Viral epidemiology

Epidemiology- definition

Study of frequency, distribution, determinants of disease in populations

• POPULATION level impact

Biological V mechanical vector

• Biological → virus replicates inside vector

  • Bluetongue → virus replicates inside midge and ruminant

• Mechanical → virus only moved by vector (living or fomite)

  • Myxoma virus → flea moves it between hosts

Common viral strategy control

• Enhance surveillance

• Change host movement

  • Control zone (3km radius)

    • culling, testing

  • Surveillance zone (10km radius)

    • movement restrictions, testing

  • Quarantine

• Physical measures

  • disinfection

  • barrier - wall off → hens in barns

  • fencing to protect from env reservoirs

• Change host demography

  • Increase proportion protected → vaccination → herd immunity

  • Reduce population infected → culling

Notifiable diseases

Key notifying reasons:

• International trade

• Public health

• Animal welfare

• Legal requirement to notify APHA

  • Suspicion or confirmation (which is earlier)

• Rapid and coordinated action to reduce spread

  • Movement restrictions

  • Culling

  • Onsite restrictions

Rabies key info

• (Order → Mono-nega-virales)

• (Family → Rhab-do-viridae)

• Species → Lyssavirus rabies

• Rod shaped

• Enveloped

• Helical capsid

• Group V → -ve sense ssRNA

Rabies epidemiology

• Domestic dogs and bats

• US/Europe → free of domestic dog rabies

• US many wild rabies

UK rabies epidemiology

• Rabies free

• Notifiable

• Largest threat → illegal animal imports (e.g. domestic dogs)

• GB not part of EU pet travel scheme since Brexit → no pet passports

Rabies control from GB → EU (post Brexit) requirements

• Rabies vaccinated post 21 days

• Microchipped

• Animal health certificate issued within 10 days before travel

Rabies control into GB requirements

1. EU

   • GB pet health certificate/passport

     • Issued from UK or EU

2. USA

   • GB pet health certificate

3. Kenya (other countries)

   • Antibody test 30+ days after vaccination documented on health cert

   • Wait 3 months from vaccination before travelling

   • Valid if booster schedule kept

If no controls met → 4 months quarantine

• Period between animal first bitten and symptoms shown

Rabies vaccination

injectable vaccines (inactivated)

oral vaccines (mostly live attenuated)

FMDV general facts

• (Order → Picornavirales)

• (Family → Picornaviridae)

• Genus → Aph-tho-virus

• 7 serotypes

• Spread between most cloven hoofed animals

  • sylvatic in subsaharan Africa

FMDV modes of transmission [5]

VERY INFECTIOUS

• Direct contact with infected animals

  • Animals may shed asymptomatically

  • Short incubation period

• Contact with infected animal secretions

  • vesicles

  • semen

  • milk

• Wind movement

• Meat and offal (pigs)

• Fomites

FMDV impact

FMDV distribution

• Asia and Africa endemic

• UK, N America, Europe free from FMDV without vaccination

FMDV impact- disease free zone

• Much higher trade impact → threatens disease free status

• Rapidly stamp out single case and investigate intensively

  • pre-emptive cullings

FMDV impact- endemic zone with sylvatic reservoir

• Less impactful → already disease there

• Doesn’t change trading status, less possible to control

General FMDV control

UK Vaccination

Emergency

• UK legislation allows emergency use

• serve prophylaxis

• protect high yielding dairy cattle

• already lost access to global market so doesnt matter if antigen positive for FMDV

• FMDV serologial tests for no exposure

• cannot differentiate btw vaccine antibodies and infection antibodies

Prophy;axis

• enzootic countries protect production animals (high-yielding dairy) from clinical illness

FMDV vaccination info

• Provides 4-6 month protection against specific serotypes

• Only protects against clinical illness → vaccinated animals could be carriers

• Reduced access to global markets

• Herd immunity necessary to reduce transmission

• Poor thermostability of vaccine

• Risk of viral reintroduction from wildlife reservoirs