Estimation of the Farm-Level Basic Reproduction Number for African Swine Fever Outbreaks in the Philippines

Area of Science:

• Veterinary Epidemiology
• Disease Ecology
• Animal Health Economics

Background:

• African swine fever (ASF) genotype II has caused significant economic losses and food security issues in the Philippine swine industry since 2019.
• Understanding farm-level transmission dynamics is critical for effective ASF control, but national and island-specific data are lacking.

Purpose of the Study:

• To estimate the herd-level basic reproduction number (Rh) for ASF in the Philippines and its major islands (Luzon, Visayas, Mindanao).
• To analyze transmission patterns and inform region-specific management strategies for the Philippine swine industry.

Main Methods:

• Utilized ASF outbreak data from 2019 to 2022.
• Employed deterministic and stochastic models to estimate the herd-level basic reproduction number (Rh).
• Conducted epidemic descriptive analysis and Spearman's correlation to compare national and island-specific trends.

Main Results:

• ASF trends in Luzon closely mirror national epidemic patterns, while Mindanao and Visayas show distinct transmission dynamics.
• The long-term trend of ASF approaches endemicity (Rh near 1), but Rh values did not consistently stay below 1, indicating ongoing outbreaks.
• Swine farm density in Luzon correlates with national trends, whereas local factors influence transmission in Mindanao and Visayas.

Conclusions:

• Region-specific ASF management strategies are essential, with enhanced biosecurity for Luzon and community-based surveillance for Visayas and Mindanao.
• Adapting control measures to distinct regional transmission patterns can improve ASF management and support the recovery of the Philippine swine industry.