NAVLE Hemic and Lymphatic

Bovine Anaplasmosis Study Guide

📅 March 28, 2026 ⏱ 25 min read

Bovine anaplasmosis is an infectious, non-contagious, tick-borne hemoparasitic disease of cattle caused by the obligate intraerythrocytic rickettsial organism Anaplasma marginale.

Overview and Clinical Importance

Bovine anaplasmosis is an infectious, non-contagious, tick-borne hemoparasitic disease of cattle caused by the obligate intraerythrocytic rickettsial organism Anaplasma marginale. It is the most prevalent tick-transmitted disease of cattle in the United States, causing economic losses exceeding $300 million annually.

Also known as "gall sickness" or "yellow-bag" due to characteristic icterus. The disease occurs in tropical and subtropical regions worldwide (40°N to 32°S), including the USA (endemic in southeastern, gulf coast, lower plains, and western states).

High-YieldDisease severity is AGE-DEPENDENT: cattle <1 year rarely show clinical signs, 1-2 years show moderate signs, >2 years often develop severe, potentially fatal disease (up to 50% mortality without treatment).

Species	Hosts	Clinical Significance
A. marginale	Cattle, wild ruminants	Most pathogenic; primary cause of bovine anaplasmosis
A. centrale	Cattle, wild ruminants	Less pathogenic; live vaccine in some countries (not USA); CENTRAL location in RBCs
A. ovis	Sheep, goats, deer	Causes disease in small ruminants; NOT infectious for cattle

Etiology

Anaplasma marginale is classified in order Rickettsiales, family Anaplasmataceae. The organism appears as dense, blue-purple inclusion bodies (0.3-1.0 µm) located on or near the MARGIN of infected RBCs on Giemsa-stained smears.

Anaplasma Species

Phase	Duration	Characteristics
Incubation	3-8 weeks	Organism multiplies; no clinical signs; parasitemia undetectable
Acute	4-9 days	Peak parasitemia (20-70% RBCs infected); clinical signs when >50% RBCs destroyed
Convalescent	Weeks-months	Parasitemia decreases; immune response develops
Carrier	Lifelong	Persistent low-level infection; clinically normal; reservoir

Transmission and Epidemiology

Transmission occurs via: (1) biological transmission by tick vectors, (2) mechanical transmission by biting flies, and (3) iatrogenic transmission through contaminated equipment.

Tick Vectors

Dermacentor spp. (primary US vectors): D. variabilis (American dog tick), D. andersoni (Rocky Mountain wood tick)
Rhipicephalus (Boophilus) spp.: Major vectors in Australia and Africa
Other genera: Ixodes, Hyalomma, Argas

Key point: Male Dermacentor ticks are particularly important due to interrupted feeding patterns allowing transfer between hosts. As few as 1-5 infected ticks can transmit infection.

Other Transmission Routes

Biting flies: Horse flies (Tabanids) are most important mechanical vectors
Iatrogenic: Contaminated needles, dehorning equipment, ear taggers, castration instruments

NAVLE TipSevere outbreaks occur when: (1) naive animals move into endemic areas, OR (2) carrier animals are introduced into naive herds. Recovered animals become LIFELONG CARRIERS.

Age	Severity	Mortality
<6 months	None to mild; subclinical	Rare; become carriers
6-12 months	Mild; decreased PCV	Rarely fatal
1-2 years	Moderate to severe	1-20%
>2 years	Severe; often fatal	Up to 50%+

Pathophysiology

Disease Phases

Mechanism of Anemia

The anemia is primarily EXTRAVASCULAR, resulting from immune-mediated destruction:

A. marginale invades RBCs causing surface membrane changes
Infected RBCs recognized as abnormal by immune system
Erythrophagocytosis occurs primarily in spleen
Anti-erythrocyte antibodies destroy infected AND uninfected RBCs
Hemoglobin catabolized to bilirubin causing icterus

Exam Focus: CRITICAL - Because hemolysis is EXTRAVASCULAR, there is NO hemoglobinemia and NO hemoglobinuria. This distinguishes anaplasmosis from babesiosis (intravascular hemolysis with "redwater").

Test	Application	Sensitivity	Limitations
Blood Smear	Acute clinical cases	High during peak parasitemia	Cannot detect carriers
cELISA	Carrier detection; screening	96%; high specificity	May be neg in early acute
PCR	Acute infection; confirmation	Highest	Cost; detects non-viable

Clinical Signs

Age-Dependent Severity

Clinical Presentation

Fever: Fluctuating, often >40°C (104-106°F)
Anemia: Progressive; pale mucous membranes
Icterus: Yellow mucous membranes and sclera (late sign)
Depression/weakness: Lethargy, reluctance to move
Anorexia and weight loss: Often dramatic
Decreased milk production: Severe drop in dairy cattle
Tachycardia/tachypnea: Compensatory
Aggression/disorientation: Due to cerebral hypoxia
Abortion: In pregnant cows
Sudden death: Without prior observed signs

High-YieldKEY FEATURE - URINE IS NOT RED OR BROWN. This distinguishes anaplasmosis from babesiosis ("redwater"), leptospirosis, and bacillary hemoglobinuria.

Condition	Hemoglobinuria	Key Features	Blood Smear
Anaplasmosis	NO	Extravascular hemolysis	Marginal inclusions
Babesiosis	YES	Intravascular hemolysis	Ring/pear piroplasms
Leptospirosis	YES	Renal involvement; abortion	No visible organisms
Bacillary Hemoglobinuria	YES	Liver necrosis; fluke history	No RBC organisms
Copper Toxicity	YES	Exposure history; gunmetal kidneys	Heinz bodies

Necropsy Findings

Gross Pathology

Carcass: Anemic and icteric; yellow adipose tissue
Blood: Thin and watery; does not clot well
Spleen: ENLARGED (splenomegaly), soft, congested with prominent follicles
Liver: Enlarged (hepatomegaly), mottled, yellow-orange
Gallbladder: Distended with thick brown/green bile
Lymph nodes: Brown (hemosiderin)
Heart: Petechial hemorrhages; soft myocardium

Histopathology

Widespread erythrophagocytosis in reticuloendothelial organs
Hemosiderin-laden macrophages in spleen and liver
Hepatic bile stasis and fatty changes

Drug	Dose/Route	Indication	Notes
Oxytetracycline LA	20 mg/kg IM	Acute clinical cases	Most common; multiple doses may eliminate carrier
Chlortetracycline	0.5-2 mg/lb daily in feed	Prevention/control	Requires VFD; FDA-approved for control
Enrofloxacin	Per label IM/SQ	Acute anaplasmosis	Conditional FDA approval; bactericidal
Imidocarb	3-5 mg/kg IM	Treatment; carrier elimination	Not USA-approved

Diagnosis

Diagnostic Methods

Blood Smear Examination

A. marginale appears as dense, blue-purple inclusion bodies (0.3-1.0 µm) at the MARGIN of erythrocytes on Giemsa stain.

Spherical, basophilic bodies at erythrocyte margin
Differentiate from Howell-Jolly bodies (larger, more central, blue)
Differentiate from basophilic stippling and artifacts

NAVLE TipA. MARGINALE = MARGINAL location on RBCs. A. CENTRALE = CENTRAL location. This distinguishes species on blood smear.

Supporting Laboratory Findings

PCV: Markedly decreased (<15% severe; normal 24-46%)
Anemia type: Regenerative
Bilirubin: Elevated (unconjugated)
Urinalysis: NO hemoglobinuria

Differential Diagnosis

High-YieldABSENCE of hemoglobinuria is the KEY distinguishing feature. Normal-colored urine = anaplasmosis. Red/brown urine = babesiosis, leptospirosis, or bacillary hemoglobinuria.

Treatment

Treatment Protocols

Supportive Care

Blood transfusion: Indicated for PCV <10-12%
Minimize stress: Severely anemic cattle may die from minimal exertion
Fluid therapy: If dehydrated

NAVLE TipTetracyclines are BACTERIOSTATIC (pause replication). Enrofloxacin is BACTERICIDAL (kills organisms). Treated animals often become carriers unless aggressive elimination protocols used.

Prevention and Control

Prevention Strategies

Vector control: Acaricides, pasture rotation, environmental management
Test new introductions: Screen with cELISA before adding to herd
Single-use needles: Change between each animal
Equipment sanitation: Disinfect dehorning tools, taggers, castration equipment
Chemoprophylaxis: CTC in feed during vector season (requires VFD)
Vaccination: A. centrale vaccine used in some countries (not USA); killed vaccines available under state permit

"A.M. JAUNDICE" Mnemonic

A - Age matters (older = worse)

M - Marginal location on RBCs

J - Jaundice (icterus) present

A - Anemia (extravascular)

U - Urine NOT red

N - No hemoglobinuria (vs. babesiosis)

D - Dermacentor ticks (US vector)

I - Iatrogenic transmission

C - Carrier state (lifelong)

E - Endemic areas (southern/western US)

Practice NAVLE Questions

Test your knowledge with 10,000+ exam-style questions, detailed explanations, and timed exams.

Start Your Free Trial →