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Animal science and veterinary

Transboundary animal diseases: FMD, PPR, ASF, HPAI

What makes a disease transboundary: foot-and-mouth disease, PPR, African swine fever and avian influenza, their control, and a vaccination coverage sum.

Exam essential5 min readUpdated
On this page
  1. What makes a disease transboundary
  2. Foot-and-mouth disease (FMD)
  3. Peste des petits ruminants (PPR)
  4. African swine fever (ASF)
  5. Highly pathogenic avian influenza (HPAI)
  6. Principles of control
  7. Key points
  8. What the exams ask
  9. Questions people ask
  10. Sources
  11. Related on Laisha
  12. Discussion

Some animal diseases do not stay put. Carried by animals on the move, meat and other products, vehicles, people, wild birds or the wind, they cross borders quickly and can devastate livestock economies, close export markets and threaten food security. These transboundary animal diseases (TADs) need coordinated action between farmers, veterinary services and countries. Rinderpest, the cattle plague that killed millions of animals and caused famines, was declared eradicated worldwide in 2011, only the second disease ever eradicated after smallpox; others remain major threats.

Transboundary diseases, their epidemiology and control are standard topics in veterinary epidemiology, preventive medicine and livestock policy.

What makes a disease transboundary

FAO describes TADs as highly contagious epidemic diseases that can spread rapidly across national borders, with serious socio-economic and sometimes public health consequences, requiring cooperation between countries to control. Many are listed by the World Organisation for Animal Health (WOAH, formerly OIE), so countries must report outbreaks and follow international standards for trade.

Four major transboundary animal diseases compared: foot-and-mouth disease, a virus with seven serotypes affecting cloven-hoofed animals, spread by contact, air and products and controlled by vaccination and movement control; peste des petits ruminants of sheep and goats, controlled by vaccination with a global eradication goal for 2030; African swine fever of pigs, spread by pigs, pork products and ticks, controlled by biosecurity and culling; and highly pathogenic avian influenza of poultry and wild birds, controlled by biosecurity, culling and in some countries vaccination Foot-and-mouth diseaseAgent: virus, 7 serotypesHosts: cattle, buffalo, pigs, sheep, goatsSpread: contact, air, productsControl: vaccination, movement controlPeste des petits ruminantsAgent: morbillivirusHosts: sheep and goatsSpread: close contactControl: vaccination; eradication by 2030African swine feverAgent: large DNA virusHosts: domestic and wild pigsSpread: pigs, pork products, ticksControl: biosecurity, culling; vaccines limitedHighly pathogenic avian influenzaAgent: influenza A (H5, H7)Hosts: poultry, wild birds, some mammalsSpread: wild birds, contactControl: biosecurity, culling, some vaccination
Four of the most important transboundary animal diseases today, and how each is mainly controlled.Diagram: Laisha, original.

Foot-and-mouth disease (FMD)

  • Agent: an aphthovirus with seven serotypes (O, A, C, SAT1, SAT2, SAT3 and Asia1) and many strains; immunity to one serotype does not protect against others.
  • Hosts: cattle, buffalo, pigs, sheep, goats and many wild cloven-hoofed animals.
  • Signs: fever, blisters in the mouth and on feet and teats, drooling, lameness, sharp falls in milk; deaths mainly in young animals.
  • Spread: direct contact, airborne virus over long distances in some conditions, contaminated products, vehicles and people.
  • Impact: production losses in endemic regions; in free countries, outbreaks cause trade bans and mass culling, as in the United Kingdom in 2001.
  • Control: vaccination matched to circulating strains, movement control, and in free countries rapid culling. FAO and WOAH's Progressive Control Pathway guides endemic countries.

Peste des petits ruminants (PPR)

  • Agent: a morbillivirus related to rinderpest.
  • Hosts: sheep and goats, especially goats.
  • Signs: fever, eye and nose discharge, mouth sores, pneumonia and diarrhoea; mortality can exceed 50 per cent in naive flocks.
  • Spread: close contact, often through markets and nomadic movement.
  • Control: a cheap live vaccine giving lifelong immunity. FAO and WOAH launched a Global Strategy in 2015 aiming to eradicate PPR by 2030.

African swine fever (ASF)

  • Agent: a large DNA virus (asfivirus).
  • Hosts: domestic pigs and wild boar; warthogs and soft ticks in Africa carry it without disease.
  • Signs: high fever, haemorrhages, death in up to nearly 100 per cent of infected pigs with virulent strains.
  • Spread: pigs, wild boar, pork products (the virus survives long in meat and cured products), swill feeding, vehicles and people.
  • Control: strict biosecurity, bans on swill feeding, culling and movement control. Spreading from Africa to Georgia in 2007 and to China in 2018, it killed or led to the culling of a large share of the world's pigs. Vaccines have been licensed in a few countries but are not widely available or approved.

Highly pathogenic avian influenza (HPAI)

  • Agent: influenza A viruses of the H5 and H7 subtypes that become highly pathogenic in poultry.
  • Hosts: poultry and wild birds; H5N1 clade 2.3.4.4b has since 2020 spread across continents in wild birds and infected many wild and domestic mammals, including dairy cattle in the United States from 2024.
  • Control: biosecurity to keep wild birds away from poultry, early detection and culling, movement control, and vaccination in some countries.

Principles of control

  • Early detection and reporting: surveillance, laboratories and farmer awareness.
  • Biosecurity at farm, market and border.
  • Movement control and zoning: protection zones (often 3 km) and surveillance zones (often 10 km) around outbreaks.
  • Vaccination, where effective vaccines exist.
  • Stamping out: culling infected and in-contact animals with compensation, so farmers report disease.
  • Compartmentalisation and regionalisation, letting disease-free zones or production units keep trading.
  • Regional cooperation: shared surveillance and synchronised vaccination across borders.
Worked example

How many animals must be vaccinated?

To stop sustained spread, enough animals must be immune that each case infects, on average, fewer than one other. If the basic reproduction number is R0, the critical proportion immune is:

pc = 1 − 1 ÷ R0

Suppose PPR in a goat population has R0 ≈ 4:

  • pc = 1 − 1 ÷ 4 = 0.75: at least 75 per cent must be immune.
  • With a vaccine that protects 90 per cent of vaccinated animals, coverage must be at least 0.75 ÷ 0.90 ≈ 83 per cent.

Because goat flocks turn over quickly, with many young animals born each year, coverage falls fast after a campaign, so campaigns are repeated. Zones: a 3 km protection zone covers π × 32 ≈ 28 km2, and a 10 km surveillance zone about 314 km2, which shows how quickly control efforts grow with distance.

Key points

  • TADs are highly contagious diseases that spread rapidly across borders and need international cooperation; rinderpest was eradicated in 2011.
  • FMD: seven serotypes; cloven-hoofed animals; vaccination and movement control.
  • PPR: goats and sheep; effective vaccine; global eradication target 2030.
  • ASF: pigs and wild boar; no widely available vaccine; biosecurity and culling.
  • HPAI: poultry and wild birds; H5N1 2.3.4.4b now also infects many mammals.
  • Control: surveillance, biosecurity, zoning, vaccination, stamping out with compensation, and regional cooperation.
  • Critical vaccination coverage = (1 − 1 ÷ R0) ÷ vaccine efficacy.

What the exams ask

  • School-leaving and entrance papers: names and signs of major contagious livestock diseases.
  • Degree and research-fellowship entrances: aetiology, hosts, transmission, diagnosis and control of FMD, PPR, ASF and HPAI, and WOAH listing.
  • Veterinary and policy examinations: emergency response, zoning and compartmentalisation, vaccination strategies, trade implications and eradication programmes.

Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.

Questions people ask

Why do farmers sometimes hide outbreaks?

Fear of culling without fair compensation, loss of income and stigma. Rapid, fair compensation and trust in veterinary services encourage reporting.

Can people catch these diseases?

FMD, PPR and ASF do not infect people. Avian influenza can occasionally infect humans in close contact with infected birds or animals, so protective measures are important.

Why was rinderpest eradicated but not FMD?

Rinderpest had one serotype, an effective long-lasting vaccine, no carrier wildlife reservoir of importance and clear signs. FMD has seven serotypes, many strains, wildlife hosts and vaccines giving shorter immunity.

Sources

  1. FAO. Emergency Prevention System (EMPRES) for Transboundary Animal and Plant Pests and Diseases. FAO, online.
  2. World Organisation for Animal Health. Terrestrial Animal Health Code. WOAH, updated annually.
  3. FAO and OIE. Global Strategy for the Control and Eradication of PPR. FAO and OIE, 2015.
  4. Dixon, L. K. et al. "African swine fever epidemiology and control." Annual Review of Animal Biosciences 8, 221–246 (2020).
  5. Roeder, P., Mariner, J. and Kock, R. "Rinderpest: the veterinary perspective on eradication." Philosophical Transactions of the Royal Society B 368, 20120139 (2013).

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