Experimental infection of calves with Haemonchus placei and Haemonchus contortus: Assessment of parasitological parameters.

The present study evaluated the viability and possible effects of Haemonchus contortus infections in experimentally prime infected calves, comparing them to infections by Haemonchus placei. Ten male Holstein newborns were used. All calves were individually weighed for subsequent group formation, in which two animals were kept as a control group, inoculated with water (GI); four animals were inoculated with 10,000 third stage (L3) Haemonchus contortus larvae (GII); and the remaining four calves were inoculated with 10,000 third stage (L3) H. placei larvae (GIII). All experimental animals were necropsied on the 42nd day after inoculation. Based on results obtained by the present study, it can be concluded that bovine calves were susceptible to infections by both Haemonchus species (placei and contortus). H. contortus presented an inferior pre-patent period when compared to H. placei. No significant difference (P>0.05) was observed between Haemonchus burdens recovered from both infected groups (GII and GIII). Moreover, H. contortus females maintained an egg production rate similar to H. placei females in young animals, which can contribute to pasture contamination by both Haemonchus species. This could possibly lead to negative reflexes on helminth control based on a mixed pasture with bovines and ovines, especially when it involves younglings.

Climate-driven changes to the spatio-temporal distribution of the parasitic nematode, Haemonchus contortus, in sheep in Europe.

Recent climate change has resulted in changes to the phenology and distribution of invertebrates worldwide. Where invertebrates are associated with disease, climate variability and changes in climate may also affect the spatio-temporal dynamics of disease. Due to its significant impact on sheep production and welfare, the recent increase in diagnoses of ovine haemonchosis caused by the nematode Haemonchus contortus in some temperate regions is particularly concerning. This study is the first to evaluate the impact of climate change on H. contortus at a continental scale. A model of the basic reproductive quotient of macroparasites, Q0 , adapted to H. contortus and extended to incorporate environmental stochasticity and parasite behaviour, was used to simulate Pan-European spatio-temporal changes in H. contortus infection pressure under scenarios of climate change. Baseline Q0 simulations, using historic climate observations, reflected the current distribution of H. contortus in Europe. In northern Europe, the distribution of H. contortus is currently limited by temperatures falling below the development threshold during the winter months and within-host arrested development is necessary for population persistence over winter. In southern Europe, H. contortus infection pressure is limited during the summer months by increased temperature and decreased moisture. Compared with this baseline, Q0 simulations driven by a climate model ensemble predicted an increase in H. contortus infection pressure by the 2080s. In northern Europe, a temporal range expansion was predicted as the mean period of transmission increased by 2-3 months. A bimodal seasonal pattern of infection pressure, similar to that currently observed in southern Europe, emerges in northern Europe due to increasing summer temperatures and decreasing moisture. The predicted patterns of change could alter the epidemiology of H. contortus in Europe, affect the future sustainability of contemporary control strategies, and potentially drive local adaptation to climate change in parasite populations.

Environmental factors influencing the transmission of Haemonchus contortus.

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.

Vertical migration of Haemonchus contortus infective larvae on Cynodon dactylon and Paspalum notatum pastures in response to climatic conditions.

Observations were made on vertical migration patterns of Haemonchus contortus infective larvae on Cynodon dactylon (bermudagrass) and Paspalum notatum (bahiagrass) pastures under summer climatic conditions typical of East Texas. Ten thousand H. contortus infective larvae (L3) were introduced to 100 cm(2) subplots of each pasture species within a plot area of 1m(2). Subplots were inoculated with larvae by applying them in an aqueous medium to the soil or mat beneath the vegetation. Herbage from the inoculated areas was harvested on 5 sampling days over a span of 21 days. L3 recoveries were observed and recorded each day on four herbage strata viz. 0-5, 5-10, 10-20 and >20 cm from ground level. The log transformed larval recovery data were analyzed for effect of day, stratum, and day x stratum interaction for each grass species during two separate experimental periods. Precipitation, relative humidity and temperature during the study were subjected to correlation and multiple regression analyses with the larval counts. Significant (Por=0.93) between rainfall and total average daily larval counts was apparent. The multiple regression analysis did not show significant results for any of the climatic factors tested. This study showed that the H. contortus infective larvae can survive beyond 21 days in the soil and infest pasture grasses when the climatic conditions are favorable. Avoiding use of H. contortus contaminated pasturelands in summer at the onset of rainfall following a dry spell may effectively reduce nematode loads in susceptible farm animals. Additional studies should focus on factors affecting long term L3 survivability, migrational pattern on these and other plant species and the relationship between climatic factors and larval migration patterns throughout the year. Total larval recovery of H. contortus in this study was greater in bahiagrass than bermudagrass. While the design of this study did not allow for testing one pasture species against another, studies with potted plants would allow for some valid comparisons. Soil characteristics may also play a role in L3 survival and subsequent migration.

Vertical migration of Haemonchus contortus third stage larvae on Brachiaria decumbens grass.

The present study aimed at evaluating the vertical migration of Haemonchus contortus third stage larvae (L3) on Brachiaria decumbens grass, as well as at verifying whether larval numbers on pasture varies over the day due to climatic conditions. Feces containing H. contortus L3 were deposited on the soil in the middle of herbage which was initially 30 cm high. Seven days later, samples of different herbage strata (0-10, 10-20 and >20 cm), remaining feces and a layer of approximately 1cm soil were collected. Tests were carried out in four periods: September 2006, December 2006, March 2007, and June 2007. Samples were collected at sunrise, mid-day, sunset, and mid-night. The humidity and temperature conditions observed in different months influenced larval migration from the feces to the grass. In September, December and March, it rained after fecal deposition on pasture, which favored migration of larvae from the feces to the herbage. Conversely, in June 2007, when there was no rainfall after fecal deposition and temperatures were lower, L3 were mainly recovered from feces. As regards the vertical migration of larvae, the numbers of H. contortus L3 in the forage strata remained relatively constant over the day. This indicates there is not a determined period in which sheep on pasture are at higher risk of infection. Finally, in all collection periods a considerable amount of third stage larvae was observed on the herbage top, which is the first plant part consumed by sheep.

Development and survival of Haemonchus contortus infective larvae derived from sheep faeces under sub-tropical conditions in the Potohar region of Pakistan.

Assessment on the development and survival of Haemonchus contortus larvae was made to evaluate the influence of microclimatic variables viz., relative humidity (%), temperature (degreesC), rainfall (mm) and intensity of sunlight (hrs). Pasture plots in a subtropical area, Pakistan were contaminated with H. contortus eggs at the start of every month. The plots were sampled on fortnightly basis after contamination for three consecutive months. The overall pattern indicated the most favorable conditions for survival, development and translation to herbage was during the wet season from July to October and the least favorable was during the dry season from April to June. Peak infective larvae (L3) recovery was during the 15-45 day interval for each plot and the lowest number was during the 75-90 day interval. Herbage was collected in the morning, afternoon and evening and greatest recovery of L3 was in the morning time and least in the afternoon. The number of L3 on pasture was directly related to the pattern of rainfall and relative humidity with a significant (P<0.05) positive correlation and temperature and intensity of sunshine were negatively correlated (P<0.05). The results suggest that pastures can remain infective for up to 2 months and become relatively clean by 90 days after contamination. Thus, long pasture rest periods, especially during the high risk wet season, may be a helpful strategy to reduce the infection levels.

Towards the eradication of Haemonchus contortus from sheep flocks in Sweden.

Previous studies have shown that between-year transmission of Haemonchus contortus in Swedish sheep flocks is almost entirely as over-wintered populations within housed animals, and not on pasture. This suggests that eradication of this parasite is a realistic possibility. Thus, two sheep farms with a history of H. contortus infection on the Swedish island of Oland were selected for study. During the winter housing period of 2003/2004 all ruminants (sheep and cattle) on both farms were treated with ivermectin. Monitoring by faecal egg counts and infective larval differentials of ewes and lambs for the subsequent two grazing seasons, together with total abomasal worm counts of 10 lambs from each farm at the end of the first grazing year, showed that this objective was achieved.

Experimental cross-infections of Haemonchus placei (Place, 1893) in sheep and cattle.

To examine effects on biology and morphology, Haemonchus placei infections were propagated in cattle or sheep and infective larvae were introduced into the same or opposite host. Ovine source larvae had a geometric mean (GM) prepatent period of 26.5 days regardless of host species, compared to 30.6 days for bovine source larvae regardless of host species. Similarly, ovine source H. placei had a higher GM percentage establishment versus bovine source larvae (9.6% versus 3.4%) regardless of host species. The patent daily egg count for ovine source versus bovine source H. placei was 109.1 versus 50.0 FEC regardless of host species. Mean spicule length for ovine source H. placei was 492.5 microm while bovine source measured 496.5 microm. Mean female tail length for ovine source H. placei was 586.5 and 589.5 microm for bovine source H. placei. Using synlophe morphology, all worms that were measured were identified as H. placei. Sixty-three percent of females examined for vulvar flap morphology had knob-like vulvar flaps while the remaining 37% had linguiform vulvar flaps.

Chemo- and thermosensory neurons: structure and function in animal parasitic nematodes.

Nematode parasites of warm-blooded hosts use chemical and thermal signals in host-finding and in the subsequent resumption of development. The free-living nematode Caenorhabditis elegans is a useful model for investigating the chemo- and thermosensory neurons of such parasites, because the functions of its amphidial neurons are well known from laser microbeam ablation studies. The neurons found in the amphidial channel detect aqueous chemoattractants and repellants; the wing cells-flattened amphidial neurons-detect volatile odorants. The finger cells-digitiform amphidial neurons-are the primary thermoreceptors. Two neuron classes, named ADF and ASI, control entry into the environmentally resistant resting and dispersal dauer larval stage, while the paired ASJ neurons control exit from this stage. Skin-penetrating nematode parasites, i.e. the dog hookworm Ancylostoma caninum, and the threadworm, Strongyloides stercoralis, use thermal and chemical signals for host-finding, while the passively ingested sheep stomach worm, Haemonchus contortus, uses environmental signals to position itself for ingestion. Amphidial neurons presumably recognize these signals. In all species, resumption of development, on entering a host, is probably triggered by host signals also perceived by amphidial neurons. In the amphids of the A. caninum infective larva, there are wing- and finger-cell neurons, as well as neurons ending in cilia-like dendritic processes, some of which presumably recognize a sequence of signals that stimulate these larvae to attach to suitable hosts. The functions of these neurons can be postulated, based on the known functions of their homologs in C. elegans. The threadworm, S. stercoralis, has a complex life cycle. After leaving the host, soil-dwelling larvae may develop either to infective larvae (the life-stage equivalent of dauer larvae) or to free-living adults. As with the dauer larva of C. elegans, two neuron classes control this developmental switch. Amphidial neurons control chemotaxis to a skin extract, and a highly modified amphidial neuron, the lamellar cell, appears to be the primary thermoreceptor, in addition to having chemosensory function. The stomach worm, Haemonchus contortus, depends on ingestion by a grazing host. Once ingested, the infective larva is exposed to profound environmental changes in the rumen. These changes stimulate resumption of development in this species. We hypothesize that resumption of development is under the control of the ASJ neuronal pair. Identification of the neurons that control the infective process could provide the basis for entirely new approaches to parasite control involving interference with development at the time and place of initial host-contact.

Studies on cross-transmission and pathogenicity of Haemonchus contortus in white-tailed deer, domestic cattle and sheep.

Experiments were conducted to compare the relative pathogenicity and infectivity of deer- and cattle-derived Haemonchus contortus for three hosts, viz., white-tailed deer, cattle and domestic sheep. Parameters evaluated for all animals were: general physical condition, basic hematologic values, fecal egg counts and parasite infectivity rates. Clinical signs attributable to H. contortus infections were not observed in any of the experimental animals. Deer harboring H. contortus burdens greater than 70 worms/kg body weight had decreased packed cell volume, hemoglobin and total serum protein values. Statistical analyses indicated there was not a significant difference (P greater than .05) in infectivity of deer-derived H. contortus in these hosts. No significant difference (P greater than .05) in infectivity for deer was noted between deer-derived H. contortus and cattle-derived H. contortus. Morphometric comparisons of helminths recovered indicated that parasites of deer and cattle origin were both compatible with the description for H. contortus. Results suggest that cross-transmission of H. contortus occurs between deer and domestic livestock.

Seasonal transmission of bovine gastrointestinal nematodes in the Texas Gulf Coast.

Sentinel calves were placed in pastures for 1 month in two environmentally dissimilar areas of the Texas Gulf Coast to determine the seasonal transmission of various gastrointestinal nematodes. Transmission was determined for Cooperia spp, Haemonchus placei, Ostertagia ostertagi, and Trichostrongylus axei. Large numbers of Cooperia spp were acquired from May through November, with the peak of transmission occurring in July and August. Haemonchus placei was encountered on both field sites but was transmitted in large numbers only at one site, during August. Ostertagia ostertagi was acquired primarily from November through May, with the peak of transmission occurring in January and February. January through March was the period when the greatest numbers of Ostertagia larvae undergoing arrested development were acquired. Trichostrongylus axei was abundance in December and January at one field site. In general, trends of transmission were the same in both areas, indicating that weather conditions were most important than vegetation type in larval transmission.