Human Ehrlichiosis

Human Ehrlichiosis

Article
Skin Care
Diseases & Conditions
+3
Contributed byLester Fahrner, MD+1 moreMay 23, 2022

What are the other Names for this Condition? (Also known as/Synonyms)

  • Human Ehrlichia Infection

What is Human Ehrlichiosis? (Definition/Background Information)

  • Human Ehrlichiosis (or simply Ehrlichiosis) is a term used to describe a group of rare, non-contagious, tick-borne infections caused by bacteria belonging to the family Anaplasmataceae
  • The Anaplasmataceae family of bacteria comprises the following species:
    • Ehrlichia ewingii: Very few cases of infection are reported with this bacterium type
    • Ehrlichia muris-like (a provisional name): It is the causative organism for very few cases of infection
    • Ehrlichia chaffeensis: This bacterium targets monocytes, causing human monocytic ehrlichiosis (HME)
    • Ehrlichia canis: It has been discovered to cause Ehrlichiosis more recently. In some patients in Venezuela, the bacteria were found to affect the monocytes (in blood)
    • Neorickettsia sennetsu, a bacterium belonging to the same family, can also cause infection in humans (Sennetsu fever). Individuals in Southeast Asia are known to be infected by eating raw, undercooked, or fermented fish
  • The exact global prevalence of Human Ehrlichiosis is not known. It is known to occur in the US, in the rural areas of South-Atlantic and Southeastern regions, and in certain South Central states. Most the cases are reported in males, probably owing to a larger percentage of males being outdoors for work or recreational purposes
  • The primary vector for Ehrlichiosis is ticks, such as American dog ticks, deer ticks and lone star ticks. However, fleas and mites can also spread the infection. The vector for Sennetsu fever is certain types of fish that are ingested
  • In a majority of cases, the transmission of infection occurs when an infected tick attaches itself onto the skin and feeds on human blood. In this process, the bacteria get transmitted to a healthy host. The bacteria enter the skin through the tick bite, and then move into the bloodstream resulting in an infection
  • Additionally, Ehrlichiosis can be transmitted through direct contact with an infected animal or its tissue (from infected slaughtered animals). Transmission can also occur through contaminated blood transfusions, or from an infected pregnant mother to her unborn child
  • The bacteria attack white blood cells, and cause their levels to drop. In addition, circulating levels of blood platelets may be affected. An inflammatory immune response in the liver can also take place, causing an elevation in certain liver enzymes
  • The symptoms of the condition may include fever, muscle pain, nausea, vomiting, diarrhea, rashes, and confusion. The diagnosis of Human Ehrlichiosis is made based on the presenting symptoms, physical examinations, history of outdoor activities, blood tests and polymerase chain reaction (PCR) to identify the causative bacterium
  • Generally, antibiotics are prescribed for the treatment of Human Ehrlichiosis. In places where ticks are common, the treatment may be started even before the blood test results are final, to avoid complications from the infection. The complications may include respiratory problems, kidney failure, and seizures
  • Wearing long-sleeved, light-colored clothing while being outdoors, using insect repellants and removing ticks attached to the skin, as soon as they are detected, are some tips for preventing tick bites, and thus preventing Human Ehrlichiosis infection
  • The prognosis of Ehrlichiosis is good in healthy individuals with prompt treatment. However, a development of complications, particularly in the elderly, may prolong the recovery process

Who gets Human Ehrlichiosis? (Age and Sex Distribution)

  • The bacteria causing Ehrlichiosis occur worldwide, in areas where ticks are present. The exact global prevalence of the condition is not known
  • In the United States, the rate of occurrence is approximately 3 individuals per a million population. The infection occurs predominantly in the South-Eastern, South Atlantic, and South Central states of America. There have been reports of the infection in the state of New York as well
  • The condition can affect individuals of all ages in areas where ticks abound. However, those over the age of 60 are more susceptible to these bacterial infections
  • Both genders may be affected, although males get infected more often probably owing to their activities outdoors
  • In Southeast Asia, a type of Ehrlichiosis (Sennetsu fever) is contracted by eating raw, undercooked, or fermented fish

What are the Risk Factors for Human Ehrlichiosis? (Predisposing Factors)

The risk for contracting Human Ehrlichiosis is greatest in the endemic regions. The risk factors may include:

  • Recreational activities such as hiking, golfing, gardening and camping, especially in tick-infested areas
  • Living in a tick-infested region
  • Professional necessity of being outdoors (such as forest workers)
  • Being over the age of 60 years
  • Being outside/outdoors during the spring and summer months (warm weather), when the population of the ticks are at their highest
  • Eating raw, undercooked, or fermented fish is a risk factor for Sennetsu fever

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Human Ehrlichiosis? (Etiology)

  • Human Ehrlichiosis is a tick-borne infection caused by bacteria belonging to the family of Anaplasmataceae. It comprises of the following species:
    • Ehrlichia ewingii
    • Ehrlichia muris-like
    • Ehrlichia chaffeensis
    • Ehrlichia canis
  • The infection spreads to humans through tick bites (such as by the American dog ticks, Lone star ticks, western black-legged ticks, and deer ticks), as well as through flea and mite bites. The ticks bite and attach themselves onto human skin, to feed on blood
  • The infected tick can stay attached to the skin for a long duration. When it stays attached for a long period, the bacteria enter the body through the broken skin, and subsequently into the bloodstream, causing an infection
  • The bacteria infect different types of white blood cells, such as monocytes or granulocytes. This causes a decrease in the number of white blood cells, a condition known as leukopenia. The infection can also cause circulating levels of blood platelets and red blood cells to decrease, causing thrombocytopenia and anemia, respectively
  • Additionally, an immune response in the liver cells to the infection can cause liver inflammation, and change the levels of enzymes such as hepatic transaminases

In addition to tick bites, Ehrlichiosis can also be transmitted in the following manner:

  • Blood transfusions, when blood or blood products are contaminated
  • From an infected pregnant woman to her unborn child
  • Through direct contact with an infected animal or animal tissue

The Sennetsu fever is caused by infection of Neorickettsia sennetsu, a bacterium closely related to Ehrlichia species. This infection spreads from fish to man, through eating raw, undercooked, or fermented fish.

What are the Signs and Symptoms of Human Ehrlichiosis?

Irrespective of the species of bacterium causing the infection, the symptoms of Ehrlichiosis are very similar, and begin appearing between 7-14 days of the tick bite. The type and severity of symptoms may vary between individuals. Some individuals may remain asymptomatic, while others may exhibit significant symptoms.

The common signs and symptoms associated with Ehrlichiosis include:

  • Fever (may be very mild), chills
  • Headaches
  • Muscle pain, pain in the joints
  • Hepatitis
  • Vomiting, diarrhea
  • Anemia
  • Confusion
  • Skin rashes
  • Cough

How is Human Ehrlichiosis Diagnosed?

The diagnosis of Ehrlichiosis is made using the following tools:

  • Complete physical examination and assessment of symptoms
  • Seeking information about the affected individual’s place of stay, outdoor activities (hobbies), travel history to tick-infected regions, if he/she has visited Southeast Asian countries and eaten uncooked or under-prepared fish, etc.
  • Blood tests to evaluate blood cell count
  • Liver function tests: An inflammatory response in liver cells is observed in Ehrlichiosis
  • Polymerase chain reaction (PCR) test: To identify the specific bacterial species that caused the infection
  • Indirect fluorescent antibody (IFA) test (this test is less frequently performed than PCR): To measure the levels of antibodies in blood to the specific bacteria causing Ehrlichiosis

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Human Ehrlichiosis?

Some potential complications of untreated Human Ehrlichiosis may include:

  • Dyspnea or shortness of breath
  • Problems with blood clotting process
  • Bleeding in the gastrointestinal tract
  • Stiff neck, facial paralysis
  • Neurological problems such as excessive response to sensory stimuli (hyperreflexia)
  • Problems with voluntary muscle coordination (ataxia)
  • Meningitis
  • Seizures
  • Kidney and heart failure
  • Respiratory failure
  • Severe cases of Ehrlichiosis can result in a coma state

How is Human Ehrlichiosis Treated?

  • The treatment for Ehrlichiosis may be commenced before the blood test results are procured, normally if the affected individual resides in or frequents a tick-infested region
  • In general, an antibiotic course is recommended for 10 days, which may be extended for severe cases. Typically, the tetracycline class of antibiotics (such as doxycycline) is used to treat this condition
  • Infected pregnant women may be prescribed a different antibiotic, since the tetracycline family of antibiotics may be harmful to the fetus

How can Human Ehrlichiosis be Prevented?

The following are some tips to prevent Ehrlichiosis:

  • Avoid tick bites by wearing full length pants and closed-toe shoes: The ticks are known to attach to the lower legs and feet when individuals walk on grassy or wooded areas. They may also attach themselves to the back of the knees, groin area, underarms, ears and back of the neck
  • While being outdoors, avoid grassy and dense woody areas, when possible
  • Wearing long-sleeved shirt and long pants to minimize exposed skin
  • Tuck-in the shirt into pants and pants into socks, to help prevent tick bites
  • Wearing light-colored clothing to help find the attached ticks easily
  • After each outdoor session, a full body tick examination is recommended
  • Immediately remove ticks attached to the body on finding them, to reduce the risk of infection
  • Use insect repellants containing DEET
  • Individuals with long hair should tie-up their hair for easy visibility of the attached ticks
  • Check clothes and body for ticks after a visit to the woods or tick-infested areas
  • Inspect pets after a walk outside, to see if they have any attached ticks
  • Not consuming raw, undercooked, or fermented fish in regions of the world (southeast Asian) where Sennetsu fever is endemic
  • Being aware of potential illnesses/infections in the region of the world one is planning to visit

What is the Prognosis of Human Ehrlichiosis? (Outcomes/Resolutions)

  • The prognosis of Ehrlichiosis is determined by the age and overall health of the affected individual
  • The outcome is generally good for healthy individuals, with prompt treatment
  • However, if complications arise, the recovery may be prolonged (particularly in individuals who are immunocompromised and the elderly)

Additional and Relevant Useful Information for Human Ehrlichiosis:

The US National Institute of Allergy and Infectious Diseases (NIAID) supports research on Ehrlichiosis that is aimed at:

  • Studying the basic biology of the microbes that cause the infection
  • Developing vaccines for prevention
  • Identifying better ways of diagnosis and treatment

Recently, NIAID-supported researchers helped in the completion of the genome sequence of both Anaplasma phagocytophilum and Ehrlichia chaffeensia which can help in developing vaccines for prevention and better methods of diagnosis and treatment.

The infection caused by Anaplasma phagocytophilum bacterium was known as “human granulocytic ehrlichiosis”, which has since been re-named “human granulocytic anaplasmosis,” an infection distinct from Ehrlichiosis.

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Krish Tangella MD, MBA picture
Approved by

Krish Tangella MD, MBA

Pathology, Medical Editorial Board, DoveMed Team
Lester Fahrner, MD picture
Reviewed by

Lester Fahrner, MD

Chief Medical Officer, DoveMed Team

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