Anaplasmosis/Equine granulocytic anaplasmosis/EGA
What is it? Anaplasmosis or EGA is a bacterial infection (of Anaplasma phagocytophilum bacteria), i.e. an infectious disease, spread by Ixodes ticks. Equine granulocytic anaplasmosis was previously known as equine granulocytic ehrlichiosis or Ehrlichia equi. Ticks may carry anaplasmosis alongside other tick-born diseases e.g. Lyme disease or piroplasmosis, and horses can be infected with several diseases from the same tick. Humans, dogs, cats and ruminants can also be infected with anaplasmosis from the same ticks. Anaplasmosis infects white blood cells (neutrophils and sometimes eosinophils) during the acute stage of infection and clinical signs may be seen one to three weeks after being bitten by a tick. Anaplasmosis is seasonal with cases being seen in late autumn, winter and spring. |
Clinical signs
Clinical signs develop after an incubation period of around 10 days and may include:
fever (pyrexia) - this is often the first and main clinical sign, can be severe, and may last for around 10-14 days; temperature may be highest around 5 days after infection, typically around 39.5-40.0'C but can be as high as 42.2'C,
depression/lethargy,
going off feed/anorexia,
weakness/ataxia (incoordination/wobbliness/collapse) (note this can lead to wounds if the horse falls or stumbles)
ventral swelling/oedema (of the legs and/or belly/abdomen),
petechial hemorrhage (tiny red/purple dots on the gums),
jaundice/icterus (yellowing e.g. of the whites of the eyes or gums),
reluctance to move (intermittent lameness has also been documented),
worsening of existing/concurrent infections (e.g. wounds or respiratory infections).
In rare severe cases horses may have transient heart arrhythmia, recumbency (lying down a lot), severe myopathy (muscle weakness/cramps/spasms), and very rarely horses with EGA may die.
Horses can also have mild clinical signs, often starting with a horse being "not quite right", depressed or lethargic and going off feed/losing weight, or may be infected but not show clinical signs of illness.
Anaplasmosis is usually less severe in young horses (<4 years old), with older horses tending to show more obvious clinical signs.
Clinical signs may last from 3 to 16 days (typically 7-14 days). Horses that are not treated will generally get better after that time (i.e. the disease is often self-limiting).
See Liphook Equine Hospital table comparing clinical signs of Lyme disease and Anaplasmosis.
Diagnosis
Diagnosis is based on:
1. clinical signs
2. a complete blood count (red and white blood cell count), which would be likely to show
- a decreased white blood cell count (leukocytopenia/neutropenia),
- a decreased red blood cell count, i.e. anaemia (this will be hemolytic anaemia, caused when red blood cells are destroyed inside the body - iron supplements should NOT be given),
- a low platelet count (thrombocytopenia).
- Serum Amyloid A (a marker of inflammation) may also be increased.
3. examining a stained blood smear under a microscope - seeing Anaplasma bodies (morulae) in neutrophils (and eosinophils) is diagnostic, but a negative blood smear doesn't rule out the disease, and the bodies may not be seen for the first 48 hours or so after infection (the presence of infective bodies in the white blood cells may correlate with the horse having a raised temperature). During peak infection 5% to 40% of circulating neutrophils may contain Anaplasma bodies.
4. PCR testing - this is the optimal test for anaplasmosis, particularly in the early or late stages when the bodies may be difficult to detect on a blood smear; PCR testing can detect anaplasmosis around 3 days before clinical signs appear, and 9 days after clinical signs resolve.
Same day PCR testing is carried out at Equisyn Equine Vet Clinic near 16260 Chasseneuil-sur-Bonnieure. The PCR profile run is the Piro-Like/tick-borne disease profile also run by Frank Duncombe/Labeo, supported by Labeo, and includes anaplasmosis, both forms of piroplasmosis, Lyme disease and leptospirosis. PCR testing is available to non-clients as well as clients of the clinic.
Other laboratories in France that test for anaplasmosis include Frank Duncombe/Labeo and Vetodiag.
PCR (polymerase chain reaction) looks for and confirms the presence of parasite DNA and is considered highly specific and sensitive. PCR can detect low levels of parasitic infection and can be used for chronic infections.
Other laboratories in France that test for anaplasmosis include Frank Duncombe/Labeo and Vetodiag.
PCR (polymerase chain reaction) looks for and confirms the presence of parasite DNA and is considered highly specific and sensitive. PCR can detect low levels of parasitic infection and can be used for chronic infections.
Treatment
Treatment with tetracycline antibiotics (oxytetracycline/doxycycline) is very effective against Anaplasmosis phagocytophilum. Systemic intravenous treatment with 7 mg/kg/day tetracycline for 5-8 days has been shown to eliminate infection. Anti-inflammatory treatment may also be recommended in severe cases - NSAIDs or corticosteroids (but be aware that corticosteroid use increases insulin resistance and therefore the risk of laminitis, and assess insulin status before using corticosteroids/avoid use of corticosteroids unless life-threatening in horses with a history of insulin dysregulation or laminitis).
Horses should receive good nursing/supportive care - a quiet stress-free environment with good shelter and a deep bed to encourage them to rest, small tempting easy to eat feeds e.g. mashes (but avoid making significant changes to their diet), rugs as dictated by fever/sweating, clean water perhaps with the chill taken off/slightly flavoured to encourage drinking. More severe cases may require fluid therapy (a drip).
There is no vaccine against anaplasmosis for horses.
Horses that have been infected with anaplasmosis appear to have immunity for at least 2 years after having the disease.
References/further information
Equine Granulocytic Anaplasmosis - Janet Foley MSD Manual October 2022
Equine Anaplasmosis - Jean-Yin Tan, thehorse.com November 2022
Equine granulocytic anaplasmosis - Visavet Health Surveillance Centre (Madrid University) 2022
Equine granulocytic anaplasmosis - Kristiina Ruotsalo, University of Guelph 2021
French/en francais
Anaplasmose - RESPE
Syndrome Piro-Like Equine - Vetodiag (a guide to tick-borne diseases in France)
Ehrlichiose - Anaplasmose - Labaratoire Orbio
Dallenogare Chloe
L'anaplasmose granulocytaire equine, connaissances scientifiques, prevalence mondial et cas cliniques
Liege Universite 2019
Treatment with tetracycline antibiotics (oxytetracycline/doxycycline) is very effective against Anaplasmosis phagocytophilum. Systemic intravenous treatment with 7 mg/kg/day tetracycline for 5-8 days has been shown to eliminate infection. Anti-inflammatory treatment may also be recommended in severe cases - NSAIDs or corticosteroids (but be aware that corticosteroid use increases insulin resistance and therefore the risk of laminitis, and assess insulin status before using corticosteroids/avoid use of corticosteroids unless life-threatening in horses with a history of insulin dysregulation or laminitis).
Horses should receive good nursing/supportive care - a quiet stress-free environment with good shelter and a deep bed to encourage them to rest, small tempting easy to eat feeds e.g. mashes (but avoid making significant changes to their diet), rugs as dictated by fever/sweating, clean water perhaps with the chill taken off/slightly flavoured to encourage drinking. More severe cases may require fluid therapy (a drip).
There is no vaccine against anaplasmosis for horses.
Horses that have been infected with anaplasmosis appear to have immunity for at least 2 years after having the disease.
References/further information
Equine Granulocytic Anaplasmosis - Janet Foley MSD Manual October 2022
Equine Anaplasmosis - Jean-Yin Tan, thehorse.com November 2022
Equine granulocytic anaplasmosis - Visavet Health Surveillance Centre (Madrid University) 2022
Equine granulocytic anaplasmosis - Kristiina Ruotsalo, University of Guelph 2021
French/en francais
Anaplasmose - RESPE
Syndrome Piro-Like Equine - Vetodiag (a guide to tick-borne diseases in France)
Ehrlichiose - Anaplasmose - Labaratoire Orbio
Dallenogare Chloe
L'anaplasmose granulocytaire equine, connaissances scientifiques, prevalence mondial et cas cliniques
Liege Universite 2019
[Copied from Horse Nutrition and Health, a website available to Friends of The Laminitis Site, with permission of the author Andrea Jones/The Laminitis Site).
Information is given as a guide only and must not be relied upon. Please consult your vet for all equine medical matters.