Table 1.

Summary of epidemiological features of Haemonchus contortus infections according to climatic regions.

Climatic Zones	Regions	Ecological Features	Parasite Epidemiology
Tropical and subtropical regions	Tropical regions of Africa and America, tropical islands of the Pacific Ocean, southern and south-east Asia, northern part of Australia, southern USA, the Caribbean	L3 not surviving on pasturelands for long; moisture allowing larval development during dry seasons; increased period of larval survival and development when adequate moisture	Larval populations developing constantly, and animals continuously challenged; in dry weather, L3 increasing seasonally; hypobiotic L4 developing during dry seasons
Warm temperate and summer rainfall regions	Parts of southern USA and South America, southern and eastern Asia, southern Africa, eastern Australia	Combination of high temperature/moisture supporting development of L3; under cold conditions, larval survival and development slowing down	Significant problem, depending on rainfalls; when mild temperatures during winter, L3 potentially throughout a year; in areas with low temperatures, outbreaks depending on seasonality; hypobiosis predominating during cold winters
Mediterranean climatic regions	South-west cape of South Africa, para-Mediterranean basin, south-east Australia, western Australia	Suspension of survival and development of free-living stages; larval populations reaching peak numbers in autumn and spring; during mild temperature in winter, possible survival of L3	Highest populations from late autumn to early winter and late spring to early summer; varying hypobiosis, in accord with duration and intensity of hot/dry conditions
Cool and cold temperate regions	Northern USA and Canada, New Zealand, south east-Australia, northern Europe	Cessation of larval development until the onset of milder environmental conditions	Low risk, limited to warmer months; hypobiosis permitting overwintering; high temperatures favouring rapid development of hypobiotic larvae
Arid regions	Deserts of southern and sub-Saharan Africa, continental Australia, Middle East	Lack of moisture limiting survival and development of larval populations, favoured during rainfall periods	Not a significant threat; rainfall periods increasing larval availability; hypobiosis of varying importance; hot conditions reducing L3