Bacterial Diseases > Coxiella burnetii and Q Fever

Coxiella Infection in Ruminants

Domestic ruminants - cattle, goats and sheep - are the primary reservoirs for C. burnetii and the predominant source of organism transmitted to humans. Clinical signs of infection in ruminants are almost always absent, including a lack of fever.

A key to understanding the importance of ruminants in transmission of Coxiella is that the organism colonizes and replicates massively in the pregnant uterus and, to a lesser degree, in the mammary gland. Infection of the placenta and fetus can indeed result in abortion or stillbirth, but crucially leads to shedding of massive quantities of Coxiella in birthing fluids and delivery of a highly contaminated placenta. Urine, feces and milk also can contain large quantities of bacteria. As noted, Coxiella from such sources is spore-like and resistant to degradation, which results in long lasting contamination of the birthing environment, and a major route of transmission to humans is inhalation of contaminated dust. Humans can also be infected by ingestion of raw milk from infected ruminants, but this appears to be a relatively minor risk. Nonetheless, currently recommended time-temperature for pasturization of milk was set based in killing of Coxiella.

Shedding of C. burnetii from infected ruminants is not a simple phenomenon and shows considerable variability depending on several factors. What is clear is that the organism has a propensity to replicate in the placenta and mammary gland.

Serologic Responses of Naturally Infected Ruminants In a study of cattle, sheep and goats from infected herds in France, serological responses were assayed using an ELISA kit from Idexx, and a substantial number of animals from each species were seronegative despite detection of organisms in milk, feces or vaginal secretions; the fraction of seropositive animals was higher when milk was tested rather than serum (Rodolakis, et al. 2007). In a study of ewes from a flock that had undergone Coxiella-induced abortion and was then followed through two subsequent gestations, ewes that were seropositive at the outset remained so, while ewes that were seronegative – some of which had PCR-positive vaginal swab samples – remained negative (Berri et al. 2002). The authors of this paper state that serologic testing should never be used as the basis for selecting uninfected animals for research. Shedding in Naturally Infected Ruminants The routes of shedding C. burnetii was evaluated in naturally infected cows, ewes and goats from France by Rodolakis and colleagues (2006). Approximately 100 females of each species from 3 farms were studied over a period of 90 weeks; the farms were chosen because of positive identification of C. burnetii in bulk milk samples. The bacteria were detected using a PCR kit (unknown reagents) applied to samples of milk, vaginal swabs and feces; the manuscript also indicates that blood was tested, but no further mention of this was provided. Abortions were observed in the herds of goats and flocks of sheep under study, but not in cattle. For both cattle and goats, organisms were shed almost exclusively in milk, although sometimes sporadically. In contrast, sheep shed primarily in feces and vaginal secretions and only a limited amount in milk. The origin or pathogenesis of shedding was not addressed. Interestingly, there was no correlation between shedding and the time from parturition; indeed, some animals did not shed until 8 or 10 weeks after they gave birth. In another study from France, 20 (?) ewes from a flock in which two other ewes had experienced Coxiella-associated abortion were followed serologically and by PCR through two subsequent gestations (Berri et al. 2002). All but one of the ewes failed to excrete organisms in vaginal secretions at the time of second or third lambings. Coxiella DNA was however detected in vaginal swabs taken after the third lambing, indicating a small fraction of ewes developed a chronic infection [however, no way to determine if this was a different infection or possibly even environmental contamination]. The pathogenesis of Coxiella infection in pregnant goats was evaluated in detail using a strain of bacteria from the Dutch outbreak (Roest et al. 2012). The first evaluated three routes of exposure and found that all resulted in placental infection, but that intranasal appeared to be the best. They infected additional goats on day 76 of gestation with 1e6 MID of bacteria and made the following observations: • There was strong tropism for infection of the placenta. Coxiella DNA but not antigen was detected in multiple organs of fetuses, indicating that the organism was not replicating in the fetus. • Coxiella was never detected from feces or vaginal swabs prior to abortion or parturition, but the routinely thereafter. • The load of Coxiella in the placenta of kids that were aborted versus those that were born alive was not different. • Kids and dams cleared the organism after parturition. • They were able to detect environmental contamination, including using air filters. C. burnetii was detected by PCR in greater than 90% of bulk milk samples collected from across the U.S. over a three year period (Kim et al. 2005). Live cell therapy and Q fever LCT is an alternative treatment (without medical evidence of effectiveness) that is marketed worldwide online. It consists of intramuscular injections of cell suspensions from fetal sheep to human recipients for rejuvenation (anti-aging) and other ailments. Report of an outbreak of Q fever in patients that received these sheep tissues. Promed Sun 16 Apr 2017 SHOULD DISCUSS ANIMAL VACCINES

References and Reviews

Coxiella Infection in Humans

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