The effects of amount, timing and distribution of simulated rainfall on the development of Haemonchus contortus to the infective larval stage

O'Connor, Lauren Johanna; Kahn, Lewis; Walkden‐Brown, Stephen W.

doi:10.1016/j.vetpar.2007.02.002

Cited by 33 publications

(13 citation statements)

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“…This finding clearly indicates that the free living stages of H. contortus were able to survive during the winter, despite the absence of rains. Although first and second stage larvae are considered highly vulnerable to desiccation, once their development to the L3 stage is complete, all the major trichostrongylidae species are considerably less susceptible to unfavorable climate conditions (O'CONNOR et al, 2007). It has been reported that, in the laboratory and in the field, infective larvae are able to survive several cycles of desiccation/ rehydration, in a process called anhydrobiosis, in which metabolic activity is decreased and larval survival is extended (LETTINI; SUKHEDEO, 2006).…”

Section: Discussionmentioning

confidence: 99%

Gastrointestinal nematode infections in sheep raised in Botucatu, state of São Paulo, Brazil

Wilmsen

Silva

Bassetto

et al. 2014

Rev. Bras. Parasitol. Vet.

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Gastrointestinal nematode infections were evaluated in sheep raised in Botucatu, state of São Paulo, Brazil between April 2008 and March 2011. Every month, two tracer lambs grazing with a flock of sheep were exposed to natural infection with gastrointestinal nematodes for 28 consecutive days. At the end of this period, the lambs were sacrificed for worm counts. Haemonchus contortus presented 100% of prevalence. The seasons exerted no significant influence on the mean intensity of H. contortus, which ranged from 315 worms in November 2010 to 2,5205 worms in January 2011. The prevalence of Trichostrongylus colubriformis was also 100%, with the lowest mean intensity (15 worms) recorded in February 2011 and the highest (9,760 worms) in October 2009. In the case of T. colubriformis, a significant correlation coefficient was found between worm counts vs. rainfall (r = -0.32; P < 0.05). Three other nematodes species were found in tracer lambs, albeit in small numbers. Their prevalence and mean intensity (in parenthesis) were as follows: Oesophagostomum columbianum 28% (25.2), Cooperia curticei 7% (4.5) and Trichuris spp. 2% (1). In conclusion, the environmental conditions of the area proved to be highly favorable for the year-round transmission of H. contortus and T. colubriformis.Keywords: Haemonchus contortus, Trichostrongylus colubriformis, tracer lamb, nematode burden, seasonal variation. ResumoA ocorrência de infecções por nematódeos gastrintestinais foi avaliada de abril de 2008 até março de 2011em ovinos criados em Botucatu, estado de São Paulo. Todos os meses, dois cordeiros traçadores foram expostos à infecção natural por nematódeos gastrintestinais, durante 28 dias consecutivos, ao pastejar junto com um rebanho de ovelhas. Ao final desse período, os animais foram sacrificados para a identificação e quantificação dos helmintos. Haemonchus contortus apresentou prevalência de 100%. Não houve influência significativa das estações do ano na intensidade média de H. contortus, que variou de 315 vermes em novembro/2010 a 25.205 vermes em janeiro/2011. Trichostrongylus colubriformis também apresentou prevalência de 100% com a menor intensidade média (15 vermes) em fevereiro/2011 e a maior (9.760 vermes) em outubro/2009. No caso de T. colubriformis, houve correlação significativa entre as contagens de vermes x precipitação (r = -0,32; P < 0,05). Outras três espécies de nematódeos foram encontradas nos cordeiros traçadores, no entanto em pequenas quantidades, com as seguintes prevalências e intensidades médias (entre parênteses): Oesophagostomum columbianum 28% (25,2), Cooperia curticei 7% (4,5) e Trichuris spp. 2 % (1). Em conclusão, as condições ambientais da área foram muito favoráveis durante todo o ano para a transmissão de H. contortus e T. colubriformis.

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Section: Discussionmentioning

confidence: 99%

Gastrointestinal nematode infections in sheep raised in Botucatu, state of São Paulo, Brazil

Wilmsen

Silva

Bassetto

et al. 2014

Rev. Bras. Parasitol. Vet.

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“…On the other hand, the susceptibility of H. contortus eggs to desiccation and low temperatures is likely to make them just as susceptible to rapid rotational grazing as they would be under tropical conditions, but probably for different reasons. Temperature and moisture are often limiting in the Northern Tablelands for development of H. contortus eggs to L 3 (O'Connor et al 2006(O'Connor et al , 2007, and failure of development is likely to be a major mechanism operating in this environment. The superior ability of Trichostrongylus and Teladorsagia species to survive in the embryonated egg stage during cool dry conditions relative to Haemonchus could account for the species difference in response to IRG observed in this experiment.…”

Section: Discussionmentioning

confidence: 99%

Grazing systems and worm control in sheep: a long-term case study involving three management systems with analysis of factors influencing faecal worm egg count

et al. 2013

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Abstract. Managing infections of sheep with gastrointestinal nematode parasites (worms) and problems of resistance to anthelmintic treatments continue to be major challenges for graziers on the Northern Tablelands of New South Wales, Australia. The whole-farmlet study of grazing enterprises undertaken by the Cicerone Project tested the broad hypotheses that compared with typical management (farmlet B), internal parasites can be more effectively managed with improved nutrition (farmlet A) or by intensive rotational grazing (farmlet C). Further aims were to identify the major sources of variation in faecal worm egg count (WEC) over the 6-year period and to examine the efficacy of the various anthelmintic treatments used during the experiment. This paper describes the management of sheep worms at the whole-farmlet level during the experiment, and analyses data from the routine WEC monitoring (5644 records) and larval differentiation tests (322 records) carried out on behalf of the Cicerone Management Board and by a doctoral candidate. It complements more detailed investigations published elsewhere.Over the period from July 2000 to December 2006, worm infections in ewes, lambs, hoggets and wethers were, with some exceptions, successfully controlled on the farmlets through a combination of regular monitoring of WEC, treatment with a wide array of anthelmintics and grazing management. Farmlet C had lower mean WEC (444 epg) and annual anthelmintic treatment frequency (3.1 treatments/year) over the whole experimental period than farmlets B (1122 epg, 4.3 treatments/year) or A (1374 epg, 4.7 treatments/year). The main factors influencing WEC were the time since the last anthelmintic treatment, and the anthelmintic used at that treatment. The magnitude of these effects dwarfed those of climatic and management factors that might be expected to influence the epidemiology of gastrointestinal nematode infections via environmental or host-mediated mechanisms. Nevertheless management factors associated with stocking rate and grazed proportion (proportion of each farmlet grazed at any one time), and climatic indicators of both temperature and moisture availability had significant effects on WEC.The results show that, in a region with Haemonchus contortus as the major sheep nematode, improved host nutrition in a higher input system (farmlet A) did not provide more effective control of gastrointestinal nematodes than typical management (farmlet B); however, it was observed that gastrointestinal nematode control was no worse on farmlet A than on farmlet B in spite of farmlet A supporting a 48% higher stocking rate by later in the trial period (2005). The study provided strong support for the proposition that intensive rotational grazing (farmlet C) provides more effective control of gastrointestinal nematodes than typical management (farmlet B) as evidenced by significantly lower WEC counts and anthelmintic treatment frequency. Tactical worm control based on routine monitoring of WEC provided adequate control of worms on all three ...

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“…Thus, faecal desiccation can rapidly reach levels which are limiting to nematode development (Young 1983;Besier and Dunsmore 1993;Rossanigo and Gruner 1995;O'Connor et al 2007). Under more temperate conditions the rate of drying will be slower even in the absence of rain, and it is likely that sufficient moisture will be present in the faeces at the time of deposition to allow some development without additional moisture (O'Connor et al 2006).…”

Section: Discussionmentioning

confidence: 99%

“…The timing of rainfall events has previously been shown to be important for the successful development of the free-living stages of H. contortus, with rainfall in the 7 days after faecal deposition being most critical (O'Connor et al 2007). In our study, rainfall entropy, which is a measure of both the quantity and spread of rainfall, in the first 14 days after deposition was more important than entropy in the last 14 days or total rainfall over the sampling period.…”

Section: Discussionmentioning

confidence: 99%

Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 2. Weather variables associated with development

Reynecke

Waghorn

Oliver

et al. 2011

New Zealand Veterinary Journal

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Temperature was the most important determinant of developmental success of free-living nematodes on pasture at the study sites, and probably also for other parts of New Zealand with similar climates. Moisture was not significant in the development of T. circumcincta or T.colubriformis, implying that under the generally moist temperate climate in New Zealand, moisture is seldom limiting for development of these species. Haemonchus contortus appeared to be sensitive to moisture availability and precipitation in the first 14 days after deposition of faeces. The results of this study will be further developed as part of species-specific climate-driven models of parasite development in New Zealand.

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The effects of amount, timing and distribution of simulated rainfall on the development of Haemonchus contortus to the infective larval stage

Cited by 33 publications

References 11 publications

Gastrointestinal nematode infections in sheep raised in Botucatu, state of São Paulo, Brazil

Gastrointestinal nematode infections in sheep raised in Botucatu, state of São Paulo, Brazil

Grazing systems and worm control in sheep: a long-term case study involving three management systems with analysis of factors influencing faecal worm egg count

Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 2. Weather variables associated with development

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