Back To CourseBiology 103: Microbiology
16 chapters | 156 lessons | 12 flashcard sets
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Angela has taught college Microbiology and has a doctoral degree in Microbiology.
Don't you hate it when people get your name wrong? My name is Angela, but I have been called Andrea more times than I can count. At least these two names are close, so I have no problem correcting people and forgetting about it. But there is a bacterium that was called the wrong name for decades, and it had no way to correct scientists and doctors. To make matters worse, the name it was called sounds nothing like its actual name.
The bacterium I'm referring to is correctly named Anaplasma, but for years it was incorrectly called Ehrlichia, a similar, yet distinctly different genus of bacteria. It wasn't until 1990, when DNA sequencing became more affordable and accessible, that this bacterium finally started getting the recognition and distinction it deserved. For this lesson, I'm going to attempt to right some wrongs and focus all my attention solely on Anaplasma. But if you happen to be one of those people who is always getting names wrong, check out my lesson dedicated to Ehrlichia. Together, they might help you keep things straight in your brain and avoid offending either bacteria.
Anaplasma phagocytophilum is an obligate, intracellular bacterial pathogen of animals and humans spread through the bite of an infected tick. As an obligate, intracellular pathogen, Anaplasma must invade the cells of its host organism in order to grow and reproduce. In this case, Anaplasma invades white blood cells, specifically neutrophils, the body's primary defensive immune cells. It is here that this parasite multiplies and causes disease. But it is not the only place Anaplasma can survive. The bacteria can also be found in the gut and salivary glands of infected ticks of the genus Ixodes. Bites from infected Ixodes ticks are the major source of infection for humans, livestock, and pets. These bites are usually painless and allow the tick to inject painkilling, blood-vessel dilating, and anticlotting factors into the host. If the tick is carrying Anaplasma, some bacterial cells can slip through as well. These Anaplasma invaders are capable of causing a potentially fatal bloodborne infection.
Anaplasmosis is the potentially deadly disease caused by infection from Anaplasma phagocytophilum. The symptoms of anaplasmosis are vague, flu-like, and vary greatly from person to person. Some of the more commonly reported symptoms include headache, fever, muscle aches, malaise, and confusion. These symptoms usually show up within two weeks of the tick bite and are often mistaken for a simple case of the flu or a cold. In older patients, people with other diseases, or those with compromised immune function, the infection can be more severe. These patients can develop difficulty breathing, hemorrhaging, and renal failure. About 1% of these cases are fatal.
How Anaplasma causes these symptoms is not well-understood. The current theory is that the bacteria in the blood cause body-wide inflammation, leading to the symptoms. It is possible that some symptoms are a result of the changes Anaplasma causes to the blood itself. Most patients exhibit some variable combination and severity of anemia, low white blood cell count (called leukopenia), and low platelet count (called thrombocytopenia). Also, it is often possible using a microscope to see small, dark spots in the neutrophils. These spots are made up of clusters of dividing and growing bacteria. These features of the blood can be valuable diagnostic tools.
Diagnosing tick-borne diseases is difficult in general. Anaplasma is no exception. Many blood tests will be negative for the first 7-10 days, when beginning treatment is most effective. The polymerase chain reaction (PCR) can detect Anaplasma DNA in the blood of the host during this early period, but the test is not commonly ordered. As a result, diagnosis is usually based on symptoms combined with a recent tick exposure. If anaplasmosis is suspected, doctors can also examine the blood for the dark spots of dividing bacteria in the neutrophils and check the patient for anemia, thrombocytopenia, and leukopenia.
If discovered early, treatment is very effective. As a result, treatment is usually ordered based only on suspected infection. The antibiotic doxycycline is the first line of defense for all patients. Often, this treatment will completely eliminate the infection. More intensive measures, like intravenous antibiotics and hospitalization, are only necessary in very severe cases in high-risk patients.
It is important to note that just because anaplasmosis is suspected and treatment has been started, a positive diagnosis is still needed. Many tick-borne infections have similar symptoms and can often be misdiagnosed. A proper diagnosis can ensure the appropriate treatment. Delays from misdiagnosis can result in prolonged infections and long-term health problems.
Anaplasmosis can be difficult to diagnose, but it is very easy to prevent. Simply protecting yourself from tick bites is the best defense. That means avoiding tick habitats, like woody and brushy areas. If you can't make it through an entire summer without hiking, you should take precautions, like covering exposed skin, wearing insect repellants containing DEET, and performing frequent tick-checks. If you pick up a few hitchhiking ticks, promptly remove them, but make sure you do it correctly. The correct method of tick removal is to grasp the tick with tweezers as close to the skin as possible and pull straight out. Common home remedies, like coating the tick with nail polish or heating the tick with a match, will only cause the tick to regurgitate its stomach contents into your blood. This tick vomit can include blood from other animals and thousands to millions of bacteria and protozoa living inside the tick!
Despite these easy prevention methods, cases of anaplasmosis have been increasing every year since the organism was properly named in 1990. In 2010, there were nearly 2,000 confirmed cases. This rise is most likely due to increased awareness and vigilance by doctors and not to an increase in infected ticks or tick bites.
Anaplasma phagocytophilum is an obligate, intracellular bacterial pathogen of animals and humans spread through the bite of an infected tick. When an infected Ixodes tick bites a human, it injects Anaplasma into the host's bloodstream. The bacterial pathogen invades the white blood cells, specifically neutrophils, initiating a body-wide inflammatory response. This inflammation leads to the variable flu-like symptoms of anaplasmosis. These include headache, fever, muscle aches, malaise, and confusion. In rare, severe cases patients can develop difficulty breathing, hemorrhaging, and renal failure. About 1% of these cases are fatal.
In addition to these symptoms, anaplasmosis can cause anemia, leukopenia, thrombocytopenia, and microscopic dark spots inside the neutrophils containing multiplying Anaplasma cells. These blood changes combined with the flu-like symptoms and recent tick exposure are all a doctor needs to make a preliminary diagnosis and start treatment. The antibiotic doxycycline is the first line of defense for all patients. A concrete, positive diagnosis is still recommended to prevent misdiagnosis and problems related to incorrect or delayed treatment.
Prevention of anaplasmosis is as simple as reducing tick exposure. Avoiding tick habitats, covering exposed skin, wearing insect repellants containing DEET, performing frequent tick-checks, and promptly removing any attached ticks correctly are the best preventative measures.
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Back To CourseBiology 103: Microbiology
16 chapters | 156 lessons | 12 flashcard sets