Authors : Laura Garcia Celis , Jehieli Girela alvarez , Beatriz Arellano-Reynoso , Victor Tenorio Gutierrez , Francisco Aguilar Romero , Pedro Mejia Sanchez , Francisco Suarez-Guemes and Efren Diaz-Aparicio
Abstract: There are no assays of experimental infection of sheep with Histophilus somni and their immune response. In order to know the humoral immune response of sheep experimentally infected by respiratory tract with H. somni, 19 male, 6 month-old sheep were immuno-suppressed with dexamethasone, 1 day before being inoculated with Parainfluenza 3 virus and during 5 days after viral inoculation. Seven days after viral inoculation, one animal was slaughtered in order to observe lesions caused by the virus. Another 12 animals were inoculated intratracheally with H. somni (1×109 UFC mL 1), leaving 6 animals as controls that received same pathway sterile PSS. Heart and respiratory rates were taken, as well as rectal temperature, during 14 days after challenge. Serum and nasal exudate samples were collected to determine IgG, IgM and IgA levels by indirect ELISA test, using H. somni 40 kDa outer membrane protein as antigen. Two sheep from the inoculated group and one from the control group were humanely euthanized every week during 6 weeks. Samples were collected from lung, tonsils, retropharyngeal and mediastinal lymph nodes; bacteriology studies were carried out in duplicate and DNA was extracted to perform PCR with primers designed for 16S ribosomal region in H. somni. Infected animals had temperature and respiratory rate increase, cough and mucopurulent nasal exudate; areas in the apical lung lobule were consolidated and there were adherences as well as. H. somni was isolated from only one animal from retropharyngeal node. Nevertheless, from nasal exudate samples, 11 of 12 infected sheep came out positive by PCR while the 6 non-infected controls were negative. ELISA test results for IgG were significantly different between infected and control animals at days 4 and 7 after inoculation, while no differences were found in IgM and IgA. It was concluded that in sheep experimentally infected, H. somni caused an IgG isotype humoral immune response. The presence of the bacteria could be detected by PCR in 91.66% of the animals. Even though the strain used in this research was previously passed through sheep, it did not cause lesions or signs that could suggest infection and it could not be recovered by bacteriology in most of the infected sheep.
Laura Garcia Celis , Jehieli Girela alvarez , Beatriz Arellano-Reynoso , Victor Tenorio Gutierrez , Francisco Aguilar Romero , Pedro Mejia Sanchez , Francisco Suarez-Guemes and Efren Diaz-Aparicio , 2007. Humoral Immune Response Assessment in Sheep Experimentally Infected with Histophilus somni and Previously Inoculated with Parainfluenza 3 Virus . Journal of Animal and Veterinary Advances, 6: 681-685.