Ehrlichiosis

Ehrlichiosis is a tickborne^[1] bacterial infection,^[2] caused by bacteria of the family Anaplasmataceae, genera Ehrlichia and Anaplasma. These obligate intracellular bacteria infect and kill white blood cells.

The average reported annual incidence is on the order of 2.3 cases per million people.^[3]

Species

Five (see note below) species have been shown to cause human infection:^[4]

• Anaplasma phagocytophilum (which causes human granulocytic anaplasmosis,). A. phagocytophilum is endemic to New England and the north central and Pacific regions of the United States.
• Ehrlichia ewingii (which causes human ewingii ehrlichiosis). E. ewingii primarily infects deer and dogs (see Ehrlichiosis (canine)).^[3] E. ewingii is most common in the south central and southeastern states.
• Ehrlichia chaffeensis (which causes human monocytic ehrlichiosis). E. chaffeensis is most common in the south central and southeastern states.
• Ehrlichia canis
• Neorickettsia sennetsu

The latter two infections are not well studied. In 2006, human infection by Boone County, Missouri. Symptoms: high fever,severe joint and muscle aches, vomiting. Onset of symptoms began exactly 14 days after bite occurred. Symptoms affected patient on a 12-hour cycle; beginning early evening, ending early morning. No symptoms occurred for next 12 hours. CBC presented low WBC. Note: In 2008, human infection by Panola Mountain (Georgia, USA) Ehrlichia species was reported.^[5] On August 3, 2011, infection by a yet-unnamed bacterium in the genus Ehrlichia carried by deer ticks that has caused flu-like symptoms in at least 25 people in Minnesota and Wisconsin was reported; human ehrlichiosis was thought to be very rare or absent in Minnesota and Wisconsin.^[6] The new species, which is very similar genetically to an Ehrlichia species found in Eastern Europe and Japan called E. muris, was identified at Mayo Clinic Health System's Eau Claire hospital.^[6]

Ehrlichia are transported between cells through the host cell filopodia during initial stages of infection, whereas, in the final stages of infection the pathogen ruptures the host cell membrane.^[7]

Signs and symptoms

The most common symptoms include headache, muscle aches, and fatigue. A rash may occur, but is uncommon. Ehrlichiosis can also blunt the immune system by suppressing production of TNF-alpha, which may lead to opportunistic infections such as candidiasis.

Most of the signs and symptoms of ehrlichiosis can likely be ascribed to the immune dysregulation that it causes. A "toxic shock-like" syndrome is seen in some severe cases of ehrlichiosis. Some cases can present with purpura and in one such case the organisms were present in such overwhelming numbers that in 1991 Dr. Aileen Marty of the AFIP was able to demonstrate the bacteria in human tissues using standard stains, and later proved that the organisms were indeed Ehrlichia using immunoperoxidase stains.^[8]

Experiments in mouse models further supports this hypothesis, as mice lacking TNF-alpha I/II receptors are resistant to liver injury caused by ehrlichia infection.^[9]

3% of human monocytic ehrlichiosis cases result in death; however, these deaths occur "most commonly in immunosuppressed individuals who develop respiratory distress syndrome, hepatitis, or opportunistic nosocomial infections."^[10]

Treatment

Doxycycline and minocycline are the medications of choice. For people allergic to antibiotics of the tetracycline class, rifampin is an alternative.^[3] Early clinical experience suggested that chloramphenicol may also be effective, however, in vitro susceptibility testing revealed resistance.

Prevention

No human vaccine is available for ehrlichiosis. Tick control is the main preventive measure against the disease. However, in late 2012 a breakthrough in the prevention of CME (canine monocytic ehrlichiosis) was announced when a vaccine was accidentally discovered by Prof. Shimon Harrus, Dean of the Hebrew University of Jerusalem's Koret School of Veterinary Medicine.^[11]

See also

• Ehrlichia Wisconsin HM543746

References

External links

• (RO) Ehrlichiosis in dogs. Real cases Ehrlichia cases in dogs. Case studies