Anaplasmosis

Anaplasmosis is an infectious disease that is caused by a bacterium called Anaplasma phagocytophilum.  Anaplasma, formerly called Ehrlichia equi and also referred to as Ehrlichiosis, live inside of the white blood cells and can cause a variety of problems. Humans are infected when bitten by infected ticks from Ixodes ticks: the same vectors for Lyme disease, babesiosis and tick-borne encephalitis.

Although dogs and cats can be infected with Anaplasma, they cannot transmit the infection to humans: only tick bites can. Even if people cannot get the infection directly from their pets, if a pet is infected, it serves as an alert that Anaplasma is in the area and so heightens the need for vigilance of ticks. When one suspects Anaplasmosis in people or pets, it is wise to check for other infections also.  Co-infections are more difficult to resolve than is a single infection in both pets and humans.

Anaplasma phagocytophilum causes a disease called human granulocytic anaplasmosis, or HGA. "The human disease was first identified in 1990, although the pathogen was defined as a veterinary agent in 1932. Since 1990, the number of US cases have markedly increased, and infections are now recognized in Europe. A high international seroprevalence suggests infection is widespread but unrecognized.

Symptoms: HGA is clinically variable and frequently includes headache, fever, myalgia, and malaise. Less frequently patients may experience arthralgia or involvement of the gastrointestinal tract (nausea, vomiting, diarrhea), respiratory tract (cough, pulmonary infiltrates, acute respiratory distress syndrome [ARDS]), liver, or central nervous system.   A CDC study indicates that the pathogen has unique adaptations and pathogenetic mechanisms and further demonstrated interactions with host-cell signal transduction leads to permutations of neutrophil function and could permit immunopathologic changes, severe disease, and opportunistic infections. More study is needed to define the immunology and pathogenetic mechanisms and to understand why severe disease develops in some persons and why some animals become long-term permissive reservoir hosts.  Treatment for both humans and animals involves antibiotics.

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Photo: courtesy of the Centers for Disease Control