Ehrlichiosis
Ehrlichiosis is an infection caused by a group of intracellular bacteria that are transmitted to humans through the bites of infected ticks, predominantly the lone star tick (Amblyomma americanum). The condition can arise from at least three different species, including Ehrlichia chaffeensis and Ehrlichia ewingii, with symptoms typically appearing five to ten days after a tick bite. Common symptoms include fever, chills, headache, muscle aches, joint pain, and nausea. While the infection is usually acute and treatable with tetracycline antibiotics like doxycycline, some cases can lead to serious complications, including respiratory distress and neurological issues. The incidence of ehrlichiosis has been rising in the United States, with significant increases noted in the 21st century, particularly affecting vulnerable populations such as children under five and older adults. Despite being primarily recognized as an acute infection, some patients report prolonged symptoms even after recovery. The overall fatality rate is low, but it highlights the importance of early diagnosis and treatment. Understanding the increasing prevalence and potential long-term effects of ehrlichiosis is crucial for public health awareness and prevention efforts.
Ehrlichiosis
ANATOMY OR SYSTEM AFFECTED: Immune system, musculoskeletal system, nervous system
DEFINITION: Infection by one of a group of intracellular bacteria transmitted to humans through tick bites.
CAUSES: Bite of an infected tick
SYMPTOMS: Fever, chills, headache, muscle aches and weakness, joint pain, nausea
DURATION: Acute
TREATMENTS: Antibiotics
Causes and Symptoms
Human ehrlichiosis is a group of tick-borne bacterial infections known to be caused by at least three different species of bacteria: Ehrlichia chaffeensis, Ehrlichia ewingii, and a third species provisionally named Ehrlichia muris-like, which was first discovered when it caused an outbreak in Minnesota and Wisconsin in 2009. Another species, Anaplasma phagocytophilum (formerly Ehrlichia phagocytophilum), was previously considered to also cause ehrlichiosis, but since the bacterium was reclassified in 2001, the disease that it causes was similarly reclassified as a form of anaplasmosis. In addition, the bacterium Ehrlichia canis causes canine monocytic ehrlichiosis, which primarily affects dogs but has also been reported in cats and in humans.
Ehrlichia species are transmitted by the bite of various species of ticks, primarily Amblyomma americanum, commonly called the lone star tick. Once the bacteria have been transmitted, they subsequently infect circulating white blood cells (leukocytes). After an of five to ten days, the disease is typically characterized by fever, chills, and other nonspecific symptoms. A percentage of infections have also been documented. Confirmation of ehrlichiosis infection is accomplished via laboratory methods, including blood-smear examination, polymerase chain reaction, culture, and serologic analysis for the presence of anti-Ehrlichia antibodies.
Treatment and Therapy
Ehrlichiosis is effectively treated with a tetracycline antibiotic, most commonly doxycycline. With the increased number of diagnoses, more significant cases requiring hospitalization and condition-appropriate treatment have been documented. Significant complications include respiratory distress, myocarditis, neurological complications, hepatitis, septicemia, and opportunistic infections. Despite clinical similarities between the causative agents, a higher percentage of opportunistic infection has been documented with human granulocytic anaplasmosis (HGA), caused by A. phagocytophilum, whereas increased disease severity and higher mortality has been associated with human monocytic ehrlichiosis (HME), caused by E. chaffeensis. (Forms of the disease caused by E. ewingii, E. canis, and E. muris-like occur in negligible numbers and are rarely fatal.)
Perspective and Prospects
The reported prevalence and incidence of human ehrlichiosis has been on the rise in regions where specified tick vectors are found. According to the Centers for Disease Control and Prevention (CDC), the number of reported cases of HME in the United States rose steadily from 200 in 2000, or 0.8 cases per million persons, to 1,518 in 2013, or 5.1 cases per million. According to a 2020 study published in the journal JAMA Network Open, cases of ehrlichiosis increased more than eight times in the United States in the twenty-first century. About 57 percent of patients require hospitalization and 11 percent face serious medical consequences. The overall fatality rate for ehrlichiosis was 1 percent, but it increased to 14 percent in children under five and 53 percent in those over seventy.
Although historically considered an acute infection conferring long-term immunity, one study found a percentage of HME patients experienced a significantly higher than expected rate of fever, chills, sweats, and one to three years after the initial illness. Because these symptoms did not correlate with the severity or duration of the initial episode, nor did serological tests confirm the presence of Ehrlichia, determination of whether these findings are attributed to a persistent or recurrent infection or a type of postinfection syndrome is still under investigation.
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