Full text
| |
| Author(s): |
Rafael Carneiro Costa
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD) |
| Defense date: | 2020-03-10 |
| Examining board members: |
Paulo César Maiorka;
Eric Francelino Andrade;
Cristina de Oliveira Massoco Salles Gomes;
Débora Ribeiro Orlando;
Mary Suzan Varaschin
|
| Advisor: | Paulo César Maiorka |
| Abstract | |
The present work comprises the study of different strains of Neospora caninum, from Brazil and Scotland, regarding their genetic characteristics, pathogenicity, virulence and attempts at isolation. The first chapter consists of an article published in the journal Veterinary Parasitology and describes an attempt to isolate parasite strains using placental tissue from naturally infected goats in a bioassay using gerbils. Although gerbils are described in the literature as highly susceptible to N. caninum infection, successful infection of animals has only been achieved after immunosuppression with high doses of methylpredinisolone. Immunosuppressed animals showed clinical signs of weight loss, fur and proprioception changes such as Head tilt. Histopathological analysis revealed inflammatory reactions in the brain consisting of multifocal mononuclear inflammatory infiltrates associated with perivascular cuffs, cyst-like and tachyzoite-like parasitic structures, along with areas of necrosis associated with macrophage inflammatory infiltrate and skeletal muscle scar formation. Despite the success in gerbil infection, it was not possible to obtain isolation of the parasite in cell culture in a first attempt, which led to the second part of the work. The chapter two consists of an article published in the journal Experimental Parasitology. Tissues from the previously described infected gerbils and new samples from the central nervous system of naturally infected goats were used in a bioassay using C57BL6 interferon gamma Knockout mouse (KO mice). Knockout mice, being unable to develop an adequate immune response to N. caninum, allowed the rapid replication of tachyzoites mainly in peritoneal macrophages, showing marked weight loss, lethargy and ascites 15 to 30 days after inoculation, when they were euthanized, and the peritoneal fluid used for infection of VERO cell monolayers. The large amount of tachyzoites in the peritoneal fluid of KO mice allowed their rapid adaptation and growth in cell culture, resulting in two goat isolates named NC- Goat1 and NC-Goat2. Both isolates were tested for pathogenicity in a widely used experimental BALB/c mouse infection model. The strains did not show high pathogenicity and virulence in the mouse infection model, although both strains were associated with clinical disease in goats, with abortions, stillbirths and encephalitis in young and adult goats. The third chapter presents the results of a genetic genotyping study of the isolates NC- Goat1 and NC-Goat2, clinical samples from goats and cattle from southern Minas Gerais and samples from cattle from the Dumfries and Galloway region of Scotland. Using the microsatellite genotyping technique, phylogenetic analyzes showed that N. caninum strains present in the isolates and clinical samples of goats had a close relationship with the Brazilian isolates NC-SP1, NC-Bahia and NC-Goiás, while the samples from Minas Gerais cattle did not correlate closely to the others. Analysing samples from Scottish herds, all tended to relate closely to each other and to other Scottish samples previously described in the literature. Additional analyses using microsatellite markers described by the Moredun Institute research group showed mixed genotypes associated with the standard N. caninum isolate (NC-1), suggesting that the isolate could have been composed of multiple genotypes on isolation and as it was replicated in cell culture they converged to a more homogeneous population of parasites. (AU) | |
| FAPESP's process: | 16/05010-2 - Isolation and pathogenicity evaluation of a new Neospora caninum strain from naturally infected goats |
| Grantee: | Rafael Carneiro Costa |
| Support Opportunities: | Scholarships in Brazil - Doctorate |