Anaplasmosis in Cattle: Symptoms, Treatment, and Prevention
Anaplasmosis — sometimes called tick fever or yellow fever of cattle — is one of the most economically damaging tick-borne diseases of beef and dairy cattle in North America, with a presence that has expanded significantly northward in the past decade as tick populations spread. Caused by the obligate intracellular parasite Anaplasma marginale, the disease destroys red blood cells and causes severe anemia, jaundice, and often death in naive adult cattle — while younger animals frequently experience subclinical infection and become lifelong carriers that perpetuate transmission within herds. This guide covers the complete clinical picture of bovine anaplasmosis in 2026 — including transmission routes, the four clinical stages, diagnosis, antibiotic treatment protocols, chemoprophylaxis, vaccination, and the multi-pronged prevention strategies that effectively control this disease in endemic areas.
Table of Contents
- What Is Bovine Anaplasmosis?
- Transmission: Ticks and Beyond
- Geographic Distribution and Endemicity in 2026
- Four Clinical Stages of Anaplasmosis
- Symptoms by Disease Stage
- Diagnosis: Laboratory and Clinical Methods
- Treatment Protocols: Antibiotics and Supportive Care
- Chemoprophylaxis: Feed-Grade Chlortetracycline
- Integrated Prevention Program
- Economic Impact and Prevention Value Chart
- Anaplasmosis Management Calendar
- Frequently Asked Questions
1. What Is Bovine Anaplasmosis?
Bovine anaplasmosis is a tick-borne hemolytic disease of cattle caused by Anaplasma marginale, an obligate intracellular gram-negative bacterium that infects and destroys red blood cells. The organism is not a true bacterium in the traditional sense — it cannot survive outside a host cell — but it responds to tetracycline-class antibiotics, which is the cornerstone of both treatment and prevention.
The disease was first formally described in the United States in 1910 and has been endemic in the Gulf Coast states, parts of the Southeast, and the Southwest ever since. In the past decade, a significant northward geographic expansion has occurred — driven by the spread of the primary tick vector (Dermacentor variabilis, the American dog tick) and potentially by climate warming extending tick habitat ranges. States that historically saw only occasional anaplasmosis cases — Kansas, Nebraska, Missouri, Iowa, Indiana, and parts of the Pacific Northwest — are now reporting endemic transmission.
2. Transmission: Ticks and Beyond
Unlike many cattle diseases where a single transmission route dominates, anaplasmosis can be transmitted through multiple biological and mechanical pathways — which complicates control and means that tick management alone is insufficient for complete disease prevention in endemic operations.
- Tick Transmission — The Primary Biological Vector: Dermacentor andersoni (Rocky Mountain wood tick), D. variabilis (American dog tick), D. albipictus (winter tick), and Rhipicephalus (Boophilus) microplus (southern cattle tick in Texas and Mexico) are the confirmed tick vectors for A. marginale in North America. Ticks transmit the organism transstadially (from larva to nymph to adult as the tick develops) but not transovarially (a mother tick does not transmit to her eggs). This means nymphs and adults are infectious but larvae of the same tick are not. Tick season in most endemic areas runs April–October, explaining the strong seasonal pattern of anaplasmosis cases peaking in late summer and fall.
- Mechanical Transmission — Blood-to-Blood Contact: Any procedure that transfers blood from an infected animal to a susceptible animal can transmit A. marginale. This includes: reuse of needles without changing between animals during vaccination, deworming, or other injections; reuse of dehorning equipment, ear taggers, or castration instruments without disinfection; and shared blood on rectal sleeves during pregnancy examination. Mechanical transmission explains why anaplasmosis can spread rapidly through a herd during processing events even when tick exposure is minimal.
- Biting Insects: Stable flies (Stomoxys calcitrans), horse flies (Tabanus spp.), and deer flies (Chrysops spp.) can mechanically transmit A. marginale when they begin feeding on an infected animal and are interrupted before completing their meal, then immediately feed on a susceptible animal. The blood remaining on the mouthparts of a biting fly contains sufficient A. marginale to initiate infection. This route is particularly important during peak biting insect season and in high-density confinement situations where fly pressure is intense.
- In-Utero Transmission: Anaplasma marginale can be transmitted from infected cows to their fetuses during pregnancy — resulting in calves born already infected (congenitally infected). These calves typically show no clinical signs and may not be recognized as a source of anaplasmosis transmission within the herd. The frequency of congenital transmission is estimated at 1–5% of pregnancies in infected cows, making it a minor but real contributor to herd-level perpetuation of the organism.
3. Geographic Distribution and Endemicity in 2026
Anaplasmosis has undergone significant geographic expansion in the United States over the past 15 years. Several factors drive this expansion: climate warming extending tick vector habitat ranges northward, increased deer populations (deer are reservoir hosts for A. marginale), expanding cattle movements between endemic and historically non-endemic regions, and the northward range expansion of Dermacentor tick species.
| Endemicity Level | States / Regions | Typical Herd Seroprevalence | Recommended Management |
|---|---|---|---|
| Highly Endemic | Texas, Florida, Alabama, Mississippi, Louisiana, Arkansas, Oklahoma, Kansas, parts of California and Arizona | 50–90% of adult cattle antibody-positive | Year-round chemoprophylaxis; rigorous vector control; avoid moving naive adults into herds |
| Moderately Endemic | Missouri, Tennessee, Kentucky, Georgia, South Carolina, North Carolina, parts of Colorado, New Mexico, Nevada | 20–50% seroprevalence | Seasonal chemoprophylaxis (tick season); testing incoming cattle; vaccination where available |
| Emerging / Sporadic | Nebraska, Iowa, Indiana, Ohio, Illinois, parts of Pacific Northwest, upper Midwest | Under 20%; increasing prevalence documented | Awareness; test cattle from southern origins; consider seasonal chemoprophylaxis; establish baseline herd prevalence |
| Historically Minimal Risk | Northern tier states (Minnesota, Wisconsin, New England, Dakotas) | Under 5%; but risk increasing | Be alert to introduction risk from purchased cattle; test animals from southern origins; monitor tick vectors |
4. Four Clinical Stages of Anaplasmosis
Bovine anaplasmosis follows a predictable four-stage clinical progression in naive adult cattle. Understanding the characteristics of each stage guides treatment timing — early intervention dramatically improves outcomes, while late-stage intervention has lower success rates and higher mortality risk.
5. Symptoms by Disease Stage
Recognizing anaplasmosis early enough to initiate effective treatment is the most critical practical skill for cattle producers in endemic areas. The clinical presentation is distinct enough from other cattle diseases that experienced producers can identify it reliably — but the early signs are subtle and require regular and attentive pen observation.
| Clinical Sign | Early Stage | Acute Stage | Severe Stage | Diagnostic Significance |
|---|---|---|---|---|
| Attitude / Behavior | Mildly dull, trailing the herd | Profoundly depressed, reluctant to move | Unable to stand, lateral recumbency | One of the earliest observable changes; attentive daily observation critical |
| Mucous Membrane Color | Slightly pale gums and conjunctiva | Pale to white; beginning icterus | Icteric (yellow): gums, sclera, vulva, muzzle | Jaundice (icterus) is pathognomonic for severe hemolytic anemia — immediately suspect anaplasmosis in endemic area |
| Body Temperature | Normal to mildly elevated (103–104°F) | Variable — may be elevated or normal | Often subnormal in shock state (100°F or below) | Unlike BRD, high fever is NOT a reliable anaplasmosis indicator; subnormal temp = severe prognosis |
| Respiratory Pattern | Normal to mildly increased rate | Increased rate compensating for anemia | Rapid, labored breathing (oxygen deficit from anemia) | Respiratory distress from anemia, not pneumonia — important differentiation from BRD |
| Milk Production | Mild reduction | Dramatic drop or complete cessation | None | Sudden significant milk drop in dairy cattle in endemic area is an early warning sign for anaplasmosis |
| Urine Color | Normal | May be slightly discolored | Dark (hemoglobinuria) in severe cases | Dark urine indicates severe hemolysis; important to distinguish from other causes of "red water" |
| Aggression / Aberrant Behavior | None | May show confusion or disorientation | Brain hypoxia can cause aggressive behavior — cattle safety concern | Acutely anaplasmotic cattle are DANGEROUS when handled — hypoxic brain produces unpredictable behavior; approach carefully |
6. Diagnosis: Laboratory and Clinical Methods
Timely and accurate diagnosis of anaplasmosis is essential — both for individual animal treatment decisions and for understanding herd-level exposure status. The diagnostic method appropriate depends on the clinical situation: acutely ill animals require rapid clinical diagnosis, while testing for carrier status requires laboratory methods.
- Blood Smear (Giemsa Stain) — Acute Cases: In animals with acute clinical signs and suspected anaplasmosis, a blood smear stained with Giemsa stain allows microscopic visualization of A. marginale inclusion bodies (marginal bodies) on the periphery of red blood cells — giving the organism its species name. This test is highly specific when positive and can be performed by most veterinary diagnostic labs within hours. However, sensitivity in early or late disease may be lower as parasitemia levels fluctuate.
- PCR Testing — Gold Standard for Carrier Detection: Polymerase chain reaction (PCR) testing on whole blood is the most sensitive method for detecting A. marginale, including in carrier animals with very low-level parasitemia that are negative on blood smear. PCR is the recommended method for testing cattle before introducing them to a new herd, for confirming subclinical carriers, and for herd-level prevalence surveys. Most state veterinary diagnostic laboratories run PCR for anaplasmosis with 24–72 hour turnaround.
- Competitive ELISA (cELISA) — Serology: The cELISA detects antibodies against A. marginale, indicating prior exposure and current carrier status. It is less sensitive than PCR for detecting acute early infection (before antibody development) but is excellent for herd-level serosurveillance and for identifying carrier cattle with past exposure. ELISA testing is commonly used for pre-purchase herd testing and for understanding endemic exposure levels in a herd. Animals may remain seropositive for years after infection.
- PCV (Packed Cell Volume) — Severity Assessment: Measuring PCV (hematocrit) provides objective severity assessment for individual clinical cases and guides treatment intensity and prognosis. Normal PCV in cattle: 24–46%. Treatment is urgent at PCV below 20%; blood transfusion consideration at PCV below 12%. Serial PCV monitoring every 12–24 hours in treated cases guides decisions about whether additional support is needed.
7. Treatment Protocols: Antibiotics and Supportive Care
Successful anaplasmosis treatment depends on two parallel interventions: antibiotic therapy to eliminate A. marginale replication in red blood cells, and supportive care to manage the severe anemia and physiological stress of the hemolytic crisis. Treatment should be initiated as early as possible — ideally at the first clinical signs, before severe anemia develops.
First-Line Antibiotic: Oxytetracycline (LA-200)
Long-acting oxytetracycline (LA-200 or equivalent) at 6.6–11 mg/kg IV or IM (depending on severity) is the most commonly used and most cost-effective first-line treatment for acute bovine anaplasmosis. For mild-moderate cases, 11 mg/kg IM every 48 hours for 2–3 treatments is typical. For severe cases, IV administration provides more rapid achievement of therapeutic blood levels. Multiple consecutive IM injections at the same site should be avoided — rotate injection sites and use BQA protocols. Oxytetracycline is often curative in early disease but less reliable in severe late-stage cases.
Alternative: Doxycycline (Under Veterinary Direction)
Doxycycline is not labeled for cattle in the United States but may be used under veterinary extra-label drug use (ELDU) provisions in refractory or severe cases where oxytetracycline is insufficient. Its use requires explicit veterinary prescription, extended withdrawal periods, and documentation. Imidocarb dipropionate — the standard treatment for anaplasmosis in many international markets — is not currently approved for use in cattle in the United States, though it is highly effective and may be used in some research or special circumstances under veterinary guidance.
Supportive Care for Severe Cases
For cattle with PCV below 15% and signs of cardiovascular compromise (weakness, inability to stand, rapid heart rate), antibiotic therapy alone may be insufficient to prevent death before A. marginale replication is controlled. Supportive interventions include: whole blood transfusion (4–8 liters from a compatible donor) to rapidly increase oxygen-carrying capacity; IV fluid therapy to maintain cardiovascular function; B-vitamin supplementation (particularly B12 and B complex) to support erythropoiesis (red blood cell production); dexamethasone (under veterinary direction only) to reduce immune-mediated RBC destruction in the most severe cases; and absolute rest — minimal handling, calm environment, shade, fresh water access. The decision to transfuse requires veterinary guidance but is life-saving in severe cases.
Monitoring Treatment Response
Serial PCV measurements every 12–24 hours in treated acute cases provide objective monitoring of treatment response. A rising PCV (increased reticulocyte count indicating bone marrow erythropoiesis response) indicates successful treatment. A continuing decline in PCV despite 48–72 hours of antibiotic treatment indicates either inadequate antibiotic dosing, the organism's antibiotic resistance (rare for A. marginale with oxytetracycline), concurrent severe nutritional deficiency, or disease too advanced for recovery. Contact your veterinarian immediately if PCV continues declining after 48–72 hours of appropriate therapy.
Post-Recovery Management
Animals that recover from acute anaplasmosis require several weeks of reduced stress and adequate nutrition before returning to normal production levels. Red blood cell mass takes 4–6 weeks to fully recover after severe hemolysis. Pregnant cows that survived acute anaplasmosis may abort 1–3 weeks after recovery as a delayed consequence of the hypoxic stress — monitor pregnant cows closely. Recovered animals are permanently immune to clinical disease from the same A. marginale strain but remain persistent carriers — they should be tested and identified as carriers in your herd records to inform purchasing and herd management decisions.
8. Chemoprophylaxis: Feed-Grade Chlortetracycline
In endemic areas, the most practical and economically effective anaplasmosis prevention strategy for most beef cattle operations is continuous or seasonal chemoprophylaxis using feed-grade chlortetracycline (CTC) — a strategy that prevents clinical disease by suppressing A. marginale replication below the level that causes anemia and clinical signs.
| CTC Protocol | Daily Dose Target | Delivery Method | Season | Prevents vs Clears Carriers |
|---|---|---|---|---|
| Prophylactic (Prevention) | 0.5–2.0 mg/kg body weight daily (1.1 mg/lb) | Mineral mix, block, or free-choice supplement — must achieve consistent intake | Year-round in highly endemic; tick season (Apr–Oct) in moderate risk | Prevents clinical disease; does NOT eliminate carrier state |
| Treatment Level (Therapeutic) | 22 mg/kg body weight daily × 5 days | Individual animal dosing through VFD-prescribed medicated feed; must be individual not group | During active treatment of sick animals | May reduce parasitemia; should be combined with injectable oxytetracycline for acute cases |
| Carrier Elimination (High Dose) | 22 mg/kg × 5–7 consecutive days (injectable OTC protocol under vet direction) | Injectable oxytetracycline only; not achievable through feed supplementation | Applied to confirmed carriers before moving to non-endemic areas | May eliminate carrier state in some animals; requires confirmation by PCR 90 days post-treatment |
9. Integrated Prevention Program
Effective anaplasmosis control in endemic operations requires an integrated program that addresses multiple transmission routes simultaneously — because tick control alone, chemoprophylaxis alone, or vaccination alone each leave significant transmission gaps.
Tick Vector Control
Acaricide (tick control) products applied to cattle reduce tick burden and the probability of tick-mediated A. marginale transmission. Pour-on and injectable acaricides (ivermectin-based products kill attached ticks; specific acaricides target tick attachment stages), ear tag acaricides (Cylence, Python), and back rubber or oiler-applied acaricide formulations all reduce tick exposure. No tick control product eliminates all ticks — ticks that feed briefly before detachment can still transmit. Combine with habitat management (brush clearing around water and feeding areas reduces tick habitat; rotational grazing interrupts tick life cycle).
Needle and Equipment Biosecurity
Mechanically-transmitted anaplasmosis during processing events is entirely preventable. Use a new needle for each animal during all injections — this one practice also reduces injection site infections and respects antibiotic stewardship. Disinfect dehorning equipment and ear taggers between animals with an effective disinfectant solution (1% sodium hypochlorite is effective). Change rectal examination gloves between animals. These practices prevent anaplasmosis transmission during processing events and simultaneously improve overall herd biosecurity against multiple pathogens.
Test Purchased Cattle Before Herd Entry
Every cattle purchase from an endemic region represents a potential carrier introduction risk. PCR testing (most sensitive) or cELISA serology testing of all purchased cattle before herd entry allows identification of carriers that would otherwise be introduced silently. This is particularly important for operations moving cattle from endemic to non-endemic areas, or from highly endemic areas into herds with significant numbers of naive adult animals. A positive test result does not necessarily mean the animal must be rejected — it means the management decisions (isolation, treatment, or acceptance as a known carrier) can be made deliberately rather than discovered during an outbreak.
Vaccination (Where Available)
A commercially produced, conditionally-licensed anaplasmosis vaccine using killed A. marginale was available in the United States for several decades but was withdrawn from commercial production. As of 2026, no USDA-licensed commercial anaplasmosis vaccine is available for cattle in the U.S. Some state veterinary diagnostic laboratories (notably in Oklahoma, Texas, and California) have historically produced autogenous or conditionally-licensed vaccines for use in their states under veterinary authorization. Research into recombinant subunit anaplasmosis vaccines is active, with several candidates in advanced development stages as of 2025–2026. Consult your state veterinarian and your veterinarian for the current status of vaccine availability in your region.
Managing Introduction of Naive Adults Into Endemic Herds
The highest-risk anaplasmosis scenario is moving naive adult cattle (over 3 years old with no prior exposure) into a highly endemic area during tick season. If this introduction is unavoidable, options include: beginning CTC chemoprophylaxis at full prophylactic dose 2–4 weeks before introduction; vaccinating if a conditionally-licensed vaccine is available in your state; introducing during low-tick-season months (November–March in most northern endemic areas); or accepting the introduction risk with intensive monitoring protocol (twice-daily observation for early clinical signs during the first 90 days, with PCV testing of any animal showing depression or reduced feed intake).
10. Economic Impact and Prevention Value Chart
11. Anaplasmosis Management Calendar
| Month | Key Actions | Rationale | Priority |
|---|---|---|---|
| January–March | Test purchased cattle before spring arrival; review VFD with veterinarian; order CTC mineral | Pre-season preparation; lower tick pressure allows herd assessment; VFD renewal needed annually | High — preparation window |
| April–May | Begin CTC chemoprophylaxis in endemic areas; initiate tick control program (acaricide ear tags or pour-on) | Tick season beginning; prophylaxis needs 2–3 weeks to establish effective blood levels before peak tick pressure | Critical — start of risk season |
| June–August | Peak vigilance — twice-daily observation; monthly CTC mineral consumption monitoring; fly control concurrent with tick control | Peak tick and biting fly season; highest transmission risk period; most anaplasmosis cases occur July–September | Critical — peak risk period |
| September–October | Continue CTC and tick control; be aware that fall processing of cattle from multiple sources creates mechanical transmission risk | Second tick activity peak in many regions; fall weaning and processing events create mechanical transmission risk; cases continue into October | High — continued risk |
| November–December | Discontinue tick season chemoprophylaxis (or continue year-round in highly endemic); document any cases for annual veterinary review | Tick activity declining; winter management transition; annual herd health review with veterinarian | Moderate — transition period |