Randomized Controlled Trial Evaluating Adeno-MOMP and MOMP DNA Vaccines Against Chlamydophila psittaci Challenge in Cockatiels (Nymphicus hollandicus)

by Sanchez-Migallon Guzman, David

Chlamydophila psittaci causes severe disease in birds and humans, and important economical losses in the avian companion and poultry industry. Vaccines are the most cost-effective measure to control and help prevent infectious diseases, but to date there is no commercial vaccine available. A randomized clinical trial was conducted to assess the efficacy of two recombinant DNA vaccines against C. psittaci in Cockatiels (Nymphicus hollandicus). The first recombinant DNA vaccine has a gene encoding MOMP and the immunostimulant chitosan (MOMP DNA vaccine). The second recombinant DNA vaccine, contained the gene encoding MOMP that was vectored by a replication defective human adenovirus (adeno-MOMP vaccine). Forty adult cockatiels (Nymphicus hollandicus) were used for this study, and divided into each of the vaccinated groups (n=10), positive control (n=10) and a negative control (n=10). The animals were vaccinated on days 0 and 21 with the corresponding vaccine (DNA MOMP vaccine group, adeno-MOMP vaccine group, negative control group) or placebo (positive control group), and both vaccine groups and the positive control were challenged on day 42 Receiving 0.1 ml of inoculum IN containing approximately 106 C. psittaci live organisms. The negative control group was not challenged with any live organisms. The animals were monitored daily for the presence of rhinitis, conjunctivitis, dyspnea, diarrhea and depression. On days 46, 49, 52, 55, 70 and 82, combined choanal and cloacal swabs were taken and submitted for C. psittaci PCR. The surviving birds were tested on day 82 for antichlamydial antibodies (IFA) and for the presence of C. psittaci (PCR) from whole blood and combined choanal-cloacal swabs, and then humanely euthanized. The birds were submitted for necropsy and examined for the presence of macroscopic lesions on conjunctiva, lungs, airsacs, heart, spleen and liver. Individual samples from each of those tissues were taken for histopathology and pooled samples were submitted for C. psittaci culture. There was a failure to detect antibody response by indirect immunofluorescent assay. The cockatiels developed mild clinical signs and minimal mortality after challenge. The necropsy and histopathologic evaluation of the tissues revealed mild to moderate lesions and no significant difference with positive control. Further studies are needed to evaluate the efficacy of the vaccines.