Anaplasmosis

Anaplasmosis 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 by a number of haematophagous species of ticks. It can also be transmitted iatrogenically by the use of surgical, dehorning, castration, and tattoo instruments and hypodermic needles that are not disinfected between uses.

Although the term is often associated with animal infection, it is also used to describe infection in humans.^[1]

Life cycle

The organism can go through a complete lifecycle in the gut of certain species of ticks but the flies appear to be only a mechanical vector, thus, not as important in the maintaining the disease in any given area. The disease causes severe anemia and wasting in adult cattle which are infected. Young cattle and most other ruminants will not show clinical signs if infected but may serve as carriers. Since the organism "hides" from the body's immune system in red blood cells, it is difficult if not impossible for an infection to be totally cleared. As the immune response wanes, the organism again builds up and the host relapses.

Distribution

In the United States, anaplasmosis is notably present in the south and west where the tick hosts Dermacentor spp. are found. Although vaccines have been developed, none is currently available in the United States. Early in the 20th century, this disease was considered one of major economic consequence in the western United States. In the 1980s and 1990s, control of ticks through new acaricides and practical treatment with prolonged-action antibiotics, notably tetracycline, has led to the point where the disease is no longer considered a major problem.

Cases of coinfection with tick-born microorganisms are being increasingly reported in the last decade ^[2][3][4], perhaps explaining the variable manifestations and clinical responses noted in some patients with tick-transmitted diseases. In such clinical settings, laboratory testing for coinfection is indicated to ensure that appropriate antimicrobial treatment is given.

In 2005, Anaplasma ovis was found in reindeer populations in Mongolia^[5]. This pathogen and its associated syndrome (characterized by lethargy, fever and pale mucous membranes) was previously only observed in wild sheep and goats in the region, and is the first observed event of A. ovis in reindeer.

Notable cases

On July 30, 2009, David Letterman announced that he had been infected with anaplasmosis.^[6] He believes he was most likely bitten by an infected tick while camping with his 5-year-old son in their tree house.

References

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