control of infectious disease

endemic

constant presence of a disease within a certain geographical area or population.

predictable level of disease occurence

eg pasteurella pneumonia in UK cattle

epidemic

rapid increase in disease incidence within a certain geographical area or population

unpredictable level of disease occurence

eg FMDV outbreak

pandemic

an epidemic occuring over a wide geographical area and affecting a large number of individuals. extremely unpredictable level of disease occurence

eg swine flu and covid 19

routes of pathogen spread

• direct contact (esp skin infections)

• aerosol transmission (esp respiratory infections)

• orofaecal (esp alimentary)

• transplacental (vertical)

• vector (blood borne)

what are the control measures

• prevent exposure to pathogen

  • import controls

  • quarantine

  • vector control

• eradicate pathogen following exposure

  • notification - legislation through DEFRA/APHA

  • isolation and movement restriction

  • slaughter and decontamination

  • treatment/ vaccination

import control

• biosecurity of country and individual farm

• source of animals- prevent importation from countries where pathogen is endemic. buy in stock from a reputable source

• border security important at a national level

• identification and traceability important

• there may be smuggling, animal trafficking, fraudulent documentation

who must be notified when a notifiable disease is suspected

DEFRA/APHA

isolation measures

if a pathogen is suspected all aniamsl at source of potential outbreak are prevented from leaving the premises until such time as tests cornform or refute the suspicion

a control zone is established to prevent movement of animals onto adjacent

DEFRA / APHA may impose a total ban on animal movement across the UK

eradication

• slaughter and disposal of animals at the source of outbreak and often contiguous cull

• compensaition from gov to farmer for loss

• decontaminaiton/disinection of the environment

• some pathogens are very resistant despite decontamination

what are the drawbacks of therapeutic control of infection

• cost

• efficacy- pathogen load is diminished to a point that the animal recovers but carrier status ensues and pathogen shedding continues

• risk of resistance

vaccination

• prevention of infection in susceptible animals

• prophylactic measure usually

• killed vaccine- inactivated

• live vaccine- low virulence mutant

• subunit- only one or small number of protein antigens from the pathogen are administered

what are the drawbacks to vaccnation

• an admission that infection control has failed and we have to live with the pathogen present in the population/ environment

• loss of disease free status

• difficult to distinguish between a vaccinated animal and one that has been infected with the pathogen

ring vaccination

cull animals at the source of outbreak and vaccinate all animals within the control/surveillance zone

obstacles to the control of infectious disease

• poor infrastructure

• global transport of animals and animal products

• pathogen mutation- new strains, no longer effective, pathogens jump species barriers

• reservoir host- wildlife

• inadequate control of an insect vector

• vaccine breakdown/failure

vaccine factors

• vaccine strain does not cross protect against wild type pathogen

• does not elicit high enough levels of protective immunity

• has gone off through inappropriate storage

• vaccine has not been administered properly

host factors

• not enough are vaccinated in the population

• animals were already infected prior to vaccination

• animals are too young or old to generate protedctive immunity

• vaccine immunity has waned- booster required