Veterinary advice should be sought before applying any treatment or vaccine.


Equine Ehrlichiosis, Equine Granulocytic Ehrlichiosis

Anaplasmosis is a common tick-transmitted disease of horses. It is caused by Anaplasma phagocytophilum, a bacterium that was previously called Ehrlichia equi and associated with the disease Equine Ehrlichiosis. Ticks transmit this bacteria to horses as well as other animal species, including humans.

Younger horses under 4 years of age tend to have mild or no clinical signs where as older horses may become more ill. Once bitten by an infected tick, the horse generally starts to show early signs of the disease within 3-14 days.

During the early stages of the disease, the horse develops a very high fever of 103 to 106°F (39.4°C to 41.3°C). Other clinical signs include reluctance to move, depression, reduced appetite, occasional staggering, and mild edema in the lower limbs.

Diagnosis is based on clinical signs and testing for the presence of the organism from a blood sample.

Treatment is usually very effective if started soon after the signs of illness begin. Horses are usually given a course of antibiotics (oxytetracycline), administered intravenously followed by oral doxycycline. Other supportive care includes stall rest, nonsteroidal anti-inflammatory drugs (NSAID, eg. Banamine), and wrapping the legs for support.


High, fluctuating or intermittent fever (102.9-106.3°F)
Partial loss of appetite
Increased heart rate (50-60 beats/min)
Reluctance to move
Lower limb edema in all four legs
Poor body condition
Base-wide stance


  • Clinical signs
  • Geographical region
  • PCR - positive for Anaplasma phagocytophilum
  • Indirect fluorescent antibody (IFA) titer greater than 160

While waiting for your veterinarian

  • Keep horse hydrated: Horses with a high fever often will drink and eat less than normal. When horses become dehydrated they have an increased risk of colic. Therefore, it is important to encourage horses to keep drinking by using various strategies such as soaking hay, adding water to feed, dropping treats or pieces of apples in water buckets, etc.



Oxytetracycline7 mg/kg of body weight IV q24h for 5 to 7 daysN Pusterla et al; M Restifo et al; F Uehlinger et al.
Management of high feverFlunixin meglumine at 0.5 mg/kg IV once initiallyF Uehlinger et al.
Supportive therapyLeg wraps applied to all 4 limbs and stall confinement to help with limb edema, minimize risk of secondary injury, and to monitor body temperature
Fluid and electrolyte therapyMay be indicated for severe cases.


  • Application of tick repellents
  • Keep horse pastures mowed
  • Fence off pastures from white tailed deer
  • Minimize rodent populations
  • Check horses daily for the presence of ticks


Prognosis is usually excellent for uncomplicated cases.

Scientific Research

General Overviews

Risk Factors

  • Not keeping pastures mowed, as ticks are found more frequently on long grass
  • High populations of white tailed deer present in or near horse pastures.



Causative agent