Have you ever heard of Q fever? If you’re interested in witnessing the miracle of birth, you might want to educate yourself on the bacteria, Coxiella burnetii, the causative agent of Q fever.
Deadly Infection at the Poker Table
One of my favorite things to do is play cards. I really got hooked on Texas Hold ‘Em poker, so several of my friends and I started a weekly game so we could get together for a couple of hours and just play. There are countless friendly games like this going on in countries all over the world. But, there is one game in particular that is especially interesting to the microbiologists in the group.In Canada, on Valentine’s Day, 1987, a group of 12 friends got together for their regularly scheduled game. This game turned out to be special.
During play, the family cat entered the room and gave birth to three kittens. Of course, this attracted the attention of the players who marveled at the miracle of birth. Within a few weeks, that marveling ended. Everyone present at the birth developed flu-like symptoms. One of the players, who had a history of heart disease, died. Doctors examined the lungs of the player and the uterus of the cat and found the same bacteria: Coxiella burnetii.
Never heard of Coxiella burnetii? I’m not surprised. Illnesses caused by Coxiella are rare, but can be very serious. So, let’s take a closer look at this elusive pathogen.
Coxiella burnetii is a small, Gram-negative, intracellular pathogenic bacteria common throughout the world. Gram-negative refers to the thin layer of peptidoglycan and outer membrane that make up the cell wall, making Coxiella cells appear red in the classic Gram stain.
Coxiella is a very hardy bacteria, able to survive drying out, heat, and common disinfectants by forming very resistant structures similar to endospores. The bacteria are commonly found in cattle, sheep and goats, but most often does not cause disease in these animals. Ticks and other biting insects can pick up Coxiella from one animal and pass it to another animal, spreading the bacteria.It is interesting to note that humans rarely, if ever, acquire the bacteria from tick bites.
Infected animals that harbor Coxiella shed large numbers of bacteria in milk, urine, feces, and amniotic fluids. Most humans acquire the bacteria through direct contact with one of these fluids. Like the poker players, the most common source of infection is contact with fresh or dried amniotic fluids or the placenta of infected farm animals. Residual birthing fluids left behind after a birth can dry, leaving dormant Coxiella bacteria behind. Later, these dried bacteria can be stirred up and inhaled, contaminate open wounds, get swallowed, or get into the eyes. Even one bacterium in one of these portals of entry can cause an active and dangerous infection.
Because of the extremely low infectious dose and the ability to aerosolize, Coxiella is a potential bioterrorism threat.
Not every person who comes into contact with Coxiella will get sick. About 50% of infected people will never show any symptoms and many others will develop only a very mild, flu-like illness that goes away on its own in a few days. But, some people will develop a potentially fatal infection called Q fever.
Q fever is an infectious disease of humans and animals caused by the bacterium Coxiella burnetii. The bacteria invade the cells of the body, filling the inside of infected cells with bacteria. This destroys the cells and initiates an immune system response to the pathogen.About two to three weeks after exposure, patients develop a wide variety of flu-like symptoms, including high fever, headache, muscle pain, chills, sweats, coughing, vomiting, diarrhea, abdominal pains, and chest pains. The frustrating aspect of Q fever is that no two patients ever seem to exhibit the same combination of these symptoms. Some patients will also develop pneumonia and inflammation of the liver and heart. Fortunately, most of these patients will fully recover with treatment.
In about 25% of cases, Q fever can become a chronic infection. As early as six weeks to several years after the initial exposure, patients develop endocarditis, which is inflammation of the inner layer of heart muscle, often including the heart valves. The bacteria also damage the blood vessels. Without treatment, 25-60% of chronic Q fever patients will die. The one person at the poker table who had a history of heart disease ended up dying, likely due to complications of chronic Q fever combined with existing heart damage.
Diagnosis and Treatment
Prompt diagnosis and treatment can reduce the fatality rate to less than 2%. Unfortunately, Q fever is notoriously difficult to diagnose. The symptoms are so vague and variable between individual patients that patterns are not readily discernible. Blood tests for antibodies to Coxiella are often negative for 7-10 days after the start of symptoms. Treatment is most effective if started within three days of the start of the disease, so a positive diagnosis is often based solely on the judgment of the doctor. Flu-like symptoms combined with a probable source of exposure are enough to begin treatment.
It is best to never delay treatment in a suspected Q fever case while waiting for confirmation. Heart damage can occur in even a few extra days.In the case of the poker game gone wrong, the circumstances pointed to Q fever when all players got sick and it was found they had common exposure to the birthing cat. The treatment of choice for Q fever is the antibiotic doxycycline. If started within the optimum first three-day window, symptoms frequently subside within the next three days. Most of these patients will make a full recovery with few to no recurring symptoms.
About 3% of the general population worldwide tests positive for Coxiella exposure.
About 15% of people with high-risk jobs, like farm workers and veterinarians, test positive. The vast majority of these people never showed any symptoms or had a mild case they attributed to the flu. Still, there are between 140 and 180 cases of Q fever that require treatment in the United States every year.For the general population, where people are not routinely exposed to birthing fluids, the only preventative measure is to avoid consuming unpasteurized dairy products. Farm workers and vets should always properly dispose of birthing fluids and restrict access to and treat farm animals known to be infected with Coxiella.
There is a vaccine for Q fever, but it is currently not available in the United States. The vaccine is effective at protecting against an initial exposure, but if you have already been exposed and get the vaccine, a serious reaction will occur at the injection site.
It’s time to review.
Coxiella burnetii is a small, Gram-negative, intracellular pathogenic bacteria common throughout the world. The bacteria are commonly found in the body fluids of farm animals, including sheep, cattle, and goats. Most humans are exposed to Coxiella through direct contact with animal birthing fluids. The bacteria are hardy, forming resistant endospore-like structures, allowing them to survive drying out. These dried bacteria can be aerosolized and inhaled, contaminate open wounds, get swallowed, or get into the eyes.
Q fever is an infectious disease of humans and animals caused by the bacterium Coxiella burnetii. Even one bacterium can cause a wide variety of flu-like symptoms in humans. Most cases are mild or never develop symptoms and resolve without treatment in several days. In about a quarter of cases, Coxiella becomes a life-threatening chronic infection characterized by damaged blood vessels and endocarditis. Diagnosis can be tricky due to the vague and variable nature of the symptoms.
Treatment is most effective if started during the first three days, so suspected cases are treated immediately based on the judgment of the doctor, not a positive blood test. Doxycycline is the antibiotic of choice.
After watching this lesson, you’ll have the ability to:
- Understand the structure of Coxiella burnetii and explain how it is transmitted
- List the symptoms of Q fever and explain why it is difficult to diagnose
- Recognize the fact that some infections of Coxiella burnetii are mild while others lead to more severe symptoms
- Mention a measure for guarding against Q fever
- Name the antibiotic used to treat Q fever