Biology • Year 12 • Module 7 • Lesson 7
Disease in Agriculture — Animals
Apply knowledge of animal disease pathogen types, transmission and economic effects to real Australian and international data, case studies and novel scenarios.
1. Interpret economic data — BVD vs FMD outbreak scenarios
The table below compares two animal disease scenarios modelled for a 10,000-head beef cattle enterprise in northern New South Wales. Scenario A: an undetected BVD persistently infected (PI) problem running for 3 years. Scenario B: a confirmed FMD outbreak lasting 6 months before eradication. 8 marks
| Cost category | Scenario A — BVD PI (3 yrs) | Scenario B — FMD outbreak (6 mths) |
|---|---|---|
| Animal deaths | ~80 calves/yr from PI-related disease | ~400 animals culled (infected/at-risk) |
| Reduced productivity | 15% reduced weaning rates; 12% slower weight gain | Growth halted during outbreak; feedlot placement cancelled |
| Veterinary/treatment costs | $45,000/yr (vaccines, testing, vet fees) | $220,000 (emergency response, testing) |
| Export market loss | None (BVD not notifiable at national level) | All exports suspended; estimated $1.8 million revenue lost |
| Movement restrictions | None | Property-level quarantine for 4 months; cannot sell cattle |
| Government compensation | Not applicable | $180,000 for culled animals |
| Estimated total cost | ~$420,000 over 3 years | ~$2.4 million over 6 months |
Modelled data based on published Australian BVD cost-benefit analyses (McPherson et al., 2013, Animal Production Science) and FMD economic impact modelling (Garner & Lack, 1995, updated estimates).
1.1 Identify the cost category that is present in Scenario B but absent from Scenario A. Explain why this difference exists, referring to the pathogen types involved. 3 marks
1.2 Calculate the approximate annual cost of Scenario A and the approximate monthly cost of Scenario B. Which disease imposes a higher cost per unit time? What does this suggest about the relationship between disease notifiability and economic impact? 3 marks
1.3 A beef producer argues: “BVD is not worth testing for because it does not shut down exports.” Use the data to evaluate this claim. 2 marks
2. Interpret the graph — estimated economic cost of an FMD incursion in Australia
The bar graph below shows the estimated economic cost distribution of a modelled FMD incursion in Australia under three response scenarios. 7 marks
Figure 2.1. Estimated distribution of economic costs of a hypothetical FMD incursion in Australia under three response scenarios. Data modelled after Garner & Lack (1995) updated with 2020 trade values. Figures are approximate.
2.1 Describe the trend in total economic cost and in the relative size of the ‘export market loss’ component across Scenarios A, B and C. 2 marks
2.2 In Scenario A, estimate the export market loss as a percentage of total cost. What does this tell you about which type of economic effect (direct or indirect) dominates even in the best-case outcome? 2 marks
2.3 Using the graph, justify the statement: “The speed of government response to an FMD outbreak is the single most important determinant of economic outcome for Australian agriculture.” 3 marks
3. Compare and contrast — FMD vs Newcastle disease vs hydatid disease
Complete the comparison table using lesson content. You must write a specific entry for each cell — do not leave any blank. 9 marks (1 each)
| Feature | FMD | Newcastle disease | Hydatid disease |
|---|---|---|---|
| Pathogen type | |||
| Named pathogen species | |||
| Animals affected | |||
| Primary route of spread | |||
| Main economic effect type (direct / indirect / both) | |||
| Primary control strategy | |||
| Notifiable in Australia? | |||
| Zoonotic potential (infects humans?) | |||
| Australia’s current status |
4. Case study — 2020 Victorian avian influenza outbreak
Read the stimulus then answer the questions below. 5 marks
Stimulus. In July 2020, highly pathogenic avian influenza (HPAI H7N7) was confirmed on three commercial poultry farms in Victoria’s Mornington Peninsula. The Victorian Department of Agriculture ordered the immediate depopulation (culling) of approximately 465,000 birds across the affected premises and adjacent farms as a precautionary measure. A 10 km quarantine zone was established, restricting the movement of all poultry, poultry products and equipment. Major supermarket chains reported short-term egg shortages in Victoria. Several Asian export markets that had been purchasing Australian chicken meat suspended orders pending investigation. The total estimated economic cost exceeded $20 million. No human H7N7 infections were recorded in this outbreak.
4.1 Classify the following costs from the stimulus as either direct or indirect economic effects: (i) culling 465,000 birds; (ii) Asian export market suspension; (iii) egg shortages in Victoria. 2 marks
4.2 Explain why the quarantine zone applied to adjacent farms that had no confirmed H7N7 infections. Use lesson content about avian influenza transmission in your answer. 2 marks
4.3 Predict one additional economic consequence of this outbreak that is not mentioned in the stimulus. Justify your prediction. 1 mark
Q1.1 — Export market loss absent from BVD (3 marks)
The cost category present in Scenario B but absent from Scenario A is export market loss [1]. BVD is caused by a virus (Pestivirus) that is endemic in many countries and is not classified as a notifiable exotic disease at the national level; it does not trigger automatic import bans by trading partners [1]. FMD, by contrast, is caused by a highly contagious exotic virus (Aphthovirus) that is a notifiable disease internationally; its detection immediately triggers import bans from all major livestock product markets, as importing countries cannot guarantee the disease-free status of any product from the affected country [1].
Q1.2 — Annual/monthly cost comparison (3 marks)
Scenario A annual cost: $420,000 ÷ 3 = $140,000/year [1 mark for correct calculation]. Scenario B monthly cost: $2,400,000 ÷ 6 = $400,000/month, or $4,800,000 annually if extrapolated [1 mark for correct calculation]. FMD imposes a far higher cost per unit time than BVD [½ mark]. This suggests that notifiability (and the associated export market loss it triggers) is the primary driver of economic severity, not the direct production losses from the disease itself — a disease can have lower direct impact yet massively higher total economic consequence if it triggers export bans [½ mark].
Q1.3 — Evaluate the producer’s claim (2 marks)
The claim is flawed. Although BVD does not shut down exports, the data show that over 3 years BVD costs this enterprise approximately $420,000 through direct production losses (reduced weaning rates, slower weight gain, calf deaths) and ongoing veterinary costs [1]. This is a very significant ongoing drain. Testing for PI cattle and removing them from the herd is the primary BVD control strategy, and economic models show that testing programs pay for themselves within 1–2 years in moderately affected herds [1].
Q2.1 — Trend in total cost and export component (2 marks)
Total estimated economic cost increases substantially from Scenario A (~$9.5B) to Scenario B (~$28.5B) to Scenario C (~$38B+) [1]. The export market loss component (red) grows disproportionately with each scenario, accounting for roughly 63% of costs in Scenario A but an even larger proportion in Scenarios B and C, indicating that export market loss amplifies faster than direct production or government response costs as the outbreak becomes less controlled [1].
Q2.2 — Export market loss as % of Scenario A total (2 marks)
Export market loss in Scenario A = approximately $6B out of ~$9.5B total ≈ 63% [1]. Even in the best-case (rapid eradication) scenario, indirect effects (export market loss) represent the majority of total economic cost — demonstrating that indirect effects dominate over direct production losses for Australia in any FMD scenario [1].
Q2.3 — Speed of response justification (3 marks)
The graph shows that moving from Scenario A (rapid eradication) to Scenario B (delayed response) roughly triples the total economic cost from ~$9.5B to ~$28.5B [1]. The export market loss component (which dominates all scenarios) grows from ~$6B to ~$22.8B — an increase of nearly $17B attributable specifically to the delayed response, not to greater numbers of infected animals per se [1]. A delayed response allows the virus to spread further, extends the period during which Australia cannot certify disease-free status (prolonging export bans), and increases the total area under quarantine. Because export market access is the largest single component of FMD economic cost in all scenarios, the duration of loss of disease-free status is the critical variable, and that duration is directly controlled by the speed of eradication response [1].
Q3 — Compare and contrast table answers
| Feature | FMD | Newcastle disease | Hydatid disease |
|---|---|---|---|
| Pathogen type | Virus | Virus | Parasitic tapeworm |
| Named pathogen | Aphthovirus (Picornaviridae) | Avian paramyxovirus type 1 | Echinococcus granulosus |
| Animals affected | All cloven-hoofed (cattle, pigs, sheep, goats, deer) | Poultry (chickens, turkeys) | Sheep & cattle (intermediate); dogs (definitive) |
| Primary spread | Direct contact, aerosol, fomites | Infected birds, faeces, contaminated equipment | Dogs shed eggs in faeces; livestock ingest eggs from pasture |
| Main economic effect type | Primarily indirect (export bans) | Both direct (mortality) and indirect | Primarily direct (condemned organs at slaughter) |
| Primary control | Quarantine, culling, border biosecurity | Vaccination programs | Regular deworming of farm dogs |
| Notifiable in Australia? | Yes (exotic — not present) | Yes (exotic — virulent strains) | Not nationally notifiable |
| Zoonotic potential | No | Yes (mild conjunctivitis in poultry workers) | Yes (humans can be accidental intermediate hosts) |
| Australia’s current status | FMD-free since 1872 | Free from virulent strains; vaccine strains present | Endemic; ongoing cyst losses at slaughter |
Q4.1 — Classify costs as direct or indirect (2 marks)
(i) Culling 465,000 birds = direct economic effect (direct loss of productive animals). (ii) Asian export market suspension = indirect economic effect (trade restriction triggered by notifiable disease detection). (iii) Egg shortages in Victoria = indirect economic effect (market disruption from movement restrictions and loss of production capacity, affecting even consumers far from the outbreak). [1 mark for all three correctly classified; accept 1 mark for 2/3 correct]
Q4.2 — Why quarantine zone applied to adjacent farms (2 marks)
Avian influenza spreads via respiratory secretions and faeces of infected birds [1]. During the incubation period, birds on adjacent farms may have been exposed to the virus through shared airborne aerosol, contaminated personnel, vehicles or equipment moving between farms — without yet showing symptoms. Applying the quarantine zone to adjacent farms prevents movement of potentially exposed (but not yet symptomatic) birds, interrupting spread before it can be confirmed, and is standard practice for containing highly contagious poultry diseases [1].
Q4.3 — Additional economic consequence (1 mark)
Accept any one of: consumer confidence collapse reducing domestic chicken and egg purchases across Victoria and possibly nationally, including from farms with no disease (media “bird flu scare” effects); long-term market re-entry costs (Australia must satisfy Asian importers that disease-free status is restored before exports resume, requiring certification processes); flow-on effects to feed suppliers, transport companies, and processing facilities that service the affected poultry farms. [1 mark for any justified additional indirect effect not directly named in the stimulus]