Indirect fluorescent antibody test in occult dirofilariasis

Area of Science:

• Veterinary Parasitology
• Immunology
• Canine Infectious Diseases

Background:

• Occult dirofilariasis, a heartworm infection without circulating microfilaria, presents diagnostic challenges.
• Understanding the immune response in occult infections is crucial for accurate diagnosis and management.

Purpose of the Study:

• To investigate the utility of indirect fluorescent antibody titers to Dirofilaria immitis microfilaria (IFA-mf) in diagnosing occult heartworm disease.
• To assess the correlation between IFA-mf titers, eosinophilia, and the presence of adult heartworms.

Main Methods:

• Experimentally infected dogs with occult Dirofilaria immitis infection were monitored for IFA-mf titers and peripheral eosinophilia.
• Angiocardiography was used to confirm the presence of adult worms.
• Dogs were monitored for up to 52 months, including post-treatment and re-infection phases.

Main Results:

• Antimicrofilarial antibodies (IFA-mf) were detected in dogs with occult dirofilariasis, with titers becoming apparent as microfilaremia ceased or from the end of the prepatent period.
• Significant IFA-mf titers (≥1:8) persisted after adulticide treatment and re-infection reestablished occult dirofilariasis.
• Peripheral eosinophilia was present in all infected dogs, peaking at specific intervals post-inoculation.

Conclusions:

• Indirect fluorescent antibody titers to Dirofilaria immitis microfilaria are valuable diagnostic markers for occult heartworm infection in dogs.
• Eosinophilia is a common indicator in dogs with occult dirofilariasis.
• The study confirms the presence of adult worms in experimentally infected dogs and highlights the potential for reinfection.