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

• HME (Human Monocytic Ehrlichiosis)
• Human Ehrlichial Infection, Human Monocytic Type

What is Human Monocytic Ehrlichiosis? (Definition/Background Information)

• Human Monocytic Ehrlichiosis (HME) is a rare, non-contagious, tick-borne bacterial infection caused by Ehrlichiosis chaffeensis. It predominantly affects a type of white blood cells, called the monocytes
• The primary vector for this infection is ticks, such as American dog ticks, deer ticks and lone star ticks. However, fleas and mites can also spread the infection through their bites
• The exact global prevalence of Human Monocytic Ehrlichiosis is not known. It is known to occur in the US, in the rural areas of South-Atlantic and Southeastern regions. Most the cases are reported in males, probably owing to a larger percentage of males being outdoors, for work or recreational purposes
• 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, Human Monocytic 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
• Since the bacteria attack monocytes, the level of white blood cells decrease. In addition, circulating levels of blood platelets may get 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 Monocytic 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 towards the treatment of Human Monocytic Ehrlichiosis. In places where ticks are common, the treatment may be started even before the blood test results are received, in order 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 Monocytic Ehrlichiosis infection
• The prognosis of Human Monocytic Ehrlichiosis is good in healthy individuals with prompt treatment. However, development of complications, particularly in the elderly, may prolong the recovery process

Who gets Human Monocytic Ehrlichiosis? (Age and Sex Distribution)

• The bacteria causing Human Monocytic Ehrlichiosis occur worldwide, in areas, where ticks (including the American dog ticks, deer ticks, and lone star ticks) are present. The exact global prevalence of the condition is not known
• In the United States, the infection occurs predominantly in the South-Atlantic, Southeastern and South Central states, at a frequency of 1:400,000
• The condition can affect individuals of all ages in the endemic regions, where ticks abound. However, those over the age of 60 years are more susceptible to this bacterial infection
• Both male and female genders are affected, although males get infected more often, probably owing to more outdoor activities. It is reported that about 80% of the cases are observed in males

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

The risk for contracting Human Monocytic Ehrlichiosis is greatest in the endemic regions. The risk factors for HME 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; particularly in the age range of 60-64 years
• Being outside/outdoors during the spring and summer months (warm weather), when the population of the ticks are at their highest

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones 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 Monocytic Ehrlichiosis? (Etiology)

Human Monocytic Ehrlichiosis is an infection that is caused by the bacterium Ehrlichia chaffeensis.

• The infection easily spreads to humans through tick bites (through the American dog ticks, Lone star ticks, and deer ticks), as well as by 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 minimum period of about 24 hours, the bacteria enter the body through the broken skin, and subsequently into the bloodstream, causing an infection
• The bacteria specifically infect the monocytes, which are a type of white blood cells (WBCs or leukocytes), essential for conferring immunity. This results in a decrease in the number of white blood cells, a condition known as leukopenia
• The HME infection can also cause circulating levels of blood platelets and red blood cells (RBCs) 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, HME 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 Human Monocytic Ehrlichiosis infection is not contagious; it does not spread from one individual to another.

What are the Signs and Symptoms of Human Monocytic Ehrlichiosis?

The symptoms of Human Monocytic Ehrlichiosis 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 HME include:

• Leukopenia or reduced WBC count
• Thrombocytopenia or reduced blood platelet count
• Anemia
• Fever (may be very mild), chills
• Loss of appetite
• Headaches, muscle pain, pain in the joints
• Vomiting, diarrhea
• Hepatitis
• Confusion
• Skin rashes 
• Cough

How is Human Monocytic Ehrlichiosis Diagnosed?

The diagnosis of Human Monocytic 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, etc.
• Blood tests to evaluate blood cell count
• Liver function tests: An inflammatory response in liver cells is observed in HME
• Polymerase chain reaction (PCR) test: To confirm the presence of Ehrlichia chaffeensis, the specific bacterial species causing 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 HME

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 Monocytic Ehrlichiosis?

Some potential complications of untreated Human Monocytic 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 conditions; respiratory failure
• Severe cases of HME can result in a coma state

How is Human Monocytic Ehrlichiosis Treated?

The treatment for Human Monocytic Ehrlichiosis may be commenced before the blood test results are procured, normally if the affected individual lives 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 (such as rifampin), since the tetracycline family of antibiotics may be harmful to the fetus

How can Human Monocytic Ehrlichiosis be Prevented?

The following are some tips to prevent Human Monocytic 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
• 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

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

• The prognosis of Human Monocytic Ehrlichiosis is determined by the age and overall health of the affected individual
• The outcome is generally good in healthy individuals, with prompt treatment
• However, if complications arise, the recovery may be prolonged (particularly, in the elderly adults)
• Per case reports, approximately 2-5% of those infected with HME succumb to the disease

Additional and Relevant Useful Information for Human Monocytic Ehrlichiosis:

• Babesiosis is a rare and severe tick-borne disease, caused by a parasite. The ticks (blacklegged ticks, deer ticks, or bear ticks) are carriers to parasites of the genus babesia

The following link may help you find useful additional information on babesiosis:

http://www.dovemed.com/diseases-conditions/babesiosis/