Ehrlichiosis in humans is a relatively unknown infectious disease to date, which is transmitted by ticks. The gram-negative bacteria of the genus Ehrlichia, which otherwise mainly cause ehrlichiosis in dogs and horses, come into question as pathogens. In most cases, the disease is mild or even asymptomatic, but in some cases it can lead to severe complications.
What is ehrlichiosis?
The first case of human ehrlichiosis caused by a tick bite was described in the United States in 1986. Previously, ehrlichiosis was known only in dogs or horses. The pathogen was already discovered by the German physician Paul Ehrlich (1894 to 1915). Although the pathogens were known at an early stage, an infection with Ehrlichia was first observed in 1935 in a dog in Algeria. Then, during the Vietnam War, many dogs of American soldiers contracted ehrlichiosis. Ehrlichia has therefore long been a household name in veterinary medicine. The pathogen for ehrlichiosis in dogs is called Ehrlichia canis. In humans, Ehrlichia chaffeensis and Ehrlichia phagocytophilia are particularly responsible for causing this disease. Ehrlichia chaffeensis is so far active only in North Africa. It is the causative agent of human monocytic ehrlichiosis (HME). In Germany, only a subspecies of the pathogen Ehrlichia phagocytophilia occurs, which causes human granulocytic ehrlichiosis (HGE). The genus Ehrlichia belongs to the order Rickettsiales. Thus, their representatives are rickettsiae. All Ehrlichia are gram-negative bacteria that can infect monocytes, granulocytes, or macrophages in the blood.
Causes
The cause of ehrlichiosis is infection with ehrlichia transmitted by a tick bite. This applies to both humans and animals. In animals, horses and dogs that have come into contact with ticks are particularly affected. Dogs are infected primarily by the brown dog tick (Rhipicephalus sanguineus). In Germany, human ehrlichiosis is mainly transmitted by the wood tick. Through a tick bite, the pathogens enter the bloodstream. There they penetrate monocytes, granulocytes or macrophages and often multiply unnoticed inside the cell. Monocytes and granulocytes are part of the blood and belong to the leukocytes (white blood cells). Usually, the immune system fights off the infection very quickly. However, in immunocompromised or elderly persons, severe courses occur, which in individual cases can even lead to death.
Symptoms, complaints, and signs
In about half of the infections with ehrlichiosis, the disease runs symptomless. If symptoms nevertheless occur, they become noticeable approximately two weeks after the tick bite. They may include nausea, vomiting, abdominal pain, diarrhea, high fever and headache. Redness of the skin often occurs as well. The symptoms can be mild or, in some cases, severe. The immune competence of the organism is decisive for the course of the disease. In severe cases, respiratory problems, heart muscle inflammation or muscle fiber dissolution are also observed. Even rarer complications can manifest themselves in meningitis and cerebral inflammation. Particularly in older and immunocompromised persons, ehrlichiosis can also be fatal. The overall clinical picture is very diverse and non-specific. The symptoms that can also occur in humans have not yet been fully verified by the small number of cases observed. In Germany, the first case of confirmed ehrlichiosis was described only in the early 1990s. Furthermore, ehrlichiosis does not always occur in isolation. Sometimes it is associated with Lyme disease in the form of a so-called double infection, since several different pathogens can be transmitted via the tick. Similar symptoms also occur in dogs or horses. This has already been confirmed by many years of observation.
Diagnosis
The unequivocal diagnosis of ehrlichiosis requires a large number of differential diagnoses from other possible diseases. On the one hand, this is due to the fact that the symptoms of the disease are often very nonspecific. On the other hand, other pathogens are also transmitted by a tick bite. In addition to a variety of pathogens, autoimmune diseases or leukemias must also be excluded.However, the indication that a tick bite has occurred is important for the diagnosis. If Ehrlichiosis is initially suspected, only genetic detection of the pathogen or detection of antibodies to Ehrlichia can unequivocally confirm the diagnosis.
Complications
In ehrlichiosis, severe complications occur only in very rare cases. As a rule, the course of the disease is harmless and leads only to mild symptoms. Ehrlichiosis initially causes headaches, vomiting, and severe nausea. These symptoms may also be accompanied by diarrhea and high fever. In some cases, there are problems with the respiratory tract or inflammation of the heart muscles. In the worst case, there may also be inflammation of the brain, which can be fatal. However, these cases are very rare. Ehrlichiosis often occurs together with Lyme disease. Treatment depends on the symptoms and usually does not lead to complications. If the symptoms are weak, no treatment is necessary, in this case the ehrlichiosis disappears by itself and does not lead to any further complaints. If symptoms are more severe, treatment with antibiotics is advisable. This also leads to a positive course of the disease. As a rule, it takes two days for the ehrlichiosis to subside. In order to avoid ehrlichiosis or Lyme disease, areas with ticks should be avoided. Tick vaccinations may also be considered as a preventive measure.
When should you go to the doctor?
A doctor should always be consulted after a tick bite. If specific signs of ehrlichiosis are noticed, medical evaluation and treatment are essential. Typically, one to four weeks after the tick bite, there is a high fever, severe headache, muscle and joint pain, and a general feeling of malaise. These symptoms should be clarified immediately by a doctor. At the latest when abdominal pain and diarrhea or signs of pneumonia are noticed, medical advice is needed. If left untreated, ehrlichiosis can cause severe complications such as heart failure, kidney failure and circulatory collapse. The risk of complications is particularly high in the elderly and in patients with immunodeficiency or a severe underlying disease. Anyone belonging to these risk groups should see their family doctor immediately if they suspect they have ehrlichiosis. If any of these complications occur, call an emergency doctor or go to the nearest hospital. In severe cases, first aid measures must be taken. In addition, after the initial treatment, further visits to the family doctor are indicated, because only he can ensure that the disease is completely cured.
Treatment and therapy
Because ehrlichiosis is often asymptomatic, therapy is not always necessary. In many cases, it even goes completely unnoticed and heals on its own. This is also true for most symptomatic cases of ehrlichiosis. However, in cases of high fever, antibiotics such as doxycycline or tetracycline are given. Within 24 to 48 hours, the body responds to this therapy with a rapid drop in fever. After several weeks, complete healing occurs. Treatment with doxycycline also responds when ehrlichiosis occurs together with Lyme disease. The pathogen that causes Lyme disease is also combated by this agent.
Outlook and prognosis
The prognosis for ehrlichiosis in humans is usually good. As a rule, the disease is very mild or often even without symptoms. After healing, no secondary damage usually remains. Therefore, treatment is often not necessary. However, severe courses of the disease are also observed, including fever, chills, muscle pain, joint pain, headache and nausea. After treatment with quinolones, rifampicin or tetracyclines, the symptoms subside within 14 days. Even in more severe courses, there is usually no need to fear long-term damage. However, life-threatening complications can occur in persons with a weakened immune system. These complications include pneumonia, sepsis or impairment of the central nervous system. In these cases, rapid emergency medical assistance is required to overcome the life-threatening condition. If the CNS is involved, sequelae may develop in the form of neurologic and psychiatric disorders. However, lethal courses of ehrlichiosis are extremely rare.However, with successful treatment of the complications, a complete cure can also be expected in most cases. Since ehrlichiosis is transmitted by ticks, it can also occur in the form of a double infection together with Lyme disease. In this case, it often masks Lyme disease as part of standard therapy. However, if broad-spectrum antibiotics are used, both diseases can be successfully treated in the early stages of Lyme disease.
Prevention
Because very few cases of ehrlichiosis have occurred in Germany to date, there is also little experience with its prevention. The pathogen is not widespread everywhere. Basically, however, high grass or forest edges should be avoided during tick season. Long-legged and long-sleeved as well as light-colored clothing is preferable. Dark clothing would make it more difficult to find any ticks that may be on the loose. The risk of infection is greatly reduced by early mechanical removal of the tick from the host, such as by using tick forceps.
Aftercare
In cases of ehrlichiosis, follow-up care is proving relatively difficult. The disease is still largely unresearched at the present time, so that even a direct and rapid treatment is not possible in most cases. If the disease is not immediately examined and treated by a doctor, in the worst case severe complications and even death of the affected person can occur. For this reason, ehrlichiosis must first and foremost be detected at an early stage, so that a doctor must be consulted at the first symptoms. In most cases, the treatment of ehrlichiosis is done by taking medication, usually using antibiotics to limit the symptoms. Care must be taken to use the correct dosage with regular dosing to ensure complete relief of symptoms. The antibiotics must sometimes be taken for several weeks, even if the symptoms have already completely disappeared before that. With timely treatment, there are no further complications or discomforts and the life expectancy of the affected person is not reduced. After therapy, no further measures are necessary, so that follow-up care is not required in this case.
What you can do yourself
Ehrlichiosis in humans, unlike in dogs or horses, is a rare disease. In many cases, the infection is not even noticed by those affected, but if symptoms appear, a patient should definitely consult a doctor promptly. The best self-help measures are to avoid tick bites, strengthen the immune system, and seek immediate medical attention if the disease does occur. Ehrlichiosis is transmitted in Central Europe primarily by a particular species of tick, the wood tick. These insects live mainly in tall grass and on low bushes and shrubs. To prevent a bite and thus a possible infection with the pathogens of ehrlichiosis or other dangerous diseases, such as Lyme disease or early summer meningoencephalitis (FSME), certain preventive measures must be taken. When hiking, long pants and long-sleeved tops should always be worn. After spending time outdoors, the body should be scanned for ticks and they should be removed promptly. Those who have pets should also check them for ticks. At least in high-risk areas, it is advisable to use additional chemical insect repellent when walking or hiking through the woods or across meadows with tall grass. A healthy immune system can help ensure that an infection does not lead to an outbreak of the disease, or that it is at least brief and mild. The immune system is best supported by a healthy lifestyle that includes adequate sleep, a vitamin-rich, primarily plant-based diet, and regular exercise, preferably in the fresh air. A high-fat, meat-heavy diet, little to no physical exercise, and excessive consumption of alcohol and cigarettes weaken the immune system and should be avoided.
