Camelidae and Cervidae Foot and Mouth Disease Study Guide

Overview and Clinical Importance

Foot and Mouth Disease (FMD) is a highly contagious viral disease that affects cloven-hoofed animals, including members of the Camelidae (llamas, alpacas, dromedaries, and Bactrian camels) and Cervidae (deer species) families. Understanding FMD susceptibility in these species is crucial for veterinarians, as these animals may serve as reservoir hosts or experience subclinical infections that can complicate disease control efforts.

FMD represents one of the most economically devastating transboundary animal diseases globally, with significant implications for international trade and livestock movement. While camelids and cervids generally show different susceptibility patterns compared to traditional livestock, their role in FMD epidemiology remains clinically relevant for the NAVLE examination.

Etiology and Pathophysiology

Causative Agent

Foot and Mouth Disease virus (FMDV) belongs to the genus Aphthovirus within the family Picornaviridae. The virus is a small (25-30 nm), non-enveloped, icosahedral capsid containing a positive-sense single-stranded RNA genome of approximately 8.3 kb.

FMDV Serotypes and Global Distribution

Species Susceptibility and Clinical Manifestations

Camelidae Family Susceptibility

New World Camelids (NWC): Llamas and Alpacas

Experimental studies demonstrate that llamas and alpacas have low susceptibility to FMDV infection. While they can be infected through direct contact with infected animals, they:

• Do not readily transmit virus to other camelids or susceptible livestock species
• Do not become long-term virus carriers
• Show mild to inapparent clinical signs when infected
• Are considered epidemiologically insignificant in FMD transmission

Only one field case has been reported where alpacas showed minor clinical disease during an FMD outbreak in cattle in Peru (1971), with FMDV A24 isolated only from the affected cattle, not the alpacas.

Old World Camelids (OWC): Dromedaries and Bactrians

Conflicting evidence exists regarding OWC susceptibility to FMDV:

• Serological surveys on thousands of dromedary sera in Africa and UAE were negative
• Limited experimental infections show dromedaries can contract disease after experimental exposure
• Appear to have low susceptibility to natural infection
• Do not appear to pose significant transmission risk

Cervidae Family Susceptibility

Cervids are more susceptible to FMDV than camelids. Historical and experimental evidence includes:

• The only known FMD wildlife outbreak in the US occurred in mule deer in California (1924-1925)
• Over 22,000 deer were culled during control efforts
• Experimental studies confirm susceptibility in mule deer, elk, and bison
• Incubation period in deer: 2-3 days

Clinical Signs in Cervidae

Pathogenesis and Transmission

Routes of Infection

FMDV primarily enters through the respiratory mucosa, particularly the nasopharynx, which serves as the primary replication site. Secondary routes include:

• Direct contact with infected animals or their secretions
• Aerosol transmission (especially important in cervids)
• Contaminated feed, water, or fomites
• Skin lesions or abrasions

Disease Progression

After initial infection in the respiratory tract, FMDV spreads via viremia to secondary replication sites including oral mucosa, skin, mammary glands, and feet. Vesicles develop at sites of mechanical stress and rupture within 48 hours of formation.

Transmission Capacity by Species

Diagnostic Approach and Differential Diagnoses

Clinical Diagnosis Challenges

Clinical diagnosis of FMD in camelids and cervids presents unique challenges:

• Camelids often show mild or inapparent signs
• Cervids may not show obvious vesicles without close examination
• Clinical signs overlap with other vesicular diseases
• Species-specific normal behaviors may mask early signs

Laboratory Diagnosis

Definitive diagnosis requires laboratory confirmation through:

• Real-time RT-PCR (preferred for rapid diagnosis)
• Virus isolation in cell culture followed by serotyping
• Antigen-capture ELISA for serotype identification
• Antibody detection using structural protein (SP) and non-structural protein (NSP) ELISAs

Sample Collection Guidelines

Differential Diagnoses

Vesicular diseases that must be differentiated from FMD include:

• Vesicular Stomatitis (VS) - affects horses and cattle, transmitted by arthropod vectors
• Swine Vesicular Disease (SVD) - pigs only, enterovirus
• Vesicular Exanthema of Swine (VES) - pigs only, calicivirus
• Bluetongue - ruminants, midge-borne orbivirus
• Malignant Catarrhal Fever - especially in cervids
• Epizootic Hemorrhagic Disease - cervids, similar to bluetongue

Control Measures and Prevention

Immediate Response Measures

Upon suspected or confirmed FMD in camelids or cervids:

• Immediate notification of veterinary authorities (FMD is notifiable)
• Quarantine of affected premises and contact animals
• Movement restrictions within surveillance zones
• Enhanced surveillance of susceptible species in the area
• Biosecurity measures including disinfection of vehicles and personnel

Species-Specific Control Considerations