Coxiella burnetii antibodies in Danish dairy cattle: Prevalence, incidence, recovery, and association of dam status with calf status and calf mortality when accounting for diagnostic test quality

Abstract

Coxiella burnetii is an obligate intracellular zoonotic bacterium and domesticated ruminants including dairy cattle are considered the main reservoir for human exposure. C. burnetii was regarded as an economically insignificant pathogen for domestic livestock, but the recent outbreak of Q fever in the Netherlands have shown that Q fever infection in animals may have extensive economic implications. Q fever infection in cattle is usually subclinical although sporadic abortions occur. The almost worldwide occurrence of C. burnetii has been documented by serological studies. The infection is generally subclinical in animals (e.g. cattle, sheep and goat), although abortions in late pregnancy, stillbirths and the delivery of weak offspring, retained placenta, endometritis, infertility and low birth rates may occur.Until recently, Q fever was notified in very low numbers annually in Denmark. But during recent years in Denmark higher rates of antibodies to Coxiella burnetii have been detected in animals and humans than previously reported. So we did two studies with the aim of the first work was to 1) study the relationship between levels of C. burnetii antibodies in offspring and their dam, 2) to estimate the prevalence, incidence and recovery of C. burnetii antibody positivity under the assumption of perfect and imperfect tests, 3) to estimate the sensitivity and specificity of the CHEKIT Q-Fever Antibody ELISA TEST Kit, and 4) to estimate associations of age groups, herd status and breed with prevalence, incidence and recovery in Danish dairy cattle. The objective of the second study was to evaluate the relationship of antibody status of C. burnetii in Danish dairy cows with calf death, delivery condition of cow and birth size of calf. The thesis consists of four chapters: Chapter 1 presents a brief introduction on the history and general bacteriology of the Coxiella burnetii; a brief overview of the dairy sector in Denmark and the situation of Coxiella burnetii in Denmark; and background and objective of this thesis.Chapter 2 estimates prevalence, incidence, recovery and relations between dam and offspring when accounting for diagnostic test quality for Coxiella burnetii antibody levels in Danish dairy cattle. Prevalence and incidence of seropositive animals were medium in young calves, low in older calves and heifers and again high in cows. Recovery was higher in young animals than in cows. Antibodies in offspring blood and dam milk showed positive relationship: strongest early in life and ceased with increasing age of offspring. Sensitivity and specificity of ELISA test was standard enough for a good test. The cut-off value S/P ≥68% was specified for differentiation between infected and non-infected animals in Hidden Markov Model. Prevalence and incidence were high in calf for taking colostrum but in young and heifer the antibody disappears due to develop resistance system in this animals. But in cows the prevalence and incidence increases again for continuous exposed by organisms from environment and contacts with infected animals more. Recovery was high in young and heifer because of body immune system is start working in this time which is a normal biological phenomenon. Antibodies in offspring blood and dam milk showed positive relationship and it strongest in young calf and low in old calf. This indicates that calves have short lasting colostral antibodies and later decreasing in nature and finally disappears. In chapter 3, for calf deatha total of 3974 milk samples from 2103 dams from the selected herds were then collected in three different time periods: August-October 2008 (Time 1), January-February 2009 (Time 2) and April-June 2009 (Time 3). The general results provide relationship of Coxiella burnetii antibody status of dam with calf death in individual level of Danish dairy cattle. There was no significant association betweencalf deaths, delivery condition or birth size with parity and breed but a significant association was found betweendelivery condition andherd condition. No significant association was found between antibody status of the dam and calf death, birth size and delivery condition. A significant random effect of herd in different models was observed. It is concluded that dam antibody status of C. burnetii appears to be non-related with calf deaths,delivery condition and birth size. These results indicate that, in Denmark, C. burnetii antibody level is not an important factor for calf deaths and these calf deaths are related with other herd level variables. Chapter 4 synthesizes the knowledge derived from the previous chapters and discusses their practical relevance to the estimation of general frequencies of Coxiella burnetii antibody in Danish dairy cattle and association between Coxiella burnetii antibody of dam and their offspring. This thesis suggests that the inference from prevalence, incidence and recovery as well as association between calf death and dam antibody status in Denmark. These results could be useful for the making decision for control and prevention of Coxiella burnetii as well as reproductive disorder management in Denmark.