Anaplasmosis in Cattle – Summary
Classic Case
- Most common in adult cattle (especially >2 years old)
- Acute hemolytic anemia without hemoglobinuria
- Clinical signs include:
- Fever
- Icterus (jaundice)
- Pale mucous membranes
- Tachypnea, tachycardia
- Weakness, aggression (due to cerebral hypoxia)
- Late-term abortion
- Calves <6 months often asymptomatic due to maternal antibodies
Etiology
- Caused by Anaplasma marginale, an obligate intraerythrocytic rickettsial organism
- Transmitted by:
- Ticks (especially Dermacentor spp.)
- Biting flies, mosquitoes
- Iatrogenic via blood-contaminated needles or instruments
Diagnosis
- Blood smear: Organisms seen at the margins of RBCs
- CBC: Regenerative anemia; often with no hemoglobinuria
- PCR: Highly sensitive
- Serology (ELISA): For herd-level screening
Treatment
- Oxytetracycline (long-acting injectable) is the treatment of choice
- Severely anemic animals may require blood transfusion
- Supportive care includes minimizing stress, quiet handling
Prevention
- Tick control via acaricides and pasture management
- Sterilize instruments between animals
- Vaccines available in some regions but with limited efficacy
- Avoid introducing carrier animals into naïve herds
Pearls
- No hemoglobinuria helps distinguish from babesiosis
- Once infected, cattle become persistent carriers
- Economic impact includes weight loss, reduced productivity, and mortality in adults
Here are representative Giemsa-stained blood smear images showing the characteristic marginal inclusions of Anaplasma marginale. These appear as deeply stained basophilic bodies located at the periphery of erythrocytes—finding them is essential for confirming acute infection.
Overview and Epidemiology
Anaplasmosis is a non-contagious, tick-borne disease caused by the rickettsial organism Anaplasma marginale. Transmission occurs via biological vectors (ticks such as Dermacentor and Rhipicephalus) and mechanical vectors (contaminated needles, dehorning tools, biting flies). The disease is endemic in tropical/subtropical regions and parts of the southern U.S. Adult cattle are most clinically affected, while calves often remain subclinical carriers (merckvetmanual.com, researchgate.net).
Clinical Signs
- Fever (104–106°F), progressive anemia, pale mucous membranes, jaundice
- Weakness, decreased appetite or milk production, potential sudden death
- Hemoglobinuria is absent (distinct from babesiosis) (en.wikipedia.org, msdvetmanual.com, vet.k-state.edu)
Diagnostic Modalities
- Blood smear microscopy: Detection of marginal inclusion bodies during acute phase (msdvetmanual.com)
- PCR: Highly sensitive method for acute and carrier detection
- Serology (cELISA, IFA): Effective for identifying subclinical carriers (>4–6 weeks post-infection) (pubmed.ncbi.nlm.nih.gov)
- CBC: Non-regenerative anemia with PCV often <15%; no hemoglobinuria (vet.k-state.edu)
Treatment
- Oxytetracycline: Long-acting dose (11–20 mg/kg IM/IV), repeated every 72 hrs for 2–4 doses (dvm360.com)
- Blood transfusion: Recommended when PCV <12–15%, typically 1–2 gallons in adult cows (dvm360.com)
- Supportive care: NSAIDs, fluids, stress reduction, shade
- Carrier clearance: Long-acting oxytetracycline or chlortetracycline (5 mg/lb/day for 60 days) may eliminate carriers (pubmed.ncbi.nlm.nih.gov)
Prevention and Control
- Instrument hygiene: Disinfect needles, dehorners, tattoo equipment between animals (news.okstate.edu)
- Vector control: Tick/fly management; use of acaricides/insecticides in peak seasons (en.wikipedia.org)
- Carrier identification: Screen herds and consider culling or treatment of positives
- Vaccination: Live A. centrale vaccine used abroad; currently no FDA-approved vaccine (aphia.gov.tw)
NAVLE-Style Multiple-Choice Questions
Q1: Diagnosis
An adult beef cow in a tick-endemic region presents with pallor, fever, jaundice, and a Giemsa blood smear shows marginal inclusions in RBCs. Hemoglobinuria is absent. What is the most likely diagnosis?
A. Babesiosis
B. Anaplasmosis
C. Theileriosis
D. Leptospirosis
E. Iron deficiency anemia
Answer: B. Anaplasmosis
Explanation: Marginal RBC inclusions without hemoglobinuria are classic for A. marginale infection (msdvetmanual.com).
Q2: Treatment
A cow with acute anaplasmosis has a PCV of 8%. What is the best treatment plan?
A. Oral amoxicillin
B. Single-dose meloxicam
C. Long-acting oxytetracycline + blood transfusion
D. NSAIDs and water only
E. Doxycycline in feed
Answer: C. Long-acting oxytetracycline + blood transfusion
Explanation: Tetracycline controls infection while transfusion addresses life-threatening anemia (dvm360.com, iowabeefcenter.org).
Q3: Transmission
Several cows develop anemia and icterus four weeks after communal dehorning. Blood smear reveals marginal inclusions. What is the most likely transmission route?
A. Tick bite
B. Contaminated instruments
C. Vertical transmission
D. Airborne
E. Foodborne
Answer: B. Contaminated instruments
Explanation: Mechanical transmission via shared equipment is a common iatrogenic route (vet.k-state.edu, msdvetmanual.com, en.wikipedia.org).
References
- [Merck Veterinary Manual – Anaplasmosis in Ruminants]
- PubMed: Efficacy of oxytetracycline regimens in clearing A. marginale carriers
- MSD Veterinary Manual – Blood smear image and diagnostic criteria
- ResearchGate, Texas A&M TVMDL, Oklahoma State University news – diagnostic images and treatment strategies (merckvetmanual.com, pubmed.ncbi.nlm.nih.gov, msdvetmanual.com)