Clinical and Clinicopathological Factors Associated with Survival in 44 Horses with Equine Neorickettsiosis (Potomac Horse Fever)

Abstract

Background: The epidemiology of equine neorickettsiosis (EN) has been extensively studied but limited clinical and clinicopathological data are available concerning naturally infected horses.Hypothesis: Factors predictive of survival will be identified in horses diagnosed with EN. Animals: Convenience sample of 44 horses with EN admitted to 2 referral institutions. Methods: A retrospective study was performed. A diagnosis of EN was based on the presence of positive blood or fecal PCR.Results: The most common clinical signs included diarrhea (66%), fever (50%), anorexia (45%), depression (39%), colic (39%), and lameness (18%). The median duration of hospitalization was 6 days and 73% of horses survived to discharge. Laminitis was present in 36% of horses, 88% of which were affected in all 4 feet. Serum creatinine and urea nitrogen concentrations, as well as RBC count, blood hemoglobin concentration, hematocrit, band neutrophils, serum AST activity, serum CK activity, and anion gap, were significantly (P < .05) higher in nonsurvivors. Serum chloride and sodium, concentrations as well as duration of hospitalization were significantly lower in nonsurvivors. The results of forward stepwise logistic regression indicated that blood hemoglobin concentration on admission and antimicrobial treatment with oxytetracycline were independent factors associated with survival.Conclusions and Clinical Importance: Severity of colitis as reflected by electrolyte loss, hemoconcentration, and prerenal azotemia were predictors of survival in horses diagnosed with EN. Treatment with oxytetracycline was associated with increased survival.

Overview of Clinical Pathology and the Horse

“…PCR evaluation of diarrheic fecal samples is rewarding for establishing an infectious cause. [64][65][66][67][68] Malabsorptive enteric disease Malabsorption occurs in the horse when there is damage to the intestinal mucosa/ submucosa, which can result from inflammation that develops as the result of antigen/ antibody reactions, food intolerance, and true hypersensitivity lesions. The role of the cyathostomes must also be considered as they encyst and then can emerge in large numbers with disruption in the mucosa/submucosa that triggers fibrosis, which impedes absorption.…”

Epidemiological survey of Neorickettsia risticii in equids from the State of Rio de Janeiro, Brazil

“…The evaluation of clinical parameters and some physiological disorders were considered as an important tool for assist the differential diagnosis of this disease, since animals that presented signs suggestive of infection by N. risticii, such as depression, fever, limb edema, dehydration and colic and diarrhea syndrome (Dutta et al 1985, Mulville 1991, Dutra et al 2001, Bertin et al 2013, did not necessarily present infection by this agent.…”

Clinical Approach to Commonly Encountered Problems

“…554,555 Salmonella is of particular importance because under certain circumstances it can be highly contagious, leading to significant outbreaks of disease, especially in hospitalized patients. 562 Lawsonia intracellularis can cause equine proliferative enteropathy resulting in diarrhea, colic, edema, and weight loss. 552,[557][558][559][560][561] In certain geographic areas equine neo rickettsiosis (Potomac horse fever) caused by Neorickettsia risticii is also common.…”

“…335,539,563,572,613,614 Both rotavirus and coronavirus can also be identified in the feces by electron microscopy. [562][563][564]612,614 In the case of N. risticii, the serologic tests are of limited value in the diagnosis of disease. 539,616 Serologic methods, evaluating the presence of antibodies, have been used in the diagnosis of Neorickettsia risticii and Lawsonia intracellularis.…”

“…539,572,615 A number of commercial assays are also available for the detection of rotavirus antigen. 562 For L. intracellularis, it is recommended to use both PCR and serologic diagnostic testing as these assays have high analytic specificity but variable sensitivity depending on the circumstances. [562][563][564]612,614 In the case of N. risticii, the serologic tests are of limited value in the diagnosis of disease.…”