You are a veterinarian in a high-density livestock area in the central region of the iberian peninsula. One of the farmers you work with contacts you to discuss a problem in his dairy sheep farm of 300 heads: during the current lambing season, he is observing an abnormal peak of abortions.
Figure 1: Sheep Flock (source: VISAVET)
These reproductive failures are affecting approximately 20% of the pregnant females, occurring in the last third of gestation, and mostly affecting first-time lambing ewes.
In the previous two lambing seasons, there have already been episodes of abortions at a lower percentage, which had not been reported.
Figure 2: Sheep flock (source: Christian Gortázar)
Figure 3: Sheep fetus aborted in the last third of gestation (source: VISAVET)
Given this situation, you report the case to the health authorities and, according to their indications, you proceed to collect samples for diagnosis.
Figure 4: Sampling of vaginal swab from sheep (source: VISAVET)
Figure 5: Sampling of vaginal swab from sheep (source: VISAVET)
Figure 6: Use of Personal Protective Equipment in the handling of ruminants when zoonotic risk level III microorganisms are suspected (source: VISAVET).
The laboratory results indicate that the presence of DNA from a bacterial pathogen causing abortions in ruminants has been detected by PCR in the vaginal swab samples of all sampled females, as well as in a proportion of milk and feces samples. Additionally, the serum of all sampled females has presented specific antibodies against the same bacteria detected by PCR.
However, the microbiological culture of the samples has been negative, not allowing the isolation of the microorganism detected by PCR, neither using general nor specific culture media for different bacterial groups.
As complementary information, it should be mentioned that the farm has implemented a vaccination program against enzootic abortion and paratyphoid abortion for five years, as well as against toxoplasmosis for two years. Furthermore, the region is officially brucellosis-free.
Moreover, it should be noted that in the previous three birthing seasons, there have been similar cases in neighboring goat farms, located about 3 km from the farm under study, which have shown a high percentage of abortions.
The pathogen responsible for the abortion outbreak in this sheep farm is Coxiella burnetii, a Gram-negative bacterium and the causative agent of Q fever. This notifiable disease is a globally distributed zoonosis that can affect a large number of mammalian species, both domestic and wild, although domestic ruminants are its primary reservoir. These species are subject to surveillance and control plans in our country. In ruminants, its main manifestation is abortions in the last third of gestation. Although females typically abort only once in their lifetime, they can continue to shed the bacteria in subsequent births through vaginal secretions following the reproductive event, as well as in milk and feces, which, along with placentas and fetuses, contaminate the environment. Transmission to other animals and humans occurs mainly via aerosol, and the bacteria can be carried by the wind for several kilometers.
Figure 7: Coxiella burnetii bacteria by transmission electron microscopic (TEM) (source: National Institute of Allergy and Infectious Diseases (NIAID) - the National Institutes of Health’s (NIH) - Rocky Mountain Laboratories (RML), from Public Health Image Library from CDC).
Coxiella burnetii is also highly resistant to disinfectant treatments and environmental conditions, such as desiccation, and it has a very low infectious dose. In humans, many cases of infection can be asymptomatic or produce self-limiting flu-like illnesses. However, it can also cause conditions such as hepatitis, pneumonia, or endocarditis, among other manifestations, which can even result in the patient's death. Additionally, it can lead to chronic conditions like chronic fatigue syndrome, which is highly disabling.
Figure 8: Photomicrograph of a tissue sample that revealed the presence of numerous Coxiella burnetii bacteria (source: Public Health Image Library from CDC).
Thus, all the aforementioned characteristics make it a microorganism that requires level III biological containment according to Real Decreto 664/1997, and it is considered a potential biological weapon. Being an obligate intracellular bacterium, it cannot be cultured on bacterial culture media but requires cell lines or laboratory animals for isolation. Therefore, the diagnosis is usually based on the detection of the bacterium's genetic material in clinical samples and the detection of specific antibodies.
The control of the disease is based on the implementation of cleaning and disinfection protocols, proper waste management, including bedding and manure, and the vaccination of animals (both preventive and in already infected farms). Currently, there is only one registered commercial vaccine, Coxevac®, which limits reproductive failures and reduces shedding, thereby decreasing environmental contamination.
In Spain, there is a surveillance and control program for Q fever in accordance with Regulation 689/2020 and Directive 99/2003. This program establishes disease surveillance in cattle and small ruminants, proposes control measures for these species, and outlines a response protocol in the event of zoonotic outbreaks.
Figure 9: Scanning electron microscopic (SEM) image, digitally colorized, of a dry fractured Vero cell, revealed its contents, and the ultrastructural details at the site of an opened vacuole, inside of which you can see numerous Coxiella burnetii bacteria (source: National Institute of Allergy and Infectious Diseases (NIAID) from Public Health Image Library from CDC).