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Human Granulocytic Anaplasmosis

Last updated Feb. 7, 2017

Human Granulocytic Anaplasmosis (HGA) is a rare, non-contagious, tick-borne bacterial infection caused by Anaplasma phagocytophilum, which targets neutrophils (a type of white blood cells).


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

  • Anaplasma Phagocytophilum Infection
  • Anaplasmosis
  • HGA (Human Granulocytic Anaplasmosis)

What is Human Granulocytic Anaplasmosis? (Definition/Background Information)

  • Human Granulocytic Anaplasmosis (HGA) is a rare, non-contagious, tick-borne bacterial infection caused by Anaplasma phagocytophilum, which targets neutrophils (a type of white blood cells)
  • The exact global prevalence of Human Granulocytic Anaplasmosis is not known. It is known to occur in the US, in New England and North Central states. Generally, older adults and individuals with decreased immunity have a higher risk for HGA infection
  • The primary vector for this infection is ticks, such as deer ticks and blacklegged ticks. 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. The bacteria can also be transmitted through contaminated blood transfusions and from an infected mother to her unborn child
  • When the bacteria enter the bloodstream, they specifically target the neutrophils, and reside inside these cells. This alters the neutrophils resulting in “degranulation” of these cells, compromising their ability to digest the invading microbes
  • 1-2 weeks after infection, the symptoms of Human Granulocytic Anaplasmosis, such as fever, chills, muscle pain, vomiting, diarrhea, confusion, and a general feeling of ill-health, may be experienced. If left untreated, the infection can lead to complications such as respiratory problems, liver damage, kidney failure, and bleeding in the gastrointestinal tract
  • The diagnosis of Human Granulocytic Anaplasmosis is made based on the presenting symptoms, physical examinations, history of outdoor activities, blood tests, etc. A confirmation of the infection is generally undertaken through a polymerase chain reaction test (PCR test, to identify the causative bacterium)
  • A 10-14 day regimen of tetracycline class of antibiotics is the typical treatment modality for Human Granulocytic Anaplasmosis. The duration may be extended for severe cases, or, if HGA occurs with another infection such as Lyme disease
  • 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 Granulocytic Anaplasmosis infection
  • The prognosis of Human Granulocytic Anaplasmosis is good in healthy individuals with prompt treatment. However, development of complications or co-existence of another infection, may prolong the recovery process 

Who gets Human Granulocytic Anaplasmosis? (Age and Sex Distribution)

  • The bacteria causing Human Granulocytic Anaplasmosis may occur in areas where ticks (including the deer ticks and blacklegged ticks) are present. The exact global prevalence of the condition is not known
  • In the United States, the rate of infection is approximately 6 individuals per million population. The infection predominantly occurs in New England and certain north central states
  • HGA can affect both males and females of all ages, although males get infected more often, probably owing to more outdoor activities
  • Elderly adults and those with compromised immunity are more susceptible to these bacterial infections

What are the Risk Factors for Human Granulocytic Anaplasmosis? (Predisposing Factors)

The risk for contracting Human Granulocytic Anaplasmosis is greatest in the endemic regions. The risk factors for HGA 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)
  • Older adults have a higher vulnerability
  • Having reduced immunity, owing to factors such as:
    • Being on immune suppressant drugs, such as those given after an organ transplantation
    • HIV infection
    • Undergoing treatment for cancer
  • 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 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 Granulocytic Anaplasmosis? (Etiology)

Human Granulocytic Anaplasmosis is an infection that is caused by the bacterium Anaplasma phagocytophilus.

  • This bacterial infection spreads to humans through tick bites; particularly, through the bite of the blacklegged ticks and deer ticks. The ticks bite and attach themselves onto human skin, to feed on blood
  • The bacteria enter the body through the broken skin, and subsequently the bloodstream, causing an infection. The bacteria infect a type of white blood cells called the neutrophils
  • The neutrophils, along with eosinophils and basophils, form the granulocyte cells. These cells have enzyme and protein granules, which digest and destroy any invading microbes
    • When the bacteria enter the neutrophils, it alters their nature/properties. It leads to a loss of granules inside these cells (called degranulation) and a resultant compromise in their infection-fighting capacity
    • This may lead to 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, termed thrombocytopenia and anemia, respectively
    • There may also be a drop in the levels of albumin protein in blood (hypoalbuminemia). 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, HGA 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

The Human Granulocytic Anaplasmosis infection is not contagious; it does not spread from one individual to another.

What are the Signs and Symptoms of Human Granulocytic Anaplasmosis?

The symptoms of Human Granulocytic Anaplasmosis may begin 1-2 weeks after infection. The type and severity of symptoms may vary between individuals, depending on the general health status of the affected individual.

The common signs and symptoms associated with HGA include:

  • Fever, chills
  • Severe headache
  • Muscle and joint pain
  • Anemia
  • Vomiting, diarrhea
  • Hepatitis
  • Confusion
  • Skin rashes
  • Cough

How is Human Granulocytic Anaplasmosis Diagnosed?

The diagnosis of Human Granulocytic Anaplasmosis is made using the following tools:

  • Physical examination
  • 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 check for the following:
    • The levels of different blood cell types and blood albumin
    • Liver function: An inflammatory response in liver cells is observed in HGA
  • Polymerase chain reaction (PCR) test to identify and confirm the presence of Anaplasma phagocytophilus
  • 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 HGA. Generally, the results of this test may be negative in the first few days following an infection

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 Granulocytic Anaplasmosis?

Some potential complications in individuals with Human Granulocytic Anaplasmosis may include:

  • Dyspnea or shortness of breath
  • Problems with blood clotting process
  • Bleeding in the gastrointestinal tract
  • Damage to liver
  • Respiratory failure
  • Kidney failure

How is Human Granulocytic Anaplasmosis Treated?

  • The treatment for Human Granulocytic Anaplasmosis 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 Granulocytic Anaplasmosis be Prevented?

The following are some tips to prevent Human Granulocytic Anaplasmosis:

  • 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 Granulocytic Anaplasmosis? (Outcomes/Resolutions)

  • The prognosis of Human Granulocytic Anaplasmosis is determined by the age and general 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 the elderly adults and immunocompromised individuals)
  • Since the black-legged ticks also cause Lyme disease, the recovery may be prolonged if an individual is affected by both HGA and Lyme disease
  • Per case reports, approximately 0.5-3% of those infected with HGA succumb to the disease

Additional and Relevant Useful Information for Human Granulocytic Anaplasmosis:

  • Human Granulocytic Anaplasmosis was classified under ehrlichiosis as ‘human granulocytic ehrlichiosis’ till 2001. HGA has since been recognized as a separate class of infection
  • The blacklegged ticks, which are vectors of HGA, also carry Lyme disease. Therefore, an individual may get infected with both HGA and Lyme disease at the same time. In such cases, he/she may exhibit symptoms of both diseases to varying degrees, and the recovery may be prolonged

What are some Useful Resources for Additional Information?

Centers for Disease Control and Prevention (CDC)
1600 Clifton Rd. Atlanta, GA 30333, USA
Phone: (404) 639-3534
Toll-Free: 800-CDC-INFO (800-232-4636)
TTY: (888) 232-6348
Email: cdcinfo@cdc.gov
Website: http://www.cdc.gov

References and Information Sources used for the Article:

(2016, June 23). Retrieved January 19, 2017, from https://www.cdc.gov/anaplasmosis/

Ehrlichiosis/Anaplasmosis. (n.d.). Retrieved January 18, 2017, from http://columbia-lyme.org/patients/tbd_ehrli-anapla.html

Human Granulocytic Ehrlichiosis (HGE). (n.d.). Retrieved January 19, 2017, from https://rarediseases.org/rare-diseases/human-granulocytic-ehrlichiosis-hge/

Helpful Peer-Reviewed Medical Articles:

Choi, K., Grab, D. J., & Dumler, J. S. (2004). Anaplasma phagocytophilum Infection Induces Protracted Neutrophil Degranulation. Infection and Immunity, 72(6), 3680-3683. doi:10.1128/iai.72.6.3680-3683.2004

Dumler, J. S., Choi, K., Garcia-Garcia, J. C., Barat, N. S., Scorpio, D. G., Garyu, J. W., . . . Bakken, J. S. (2005). Human Granulocytic Anaplasmosis and Anaplasma phagocytophilum. Emerging Infectious Diseases, 11(12), 1828-1834. doi:10.3201/eid1112.050898

Weil, A. A., Baron, E. L., Brown, C. M., & Drapkin, M. S. (2012). Clinical Findings and Diagnosis in Human Granulocytic Anaplasmosis: A Case Series From Massachusetts. Mayo Clinic Proceedings, 87(3), 233–239. http://doi.org/10.1016/j.mayocp.2011.09.008

Dumler, J. S., Madigan, J. E., Pusterla, N., & Bakken, J. S. (2007). Ehrlichioses in Humans: Epidemiology, Clinical Presentation, Diagnosis, and Treatment. Clinical Infectious Diseases, 45(Supplement 1), S45-S51. doi:10.1086/518146

Bakken, J. S., & Dumler, J. S. (2015). Human Granulocytic Anaplasmosis. Infectious Disease Clinics of North America, 29(2), 341–355. http://doi.org/10.1016/j.idc.2015.02.007

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Feb. 7, 2017
Last updated: Feb. 7, 2017

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