Bovine Infectious Diseases — High-Yield NAVLE Summary for Efficient Study

The following high-yield review summarizes the most important bovine infectious diseases you are expected to recognize, organized by NAVLE relevance and supported by classic clinical clues frequently used in exam questions.

Bovine Respiratory Disease Complex (BRD)

BRD is one of the most significant causes of economic loss in feedlot cattle. NAVLE questions commonly ask about its multifactorial nature: viral priming (IBR/BoHV-1, BRSV, PI3, BVDV) followed by bacterial invasion (Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Mycoplasma bovis).

Key exam clues include:

• Stressors such as transport, commingling, and weaning

• Mannheimia → fibrinous pleuropneumonia with leukotoxin

• BRSV → subcutaneous emphysema and interstitial pneumonia

• IBR → necrotic tracheitis (“red nose”)

• Prevention emphasize vaccination, low-stress weaning, and metaphylaxis in high-risk groups.

Bovine Viral Diarrhea Virus (BVDV)

A major NAVLE disease due to its reproductive impacts and persistent infection (PI) calves. Fetal infection before 120 days of gestation produces PI animals that shed virus for life.

High-yield clues:

• Acute disease → diarrhea, immunosuppression

• Mucosal disease (PI + cytopathic strain) → erosions from mouth to GI tract, 100% fatal

• Reproductive outcomes → early embryonic death, abortion, congenital cerebellar hypoplasia

• Diagnostics commonly tested: ear notch IHC, antigen ELISA, PCR.

Infectious Bovine Rhinotracheitis (IBR)

Caused by BoHV-1, this disease appears as respiratory illness, conjunctivitis, infectious pustular vulvovaginitis, and abortion.

Important NAVLE points:

• Latency in trigeminal ganglia

• Modified-live vaccine risks in unvaccinated pregnant cows

• Aborted fetuses → small necrotic foci in the liver and classic herpesviral lesions

Johne’s Disease (Paratuberculosis)

A chronic, progressive gastrointestinal disease caused by Mycobacterium avium subsp. paratuberculosis. NAVLE focuses on its clinical picture and control challenges.

Key exam markers:

• Adult cattle with severe weight loss and profuse watery diarrhea

• Normal appetite despite weight loss

• Thickened, corrugated intestines on necropsy

• Diagnostic strategies: ELISA for herd screening, fecal PCR for early detection

• No treatment → long-term management involves test-and-cull and strict hygiene

Bovine Leukemia Virus (BLV)

A retrovirus producing enzootic bovine leukosis. NAVLE emphasizes the small percentage that develop lymphosarcoma in characteristic anatomic locations.

High-yield predilection sites:

• Right atrium

• Abomasum

• Uterus

• Spinal canal

• Retrobulbar space

• Transmission is iatrogenic (needles, palpation sleeves), via blood, or perinatally.

• No vaccine or treatment.

Malignant Catarrhal Fever (MCF)

A fatal herpesvirus disease typically transmitted from sheep to cattle (OHV-2).

NAVLE questions often highlight:

• Corneal edema (“blue eye”)

• Copious mucopurulent nasal discharge

• High fever, lymphadenopathy, diarrhea

• Severe lymphoproliferation and vasculitis on histology

• Disease is nearly always fatal; control is based on preventing contact with carrier species.

Foot-and-Mouth Disease (FMD)

A highly contagious Aphthovirus infection, important on NAVLE due to its reportable status.

Classic clues:

• Vesicles on mouth, tongue, teats, and coronary band

• Excess salivation, lameness

• Very high morbidity, low mortality

• Although exotic to North America, recognition and differentiation from other vesicular diseases (especially VS) is essential.

Vesicular Stomatitis (VS)

• A zoonotic rhabdovirus producing vesicles indistinguishable from FMD.

• The test-friendly differentiator: VS affects horses, FMD does not.

• Seasonal outbreaks linked to blackflies and sandflies.

Bluetongue

An orbital virus spread by Culicoides midges. While sheep develop severe disease, cattle serve as reservoirs.

NAVLE clues include:

• Facial edema, mucosal ulcerations

• Cyanotic, swollen tongue (“bluetongue”)

• Reproductive signs: hydranencephaly and abortion

  Seasonal and vector-dependent.

Listeriosis

Typically associated with feeding poorly fermented silage.

High-yield neurologic findings:

• Unilateral cranial nerve deficits

• Circling, head tilt

• Microabscesses in the brainstem (medulla/pons)

• Treatment relies on high-dose penicillin and NSAIDs, with prevention through proper silage management.