Environmental factors influencing the transmission of Haemonchus contortus

Abstract

Infection with the gastrointestinal nematode Haemonchus contortus causes considerable losses in the sheep industry. In this study, we evaluated the effect that climate has on third-stage larvae (L3) of H. contortus in terms of their migration from sheep feces to Brachiaria decumbens grass, as well as their distribution among the forage plants. Fecal samples containing H. contortus L3 was deposited on the soil among the herbage at an initial height of 30 cm. Sample collection began 24h after contamination and was performed on alternate days over 13 days. The L3 were recovered and quantified in three strata (heights) of grass (0-10 cm, 10-20 cm and >20 cm) as well as in the remaining feces and a superficial layer of soil, collected from beneath the feces. In order to obtain results under different environmental conditions, fecal samples containing H. contortus L3 were deposited on pasture in January (summer), in April (autumn), and July (winter). In all of the periods, the L3 were able to migrate from the feces to the herbage. However, rains, accompanied by high relative humidity and high temperatures, apparently favored migration. The highest L3 recovery rate in the pasture was in the summer observation period, which had the highest number of days with measurable precipitation, high relative humidity (>68.2%), and the highest temperatures at the soil level (minimum and maximum means of 19°C and 42°C, respectively). Under those conditions, larvae began to reach the upper stratum of the grass (>20 cm) by 24h after the deposition of fecal matter, the number of larvae having reached that stratum peaking at seven days after deposition. In the autumn observation period, there was no rainfall in the first five days post-contamination. During that period, high numbers of larvae were found in the fecal samples demonstrating that feces can act as a reservoir of larvae in the absence of rain. Except for two days in the summer observation period, when most of the L3 were recovered from the tops of blades of grass, L3 where located predominantly at the base of the herbage. In conclusion, rainfall favors the migration of L3 from feces to herbage. In addition, larval migration up and along blades of grass can occur relatively rapidly when the temperature is high.

Distribution of infective gastrointestinal helminth larvae in tropical erect grass under different feeding systems for lambs

“…In spring, in both grasses, most larvae were recovered from the upper portions of the plants. Studying the survival and migration of Haemonchus contortus, Santos et al (2012) verified that during summer, there was no difference in larval recovery among the different strata analyzed (0-10, 10-20, and >20 cm). During autumn and winter, most L3 were recovered from the lower stratum (0-10 cm).…”

“…These authors stated that temperatures below 16°C or above 36°C limit the development of Haemonchus and Trichostrongylus, the main nematodes found in the present study. Santos et al (2012) observed that precipitation favors L3 movement from feces to pasture and, despite high temperatures, can speed the movement of larvae to the tops of grass blades. These factors may explain the The variance analysis was carried out with the logarithmically transformed (log (y)) data.…”

“…Bowman et al (2003) stated that less than 5 % of the parasite population of a sheep flock is in the animals' gastrointestinal tracts, while the remainder (about 95 %) is on the grasslands. Many studies have been conducted to understand the dynamics of the free-living phase of gastrointestinal nematodes in response to weather, microclimate, and the size and characteristics of the pasture (Amaradasa et al 2010;Santos et al 2012;Khadijah et al 2013). These factors may influence the development and survival of the free-living stages and may or may not favor the migration of the infective larvae from feces to grass.…”

Gastrointestinal Parasites of Cattle in Central Java

“…In the rainfall season the humidity increases 70-85%. For example for Haemonchus contortus high rainfall is related to a proportional increase of the number of migrated L3 from fecal material to pasture (Santos et al, 2012;Silva et al, 2008).…”

Genotyping of benzimidazole resistant and susceptible isolates of Haemonchus contortus from sheep by allele specific PCR

“…Hematophagus gastrointestinal nematodes cause emaciation, anemia and even death of infected animals, ultimately leading to substantial economic losses to the livestock production (Ghisi et al 2007). Among various helminthic infections of small ruminants, major threat and impediment to ruminant livestock farming occurs in the form of gastroenteritis caused by Haemonchus contortus (Santos et al 2012). McLeod (2004) approximated the annual treatment cost due to H. contortus to be around $103 m in India.…”