotoxicity, n = 1; grade 2 colic, n = 1; grade 1 hypersensitivity, n = 1; grade 2 hypersensitivity, n = 2; grade 5 hypersensitivity, n = 1). Higher grade adverse effects most commonly were associated with doxorubicin administration (n = 4), including 1 horse that died 18 hours post-administration. Conclusions and Clinical Importance: Chemotherapy can be used successfully for treatment of horses with lymphoma. Adverse effects, most commonly mild, occurred in approximately two-thirds of treated horses.

Fibrinous parapneumonic pleural effusions are associated with decreased efficacy of pleural fluid drainage and increased risk of medical treatment failure in people, but similar associations have not been established in horses. We hypothesized that fibrin deposition in the pleural cavity of horses with parapneumonic effusions increases the risk of poor outcome. Seventy four horses with bacterial pleuropneumonia diagnosed by culture and cytology of tracheal aspirates, pleural fluid, or both, and pleural effusion diagnosed by ultrasonographic examination. Retrospective study of cases was from 2002 to 2012. Information obtained from the medical records included signalment, history, sonographic findings, treatments, and outcome. The primary outcome investigated was survival and secondary outcomes were development of complications and surgical intervention. Fisher's exact test and logistic regression were applied for categorical variables. A t-test was used to find differences in continuous variables between groups. Seventy four horses met study criteria and 50 (68%) survived. Fibrinous pleural effusion was associated with higher respiratory rate and pleural fluid height at admission, necrotizing pneumonia, increased number of indwelling thoracic drains required for treatment, and decreased survival. Fibrin accumulation in parapneumonic effusions is associated with increased mortality. Direct fibrinolytic treatment might be indicated in affected horses.