Muscle spasms associated with ear tick (Otobius megnini) infestations in five horses.

The research discusses how five horses with ear tick infestations developed severe muscle cramping not linked to physical exercise. Symptoms were often mistaken for signs of colic, and while serum electrolytes and acid-base balance remained normal, specific enzyme activities were moderately high. No muscle biopsy abnormalities were found, except for some necrotic muscle fibers. Muscle spasms stopped only when ear tick treatment began.

Observation and Misinterpretation of Symptoms

• The study begins with the observation of severe, non-exercise related muscle cramping in five horses. This phenomenon was recognized by intermittent visible muscular contraction in different areas on the horses.
• Surrounding symptoms included the temporary prolapse of the third eyelid, sweating, pawing, muscle tremors, and muscle fasciculations or twitching of small areas of muscle under the skin.
• These clinical symptoms were initially interpreted as signs of colic. Colic in horses refers to abdominal discomfort, which can manifest via the symptoms described such as sweating and pawing.
• This misinterpretation reinstates the point that the symptoms were unusual and not traditionally associated with muscular issues, thus leading to confusion in diagnosis.

Investigation and Findings

• Muscular contraction was induced by percussion, another indicator of muscular health abnormalities.
• When analyzed, the horses’ concentrations of serum electrolytes and acid-base balance were found within the normal limits, ruling out conditions such as dehydration or metabolic disorders.
• However, activities of creatine kinase and aspartate transaminase, enzymes associated with muscle damage or inflammation, were moderately high. This pointed towards some form of muscular damage or stress.
• Further investigation through a muscle biopsy revealed no widespread abnormalities, only a few necrotic muscle fibers undergoing phagocytosis, the disposal of dead or dying cells.
• Electromyography of one horse indicated increased motor unit activity, further supporting the evidence of muscle damage or abnormal activity.

The Underlying Cause: Ear Tick Infestations

• The common thread among these horses turned out to be infestations with Otobius megnini, also known as the ear tick.
• The infestation was making the horses’ muscles go into spasms, and despite muscle cramps being a highly unusual symptom of tick infestations, this was the only commonality found among the horses.
• The recurrence of muscular symptoms until the treatment for ear ticks demonstrates the correlation for the cause of these unusual muscle spasms.

Implication of the Findings

• This research implies a yet unexplored area for muscle spasms in horses, linked to tick infestations.
• It is an important finding for the veterinary community as it may help to prevent misdiagnosis in the future.
• Moreover, it raises the need for further studies on the exact link between such infestations and muscular behavior in horses and possibly other animals.