Verminous mastitis caused by Cephalobus cubaensis infection in a mare.

Overview

• This study reports a rare case of verminous mastitis caused by the nematode Cephalobus cubaensis in a mare, highlighting diagnostic challenges and treatment failure leading to euthanasia.

Case Presentation

• A 7-year-old American Quarter Horse mare was admitted for reproductive monitoring and endometritis management.
• During examination, nodular lesions were found on the mare’s mammary glands; their origin and duration were initially unknown.

Histological and Molecular Diagnosis

• Biopsies of the lesions revealed severe granulomatous mastitis containing intralesional rhabditid nematodes (a type of parasitic worm).
• Based on morphology, a tentative diagnosis of infection with either Cephalobus or Pelodera species was made.
• PCR was performed targeting specific gene sequences to identify the nematode species accurately, confirming Cephalobus cubaensis infection.

Treatment and Outcome

• Praziquantel ivermectin treatment (1.2 mg/kg orally) was administered every two weeks.
• The mammary lesions persisted despite four doses of ivermectin, indicating drug resistance or inefficacy.
• Due to lack of response and zoonotic risks (potential transmission to humans), euthanasia of the mare was elected.

Parasitological Findings

• Examination of skin tissue sediments retrieved eggs, larvae, and female nematodes characterized by blunt tails with mucro and a rhabditid-type esophagus; these morphological features are consistent with Cephalobus species.
• Spread of infection to the left inguinal lymph node was confirmed, showing systemic involvement.

Significance and Challenges

• Cephalobus species are normally saprophytic (live on decaying matter) nematodes rarely reported to cause verminous mastitis in horses.
• There is also a documented case of fatal meningoencephalitis in a human linked to Cephalobus, indicating potential zoonotic hazard.
• Morphologically, Cephalobus, Pelodera, and other rhabditid nematodes are very similar, making differentiation by histopathology alone unreliable.
• Accurate molecular identification, such as PCR genotyping, is essential for correct diagnosis and epidemiological understanding.

Implications

• This case underscores the need for clinicians to consider rare parasitic infections in differential diagnoses of equine mastitis.
• Therapeutic challenges exist, including possible ivermectin resistance and zoonotic risks, which may necessitate drastic decisions like euthanasia.
• Improved molecular diagnostic tools are critical to differentiate among morphologically similar nematode species to inform appropriate treatment and control measures.