It is considered a good agent in part because its ID50 (number of bacilli needed to infect 50% of individuals) is considered to be one, making it the lowest known. In animals
Q fever can affect many species of domestic and wild animals, including ruminants (cattle, sheep, goats, bison, deers...), carnivores (dogs, cats, seals...), rodents, reptiles and birds. However, ruminants (cattle, goats and sheep) are the most frequently affected animals, and can serve as a reservoir for the bacteria. Clinical signs
In contrast to humans, even though a respiratory and cardiac infection could be experimentally reproduced in cattle, the clinical signs mainly affect the reproductive system. Q fever in ruminants is therefore mainly responsible for abortions, metritis, retained placenta and infertility. The clinical signs vary between species. In small ruminants (sheep and goats), it is dominated by abortions, premature births, stillbirths and the birth of weak lambs or kids. One of the characteristics of abortions in goats is that they are very frequent and clustered in the first year or two after contamination of the farm. This is known as an abortion storm.In cattle, although abortions also occur, they are less frequent and more sporadic. The clinical picture is rather dominated by non-specific signs such as placental retentions, metritis and, consequently, fertility disorders. Epidemiology
With the exception of New Zealand, which is currently free of Q fever, the disease is present throughout the world. Numerous epidemiological surveys have been carried out.
Q fever or query fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including cats and dogs. The infection results from inhalation of a spore-like small-cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick-borne. The incubation period is 9–40 days. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite. Signs and symptoms
Incubation period is usually two to three weeks. The most common manifestation is flu-like symptoms: abrupt onset of fever, malaise, profuse perspiration, severe headache, muscle pain, joint pain, loss of appetite, upper respiratory problems, dry cough, pleuritic pain, chills, confusion, and gastrointestinal symptoms, such as nausea, vomiting, and diarrhea. About half of infected individuals exhibit no symptoms.During its course, the disease can progress to an atypical pneumonia, which can result in a life-threatening acute respiratory distress syndrome, whereby such symptoms usually occur during the first four to five days of infection.Less often, Q fever causes (granulomatous) hepatitis, which may be asymptomatic or become symptomatic with malaise, fever, liver enlargement, and pain in the right upper quadrant of the abdomen. Whereas transaminase values are often elevated, jaundice is uncommon. Retinal vasculitis is a rare manifestation of Q fever.The chronic form of Q fever is virtually identical to endocarditis (i.e.