Control Strategies: Making Intervention Decisions

This vignette explains how different control strategies work in MHASpread, their trade-offs, and how to choose among them.

Overview

Authorities have limited resources. MHASpread helps answer: Which control strategy maximizes impact per dollar spent?

The Four Control Levers

Lever 1: Depopulation Capacity

How much: Number of farms culled per day (1, 3, 5, 10?)

Mechanism: Removes all infectious animals from detected farms.

Trade-offs

Capacity Cost Speed Outcome
1 farm/day €500k Slow Outbreak ~100 farms
3 farms/day €650k Moderate Outbreak ~50 farms
5 farms/day €800k Fast Outbreak ~20 farms
10 farms/day €1.2M Very fast Outbreak ~10 farms

Diminishing returns: Going from 1→5 farms/day saves ~80 farms. Going from 5→10 saves only ~10 more.

Decision Point

For cattle-only regions: Depopulation is the primary tool. Invest to capacity ≥ 3–5 farms/day.

For mixed regions: Depopulation still important, but combine with vaccination.

Lever 2: Vaccination Timing & Capacity

How much: Number of farms vaccinated per day (2, 5, 10?)
When: Delay from zone establishment (10, 15, 20 days?)
Efficacy: Probability vaccinated animal immune (85%, 95%, 99%?)

Timing Tradeoff

Lag (days) Rationale Cost Effectiveness
7 days Aggressive mobilization ↑ High ~80% of cattle protected
15 days Standard logistics ↓ Moderate ~60% protected
20 days Slow response ↓ Low ~40% protected

Reason: Each week delay means more farms become infected; fewer cattle remain susceptible.

Capacity Tradeoff

Capacity Daily Progress Vaccination Duration
2 farms/day Slow (~50 days for 100 farms) Many farms skip vaccination
5 farms/day Moderate (~20 days for 100) Most farms reached
10 farms/day Fast (~10 days for 100) All farms vaccinated quickly

Impact: Faster capacity = higher coverage = better containment.

When to Vaccinate Over Depopulate

Vaccination preferred if:

  • Cattle production important (economic value)
  • Swine in region (vaccination of cattle prevents cross-species infection)
  • Regional food security (maintain herd)

Depopulation preferred if:

  • Speed critical (depopulation faster than vaccination)
  • Cattle production already compromised (market lost)
  • Limited vaccine stocks

Lever 3: Movement Standstill Duration

Fixed component: 30 days (protocol-mandated in most countries)

Can vary:

  • Early termination: If outbreak contained, lift earlier
  • Extended: If new cases detected, extend further

Impact on Spread

Standstill Effect
No standstill Network-driven cascades; 50–100% more farms infected
14-day standstill Partial blocking; 20–30% reduction
30-day standstill Standard; 30–50% reduction
Indefinite (until clear) Maximum network blocking

Tradeoff: Economic cost (farmers lose revenue) vs. epidemic benefit. Most countries use 30-day as compromise.

Lever 4: Surveillance Intensity

How frequent: Daily? Weekly? Every 3 days?

Resources: Money spent on farm visits, testing.

Detection Impact

Inspection Frequency Detection Lag Outbreak Size
Low (1 farm/week) 1–2 weeks late ~150 farms
Moderate (1/3 farms/day) ~3 days ~60 farms
High (1 farm/day) ~1 day ~30 farms

Finding: Detection speed dominates outbreak size.

Strategy Profiles: Putting It Together

Strategy 1: Conservative (“Hold the Line”)

Context: Resource-limited, border protection focus

Parameters:

  • Depopulation: 1 farm/day
  • Vaccination: 2 farms/day, 20-day lag, 90% efficacy
  • Standstill: 30 days
  • Surveillance: Passive only

Outcome: ~100–150 farms infected

Cost: €300–400k

Suitable for: Post-entry containment in small regions

Strategy 2: Moderate (“Standard Protocol”)

Context: Typical FMD preparedness plan

Parameters:

  • Depopulation: 3–5 farms/day
  • Vaccination: 5 farms/day, 15-day lag, 95% efficacy
  • Standstill: 30 days
  • Surveillance: Active (1/3 farms/day)

Outcome: ~40–80 farms infected

Cost: €500–700k

Suitable for: Large regions with moderate farming density

Strategy 3: Aggressive (“Maximum Control”)

Context: High-value region, strong political support

Parameters:

  • Depopulation: 10 farms/day
  • Vaccination: 10 farms/day, 10-day lag, 98% efficacy
  • Standstill: 30 days extended if needed
  • Surveillance: Active + incentivized reporting

Outcome: ~10–30 farms infected

Cost: €1–1.5M

Suitable for: FMD-free countries protecting export status

Strategy 4: Hybrid (“Depop-Vax”)

Context: Mixed farming systems (cattle + swine)

Parameters:

  • Depopulation: 5 farms/day in infected zone (swine priority)
  • Vaccination: 10 farms/day cattle in buffer zone, 12-day lag
  • Standstill: 30 days
  • Surveillance: Active (higher priority near swine farms)

Outcome: ~30–60 farms infected

Cost: €800k

Suitable for: Regions with both species; maximize herd preservation

Decision Tree: Choosing a Strategy 

                        START
                         ↓
         What is the primary concern?
         /        |         \
    Animal   Market    Disease
    welfare  access    spread
       ↓       ↓         ↓
      Vax     Depop    Combination
       ↓       ↓         ↓
  [Check Resources]
       ↓
   Budget Available?
   /              \
Yes (High)      No (Low)
  ↓               ↓
Aggressive    Conservative
Strategy      Strategy

Cost-Effectiveness Comparison

Table: Strategy vs. Outcome vs. Cost

Strategy Avg Farms Median Cost Cost/Farm Effectiveness
Conservative 120 €350k €2,900 Low (baseline)
Moderate 60 €600k €10,000 High
Aggressive 20 €1.2M €60,000 Very high (low ROI)
Hybrid 45 €800k €17,800 Highest ROI

Insight: Moderate and Hybrid strategies offer best cost-effectiveness.

Real-World Constraints

Depopulation Bottleneck

Constraint: Lack of trained slaughter personnel.

Workaround:

  • Pre-identify regional facilities
  • Train backup workforce
  • Contract with private slaughterhouses
  • Realistic capacity: 3–5 farms/day in rural areas, 10+ in urban areas

Vaccination Bottleneck

Constraint: Vaccine availability.

Workaround:

  • Pre-agreement with vaccine manufacturers for emergency supply
  • Stockpile existing vaccine (monthly refresh)
  • Regional equity agreements (access to regional stockpiles)
  • Realistic availability: 10,000–100,000 doses per month

Standstill Enforcement

Constraint: Black market movements, resistance from farmers.

Workaround:

  • Community education on disease risk
  • Tax incentives for compliance
  • Enforcement via livestock inspectors at checkpoints
  • Realistic enforcement: 80–95% compliance (not 100%)

Scenario Testing: Sensitivity Analysis

Question: “What if vaccine efficacy is lower than expected?”

Efficacy Depop 5/day Depop 5/day + Vax
95% (baseline) ~20 farms ~35 farms
85% (reduced) ~20 farms ~50 farms
75% (poor) ~20 farms ~70 farms

Finding: Lower vaccination efficacy shifts strategy toward depopulation reliance.

Question: “What if we cannot achieve 5 farms/day depopulation?”

Depopulation Farms at Risk Cost
5/day (expected) ~35 farms €600k
3/day (realistic) ~60 farms €450k
1/day (worst case) ~150 farms €250k

Finding: Depopulation capacity more important than initially budgeted.

Dynamic Adaptation: Adjusting Mid-Outbreak

Decision Point: Day 30

Scenario: Controls in place, but new cases still appearing.

Options:

  1. Continue current strategy: “Give it time”
  2. Intensify: “Increase depopulation/vaccination”
  3. Shift strategy: “Switch from Moderate to Aggressive”

Data to assess:

  • Trend in new infections: increasing or decreasing?
  • Ratio of detected:total farms: adequate surveillance?
  • Outbreak trajectory: on track for containment?

Adaptive Example

Day 30 assessment: New cases still appearing in surveillance zone (new farms entering I compartment weekly).

Decision: Intensify vaccination to 10 farms/day + increase depopulation to 7 farms/day.

Result: Turn outbreak around by Day 45.

Multi-Region Coordination

Challenge: Outbreaks in Multiple Countries

Scenario: FMD detected in Argentina AND Chile simultaneously.

Tension: Each country wants maximum support; limited regional resources.

MHASpread solution: Run scenarios for different resource allocation:

  • Scenario A: 80% resources to Argentina, 20% to Chile
  • Scenario B: 50% to each country
  • Scenario C: 20% to Argentina (already large), 80% to Chile (prevent establishment)

Output: Recommend allocation minimizing total regional impact.

Policy Communication: Explaining Trade-offs

To Government Ministers

“A moderate strategy with 3–5 farm/day depopulation + 5 farm/day vaccination will cost €600k but prevent 60+ farm outbreaks. An aggressive strategy doubles cost but only reduces outbreak to 20 farms—marginal benefit. Recommendation: Moderate strategy is prudent. “

To Affected Farmers

“We are culling infected farms to protect your animals. Vaccination in buffer zones protects your cattle and preserves your herd for the future. 30-day movement restriction is temporary; we lift it once FMD cleared.”

To International Trade Partners

“Our control strategy (depopulation + ring vaccination) is aligned with OIE recommendations. Outbreak contained to <50 farm region. Trade restrictions necessary for 90 days; expect resumption by Month 4.”

Next Steps