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Neospora caninum (Protozoa: apicomplexa) infections in mice
1Zoonotic Diseases Laboratory, U.S.D.A., Beltsville, Maryland 20705.
Abstract:
Groups of mice were given 0 mg, 4 mg, or 2 mg of methylprednisolone acetate (MPA) 7 days prior to, the day of, and 7 days after subcutaneous inoculation with 0 or 2 x 10(5) tachyzoites of Neospora caninum. Clinical signs of disease were seen only in mice given both MPA and N. caninum tachyzoites. Mice given 4 mg MPA and N. caninum tachyzoites developed severe disseminated neosporosis and most died or were killed when comatose 11-13 days postinoculation (PI). Acute pneumonia, polymyositis, encephalitis, hepatitis, and pancreatitis were the main lesions in these mice. Mice given 2 mg MPA and N. caninum developed mild pneumonia and many mice began showing neurological signs 14 days PI. Neurological signs consisted mainly of pronounced head-tilting and associated impairment of movement. Grossly visible 1-2-mm single or multiple, white areas of discoloration were seen in the brains of many of these mice. Encephalitis, ganglioradiculoneuritis, pneumonia, and polymyositis were the main changes seen in these mice. Tissue cysts of N. caninum were only seen in mice given 2 mg MPA and were first seen 21 days PI. Tissue cysts were 16-34 by 13-29 microns and had a 1.5-3.0-microns-thick cyst wall. Tissue cysts were seen only in the brain. Mice given 4 mg MPA and tachyzoites and host cells that had been frozen for 1 wk did not develop clinical signs of infection, indicating that freezing kills tachyzoites and that viruses or other agents were not involved in the genesis of disease seen in mice given MPA and viable tachyzoites.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Methylprednisolone acetate (MPA) exacerbates Neospora caninum infection in mice, leading to severe neosporosis and neurological signs. The immunosuppressive effects of MPA are critical for disease development in this model.
Area of Science:
- Veterinary Parasitology
- Immunology
- Pathology
Background:
- Neospora caninum is an important protozoan parasite causing significant economic losses in the livestock industry.
- The role of immunosuppression in the pathogenesis of neosporosis is not fully understood.
- Corticosteroids like methylprednisolone acetate (MPA) are known to modulate the immune response.
Purpose of the Study:
- To investigate the effect of methylprednisolone acetate (MPA) on the pathogenesis of Neospora caninum infection in a mouse model.
- To determine the dose-dependent effects of MPA on clinical signs, lesion development, and parasite burden.
Main Methods:
- Groups of mice were inoculated with Neospora caninum tachyzoites and treated with varying doses of MPA (0 mg, 2 mg, 4 mg) or placebo.
- Mice were monitored for clinical signs, neurological symptoms, and mortality.
- Lesions were assessed through histopathological examination of various organs.
- Presence and morphology of Neospora caninum tissue cysts were documented.
Main Results:
- Mice treated with MPA and infected with N. caninum exhibited clinical signs of neosporosis, unlike control groups.
- High-dose MPA (4 mg) resulted in severe disseminated neosporosis, high mortality, and widespread lesions including pneumonia, encephalitis, and hepatitis.
- Lower-dose MPA (2 mg) led to milder pneumonia, neurological signs (head-tilting), and the presence of tissue cysts primarily in the brain.
- Freezing of tachyzoites negated disease development, confirming the etiological role of viable N. caninum.
Conclusions:
- Methylprednisolone acetate (MPA) significantly exacerbates Neospora caninum infection in mice, demonstrating a critical role for immunosuppression in disease pathogenesis.
- The severity of neosporosis is dose-dependent on MPA administration.
- This study provides a valuable model for investigating therapeutic strategies against neosporosis under conditions of immunosuppression.