Back To CourseMicrobiology 101: Intro to Microbiology
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Angela has taught college Microbiology and has a doctoral degree in Microbiology.
In the 1950s, the memory of World War II was still fresh in the minds of the American people. Not only that, but the Soviet Union was gaining in global influence and prominence. American scientists and government officials began working together to identify a potential weapon that could be used to incapacitate enemy troops while causing minimal deaths and at the same time inflict major economic damage on the enemy. In the context of our current global views, it might surprise you to learn that the United States began developing biological weapons to accomplish these tasks.
The organism they chose to weaponize was the bacterium Brucella. Brucella and the illnesses it can cause had many of the major characteristics required for a successful biological weapon: an ability to aerosolize for dispersal, prolonged illness with low mortality in humans, and abortions and more severe illness in livestock, impacting the economy. The Brucella biological weapon was developed but fortunately never used.
In the 1970s, the United States, the Soviet Union, and the United Kingdom signed an agreement that they would no longer develop or stockpile biological weapons, so Brucella is no longer part of the American arsenal. Today, about 170 countries have signed this agreement. Brucella holds the title as the first biological agent to be weaponized by the United States. In this lesson, we'll examine Brucella and the foodborne illness brucellosis.
Brucella is a genus of Gram-negative, nonmotile, coccobacillus bacteria. The term coccobacillus might be a new one to you. Basically, a bacterium with a coccobacillus shape is a short rod, or bacillus, that can easily be confused with the spherical, or cocci, shape. Gram-negative means they have a cell wall with a thin peptidoglycan layer and an outer membrane.
There are four species of Brucella that can cause disease in humans, each normally associated with a different host animal. B. abortus, which infects cattle, and B. canis, which infects dogs, are species that cause only very mild diseases in humans. B. suis, which infects pigs, and B. melitensis, which infects sheep and goats, can cause fatal disease in humans.
People acquire Brucella through direct contact with infected animals, specifically contact with animal secretions or through consumption of animal products. Any secretions, like saliva, blood, or wastes, that get into cuts and broken skin, in the eyes, or inhaled, can cause active infections. But the majority of cases result from people drinking or eating milk products and undercooked meat from infected livestock. The Brucella bacteria concentrate in the mammary glands of infected cattle and goats and can be found in high concentrations in the milk. Pasteurization will kill 100% of the Brucella cells, so it is unpasteurized milk and cheese that commonly spread the disease.
It is also possible to pass Brucella from person to person, but this is very, very rare. There have been a couple of confirmed cases in the United States acquired from breastfeeding and sexual contact, but most infections are from unpasteurized milk or cheese.
Brucellosis is a disease caused by the bacteria Brucella often acquired by ingesting the bacteria in contaminated food. Once consumed, the bacteria will be engulfed by immune cells and transported to the lymph nodes. Unfortunately, Brucella can survive this attack, pass out of the lymph nodes to the blood stream, and invade the bone marrow, spleen, and liver. For many healthy people, it is possible that no noticeable symptoms will develop. A minority of people will have very mild symptoms that can be mistaken for flu symptoms. The symptoms can be vague and include fatigue, loss of appetite, weakness, and fever.
It is the fever that makes brucellosis unique. The fever rises very high in the day, causing drenching sweats. In the evening, the fever goes down, causing chills. For this reason, brucellosis is often called undulant fever for the cyclic rise and fall of body temperature unique to the disease. Most people will completely recover from brucellosis in a couple weeks without treatment. In an unlucky few, the disease can become chronic and life-threatening. The fever and fatigue can last for months or longer.
Brucella cells can localize in the brain, lungs, heart, and bones and be very difficult to eliminate. Eventually, some patients die due to chronic inflammation in the heart muscle. It is important to note that the symptoms of brucellosis are caused by the actively growing bacteria. This makes brucellosis an example of food infection, not food poisoning, which involves ingesting only microbial toxins.
So how can you determine if that flu you have is actually brucellosis? Usually, tracking the rise and fall of the fever can be the most diagnostic. The undulant nature of the fever is a dead giveaway for Brucella. Doctors can also check blood samples for antibodies to Brucella or attempt to culture the bacteria. Culturing can be difficult, though. The organism requires very specific growth conditions, grows very slowly, and is infectious if aerosolized, putting lab technicians at risk. Once diagnosed, the antibiotics doxycycline and rifampin for a minimum of six to eight weeks is enough to eliminate most infections.
Since Brucella is a pathogen of domestic animals, anyone working in a livestock field is at risk. This includes meat packers, farmers, and veterinarians. Fortunately, B. abortus, the species that infects cattle, has been effectively eliminated in herds in the United States. Still, it pays to be careful. People working around livestock should always cover broken skin, avoid inhaling any animal secretions, wear eye protection, and wear gloves. For people that don't work in high-risk environments, thoroughly cooking foods and avoiding unpasteurized dairy products is enough to prevent the majority of infections.
Despite these easy methods of prevention, there are still about 100 cases of brucellosis in the United States every year. About half of these cases occur in California and Texas. Only about 2% of those that develop symptoms die from the disease, and these cases are almost always caused by B. melitensis.
It's time to review.
Brucella is a genus of Gram-negative, nonmotile, coccobacillus bacteria that causes the foodborne illness brucellosis. The bacteria are acquired through contact with secretions from infected animals or through consumption of animal products. They can be ingested, inhaled, splashed into the eyes, or enter through broken skin.
Once inside the human host, the bacterium survives attack by the immune system, invades the bloodstream, and infects the internal organs. Most people either won't get sick or will develop mild, flu-like symptoms that resolve without treatment. This can include fever, fatigue, appetite loss, and weakness. Brucellosis is often called undulant fever because the body temperature will alternately rise during the day and fall at night, characteristic of Brucella infection.
In some patients, chronic infections develop, lasting months or longer. The bacteria can invade the brain, lungs, heart, and bones. In about 2% of these cases, the patient dies of inflammation in the heart muscle. The undulant fever and blood tests for Brucella antibodies are often used to diagnose Brucella infection. The antibiotics doxycycline and rifampin for six to eight weeks is usually enough to cure the disease.
As long as you thoroughly cook your meat and only eat and drink pasteurized dairy products, you should be safe from Brucella. People that work with livestock should also wear protective equipment like gloves and goggles to avoid contact with contaminated secretions.
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Back To CourseMicrobiology 101: Intro to Microbiology
20 chapters | 207 lessons