Meta-analysis of the parasitic phase traits of Haemonchus contortus infection in sheep

Abstract

BackgroundThe parasitic nematode Haemonchus contortus shows highly variable life history traits. This highlights the need to have an average estimate and a quantification of the variation around it to calibrate epidemiological models.MethodsThis paper aimed to quantify the main life history traits of H. contortus and to identify explanatory factors affecting these traits using a powerful method based on a systematic review and meta-analysis of current literature. The life history traits considered are: (i) the establishment rate of ingested larvae; (ii) the adult mortality rate; (iii) the fertility (i.e. the number of eggs laid/female/day); and (iv) fecundity of female worms (i.e. the number of eggs per gram of faeces).ResultsA total of 37 papers that report single experimental infection with H. contortus in sheep and published from 1960 to 2015, were reviewed and collated in this meta-analysis. This encompassed 115 experiments on 982 animals. Each trait was analysed using a linear model weighted by its inverse variance. The average (± SE) larval establishment rate was 0.24 ± 0.02, which decreased as a function of the infection dose and host age. An average adult mortality rate of 0.021 ± 0.002) was estimated from the literature. This trait varied as a function of animal age, breed and protective response due to prior exposure to the parasite. Average female fertility was 1295.9 ± 280.4 eggs/female/day and decreased in resistant breeds and previously infected hosts. Average faecal egg count at necropsy was 908.5 ± 487.1 eggs per gram of faeces and varied as a function of infection duration and host resistance. The average sex ratio of H. contortus was 0.51 ± 0.006.ConclusionThis work is the first systematic review to summarise the available information on the parasitic phase of H. contortus in sheep. The results of the meta-analysis provide robust estimates of life history traits for parametrization of epidemiological models, their expected variation according to experimental factors, and provides correlations between these.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-017-2131-7) contains supplementary material, which is available to authorized users.

The global diversity of the major parasitic nematodeHaemonchus contortusis shaped by human intervention and climate

“…Using estimates of nucleotide diversity estimates, together with the the C. elegans 20 mutation rate and assuming a balanced sex ratio 21 , we inferred the current effective population size ( N e ) of H. contortus to be between 0.60 and 1.05 million. MSMC analysis, which models past recombination events based on heterozygosity patterns along the genome, revealed the historical N e has remained within a slightly lower range of values for most of the sampled time interval, i.e.…”

“…H. contortus populations displayed high levels of nucleotide diversity, consistent with early estimates based on mitochondrial data 39,40 , and recent re-sequencing experiments of inbred isolates 12 . These extreme levels of genetic diversity are thought to arise from both a large census population 42 and the high fecundity of H. contortus females 21 .…”

“…For each isolate, estimates were averaged across five runs, leaving one chromosome out at a time for cross-validation, using rho/mu parameter value of 6.22 (average recombination rate of 1.68 cM/Mbp 12 and considering a mutation rate similar to that of C. elegans mutation rate, 2.7 × 10 −9 per site per generation 20 ). MSMC2 times and coalescent rates were scaled to real time and population sizes by assuming the same mutation rate 20 , a balanced sex-ratio 21 and an inferred generation interval of 40 days (the sum of 10 days to reach mature free-living infective larvae from the egg stage, and a 30-day prepatent period for fully mature egg-laying females) 92 .…”

Potentials of using milk performance data and FAMACHA score as indicators for Targeted Selective Treatment in Lacaune dairy sheep in Switzerland

“…In Switzerland, H. contortus appears to have a high prevalence ( Rinaldi et al, 2015 ), which is in accordance with our results. The proportion of H. contortus was included in the models to account for its high fecundity compared with other trichostrongylids ( Cabaret et al, 1998 , Saccareau et al, 2017 ). As expected, with an increasing proportion of H. contortus an increase of EPG was observed.…”

Prediction and attenuation of seasonal spillover of parasites between wild and domestic ungulates in an arid mixed‐use system

“…Density‐dependent constraints such as host immunity are intentionally omitted from Q 0 , which rather seeks to identify instantaneous conditions under which transmission is most favoured. Among helminths, H. contortus life history lends itself well to the Q 0 framework, as egg production per female worm is high (~5,000 eggs per day) and development to infective larvae either fails or occurs quickly (Saccareau et al., ). Therefore, current external conditions for transmission are a useful predictor of population trajectory, even if population magnitude is further modified by variations in susceptibility and egg output.…”