Epidemiological modelling of chlamydial abortion in sheep flocks

Chlamydophila (C.) abortus, responsible for chlamydial abortion (commonly known as Enzootic Abortion of Ewes [EAE]), causes major financial losses to the sheep industry worldwide. There remain many uncertainties surrounding the epidemiology of EAE. The aim of this study was to construct an epidemiological model to simulate EAE based on current knowledge of the disease, and in doing so, identify knowledge gaps that need to be addressed through further research. Key parameters that impact upon the development of the disease, such as the rate of contact between na?ve ewes and infected material, are defined. Sensitivity analysis was undertaken for parameter values that are unknown to explore their impact upon the pattern of disease. The simulated results show the importance of the transmission rate (i.e. contact) and the number of infected replacements introduced at the start of an outbreak. Depending upon the rate of transmission, the year in which the peak number of affected ewes occurs and the number of years over which a high number of animals are affected varies. This suggests that a better understanding of the underlying processes that drive transmission of C. abortus is needed. Furthermore, if infected ewes could be identified prior to parturition, when they shed the organism in large numbers, the impact of EAE on sheep flocks could be greatly reduced.     

A role for tryptophan in immune control of chlamydial abortion in sheep

Tryptophan (Trp) catabolism appears to be an important mechanism for regulation of inflammatory responses, resulting in T-cell tolerance and survival of semi-allogeneic concepti during pregnancy. Trp catabolism can be induced by IFN-gamma, and is therefore an important host defence mechanism against intracellular pathogens. Chlamydophila abortus is a bacterial pathogen that can cause persistent infection in non-pregnant sheep, but invades the placenta and causes abortion in late pregnancy. IFN-gamma was found to control the growth of Chlamydophila abortus in ovine cells in a highly dose-dependent manner. Addition of 200U/ml IFN-gamma eradicated all traces of infection from the cultures, whereas concentrations less than 50U/ml failed to control the growth of the organism, resulting in cell lysis. However, concentrations in the range of 50-100U/ml were found to restrict growth to an extent that a persistent infection was established, allowing survival of the organism in tissue culture for several months. Removal of IFN-gamma resulted in the re-appearance of infectious organisms. Addition of exogenous Trp to the cells treated with 50-100U/ml IFN-gamma prevented the establishment of persistence. These effects in tissue culture are analogous to the persistent infection observed in pregnant sheep prior to abortion. These data suggest that control of C. abortus growth in the periphery is linked to the balance of pro-inflammatory cytokine production and availability of Trp during pregnancy.     

A skin allergy test in chlamydial abortion in sheep]

46 head of pregnant sheep, the Tsigaya breed, were subjected to the skin allergy test and subsequently divided into two groups. Sheep were in the 3rd month of gravidity and were a part of a flock consisting of 300 head, in which chlamydia-induced abortion was recorded in sheep. The skin allergic test was done by the Rodolakis et al. (1977) method, modified by us, to indicate the level of cell-mediated immune response. Simultaneously with it, serological examinations (complement fixation test--CFT) were performed to find out the levels of antibody against Ch. psittaci. The results of skin allergy test (SAT) and serological examination in sheep after bivalent vaccine administration are given in Tab. II. Of the total number of sheep ranked to vaccinated group, 18 head responded positively on SAT. After vaccination, 12 head responded positively though previously responded negatively. In vaccinated group one abort recorded in the sheep. No. 12 which was on the 0 day slightly positive in the skin test. High levels of antibody were found after abortion and the skin test was highly positive. The results of SAT and serological examination in sheep, when placebo was administered, are given in Tab. III. 6 sheep aborted in the group, placebo was administered, are given in Tab. III. 6 sheep aborted in the group, of which 5 were negative and one was slightly positive on the day 0 in SAT. In 4 sheep abort was accompanied with significant increase in humoral antibody against Ch. psittaci. In sheep which aborted and were negative in SAT on the day 0, a marked positivity has been indicated in the replicated SAT test.(ABSTRACT TRUNCATED AT 250 WORDS)     

Field evaluation of a PCR for the diagnosis of chlamydial abortion in sheep

A total of 94 vaginal swab samples and 195 serum samples collected from aborted ewes in 15 flocks were examined by pcr and a complement fixation test, respectively. In addition, 172 samples of stomach contents from fetuses from different flocks submitted for the diagnosis of abortion during the four lambing periods between 2000 and 2004 were tested by pcr. Chlamydial dna was detected in seven vaginal swabs obtained from five of the 15 flocks and in six samples of fetal stomach contents. The results of pcr and flock serology for Chlamydia were positive in five of the 15 flocks and negative in eight.     

Immunosuppression in toxoplasmosis: studies in sheep with vaccines for chlamydial abortion and louping-ill virus

Toxoplasma gondii infection was established in sheep seven days (acute infection) or 28 days (chronic infection) before they were given enzootic abortion (EAE) vaccine alone or simultaneously with louping-ill (LI) vaccine. Uninfected controls received the same vaccination schedule. The serological response of acute toxoplasma-infected sheep to initial LI vaccination was significantly depressed but after revaccination four weeks later these sheep demonstrated a response equal to that of the revaccinated controls. Infected sheep also gave a significantly poorer response to EAE vaccine than control animals, the effect being more marked in those with chronic infection. Revaccination evoked no clear response in any group but on three of five sampling days antibody titres of controls were significantly higher than those of infected sheep.     

Molecular evidence for chlamydial infections in the eyes of sheep

Ocular infections by chlamydiae are associated with ocular disease manifestations such as conjunctivitis and keratitis in humans and animals. Limited evidence exists that members of the order Chlamydiales can also cause ocular disease in sheep. In the current study, the prevalence of chlamydiae in the eyes of sheep was investigated by using PCR methods. Data obtained in sheep by broad-range 16S rRNA order Chlamydiales-specific PCR were compared to the prevalence of antibodies against chlamydiae detected by a competitive enzyme-linked immunosorbent assay (cELISA). Flocks tested included a clinically healthy flock and two flocks suffering from ocular disease and with histories of Ovine Enzootic Abortion (OEA). PCR detected DNA of Chlamydophila (Cp.) abortus and Cp. pecorum in the eyes of both healthy and sick animals but also identified Chlamydia (C.) suis and a variety of uncultured chlamydia-like organisms. Good correlation was found between the presence of Cp. abortus DNA in sheep conjunctival samples and seropositivity detected by cELISA. Despite these findings, no association was found between the presence of chlamydial DNA in the sheep conjunctival samples and the onset of clinical disease. These results suggest that the biodiversity of chlamydiae in the eyes of sheep is greater than that previously thought. Further investigations are needed to determine whether a causal relationship between infection by chlamydiae and ocular disease exists in these animals.     

Toxoplasma gondii-induced abortion in sheep

Twenty-nine of 200 (14.5%) ewes on a farm in Cobleskill, NY aborted or had dead lambs during the lambing seasons of 1985 and 1986. Thirteen of 15 ewes that aborted had high Toxoplasma gondii antibody titers (1,024), via the modified agglutination test, and T gondii was isolated from the tissues of 1 fetus. In the 1987 lambing season, 5 ewes aborted, but not because of T gondii infection. Toxoplasma gondii antibodies were detected in 73.8% of sera obtained from 592 ewes in January 1987, indicating enzootic toxoplasmosis on this farm. Seropositivity increased with age; 40.2% of 1-year-old ewes had detectable antibody vs 89.2% of 2-year-old ewes.     

A simple staining method for the identification of chlamydial elementary bodies in the fetal membranes of sheep affected by ovine enzootic abortion.

A dark-ground methylene blue (DGMB) staining method was used to demonstrate chlamydial elementary bodies in fetal membranes of sheep affected by Chlamydia psittaci. Before evaluation on material from clinically affected animals, the DGMB method was compared with modified Ziehl-Neelsen (MZN) and dark-ground Giemsa (DGG) staining methods for its ability to demonstrate chlamydial elementary bodies in hens' eggs which had been experimentally infected with C. psittaci. DGMB was more specific in its staining of chlamydial elementary bodies than DGG or MZN. The DGMB method was found to be a more reliable technique for the examination of fetal membranes from sheep affected with C. psittaci than DGG or MZN. Those samples diagnosed as positive using the DGMB showed a good correlation with those diagnosed as positive on macroscopic examination.     

奶牛衣原体性流产病原分离及血清学调查

应用实验室病原分离、血清学检测技术对宁夏某规模化奶牛场流产牛进行衣原体病原分离及血清学调查.结果表明,多年以来,在宁夏奶牛场中流行的以孕牛流产、早产、死产或产无活力弱犊的繁殖障碍性疾病与衣原体感染有关.采集四家规模化奶牛场380份血清,IHA试验结果牛群平均阳性率28.4%.     

乳牛衣原体性流产的病原鉴定及免疫原性研究

对采自甘肃、陕西和宁夏奶牛场的发生不明原因流产乳牛病料进行了间接血凝试验（IHA）、PCR、病原分离鉴定和MOMP基因检测，证实病原为鹦鹉热衣原体（Chlamydia psittaci）。对分离株Sx5和Nx进行毒力稳定性和免疫原性测定，用鸡胚连传20代，SX5和NX株的毒力比较稳定，毒力效价分别为10^-11ELD50和10^-10ELD50；用这2株菌对小鼠和牛做免疫效力试验，结果显示，免疫鼠5／5和5／5保护，对照鼠0／5保护；免疫牛3／3和3／3保护，对照牛0／3保护。表明，SX5和NX株具有良好的免疫原性，可以作为疫苗研制的候选菌株。