Experimental neosporosis in chickens (Gallus gallus domesticus) with oocysts and tachyzoites of two recent isolates of Neospora caninum reveals resistance to infection

Authors: OLIVERIA, SOLANGE - Universidad De Sao Paulo; AIZAWA, JULIANA - Universidad De Sao Paulo; SOARES, HERBERT - Universidad De Sao Paulo; CHIEBO, DANIELA - Universidad De Sao Paulo; DE CASTRO, BOTELHO - University Of Brazil; HORA, ALINE - Universidad De Sao Paulo; LOPES, MARCOS - Universidad De Sao Paulo; SCHARES, GEREON - Federal Research Institute; Jenkins, Mark; Kwok, Oliver; Dubey, Jitender; GENNARI, SOLANGE - Universidad De Sao Paulo; PENA, HILDA - Universidad De Sao Paulo

Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2017
Publication Date: 2/9/2018
Citation: Oliveria, S., Aizawa, J., Soares, H., Chiebo, D., De Castro, B., Hora, A., Lopes, M., Schares, G., Jenkins, M.C., Kwok, O.C., Dubey, J.P., Gennari, S., Pena, H. 2018. Experimental neosporosis in chickens (Gallus gallus domesticus) with oocysts and tachyzoites of two recent isolates of Neospora caninum reveals resistance to infection. International Journal for Parasitology. 48: 117–123.

Interpretive Summary: Toxoplasmosis, caused by the single-celled parasite, Toxoplasma gondii, continues to be a public health problem. Neospora caninum is an ancestorily and morphologically similar parasite to T.gondii and until 1988, they were considered the same organism. However, these parasites are biologically distinct. Unlike T. gondii. N. caninum is not of public health importance but it causes severe economic losses to dairy industry. Many aspects of the life cycle of N. caninum are still unknown. In the present study, authors report that chickens are resistant to experimental N. caninum infection, and probably not important in the biology of this parasite. These results will be of interest to parasitologists and biologists.

Technical Abstract: The importance of birds in the biological cycle of Neospora caninum is not clear. Here, we report unsuccessful Neospora infection in Chickens (Gallus gallus domesticus) using two isolates of N. caninum. In experiment #1 conducted in Brazil, 30 White Leghorn chickens were orally inoculated with viable N. caninum oocysts (NC-SP1 isolate, 200 oocysts per bird) via the crop at 21 days of age and observed for 10 weeks. Blood samples were collected weekly, and sera were tested using the indirect fluorescent antibody test (IFAT, cut-off 1:5). Chicken tissues were collected for molecular analysis (PCR and qPCR) and immunohistochemistry (IHC). The chicken tissues were bioassayed in two dogs approximately 45 days of age by feeding tissues from chickens euthanized at 138 and 159 days post-inoculation (p.i.). The results indicated that chickens are resistant to neosporosis as revealed by failure to seroconvert, failure to detect parasite DNA or detect N. caninum antigen in inoculated bird tissues by IHC, and no oocyst excretion by the dogs fed avian tissues. Similar results were obtained in experiment #2 conducted in USA, in which 40 one-week old chickens were each subcutaneously inoculated with 100,000 viable tachyzoites of the NcWTDMn1 isolate of N. caninum. The chickens were euthanized on days 7, 15, 22, 28, 36 and 60 p.i. At necropsy, all tissues and serum from each bird were collected. All chickens remained asymptomatic, and N. caninum antigen was not detected in histological sections of tissues by IHC. Seven chickens euthanized at day 60 p.i. developed low (1:25 dilution) level of antibodies by using the Neospora agglutination test (NAT). Two 12-week-old dogs fed tissues pooled from 10 inoculated chickens euthanized day 60 p.i. did not excrete N. caninum oocysts. Results of this investigation indicate that chickens are resistant to experimental infection by N. caninum.