Putative Otobius megnini -associated clinical signs in horses in South Africa (2012–2018)

Sean M Miller

doi:10.4102/jsava.v91i0.1983

Abstract

Otobius megnini has been associated with certain clinical conditions in horses in both California and Mexico. A number of cases similar to those described previously have been identified by the author in South Africa. This case report summarises these cases to demonstrate that the clinical condition occurs readily in South Africa and may be increasing in occurrence. The disease has minimal coverage in the literature making it more likely that a veterinarian, unfamiliar with the disease, will miss the diagnosis. The author would like to make veterinarians aware of this as a potential differential diagnosis. This study is a retrospective review of clinical data. Clinical records of patients with similar clinical signs and treatment were reviewed and grouped together as relevant cases for this case report. Ten cases of O. megnini associated neuromuscular dysfunction are reported, suggesting a link between the occurrence of the tick and the clinical condition. Clinical signs include third eyelid prolapse, localised muscle fasciculations, elevated heart rate and limb stamping. Serum chemistry changes commonly show increased aspartate aminotransferase and creatine kinase enzymes activities. The occurrence of the ticks within South Africa and the increasing number of cases presented demonstrate the need for more investigation into the pathophysiology of this condition.

Highlights

Otobius megnini-associated disease in equines has been reported by Madigan et al, showing an association of the tick and clinical disease in five horses in 1995 in California (Madigan et al 1995:74–76), whilst Zarate-Ramos et al (2014) described a similar case attributed to O. megnini in Mexico in 2014 (Zarate-Ramos et al 2014:16–20)
No neurotoxin has been described for this tick and it is possible that there may be neuromuscular dysfunction (Aleman 2011:481–506) alone or in relation to neurotoxin involvement (Pecina 2012:531–532)
Suspected paralysis of a human patient associated with O. megnini was reported in 1958 in South Africa (Peacock 1958:201–202)

Summary

Introduction

Otobius megnini-associated disease in equines has been reported by Madigan et al, showing an association of the tick and clinical disease in five horses in 1995 in California (Madigan et al 1995:74–76), whilst Zarate-Ramos et al (2014) described a similar case attributed to O. megnini in Mexico in 2014 (Zarate-Ramos et al 2014:16–20). A report in Canada of euthanasia of horses because of ‘demented horses’ had necropsy findings that revealed large numbers of O. megnini in the ear canals with associated necrosis of the auricular and adjoining nerves. A number of cases, similar to those described by Madigan (1995:74–76) and Zarate-Ramos et al (2014:16–20), have been identified by the author in KwaZulu-Natal, South Africa. This case report summarises these cases to demonstrate that this is a clinical condition that occurs readily in this region. The increase in prevalence would indicate a need for more investigation into the pathophysiology of this condition

Materials and methods

Unilateral lower abdominal wall

Discussion