Severe acute rhabdomyolysis associated with Streptococcus equi infection in four horses.

This research article focuses on the study of four horses with severe acute rhabdomyolysis associated with Streptococcus equi infection. It uncovers that despite aggressive medical treatment, most of the animals deteriorated rapidly; except one who made a full recovery.

Methodology and Findings

• Four Quarter Horses with submandibular lymphadenopathy (swelling of the lymph nodes in the submandibular region) and firm muscles indicating pain were examined. Their clinical symptoms included a stiff gait and three out of four became recumbent (lying down).
• The infection of Streptococcus equi, a bacteria that is common in equines, was confirmed through cultures from aspirates of lymph nodes or purulent (pus-filled) material collected from the auditory tube diverticula of the horses.
• Despite aggressive treatment with antimicrobials and anti-inflammatories, the horses’ condition rapidly deteriorated, leading to euthanasia within 24 to 48 hours for three of the subjects.
• The one horse that did not become recumbent was the sole survivor and eventually recovered fully.

Clinicopathologic Findings and Necropsies

• Clinicopathologic examinations found common symptoms among the four horses including neutrophilia (an increase in number of white blood cells), hyperfibrinogenemia (excess fibrinogen in the blood), and increased serum activities of creatine kinase and aspartate aminotransferase, both indicative of muscle damage.
• Necropsies of the three euthanized horses revealed damages, highlighted by large, pale areas especially evident in certain muscles, which were characterized by severe acute myonecrosis (muscle cell death) and infiltration of macrophages (a type of white blood cells) into necrotic (dead) myofibers.
• Immunofluorescent stain tests for Lancefield group C carbohydrate and S. equi M protein further established the presence of Streptococcus equi in the sections of affected muscle.

Conclusion

• The presence of acute severe rhabdomyolysis (a serious syndrome due to direct or indirect muscle injury) in the horses was associated with S. equi infection, without any clinical evidence of muscle atrophy or infarction (tissue death due to lack of blood supply).
• The reason for rhabdomyolysis was attributed to a possible inflamation response similar to streptococcal toxic shock or potentially direct toxic effects of S. equi within the muscle tissues.