Camelidae and Cervidae Bovine Viral Diarrhea Virus Study Guide

Overview and Clinical Importance

Bovine viral diarrhea virus (BVDV) is a pestivirus in the family Flaviviridae that primarily affects cattle but has been documented to infect over 50 species in the mammalian order Artiodactyla, including members of the Camelidae (llamas, alpacas) and Cervidae (white-tailed deer, mule deer, elk) families. Understanding BVDV infection in these alternative hosts is increasingly important for veterinary board examinations as these species serve as potential reservoirs and may impact cattle disease control programs.

BVDV infection in camelids and cervids presents unique diagnostic and management challenges compared to cattle. The virus can establish persistent infection (PI) in both camelids and cervids, similar to cattle, making these species epidemiologically significant. Persistently infected animals shed large quantities of virus throughout their lives, serving as primary reservoirs for herd and interspecies transmission.

Etiology

Virus Classification

BVDV belongs to the genus Pestivirus within the family Flaviviridae. Related pestiviruses include Border disease virus (sheep) and Classical swine fever virus (pigs). The BVDV genome consists of a single, linear, positive-sense, single-stranded RNA molecule of approximately 12.3 kb.

BVDV Classification and Biotypes

Transmission

BVDV transmission in camelids and cervids mirrors that in cattle. The virus can be detected in all body secretions and excretions, including respiratory and oral secretions, urine, milk, semen, and feces. Transmission routes include:

• Direct contact: Nose-to-nose contact with PI animals (highest viral load)
• Ingestion/Inhalation: Primary routes via contaminated feed, water, or aerosols
• Transplacental: Dam-to-fetus transmission resulting in PI offspring
• Fomites: Contaminated equipment, clothing, vehicles
• Interspecies transmission: Virus spread between cattle, sheep, goats, camelids, and cervids

Pathogenesis

Mechanism of Persistent Infection

The development of persistent infection is the hallmark of BVDV pathogenesis. In cattle, fetal infection with ncp BVDV during the first 40-125 days of gestation (before fetal immunocompetence develops) results in immunotolerance and lifelong viral persistence. The same mechanism applies to camelids and cervids, though specific gestational windows may vary slightly.

Outcomes of Fetal BVDV Infection by Gestational Stage

Clinical Signs in Camelids

BVDV infection in llamas and alpacas can range from subclinical to severe disease. Research suggests that camelids may be more resistant to clinical disease compared to cattle, with many infections being inapparent. However, persistent infections do occur and can cause significant morbidity.

Acute Infection

• Often subclinical or mild
• Lethargy, anorexia, depression
• Respiratory signs
• Diarrhea (less common than in cattle)
• Viremia detectable 3-10 days post-infection

Persistently Infected (PI) Crias

• Ill-thrift: Poor growth, failure to thrive
• Chronic wasting: Progressive weight loss
• Recurrent infections: Respiratory and enteric disease due to immunosuppression
• Hematologic abnormalities: Leukopenia, low hemoglobin, decreased PCV

Reproductive Effects

• Abortion and stillbirth
• Birth of weak or undersized crias
• Congenital defects (cerebellar hypoplasia, ocular abnormalities)

Clinical Signs in Cervids

White-tailed deer (Odocoileus virginianus) are the most studied cervid species for BVDV infection in North America. Clinical presentations include:

Acute Infection

• Often subclinical
• Pyrexia (fever)
• Lymphopenia
• Transient viremia

Persistent Infection in Fawns

• PI fawns documented experimentally and in free-ranging populations
• May appear clinically normal initially
• Viral shedding levels similar to PI cattle
• Sudden death possible

Reproductive Disease

• Fetal mummification
• Abortion
• Birth of PI fawns

Exam Focus: BVDV intraspecific transmission has been demonstrated among white-tailed deer. The birth of a PI fawn through contact with a PI deer proves that BVDV can be maintained within cervid populations independently of cattle under appropriate circumstances.

Pathological Findings

Gross Lesions

Pathological findings in camelids and cervids with BVDV infection are similar to those in cattle:

• Oral cavity: Erosions and ulcers of the tongue, gingiva, hard palate
• Esophagus: Linear erosions and ulceration
• Gastrointestinal tract: Erosions and ulcers in abomasum, small and large intestine
• Lymphoid tissue: Lymphoid depletion in Peyer patches, thymus, lymph nodes
• Hemorrhagic syndrome (BVDV-2): Petechial hemorrhages on mucosal surfaces, serosal surfaces

Congenital Defects

Fetal infection during organogenesis (days 80-150 in cattle) can result in:

• Cerebellar hypoplasia: Most common CNS lesion; results in ataxia, hypermetria, intention tremor
• Hydranencephaly/Porencephaly: Cavitating lesions of cerebral cortex
• Ocular defects: Retinal dysplasia, cataracts, microphthalmia
• Hypomyelination: Congenital tremor syndrome

Diagnosis

Diagnostic Testing Methods

Recommended Testing Protocol for Camelids

• Initial testing: RT-PCR on whole blood (preferred) or virus isolation
• If positive: Retest in 3-4 weeks using same methodology
• Confirm PI status: Virus detected on BOTH samples = Persistently Infected
• Serology: Can be used to identify exposed animals; PI animals typically seronegative

Treatment and Control

Treatment

There is NO SPECIFIC ANTIVIRAL TREATMENT for BVDV infection in any species. Management is supportive and involves:

• Fluid therapy for dehydrated animals
• Antimicrobials for secondary bacterial infections
• Nutritional support
• Isolation of infected animals

Control and Prevention

Vaccination

IMPORTANT: There is currently NO BVDV VACCINE LICENSED FOR USE IN CAMELIDS. Vaccination of camelids is NOT recommended because:

• May interfere with diagnostic testing
• Efficacy unproven in non-bovine species
• Complicates identification of truly infected animals

Biosecurity Measures

• Maintain closed herds: Limit introduction of new animals
• Quarantine and test: Test all incoming animals before introduction
• Test pregnant females: Screen for PI status before breeding season
• Identify and eliminate PI animals: Remove from herd immediately
• Avoid cattle contact: Minimize exposure to potentially infected cattle, especially PI cattle
• Separate species: Maintain separation between camelids and domestic ruminants

Management of PI Animals

Differential Diagnosis

When evaluating camelids or cervids with signs compatible with BVDV infection, consider:

Epidemiological Significance

Role as Potential Reservoirs

The potential for camelids and cervids to serve as BVDV reservoirs has significant implications for cattle disease control programs. For a species to be considered a potential wildlife reservoir, it must meet four criteria:

• Susceptibility: Must be susceptible to BVDV infection - CONFIRMED in both camelids and cervids
• Shedding: Must shed BVDV - CONFIRMED; PI animals shed similar levels to PI cattle
• Maintenance: Must maintain BVDV in population - DEMONSTRATED through PI offspring
• Sufficient contact: Must have contact allowing spillback to cattle - VARIABLE depending on management