Human granulocytic anaplasmosis
Encyclopedia
Human granulocytic anaplasmosis (HGA) (previously known as Human granulocytic ehrlichiosis, or HGE ) is an infectious disease
caused by Anaplasma phagocytophilum
, an obligate intracellular bacterium that is typically transmitted to humans by at least three kinds of tick
s, including Ixodes scapularis
, Ixodes pacificus
, and Dermacentor variabilis
. These ticks also transmit Lyme disease
and other diseases.
The bacteria infect white blood cells called neutrophils, causing changes in gene expression that prolong the life of these otherwise short-lived cells.
The major mammalian reservoir for A. phagocytophilum in the eastern United States is the white-footed mouse, Peromyscus leucopus. Although white-tailed deer harbor A. phagocytophilum, evidence suggests that they are not a reservoir for the strains that cause HGA.
Anaplasma phagocytophilum
shares its tick vector with other human pathogens, and about 10% of patients with HGA show serologic evidence of coinfection with Lyme disease
, babesiosis
, or tick-borne meningoencephalitis
.
, severe headache
, muscle aches (myalgia
), chills and shaking, similar to the symptoms of influenza
. Symptoms may be minor, as evidenced by surveillance studies in high-risk areas. GI
symptoms occur in less than half of patients and a skin rash is seen in less than 10% of patients. It is also characterized by thrombocytopenia
, leukopenia
, and elevated serum
transaminase
levels in the majority of infected patients.
, the infection caused by Ehrlichia chaffeensis
, and other tick-borne illnesses such as Lyme disease may be suspected. As Ehrlichia serologies can be negative in the acute period, PCR is very useful for diagnosis.
is the treatment of choice. If anaplasmosis is suspected, treatment should not be delayed while waiting for a definitive laboratory confirmation, as prompt doxycycline therapy has been shown to improve outcomes.
Presentation during early pregnancy can complicate treatment.
Rifampin has been used in pregnancy and in patients allergic to doxycycline.
genus, the term "human granulocytic ehrlichiosis" (HGE) is often used, reflecting the prior classification of the organism. E. phagocytophilum and E. equi were reclassified as Anaplasma phagocytophilum.
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
caused by Anaplasma phagocytophilum
Anaplasma phagocytophilum
Anaplasma phagocytophilum is a gram-negative bacterium that is unusual in its tropism to neutrophils...
, an obligate intracellular bacterium that is typically transmitted to humans by at least three kinds of tick
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
s, including Ixodes scapularis
Ixodes scapularis
Ixodes scapularis is commonly known as the deer tick or blacklegged tick , and in some parts of the USA as the bear tick. It is a hard-bodied tick of the eastern and northern Midwestern United States...
, Ixodes pacificus
Ixodes pacificus
Ixodes pacificus, the Western blacklegged tick, is a species of Ixodes, a parasitic tick found on the western coast of North America. It is the principal vector of Lyme Disease in that region....
, and Dermacentor variabilis
Dermacentor variabilis
Dermacentor variabilis, also known as the American dog tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia . It is one of the most well-known hard ticks.Though D...
. These ticks also transmit Lyme disease
Lyme disease
Lyme disease, or Lyme borreliosis, is an emerging infectious disease caused by at least three species of bacteria belonging to the genus Borrelia. Borrelia burgdorferi sensu stricto is the main cause of Lyme disease in the United States, whereas Borrelia afzelii and Borrelia garinii cause most...
and other diseases.
The bacteria infect white blood cells called neutrophils, causing changes in gene expression that prolong the life of these otherwise short-lived cells.
Ecology and epidemiology
A. phagocytophilum is transmitted to humans by the Ixodes persulcatus group of ticks. These ticks are found in the US, Europe, and Asia. In the US, I. scapularis is the tick vector in the East and Midwest states, and I. pacificus in the Pacific Northwest.The major mammalian reservoir for A. phagocytophilum in the eastern United States is the white-footed mouse, Peromyscus leucopus. Although white-tailed deer harbor A. phagocytophilum, evidence suggests that they are not a reservoir for the strains that cause HGA.
Anaplasma phagocytophilum
Anaplasma phagocytophilum
Anaplasma phagocytophilum is a gram-negative bacterium that is unusual in its tropism to neutrophils...
shares its tick vector with other human pathogens, and about 10% of patients with HGA show serologic evidence of coinfection with Lyme disease
Lyme disease
Lyme disease, or Lyme borreliosis, is an emerging infectious disease caused by at least three species of bacteria belonging to the genus Borrelia. Borrelia burgdorferi sensu stricto is the main cause of Lyme disease in the United States, whereas Borrelia afzelii and Borrelia garinii cause most...
, babesiosis
Babesiosis
Babesiosis is a malaria-like parasitic disease caused by infection with Babesia, a genus of protozoal piroplasms. After trypanosomes, Babesia are thought to be the second most common blood parasites of mammals and they can have a major impact on health of domestic animals in areas without severe...
, or tick-borne meningoencephalitis
Tick-borne meningoencephalitis
Tick-borne encephalitis is a viral infectious disease involving the central nervous system. The disease most often manifests as meningitis, encephalitis, or meningoencephalitis. Although TBE is most commonly recognized as a neurological disorder, mild fever can also occur...
.
Symptoms
Symptoms may include feverFever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, severe headache
Headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
, muscle aches (myalgia
Myalgia
Myalgia means "muscle pain" and is a symptom of many diseases and disorders. The most common causes are the overuse or over-stretching of a muscle or group of muscles. Myalgia without a traumatic history is often due to viral infections...
), chills and shaking, similar to the symptoms of influenza
Influenza
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
. Symptoms may be minor, as evidenced by surveillance studies in high-risk areas. GI
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
symptoms occur in less than half of patients and a skin rash is seen in less than 10% of patients. It is also characterized by thrombocytopenia
Thrombocytopenia
Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...
, leukopenia
Leukopenia
Leukopenia is a decrease in the number of white blood cells found in the blood, which places individuals at increased risk of infection....
, and elevated serum
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
transaminase
Transaminase
In biochemistry, a transaminase or an aminotransferase is an enzyme that catalyzes a type of reaction between an amino acid and an α-keto acid. To be specific, this reaction involves removing the amino group from the amino acid, leaving behind an α-keto acid, and transferring it to the...
levels in the majority of infected patients.
Diagnosis
Clinically, HGA is essentially indistinguishable from Human monocytic ehrlichiosisHuman monocytic ehrlichiosis
Human monocytotropic ehrlichiosis is a form of ehrlichiosis associated with Ehrlichia chaffeensis.This bacteria is an obligate intracellular pathogen affecting monocytes and macrophages.-Ecology & Epidemiology:...
, the infection caused by Ehrlichia chaffeensis
Ehrlichia chaffeensis
Ehrlichia chaffeensis is a species of rickettsiales bacteria.It is named for Fort Chaffee.It is the causative agent of human monocytic ehrlichiosis....
, and other tick-borne illnesses such as Lyme disease may be suspected. As Ehrlichia serologies can be negative in the acute period, PCR is very useful for diagnosis.
Treatment
DoxycyclineDoxycycline
Doxycycline INN is a member of the tetracycline antibiotics group, and is commonly used to treat a variety of infections. Doxycycline is a semisynthetic tetracycline invented and clinically developed in the early 1960s by Pfizer Inc. and marketed under the brand name Vibramycin. Vibramycin...
is the treatment of choice. If anaplasmosis is suspected, treatment should not be delayed while waiting for a definitive laboratory confirmation, as prompt doxycycline therapy has been shown to improve outcomes.
Presentation during early pregnancy can complicate treatment.
Rifampin has been used in pregnancy and in patients allergic to doxycycline.
Terminology
Although the infectious agent is known to be from the AnaplasmaAnaplasma
Anaplasma is a genus of rickettsiales bacteria.Anaplasmas reside in host red blood cells and lead to the disease anaplasmosis. The disease most commonly occurs in tropical areas of the world....
genus, the term "human granulocytic ehrlichiosis" (HGE) is often used, reflecting the prior classification of the organism. E. phagocytophilum and E. equi were reclassified as Anaplasma phagocytophilum.
See also
- Human monocytic ehrlichiosisHuman monocytic ehrlichiosisHuman monocytotropic ehrlichiosis is a form of ehrlichiosis associated with Ehrlichia chaffeensis.This bacteria is an obligate intracellular pathogen affecting monocytes and macrophages.-Ecology & Epidemiology:...
- Human ewingii ehrlichiosisHuman ewingii ehrlichiosisEhrlichiosis ewingii infection is an infectious disease caused by an intracellular bacteria, Ehrlichia ewingii. The infection is transmitted to humans by Amblyomma americanum...
- Ehrlichiosis (canine)
- AnaplasmosisAnaplasmosisAnaplasmosis is a disease caused by a rickettsial parasite of ruminants, Anaplasma spp. The organism occurs in the white blood cells and is transmitted by natural means through a number of haematophagous species of ticks...
External links
- CDC Emerging Infectious Diseases for more information about HGE