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Histopathologic features of canine heartworm microfilarial infection after treatment with ivermectin
Abstract:
Tissues of dogs treated with ivermectin were examined microscopically to learn the fate of microfilariae of canine heartworm that disappear from the peripheral circulation within a few days of treatment. Medicated dogs were killed 18 hours, 3 days, and 6 days after treatment with 0.5 mg of ivermectin/kg of body weight subcutaneously. Ivermectin was dissolved in 60% propylene glycol and 40% glycerol formal. In dogs killed at posttreatment hour 18, the peripheral microfilaremia had decreased by an average of 89%. At this time, a dense mass of RBC, WBC, and macrophages plus many microfilariae was found in pulmonary alveolar septae. Similar reactions were seen in liver, kidney, and spleen. Phagocytosis of microfilarial fragments was evident. In dogs killed at posttreatment day 3, many microfilariae were fragmented and phagocytosis of the fragments was common. In dogs killed at posttreatment day 6, microgranulomas were common, particularly in such vascular organs as lungs, kidney, and liver. Microgranulomas containing microfilariae were also seen in spleen, skeletal and cardiac muscles, diaphragm, lymph nodes, gastrointestinal tract, and pancreas. Small glial nodules were seen in the CNS. Denudation of the atrial epicardium was associated with fragments of microfilariae and granulomatous inflammatory cells. Renal epithelial crescents were observed in treated and nontreated dogs. Plasma cells were conspicuous in treated and nontreated dogs, especially in some livers and kidneys. Before treatment, all dogs were severely microfilaremic. At the end of the experiment, the peripheral microfilaremia was reduced by 98%.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Ivermectin treatment rapidly eliminates canine heartworm microfilariae, causing them to accumulate and be phagocytosed in various dog tissues, leading to significant microfilaremia reduction.
Area of Science:
- Veterinary Parasitology
- Pharmacology
- Pathology
Background:
- Canine heartworm (Dirofilaria immitis) infection is a serious parasitic disease.
- Microfilariae, the larval stage, circulate in peripheral blood.
- Ivermectin is a common treatment for heartworm disease.
Purpose of the Study:
- To investigate the fate of microfilariae after ivermectin treatment in dogs.
- To identify the tissues where microfilariae accumulate and are eliminated.
Main Methods:
- Dogs with severe microfilaremia were treated subcutaneously with ivermectin.
- Tissues were collected at 18 hours, 3 days, and 6 days post-treatment.
- Microscopic examination of tissues to identify microfilariae and inflammatory responses.
Main Results:
- Ivermectin treatment reduced peripheral microfilaremia by 98%.
- Microfilariae accumulated in pulmonary alveolar septae, liver, kidney, and spleen within 18 hours.
- Fragmentation and phagocytosis of microfilariae were observed by day 3.
- Microgranulomas containing microfilariae formed in multiple organs by day 6.
Conclusions:
- Ivermectin effectively clears circulating microfilariae.
- Degenerating microfilariae trigger inflammatory responses and are phagocytosed in various tissues.
- The study elucidates the tissue distribution and clearance mechanisms of microfilariae post-ivermectin therapy.