Molecular detection and phylogenetic characterization of Coxiella burnetii in dairy cattle from the Al Ain region, United Arab Emirates

In the world of livestock farming, a microscopic bacterium named Coxiella burnetii causes a disease known as Q fever. This germ is a master of hiding; it lives inside the cells of animals like cows and goats, often without making them look sick. While the animals may appear healthy, they can still carry the bacteria and release it into their surroundings through milk, birth fluids, or waste. For humans who work closely with these animals, the risk is real. Breathing in tiny particles of dust or aerosolized droplets contaminated with the bacteria can lead to flu-like symptoms, and in some cases, serious heart or lung infections. Because the bacteria can persist in the environment and move between animals and people, scientists call it a zoonotic disease, a term for illnesses that jump from animals to humans. Understanding where this germ lives, how it moves through a herd, and what genetic makeup it carries is essential for keeping both farm workers and the public safe.

In the United Arab Emirates, specifically in the Al Ain region, dairy cattle are a vital part of the agricultural landscape. While previous studies had found antibodies in the blood of many cows there—suggesting that the animals had been exposed to the bacteria at some point—scientists did not know much about the current state of the infection. They lacked a clear picture of whether the bacteria was actively spreading within the herds, which specific parts of the animals were releasing it, and whether the strains found in the UAE were unique or part of a global family. To answer these questions, a team of researchers from the United Arab Emirates University and local agricultural authorities set out to examine two large commercial dairy farms. They wanted to move beyond simply knowing that exposure had happened and instead find out if the bacteria was currently active and being shed by the cows.

The researchers began by visiting two farms, sampling a total of 400 cows. For each animal, they collected three types of samples: a drop of blood from the neck, a sample of milk, and a swab from the vaginal area. First, they tested the blood to see if the cows had developed antibodies, which are proteins the immune system creates to fight off an invader. Finding antibodies is like finding footprints; it proves the animal encountered the bacteria in the past, but it does not necessarily mean the bacteria is still there or being released right now. The results showed that 30 percent of the cows had these antibodies, meaning a significant portion of the herd had been exposed. The rate was nearly identical on both farms, suggesting that the exposure was widespread and consistent across the region.

To find out if the bacteria was currently active and being shed, the team turned to a more sensitive method called PCR, which acts like a molecular searchlight to find the actual genetic code of the bacteria. They tested the blood, vaginal swabs, and milk from the cows that had tested positive for antibodies. The searchlight found nothing in the blood or the vaginal swabs. However, in the milk, the story was different. The researchers detected the genetic material of Coxiella burnetii in the milk of about 22 percent of the cows that had antibodies. This was a crucial discovery. It meant that while many cows had been exposed in the past, a smaller but significant group was currently carrying the bacteria in their mammary glands and releasing it into their milk. The fact that the bacteria was found only in the milk and not in the other samples suggests that the udder is a primary hiding spot for the germ in these herds, allowing it to persist and potentially spread without causing obvious illness in the cow.

The team then took the genetic material they found in the milk and sequenced it to see exactly what kind of bacteria they were dealing with. They focused on a specific gene, a small section of the bacterial DNA that acts like a fingerprint. When they compared the fingerprints of the bacteria from the UAE cows to those from around the world, they found something striking: the bacteria in the UAE were identical to each other, and they matched perfectly with strains found in Europe, Africa, and Asia. There was no unique local variety; instead, the cows in Al Ain were carrying a strain that is part of a global, zoonotic family. This genetic uniformity suggests that the bacteria circulating in these herds likely came from a common source or has been moving between farms and regions for some time, rather than evolving into a distinct local version.

These findings paint a clear picture of the situation in the UAE dairy industry. The bacteria is not just a historical memory for these herds; it is an active, ongoing presence. The fact that the bacteria is being shed in the milk by cows that show no other signs of sickness highlights a hidden risk. For the farmers and workers handling the milk, this means there is a constant, low-level exposure happening, even if the animals look healthy. The study confirms that the infection is endemic, meaning it is regularly found in the population, and that the milk itself is a key pathway for the bacteria to survive and spread. By combining the blood tests that show past exposure with the milk tests that show current shedding, the researchers provided a complete view of the problem. Their work supports the idea that controlling this disease requires looking at the whole picture, from the animals to the workers, and understanding that the bacteria can hide in plain sight, waiting to be passed on.