Anaplasmosis

   Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Faizan Sheraz, M.D. [2] Rina Ghorpade, M.B.B.S[3]

For anaplasmosis in dogs, see Ehrlichiosis (canine). For anaplasmosis in humans, see Human granulocytic ehrlichiosis.

Overview

Human Granulocytic Anaplasmosis(HGA) is a disease caused by an intraneutrophilic rickettsial parasite of ruminants, Anaplasma phagocytophilum previously known by other names, Ehrlichia equi and Ehrlichia phagocytophilum. It is an emerging cause of tick-borne illness in the USA and Europe. The organism infects granulocytes and is transmitted by a number of hematophagous species of ticks most commonly by black-legged deer tick Ixodes scapularis and Ixodes pacificus. HGA is considered as a zoonotic disease. The disease has a variable presentation in humans, but also often present as a subclinical illness with mild symptoms of fever, myalgia, and malaise. These common symptoms make it difficult to definitively diagnose HGA. Although it present as a mild illness sometimes it leads to hospitalization in 36%, the ICU admission in 7%, and death in 0.6% of cases.. This disease can be cured with antimicrobial agent doxycycline, however, minority of patients can have debilitating illness despite antibiotic therapy.

Historical Perspective

HGA was previously known as human granulocytic ehrlichiosis (HGE). The first human cases were found in Minnesota and Wisconsin in 1993. It was renamed as Human Granulocytic Anaplasmosis in 2003.

Classification

Classification based on causative organism

The most commonly A. phagocytophilum is transmitted by two ticks namely, Ixodes scapularis and Ixodes pacificus. The following table demonstrates the main differentiating points of these two ticks.

General information	ixodes scapularis	ixodes pacificus
Distribution	Northeast and midwestern USA	West cost of the USA
Other names	Eastern black-legged tick/deer tick	Western black legged tick/deer tick
Diseases transmitted	Babesia microti (Human babesiosis) Borrelia burgdorferi (Lyme Disease) Borrelia miyamotoi (Relapsing fever borreliosis) Ehrlichia muris (Ehrlichiosis) Powassan virus (Encephalitis) Anaplasma phagocytophilum (Anaplasmosis)	Borrelia burgdorferi (Lyme Disease) Borrelia miyamotoi (Relapsing fever borreliosis) Anaplasma phagocytophilum (Anaplasmosis)
Preferred hosts	White-tailed black-tailed deer and large/medium-sized mammals	Columbian black-tailed deer and large/medium-sized mammals

Pathophysiology

Lifecycle

The life cycle of Ixodes scapularis

This image displays an example of the tick lifecycle, based on stages and the months that they are most likely to occur during.

An adult female lay eggs in clutches of approximately 1500-3000 eggs in spring, from eggs six-legged larvae emerge. Larvae usually feed on rodent/bird blood and get infected by rickettsial parasites usually in summer. Larvae transformed into an eight-legged structure called Nymph, nymphs lie dormant in fall/winter, nymphs start feeding on deer, humans, and dogs in the next spring. Nymphs then molt into adults which also has eight legs, and adults find the third host, these adults mate on or off a host, and once engorged and met, female adult tick thousands of eggs in the clutch before dying. .

Pathogenesis

Anaplasma phagocytophilum enters the bloodstream after tick bite through the dermis, and bacteremia develops 4-7 days after tick-bite. It is an obligate intracellular gram-negative organism. After gaining entry into the bloodstream the bacteria infects granulocytes, mainly, neutrophils, eosinophils, and monocytes. This period of bacteremia is characterized by fever, which can last up to 7days, and the degree of bacteremia depends on the immune status of the host.

Mechanism of survival inside neutrophils

Anaplasma phagocytophilum has the ability to grow inside the neutrophils because of it affects the phagosome-lysosome fusion. Additionally, this bacteria inhibit the respiratory burst of the neutrophils and therefore, preventing the release of reactive oxygen radicals from neutrophils.

Studies have proven that A. phagocytophilum delays the apoptosis of neutrophils.

Vector

A. phagocytophilum is transmitted by I. scapularis, which also transmit the causative agent of Lyme disease caused by Borrelia burgdorferi and Babesiosis caused by Babesia microti. The coinfection of I. scapularis tick by these organisms and a patient can have HGA, Lyme disease, and Babesiosis simultaneously.

Reservior

The principal animal reservoirs of HGA are white-tailed deer and white-footed mice.

Other modes of transmission

Even though tick bite is a common mode of transmission of A. phagocytophilum, it can also occasionally be transmitted by blood transfusion and maternal-fetal transmission.

Differentiating HGA from other tick-borne diseases

Disease		Organism	Vector	Symptoms
Bacterial Infection
Borreliosis (Lyme Disease)		Borrelia burgdorferi sensu lato complex and B. mayonii	I. scapularis, I. pacificus, I. ricinus, and I. persulcatus	Erythema migrans, flu-like illness(fatigue, fever), Lyme arthritis, neuroborreliosis, and carditis.
Relapsing Fever	Tick-borne relapsing fever (TBRF):	Borrelia duttoni, Borrelia hermsii, and Borrelia parkerii	Ornithodoros species	Consistently documented high fevers, flu-like illness, headaches, muscular soreness or joint pain, altered mental status, painful urination, rash, and rigors.
	Louse-borne relapsing fever (LBRF) :	Borrelia recurrentis	Pediculus humanus
Typhus (Rickettsia)
Rocky Mountain Spotted Fever		Rickettsia rickettsii	Dermacentor variabilis, Dermacentor andersoni	Fever, altered mental status, myalgia, rash, and headaches.
Helvetica Spotted Fever		Rickettsia helvetica	Ixodes ricinus	Rash: spotted, red dots. Respiratory symptoms (dyspnea, cough), muscle pain, and headaches.
Ehrlichiosis (Anaplasmosis)		Ehrlichia chaffeensis, Ehrlichia ewingii	Amblyomma americanum, Ixodes scapularis	Fever, headache, chills, malaise, muscle pain, nausea, confusion, conjunctivitis, or rash (60% in children and 30% in adults).
Tularemia		Francisella tularensis	Dermacentor andersoni, Dermacentor variabilis	Ulceroglandular, glandular, oculoglandular, oroglandular, pneumonic, typhoidal.
Viral Infection
Tick-borne meningoencephalitis		TBEV virus	Ixodes scapularis, I. ricinus, I. persulcatus	Early Phase: Non-specific symptoms including fever, malaise, anorexia, muscle pains, headaches, nausea, and vomiting. Second Phase: Meningitis symptoms, headache, stiff neck, encephalitis, drowsiness, sensory disturbances, and potential paralysis.
Colorado Tick Fever		CTF virus	Dermacentor andersoni	Common symptoms include fever, chills, headache, body aches, and lethargy. Other symptoms associated with the disease include sore throat, abdominal pain, vomiting, and a skin rash. A biphasic fever is a hallmark of Colorado Tick Fever and presents in nearly 50% of infected patients.
Crimean-Congo Hemorrhagic Fever		CCHF virus	Hyalomma marginatum, Rhipicephalus bursa	Initially infected patients will likely feel a few of the following symptoms: headache, high fever, back and joint pain, stomach pain, vomiting, flushed face, red throat petechiae of the palate, and potentially changes in mood as well as sensory perception.
Protozoan Infection
Babesiosis		Babesia microti, Babesia divergens, Babesia equi	Ixodes scapularis, I. pacificus	Non-specific flu-like symptoms.

Epidemiology and Demographics

n the USA the annual incidence is 6.3 million per year and it is rising. The endemic area of HGA is the upper midwestern and northeastern United States, eight states (Vermont, Maine, Rhode Island, Minnesota, Massachusetts, Wisconsin, New Hampshire, and New York) have the highest annual incidence of HGA according to the Center for Diseases (CDC). This geographic area coincides with the distribution of black-legged deer tick Ixodes scapularis. There is a seasonal variation of the reported incidence, with the highest rate in summer months, most commonly June and July.

Risk factors

The highest incidence of reported cases occurs in males above age 40, with immunocompromised patients (HIV positives, cancer patients on chemotherapy, patients with transplanted organs) are at risk of severe disease with high mortality.

Screnning

There are no methods available to screen HGA.

Natural History, Complications, and Prognosis

Clinical features

The average incubation period of HGA is 5.5 days after a tick bite. This infection causes symptoms of fever, headache, and myalgia, with GI symptoms occurring in less than half of the patients and a macular, maculopapular of patechial skin rash in less than 10% of patients. Patients who are immunocompromised and on immunosuppressive drugs like corticosteroids and chemotherapeutic medications have severe illness.

Laboratory features include thrombocytopenia, leukopenia, and elevated serum transaminase and LDH levels in the majority of infected patients, also, anemia and increased serum creatinine can be seen.

Diagnosis

The decision to start treatment depends on the history of a tick bite, and sign and symptoms of HGA in patients living in endemic areas along with lab features of thrombocytopenia, leukopenia. However, to obtain a definitive diagnosis serological tests such as ELISA, PCR, and examination of peripheral blood for the characteristic intracytoplasmic morulae can be done.

Treatment

Treatment is indicated in all symptomatic patients. Human granulocytic anaplasmosis, suspected or symptomatic

Preferred regimen: Doxycycline 100 mg PO bid (or IV for those patients unable to take oral medication) for 10 days Alternative regimen: Rifampin 300 mg PO bid for 7–10 days (For patients with mild illness due to HGA who are not optimally suited for doxycycline treatment because of a history of drug allergy, pregnancy, or age <8 years) Pediatric regimen: Children ≥ 8 years of age Preferred regimen: Doxycycline 4 mg/kg/day PO bid (Maximum, 100 mg/dose) (or IV for children unable to take an oral medication) for 10 days Children < 8 years of age

Preferred regimen: Rifampin 10 mg/kg bid (Maximum, 300 mg/dose) for 4-5 days Note (1): If the patient has concomitant Lyme disease, then Amoxicillin 50 mg/kg/day in 3 divided doses (maximum of 500 mg per dose) OR Cefuroxime axetil 30 mg/kg per day in 2 divided doses (maximum of 500 mg per dose) should be initiated at the conclusion of the course of Doxycycline to complete a 14-day total course of antibiotic therapy Note (2): Rifampin is not effective therapy for Lyme disease, patients coinfected with B. burgdorferi should also be treated with Amoxicillin OR Cefuroxime axetil

Treatment of pregnant patients

Generally tetracyclins are considered as a contraindication during pregnancy due to hepatotoxicity to the mother, and adverse effect on fetal bones on teeth formation, however, Doxycyclin rarely causes these side effects.

Alternatively, Rifampin can be used in pregnant patients.

Prevention

1. The best way to prevent infection with A. phagocytophilum is the use of insect repellents such as DEET (N, N-diethyl-3-methylbenzamid) or permethrin.
2. Thorough bating after outdoor activities, the prompt examination of the skin, and removal of the tick.
3. Wearing protective clothing for outdoor activities or avoiding outdoor activities in endemic areas.
4. Use of prophylaxis antibiotics such as Doxycyclin is not recommended, and there is no vaccine available for the prevention of HGA.