Don’t overlook zoonotic diseases

One of our local dairy herds recently experienced an increased number of negative milk cultures in cows that had high somatic cell counts (SCC). Repeated aerobic and mycoplasma cultures were negative for the common mastitis pathogens that we generally test for. 

Veterinarians from Quality Milk Production Services suggested that we test for a bacterium named Coxiella burnetii, the agent that causes Q Fever in humans. In their experience, infection with these bacteria can cause subclinical mastitis and elevated cell counts. (Coxiella cannot be cultured with standard laboratory techniques.)

The results showed that some of these cows were indeed infected with Coxiella and it was being shed in the milk. This explained the elevated SCC in these cows, but has left us looking for another explanation for the others.

But the results uncovered something else: lethargy, headaches, high fevers and general body pain. 

These were not signs in the cows that had mastitis; these were the symptoms experienced by two individuals associated with the dairy during a recent illness. While these signs can signify many diseases from the common flu virus to something more serious, both of these individuals were diagnosed with the zoonotic disease, Q Fever, caused by Coxiella.

What is a zoonosis? 

We aren’t talking about wild animals or a trip to the zoo. A zoonosis is any infectious disease that can be transmitted from animals to humans (or vice versa). Many of us who work with animals on a daily basis do not show much concern for this transmission of disease, but for some it can be very serious. Q Fever is one such infection that, if left untreated, can cause serious long term disease in humans, including liver failure and infection of the heart.

The Coxiella bacteria are commonly found in the environment of cattle, sheep and goats.  Many of us who work with livestock on a regular basis have likely been exposed and we may have protective antibodies. However, we must still be diligent with hygiene when working with animals, especially during calving.

Stop the spread

Many people think of ticks when they consider the spread of Q Fever, but amniotic fluids, placenta and fetal membranes, as well as urine, milk and feces of infected animals can all be a source of Coxiella. In general, infected cattle do not show clinical signs. This was very evident in this case herd, as many of these cows did not even have clinical mastitis, only elevated SCC.

Another common route of infection is inhalation of contaminated dust from manure or bedding or aerosolization of the bacteria when cleaning. The Coxiella bacteria are also very hardy and can persist in the environment for long periods of time.

Given the fact that Coxiella does not generally produce clinical disease in cattle, the main concern is the production of contaminated milk that can then cause human disease. For this reason, the routine pasteurization of raw milk is always advised.

Tell your doctor

Often, physicians do not consider Q Fever in their diagnosis because it is primarily thought to be spread by ticks. It is likely that this disease in underdiagnosed in many cases because testing is not performed or there is a false negative result. Fortunately, if detected early, Q Fever can be treated with antibiotics. Because it is so infectious and difficult to contain in the laboratory, positive isolation of this agent must be reported to the health department.

Let this serve as a reminder to use basic hygiene. Hand-washing, exam gloves and obstetrical sleeves are all easy to use and inexpensive. Also keep zoonotic diseases in mind if you experience any unexplained illness.

Sometimes we need to remind our physicians that we work with livestock since zoonotic diseases can sometimes be overlooked. (For more information on Q Fever, go to: http://www.ccohs.ca/oshanswers/diseases/qfever.html)

Mark J. Thomas is a veterinarian and partner in Countryside Veterinary Clinic, LLP in Lowville, N.Y.

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