Occurrence of Coxiella burnetii in Polish dairy cattle herds based on serological and PCR tests

Highlights

• Anti-C. burnetii antibodies were identified in 25.39% of 2635 bovine serum samples.

• Herd-level seroprevalence in Polish Voivodeships varied from 2.5 to 61.4%.

• Coxiella burnetii DNA was detected in almost 40% of tested bulk tank milk specimens.

Abstract

The aim of the research was to assess the prevalence of antibodies to Coxiella burnetii in dairy cattle herds in Poland and to compare the results of real-time PCR and ELISA tests performed on bulk tank milk (BTM) samples. In total, 2635 serum samples collected from 969 dairy cattle herds from all provinces were tested using ELISA. Additionally, BTM specimens from 101 herds were analysed by ELISA and real-time PCR targeting IS1111 element. Presence of anti-C. burnetii antibodies was confirmed in 25.39% of serum samples in 237 herds (24.46%) and the herd-level seroprevalence in Voivodeships varied from 2.5% to 61.4%. Moreover, 46 (45.5%) of analysed bulk tank milk samples gave postive result in ELISA and microbial DNA was detected in 40 (39.6%) of tested herds. The comparative analysis of ELISA and real-time PCR results obtained for BTM samples using the chi-square test showed statistically significant relationship between results of both methods.

Introduction

Coxiella (C.) burnetii is an obligate intracellular γ-proteobacterium and the etiological agent of zoonotic disease Q fever [1]. This pathogen was first described in 1930s [2,3] and currently is distributed almost worldwide, affecting a wide range of animal species [4]. Domestic ruminants (i.e. goats, sheep, cattle) are considered to be a major reservoir of C. burnetii, moreover, the wildlife fauna and ticks may also be an important sources of the pathogen. Taking into account that the clinical signs of coxiellosis in animals are non-specific and infection may be asymptomatic, especially in cattle, laboratory tests are crucial in Q fever diagnosis. Noteworthy is the fact that asymptomatic individuals and intermittent cattle shedders may remain negative in serological tests and unnoticeably shed the pathogen into the environment for several months or years [5,6]. The highest amounts of C. burnetii are shed during abortion and parturition in birth products (placenta, birth fluids), whereas lower levels are detected in milk, vaginal discharges, feaces, urine and semen [7]. In humans and animals inhalation of contaminated aerosols is the most common route of infection [8]. Sporadic cases of Q fever transmission by sexual contact, blood transfusion and transplantation were also reported [9,10]. The phenomenon of C. burnetti shedding in milk may pose a potential threat for public health, not only for occupationally exposed people but also for raw milk consumers [11,12].

Serological screenings of ruminant herds have been performed in many countries to assess exposure to the pathogen and the zoonotic risk [[13], [14], [15]]. The complement fixation test (CFT), indirect immunofluorescence assay (IFA) or enzyme-linked immunosorbent assay (ELISA) may be used, but the latter is thought to be the most robust and has good specificity and high sensitivity [[16], [17], [18]]. Moreover, the testing of BTM samples using ELISA allows a preliminary evaluation of the herd status, ease of sampling and reduces costs. In Poland Q fever is a notifiable disease, additionally serological monitoring survey of cattle and small ruminants has been implemented since 2010. The previous study showed that percentage of C. burnetii seropositive cattle herds in Poland is significant [19].

The objectives of this research were to estimate the prevalence of antibodies against C. burnetii in dairy cattle herds based on sera and bulk tank milk samples (BTM) analysis and to compare the results of real-time PCR and ELISA tests performed on BTM specimens.