Overview: Q Fever and Potential Emerging Infection in Ruminants and Risk of Zoonotic Transmission

Q fever is an economically significant disease in ruminants causing a range of reproductive disorders worldwide. The disease has not been reported in ruminants while low seroprevalence was reported among humans in Sri Lanka. Since factors associated with antibody against Coxiella burnetti in human has not been found and the association between human and animal has not been evaluated. However, importation of live animals may or may not be considered as a potential risk factor therefore, extensive studies are encouraged.

Q fever is caused by obligate intracellular parasite Coxiella burnetti which is an aerobic, Gram-negative organism, and highly resistant bacterium. The bacterium may infect mammals, birds, and arthropods. Q fever has been reported slightly high prevalence in cattle than in small ruminants, the disease is often considered a a neglected disease in differential diagnosis in the clinics and laboratories. Q fever is mainly associated with reproductive disorders such as abortion, metritis, weak offspring, and sterility. The organism also causes mastitis in cows. The risk of transmission is highly dependent upon the prevalence of shedders in a herd and intensity of shedding the organism by animals. Although herd size and composition of herd has been identified as no effect on epidemiology, herd density is considered an important factor in transmission of the disease within the herd. Coxiella burnetti is shed through birth products, vaginal fluids, urine, feces, and milk just after calving or parturition. The Q fever has been reported in most of the countries in the World. High seroprevalence was reported in Belgium where prevalence was 56.7%. The prevalence of Q fever at individual and herd level in France was 20% to 38% in cattle and 15% and 25% in sheep and goats respectively. In the USA, herd prevalence of Q fever was varied from 26.3% to 94.3% in 2002 and 16.7 and 5.4% in 2011, Asia. Cats are considered as the main source of human infection comparing to dogs. The bacterium had been isolated from feline vaginal mucosa and associated with reproductive disorders including abortion in cats. Inhalation has been identified as the main source of transmission both in animals and humans, infective material is infected through inhalation. Ingestion and vertical transmission have been also suspected. The organism is considered to be highly resistant in a farming environment for 2 years of post-infection.

The infection is often asymptomatic in humans and both acute and chronic forms have been reported flu-like infection, pneumonia, and hepatitis were reported common and chronic fatigues, endocarditis, pneumonia, abortion, stillbirth, and premature deliveries, were also reported. Most clinical cases reported were among the immunocompromised population, abattoir workers, farmworkers, and people who have a close association with animals. Also, a good prognosis has been observed in humans when treatment was started at early stage. High seroprevalence was reported among veterinarians and vaccination with Phase I vaccine was proven results on developing clinical disease, although side effects were reported on people who exposed to the organism previously. Fluoroquinolone was recommended only for meningoencephalitis and other human cases were treated with doxycycline, trimethoprim-sulfamethoxazole, and hydroxychloroquine.

Both humoral and cell-mediated immune mechanisms were recognized as an essential tool to protect against Coxiella burnetti infection in animals and humans. Passive actin-dependent phagocytosis in phagocyte cells and active zipper mechanism in nonphagocytic cells have been described in pathogenesis. The bacterium can be detected in different clinical samples such as milk, vaginal mucous, feces, urine, semen, birth fluid, and placental membranes. Identification of the bacterium can be done by conventional bacteriological methods; molecular methods and detection of antibodies were done by serological methods such as ELISA. Identification of the organism and serological diagnosis in bulk milk tanks is the most practical way of diagnosis in ruminants. Serological diagnosis is considered the gold standard of diagnosis of Q fever in humans. Antibiotics, vaccination, and a combination of these two are the alternative to control clinical disease in cattle. A few vaccine types have been recognized such as inactivated PI or PII, attenuated PII Coxiella burnetii. Chloroform: methanol residue fraction of Nine Mile phase I killed vaccine and used to control the excretion of the organism in sheep/goat and cattle.