Haemonchus Contortus Eggs Research Articles

Faecal water content and egg survival of goat gastro-intestinal strongyles under dry tropical conditions in Guadeloupe

Faeces from naturally infected goats were deposited on a natural grassland during the dry season in Guadeloupe (French West Indies) at different times throughout the day. The grass was either 7 or 20-30 cm tall. After a period of between several hours and 7 days, the number of viable strongyle eggs and the faecal water content were measured. Faecal temperature was recorded continuously. Faecal temperature was greater than 40 degrees-45 degrees C at midday and dehydration was rapid between 8 a.m. and 2 p.m. Egg mortality was greater on short than on tall grass and higher in morning than in evening deposits. Minimal faecal water content during the first 36 h explained the 74%, 55% and 38% mortality rate for eggs of Oesophagostomum columbianum (OC), Haemonchus contortus (HC) and Trichostrongylus colubriformis (TC), respectively. In all, 5%-22% of the eggs of the latter species remained viable in a state of anhydrobiosis after 7 days on the ground. A delay of only 2 days between goat departure and irrigation would be sufficient to ensure that greater than 95% of O. columbianum and H. contortus eggs and 70% of T. colubriformis eggs are destroyed.

Development and survival of Haemonchus contortus larvae on pasture at Vom, Plateau State, Nigeria

The development and survival of the eggs of Haemonchus contortus on pasture at Vom were studied by depositing faecal pellets on grass plots over a period of 12 months. Development and survival to the infective larvae occurred throughout the study except during the dry season months of December to April. More infective larvae were recovered from the herbage in June, July and August than in other months. The survival time of the infective larvae ranged from 2 weeks in October to 10 weeks in June, July and August. Rainfall was the most important epizootiological factor influencing the development and survival of the infective larvae. Temperature was not a limiting factor.

Effect of cool storage of faecal samples containing Haemonchus contortus eggs on the results of an in vitro egg development assay to test anthelmintic resistance

An in vitro egg development assay was used to test the resistance of eggs from a benzimidazole susceptible and a resistant strain of Haemonchus contortus to four benzimidazoles. Storage of eggs contained in faecal samples at 4 degrees C for four, 24 or 72 hours did not appear to impair the results from the in vitro egg development assay or alter the LD50. Storage for one week, however, proved to be lethal for the eggs. The average LD50 values for thiabendazole, albendazole, mebendazole and cambendazole were 0.06, 0.07, 0.96 and 2.47 ppm for the susceptible strain. For the resistant strain the values averaged 0.26, 0.24, 1.07 and 5.11 ppm.

Respiratory metabolism and thiabendazole susceptibility in developing eggs of Haemonchus contortus

Weston K. M., O'Brien R. W. and Prichard R. K. 1984. Respiratory metabolism and thiabendazole susceptibility in developing eggs of Haemonchus contortus. International Journal for Parasitology 14: 159–164. The respiratory metabolism of and uptake of thiabendazole (TBZ) by unembryonated (8–16 cells) and embryonated eggs of Haemonchus contortus have been compared. Lipid, which forms the greatest energy reserve in the eggs, decreases during embryonation and seems to be the sole source of respiratory energy. Trehalose increases to the same extent as glycogen decreases during this development. Isocitrate dehydrogenase (NADP +) and lactate dehydrogenase were not detected in the unembryonated eggs, but were present after embryonation. In addition, the activities of citrate synthase and malate dehydrogenase significantly increased during embryonation. Respiratory enzymes involving cytochrome c oxidation and reduction were detected in eggs at both stages of development. However, in line with other results indicating an increased capacity for and utilization of aerobic metabolism, the rate of oxygen uptake more than tripled during development of the eggs. Although both unembryonated and embryonated eggs took up palmitate, its metabolism to CO 2 only occurred in the embryonated eggs. The unembryonated eggs, exposed to TBZ for 4 h, concentrated it 5.9 times and the embryonated eggs 2.1 times, which are in proportion to their respective lipid contents. Uptake of TBZ was dependent on the concentration in the incubation medium and appears to be a passive process. The studies indicate that the embryonated eggs have a greater capacity for, and do utilize aerobic metabolism to a greater extent than do unembryonated eggs. The reduced susceptibility of embryonated eggs to TBZ could be associated with this metabolic difference and/or with their reduced uptake of TBZ.

Haemonchus contortus: Egg laying influenced by abomasal pH in lambs

Abomasal and duodenal concentrations of Haemonchus contortus eggs were measured in four lambs fitted with permanent abomasal and duodenal cannulas and infected with 25,000 Haemonchus contortus larvae. During the period of maximal egg laying, i.e., when the abomasal H. contortus egg concentration was above 2000 eggs/ml, the animals received cimetidine (20 mg/kg) intravenously or pentagastrin (5 μg·kg −1·h −1) for 90 min and the changes in abomasal and duodenal egg concentrations were followed for 2.5 hr. Pentagastrin infusion reduced the abomasal and duodenal pH significantly and in less than 15 min decreased the abomasal and duodenal egg concentrations which represented only 21.4 and 12.0% of the control values at the end (90 min) of infusion. During pentagastrin infusion, both the abomasal ( r = 0.56, P ⩽ 0.01) and the duodenal ( r = 0.72, P ⩽ 0.01) egg concentrations correlated positively with the corresponding pH values. After cimetidine injection, the abomasal and duodenal pH had increased 150 min later to, respectively, pH 6.16 and 6.27. During the first 30 min for an abomasal pH lower than 4.5–5.0, egg production increased by 106%; then the abomasal and duodenal egg concentrations decreased progressively, representing, respectively, only 39.3 and 16.4% of the control values 120 min later. It is concluded that the level of egg laying of adult H. contortus was related to the abomasal acidity, the maximal egg production occurring when the abomasal pH was between pH 4 and 4.5.

The action of insect juvenile hormone on the hatching of eggs of the nematode, Haemonchus contortus, and its role in the development of infective and non-infective stages

1. 1. With a gas phase of CO 2-free air the inhibitory action of the analogues of juvenile hormone, “dichlorofarnesoate” and farnesol (JH) on the hatching of eggs of Haemonchus contortus was markedly affected by [H +]. The pK of the inhibitory effect was 6.8; above pH 7 inhibition was weak, below 6.5 it was strong. 2. 2. The inhibition of hatching of eggs in 0.1 M NaCl containing JH, 3 × 10 −4 M, and under a gas phase of air, increased as the temperature was raised from 20 to 37°C. 3. 3. In buffer at pH 6 and under air, increases in temperature to 37°C did not inhibit hatching in the absence of added JH. However, when CO 2 was removed from the gas phase hatching was inhibited at the higher temperatures. 4. 4. Acetazolamide, 10 −3M, and ethoxyzolamide, 2 × 10 −5 M, inhibited the exsheatment (ecdysis) of third stage juveniles of H. contortus. 5. 5. The significance of these results in providing a hypothesis for features in the life cycle of nematodes, and in providing a hypothesis describing the action of JH on the target cell, is discussed.

The role of inhibited larvae in the epidemiology of ovine haemonchosis.

Three paddocks were contaminated with Haemonchus contortus eggs from early spring to mid summer by yearling sheep. In Paddock 1, all contamination was derived from worms that had been previously inhibited in their development. The contamination in Paddock 2 was produced only by infections recently acquired from pasture, and in Paddock 3 contamination was attributable to both sources. When the yearling sheep were replaced in mid-summer by newly weaned lambs, severe outbreaks of haemonchosis occurred on all paddocks. It was concluded that inhibited H. contortus larvae are capable of producing sufficient eggs, when they resume development, to initiate an outbreak of haemonchosis in susceptible sheep.

The interaction of insect juvenile hormone and carbon dioxide in the hatching of nematode eggs: Its significance in the physiology of infective stages

1. 1. Undissoeiated H 2CO 3 and/or dissolved gaseous CO 2 at appropriate concentrations and pH levels, reversed the inhibition of hatching of eggs of Haemonchus contortus caused by the juvenile hormone analogues, “dichlorofarnesoate” and farnesol. 2. 2. The action of H 2CO 3, in this system, and its relation to pH was similar to that of H 2CO 3 as stimulus for the hatching of infective eggs of Ascaris suum. 3. 3. The results suggest that the halt in development, characteristic of the infective stages of nematodes, is due to increased amounts of juvenile hormone and that infection occurs as the result of a stimulus from the host which overcomes this inhibition.

In vitro and in vivo studies on the ovicidal activity of fenbendazole

The in vitro ovicidal activity of fenbendazole against eggs of Ostertagia ostertagi, Haemonchus contortus and Trichostrongylus colubriformis was observed using different concentrations of active principle. The optimum concentration for ovicidal activity is evidently 0.5 ppm fenbendazole. A further increase in concentration results in a decrease in activity which is probably due to physical causes. Ovicidal activity of the product is assessed by the proportion of non embryonated eggs as well as embryonated eggs which are not capable of hatching. By this method of evaluation a higher ovicidal activity is recorded. Ten h after treating sheep with fenbendazole (dose 5 mg/kg) a large number of eggs whose development was inhibited, as well as atypical eggs were detectable in the faeces. Twelve h after treatment, the capacity for development of the eggs was largely suppressed.

Instability of benzimidazole resistance in nematode eggs

The resistance of the eggs of benzimidazole resistant Haemonchus contortus and Trichostrongylus colubriformis is not stable and will decrease in the absence of drug challenge. Dosing animals harbouring resistant H contortus with either thiabendazole or mebendazole selects for nematodes producing thiabendazole resistant eggs. The eggs of a thiabendazole selected strain of H contortus were more resistant to thiabendazole, parbendazole and oxibendazole but less resistant to cambendazole and mebendazole.

Resistance of nematode eggs to the ovicidal activity of benzimidazoles

Eggs of benzimidazole-resistant Haemonchus contortus and Trichostrongylus colubriformis are resistant to the ovicidal activity of benzimidazoles. The possiblity is raised of using this as a simple screen for detection of resistance in nematodes of domesticated animals.

Development and survival of Haemonchus contortus larvae on pastures in Ibadan.

The development and survival of the eggs of Haemonchus contortus on pasture at Ibadan were studied by spreading faeces containing eggs on grass plots from October 1973 to October 1974. Development of the eggs to the infective larvae took place within one week in May, June, July, September and October. Larvae were not recovered in the other months. Their survival times were 28, 42, 42, 35, 63 and 49 days respectively in October 1973. May, June, July, September and October 1974. Rainfall was the most important epizootiological factor which influenced the development and survival of the infective larvae. Development of the eggs to the infective larvae took place when the mean daily rainfall for the first 7 days was 3 mm or more. The survival time of the larvae appeared to be prolonged when rain fell evenly throughout the periods the larvae were on pasture.

The mechanism of hatching of eggs of Haemonchus contortus

Fluid collected from hatching eggs of Haemonchus contortus contained a lipase which hydrolysed 2-naphthyl laurate (about 0·7 μmol naphthol freed /h/10 6 eggs). The fluid also hydrolysed l-leucinamide (about 2·3 μmol leucine freed/h/10 6 eggs). The fluid when added to normal or heated eggs caused ‘hatching’. ‘Hatching’ also occurred in exsheathing fluid from infective juveniles and in a preparation of pancreatic lipase containing leucine aminopeptidase. A purified mammalian leucine aminopeptidase in combination with several different lipases did not attack egg shells. The ‘spontaneous’ hatching of eggs of H. contortus was strongly inhibited by 1,10-phenanthroline, 10 −3M, and this inhibition was reversed by Zn 2+. However, the inhibition of ‘hatching’ of eggs in externally applied hatching fluid, or the hydrolysis of leucinamide in hatching fluid was generally less marked.

Haemonchus contortus: Food of preinfective larvae

Haemonchus contortus eggs were bacterially sterilized and cultivated in three different preparations of Escherichia coli cultures and a nutrient broth at 30 C for 7 days. The following percentages of infective larvae were recovered: supernatant fluid from E. coli culture, 0%; washed E. coli, 71%; heat-killed E. coli, 40%; and nutrient broth, 0%. The evidence that preinfective larvae fed on the bacterium per se was substantiated by the autoradiograph of the larva grown on tritiated bacterial cells alone. Radioactivity was found throughout the larval body with most of the activity concentrated in the gut.

IMPROVED METHODS OF OBTAINING CLEAN LARVAE OF HAEMONCHUS CONTORTUS.

A pellet of sheep faeces containing eggs of Haemonchus contortus forms an adequate environment for the development of those eggs to third stage infective larvae, provided that it is kept moist. Observation shows a concentration of developing larvae on the external mucous coat of the pellet. These data suggest that optimum conditions for development would occur when pellets are separated one from another and standing on a water repellent surface, thus presenting the maximum free surface area and minimum opportunity for aggregation and hence of over crowding. The best method of recovering the infective larvae would be one that obtained larvae free from contamination without requiring them to expend energy in separating themselves from the contamination.

Egg sizes and differential egg counts in relation to sheep nematodes.

1. The width and length of eggs of Haemonchus contortus, Cooperia curticei, Trichostrongylus axei, T. vitrinus, Bunostomum trigonocephalum, Chabertia ovina, Oesophagostomum venulosum and Ostertagia spp. were measured.2. Frequency distributions of the linear dimensions of the eggs of each species are given, together with the frequencies calculated on the assumption that the distributions are normal.3. A method of species differentiation based on egg measurements is described, the method being based upon the statistical chances of eggs of different species falling into particular size classes.4. The application of the method and the construction of a classifying scale are described.

Haemonchus contortus Eggs: Comparison of Those in Utero with Those Recovered from Feces, and a Statistical Method for Identifying H. contortus Eggs in Mixed Infections

For the reason that normal practice requires identification of eggs voided in feces it seemed desirable that comparison should be made between eggs dissected from females and those which had been recovered from feces by ordinary isolation techniques. Tetley (1941) found that among species of Nematodirus eggs obtained from feces and measured in the course of making dilution counts by the Stoll method no change in form from that of eggs freshly dissected from females could be detected. In the present account the, by contrast, thin-shelled eggs of Haemonchus contortus are considered.