Q fever, or coxiellosis, is an infectious disease caused by the bacterium Coxiella burnetii. This organism is found across the globe and infects a wide range of animals, with cattle, sheep, and goats considered primary reservoirs. The disease is also a zoonosis, meaning it can be transmitted from animals to people, posing a public health concern for those who work with livestock.
Clinical Signs in Cattle
A significant challenge with Q fever is that the vast majority of infected cattle are asymptomatic. They can carry and shed the bacteria without showing any outward signs of illness. This subclinical nature means the disease can spread silently through a herd, complicating diagnosis and control efforts.
When clinical signs do manifest in cattle, they are almost exclusively related to reproductive problems. The disease can cause late-term abortions, stillbirths, and the delivery of weak calves that may fail to thrive. These reproductive failures represent a substantial economic loss for producers.
Beyond fetal loss, C. burnetii infection can lead to other postpartum complications in cows. Retained placentas are a common finding, which can subsequently lead to metritis, a serious inflammation of the uterus. These uterine health issues can impair a cow’s future fertility.
Transmission and Spread
The primary route of Q fever transmission is linked to the birthing process. Infected cows shed enormous quantities of Coxiella burnetii in their placenta, amniotic fluid, and other vaginal discharges during and after calving. These materials are highly infectious.
The spread of the bacterium occurs mainly through the inhalation of contaminated aerosols. When birth products dry, the bacteria can become airborne as dust particles. These infectious aerosols are easily inhaled by other cattle, which is the principal way the disease spreads within and between herds.
Coxiella burnetii is exceptionally resilient and can survive in the environment for extended periods. The bacterium is resistant to heat, drying, and many common disinfectants, allowing it to remain viable in soil and bedding for months. This environmental hardiness means contaminated areas pose a long-term risk, and wind can transport the bacteria to neighboring farms. While birth fluids are the main source, the bacteria can also be shed in milk, urine, and feces.
Herd Management and Prevention
Effective control of Q fever in a cattle herd centers on stringent biosecurity and management practices. These are designed to minimize the spread of the bacteria and include the following key strategies:
- Isolating cows during the calving period in a separate, clean maternity pen helps contain infectious materials and prevent widespread contamination.
- Properly disposing of all birth products is essential. Placentas, aborted fetuses, and contaminated bedding should be handled carefully and destroyed via deep burial or incineration.
- Implementing dust control measures, especially in dry conditions, can help reduce the airborne spread of C. burnetii.
- Maintaining a “closed herd” policy limits risk. If new animals are purchased, a quarantine period and testing are advisable.
Diagnostic tools can help identify infected animals within a herd. Blood tests, known as serology, detect antibodies to C. burnetii, indicating infection. A more direct method is the polymerase chain reaction (PCR) test, which detects the bacterium’s genetic material in samples like placental tissue or milk. In some regions, vaccination programs for cattle are an effective tool for reducing shedding and preventing reproductive losses.
Public Health Implications
Q fever is a significant zoonotic disease, and human infections are closely linked to exposure to infected livestock. The primary route of transmission to people is the same as it is between cattle: the inhalation of airborne dust contaminated with C. burnetii from animal birth products, feces, or urine.
Individuals who work closely with livestock face the greatest risk of exposure, including farmers, veterinarians, and slaughterhouse workers. The risk is not limited to direct contact, as people living near or downwind from infected farms can also be exposed to bacteria carried on the wind.
Human illness from Q fever presents on a wide spectrum, and many infections are asymptomatic. When symptoms do occur, they often resemble a severe flu-like illness with high fever, headache, and fatigue. In some cases, acute Q fever can develop into more serious conditions like pneumonia or hepatitis.
A small percentage of those infected may develop chronic Q fever, which can appear months or years after the initial infection. This form can cause a serious inflammation of the heart lining, known as endocarditis. Individuals with pre-existing heart valve conditions or compromised immune systems are at a higher risk for developing this chronic form.