What zoonotic organism is most often associated with abortion in sheep, especially after introducing new ewes?

Coxiella burnetii, the causative agent of Q fever, is the correct answer as it is a zoonotic organism known to be associated with abortions in sheep. This bacterium is particularly prevalent in environments where sheep are kept and can be introduced into a flock through new ewes that may be asymptomatic carriers. When these new animals are brought into a flock, they can shed the organism in their bodily fluids, potentially leading to outbreaks of abortion in the pregnant ewes that are already in the flock.

Coxiella burnetii not only poses a risk to sheep but can also transmit to humans, leading to flu-like symptoms or more severe health problems, especially in immunocompromised individuals. When investigating abortion cases in sheep, particularly one that follows the introduction of new animals, Coxiella is often a primary suspect due to its mode of transmission and impact on reproductive health in livestock.

In contrast, while other organisms listed are zoonotic and can cause reproductive issues in animals, they are not as strongly associated with the specific context of sudden abortion following the inclusion of new ewes into a flock. For example, Chlamydophila can cause abortion but is more commonly associated with specific strains that may not always result from new