Evaluation of potential predictor variables for PCR assay diagnosis of Anaplasma phagocytophilum infection in equids in Northern California

Inflammatory and Immune-Mediated Myopathies, What Do We Know?

Inflammatory myopathies or myositis encompass diseases characterized by the presence of inflammatory cellular infiltrates, mainly polymorphonuclear cells and/or lymphocytes, in muscle. This is in contrast to most forms of muscle disease characterized by myodegeneration that results in macrophage infiltration. Inflammatory myopathies could have infectious or noninfectious causes. Noninfectious causes consist of primary (genetic, autoimmune) or acquired immune-mediated disease. Focal, multifocal or diffuse, acute or recurrent forms of disease can occur. This article will mainly review immune-mediated myopathies in horses. Myositis directly caused by infection such as Clostridium spp and others will not be discussed here.

Common and atypical presentations of Anaplasma phagocytophilum infection in equids with emphasis on neurologic and muscle disease

BACKGROUND

Comprehensive descriptions of equids with granulocytic anaplasmosis (EGA) with neurologic or muscle disease and other atypical presentations are scarce in the literature.

OBJECTIVE

Describe the clinical signs, laboratory findings, treatment, and outcome of equids with EGA with emphasis on neurologic and muscle disease.

ANIMALS

Thirty-eight horses, 1 donkey.

METHODS

Retrospective study. Equids with EGA were included. The electronic data base was searched from January 2000 to December 2022 using the words anaplasmosis, ehrlichiosis, granulocytic, and rickettsia. Signalment and clinical data were reviewed. Data were evaluated for normality using Shapiro-Wilk test. Parametric and nonparametric statistics were used for normally and non-normally distributed data.

RESULTS

Common (41%) and other (59%) presentations were seen in horses ≥ 4 years of age (median, 14 years) with an overrepresentation of males (77%). Neurologic disease was common (41%), mainly presenting as diffuse symmetrical proprioceptive ataxia. Brain disease was less common manifesting as obtundation and cranial nerve deficits. Muscle disease was less common, with QH breeds with the variant causing myosin heavy chain myopathy (MYHM) having severe disease. Cavitary effusion, cardiomyopathy and disseminated intravascular coagulation (DIC) were uncommon. Clinical laboratory results varied depending on disease stage. Muscle enzyme activities were significantly higher in horses with muscle disease. Outcome was favorable with prompt tetracycline treatment. Death and long-term sequelae were not reported.

CONCLUSIONS AND CLINICAL IMPORTANCE

Common and atypical presentations of EGA have a favorable outcome with prompt tetracycline treatment. Quarter horse breeds with muscle disease should be genotyped for MYHM.

Transfer of naturally acquired specific passive immunity against Anaplasma phagocytophilum in foals in Southeastern Pennsylvania and Northern Maryland

BACKGROUND

Equine granulocytic anaplasmosis (EGA) is a common disease in adult horses, but clinical disease in foals is rarely reported. The relationship between equine maternal and neonatal antibodies to Anaplasma phagocytophilum is unclear.

HYPOTHESIS/OBJECTIVES

That mares in an endemic region would be seropositive for A. phagocytophilum and that mare and foal serum IgG concentrations for A. phagocytophilum would correlate. Additionally, we hypothesized that foal IgG concentrations for A. phagocytophilum acquired by passive immunity would decline by 6 months of age.

ANIMALS

Twenty-two healthy mare-foal pairs.

METHODS

This prospective observational study investigated serum IgG concentrations specific for A. phagocytophilum in mares and foals using an immunofluorescent antibody test (IFA). The association between foal titer (as a binary variable) and age in months was assessed using a mixed-effects logistic regression.

RESULTS

A positive correlation between newborn foal antibody titers and mare titers was identified at both the pre-foaling (τa  = 0.38, τb  = 0.50, P = .009) and foaling timepoints (τa  = 0.36, τb  = 0.47, P = .01). In A. phagocytophilum seropositive neonates, it was unlikely that a positive titer would be detected by 3 months of age (OR = 0.002, P = .02, 95% CI: 0.00001-0.38). Three out of 20 foals seroconverted between 3 and 6 months of age.

CONCLUSIONS AND CLINICAL IMPORTANCE

Transfer of specific passive immunity to A. phagocytophilum occurred in 80% of foals born to seropositive mares and declined by 3 months of age. A. phagocytophilum infection should be considered in foals displaying clinical signs consistent with EGA.