Arrested development of Trichostrongylus tenuis as third stage larvae in red grouse

Worms were counted in red grouse (Lagopus lagopus scoticus) in north east Scotland in March, April, August, September, November and December 1986. Immature worms occurred as third (L3) and fourth (L4) stage larvae throughout. Two kinds of evidence suggest that L3 larvae spent much of the winter in a state of arrested development. First, recently acquired L3 larvae could be distinguished by the fact that they retained outer L2 cuticles for a few days; these were present only in the August and September samples. Secondly, the mean proportion of larvae (L3 and L4) present as L3 was less than 15 per cent in August and September, but increased to 92 per cent by December and then decreased to 71 per cent by March and April. During March and April the proportion of L4 increased as overwintering L3 resumed their development.     

Observations of the sheath extension of the third stage, infective larvae of Trichostrongylus rugatus

The length of the sheath extension of third stage (L(3)), infective larvae of Trichostrongylus rugatus is reported. The total length and length of the sheath extension of L(3) recovered from the faeces of sheep originating from two localities in South Australia were measured. The total length of larvae was 615-722 microm and the length of the sheath extension was 46-56 microm (mean 51.5). The larvae of T. rugatus comprised up to 72% of the larvae recovered. Worm free sheep were infected with larvae from the two localities and L(3) were recovered following culture of faeces from these experimentally infected animals. L(3) measured 640-746 microm in total length with a sheath extension of 46-56 microm (mean 51.4). Adult nematodes recovered from gastro-intestinal tracts were identified as T. rugatus. The length of the sheath extension used in conjunction with the total length is a characteristic that enables confident differentiation of infective larvae of T. rugatus from other Trichostrongylus species infecting sheep in southern Australia and Haemonchus contortus.     

Winter survival of third stage Trichostrongylus colubriformis larvae: effects on infectivity and fecundity of adult worms

Two groups of six lambs were fed with grass cut from two plots which had been contaminated by spreading Trichostrongylus colubriformis larvae. One plot received larvae in December, the other in April. The post mortem examination results showed that the infectivity of overwintering larvae was significantly higher than that of fresh larvae. An inverse relationship was demonstrated between infectivity of larvae and egg production of adult worms developed from these larvae. The results are compared with those obtained under laboratory conditions.     

Effects of four tropical tanniniferous plant extracts on the inhibition of larval migration and the exsheathment process of Trichostrongylus colubriformis infective stage

The anthelmintic (AH) effect of Acacia pennatula, Leucaena leucocephala, Lisyloma latisiliquum and Piscidia piscipula was evaluated in the infective larvae (L(3)) of Trichostrongylus colubriformis. Different concentrations of lyophilized extracts were tested using the larval migration inhibition (LMI) test. An inhibitor of tannins (the polyvinyl polypyrrolidone [PVPP]) was used to verify whether these compounds were responsible for the AH effects. Then, the effect of extracts on larval exsheathment was examined by observing the exsheathment process at 10-min intervals for 70 min. The LMI test showed a dose-dependant AH effect for A. pennatula, L. leucocephala and L. latisiliquum (P<0.01), but not for P. piscipula. The restoration of L(3) migration to values similar to those of controls after the addition of PVPP, indicates that tannins are involved in AH effects. Trichostrongylus colubriformis exsheathment was partially or totally blocked by the four plants extracts. Tropical tanniniferous plants evaluated in the current study may have potential as AH for the control of T. colubriformis if in vivo investigations indicate useful effects.     

Climate and the distribution of intestinal Trichostrongylus spp. of sheep

The relative prevalences of Trichostrongylus vitrinus, T. colubriformis and T. rugatus in sheep in south-west Western Australia were examined for evidence of associations with climatic conditions in different localities. The region has a mediterranean-type climate with hot, dry summers and cool, wet winters. The intestinal Trichostrongylus spp. populations in sheep sampled comprised 50% T. vitrinus, 38% T. colubriformis and 12% T. rugatus. The prevalence of T. vitrinus was negatively correlated with mean autumn, winter and spring temperatures of a locality. The prevalence of T. colubriformis was positively correlated with mean autumn, winter and spring temperatures. The prevalence of T. rugatus was not correlated with temperature of any season, but was negatively correlated with mean annual rainfall and length of growing season of a locality. There were suggestions of association of amount of rainfall of a locality and prevalence of T. rugatus was not correlated with temperature of any season, but was negatively correlated with mean annual rainfall and length of growing season of a locality. There were suggestions of association of amount of rainfall of a locality and prevalence of T. colubriformis and of differences in seasonal prevalence of T. vitrinus, but the significance of these was obscured by confounding of some climatic factors. The differences in prevalence of the three Trichostrongylus spp. at different locations was attributed to differences in preferred ambient conditions for development and survival of the free-living stages.     

Inhibition of the development of Trichostrongylus spp. as third stage larvae in sheep

In non-lactating Frisian ewes slaughtered in September and November 1975 and in ewes slaughtered in March/April 1976 at lambing, the majority of Trichostrongylus axei, T. vitrinus and T. colubriformis found were inhibited third stage larvae (L₃). However, some larvae at various stages of development were found in the animals slaughtered at lambing. In contrast, in lactating ewes slaughtered 6 weeks after lambing in April 1976, almost all Trichostrongylus spp. appeared to be adults. All ewes grazed a pasture heavily contaminated with gastro-intestinal nematodes from June 1975 until at least 2 weeks before necropsy.In lambs on the pasture from April or June 1975, and slaughtered in September and November 1975 and March 1976 after at least 2 weeks of isolation, only small proportions of the Trichostrongylus spp. populations appeared to be L₃. Similar results were obtained from tracer lambs kept at pasture from August 1975 to March 1976. The implications of these findings are discussed.     

Scanning electron microscopic features of the ovine interdigital sinus

This article describes the scanning electron microscopic (SEM) features of the ovine interdigital sinus. The lumen was filled with a dense secretory material and quite a number of hairs embedded in the luminal content. For SEM purposes, the sinus was divided into three parts: base, body and neck. At the cut surface, the wall exhibited significant folds which were almost absent in the base, the very short blind end of the sinus. The wall had three layers: epidermis, dermis and fibrous capsule. Stratified epithelium with a prominent keratin layer faced the lumen. The inner surface was similar to the skin surface; however, it was coarser due to folds. The fibrous capsule was composed mainly of dense connective tissue, constituting the outermost layer of the wall. The dermis contained common skin structures including sebaceous glands, hair follicles, arrector pili muscles and apocrine glands. Sebaceous glands appeared as groups of bubbles if they were not collapsed. Apocrine glands generally appeared as a group of coiled tubules. They frequently exhibited apocrine blebs, which is a feature of apocrine secretion. SEM was able to locate some secretory vesicles in the lumen of apocrine tubules which is frequently filled by secretory content. Thus, the apocrine tubules exhibited classical features of apocrine secretion.     

Diagnostic features of ovine progressive pneumonia.

Ovine progressive pneumonia, a chronic, insidious disease of adult sheep, has a relentless course leading to dyspnea, emaciation, and death. Clinical observations and serologic tests are adequate for making a tentative diagnosis. The agar gel immunodiffusion test seems to be the best serologic procedure for indicating infection with the virus but cannot be used to predict morphologic changes or clinical disease, inasmuch as many clinically unaffected animals carry the virus. A definitive diagnosis is based on finding lesions and isolating virus. Affected lungs are large and heavy as a result of interstitial accumulation of lymphoid cells and fibromuscular tissue. Frequently, interstitial lesions are accompanied by bronchopneumonia from secondary bacterial infection. The causal virus can be isolated from infected lungs by cocultivation with primary ovine or bovine cells.     

Effect of condensed tannins on egg hatching and larval development of Trichostrongylus colubriformis in vitro

The effects of condensed tannins extracted from seven forages on the viability of the eggs and first stage (L1) larvae of the sheep nematode Trichostrongylus colubriformis were evaluated in in vitro assays. The extracts of condensed tannins were obtained from Lotus pedunculatus (LP), Lotus corniculatus (LC), sulla (Hedysarum coronarium), sainfoin (Onobrychus viciifolia), Dorycnium pentaphylum (DP), Dorycnium rectum (DR) and dock (Rumex obtusifolius). Extracts containing 200 to 500 microg/ml reduced the proportion of eggs that hatched. The larval development assay was used to evaluate the effect of the extracts on the development of either eggs or L1 larvae to L3 infective larvae. Development was allowed to proceed for seven days by which time the larvae in control incubations had reached the infective L3 stage. Extracts containing 200 microg/ml from LP, DP, DR or dock prevented egg development, and only 11, 8 and 2 per cent of the eggs developed to L3 larvae with extracts from LC, sulla and sainfoin, respectively. When the concentration was 400 microg/ml no eggs developed to L3 larvae. The addition of the extracts after hatching also inhibited the development of L1 to L3 larvae; 200 microg/ml extracted from LP, LC, sulla, sainfoin, DP, DR and dock resulted in only 14, 18, 17, 15, 14, 16 and 4 per cent of L1 larvae developing to the L3 stage compared with 85 per cent for controls, and 400 microg/ml further reduced the development of L1 larvae. Statistical analyses showed that when the extracts were added before hatching they were significantly (P<0.001) more effective at inhibiting the larval development than when they were added after hatching. The condensed tannins from dock had the greatest inhibitory effect on egg development followed by the tannins from DR, sainfoin, DP, LP, sulla and LC.     

Immunization of sheep against the larval stage of Taenia multiceps

A trial with 200 ewes and 127 lambs showed that vaccination of lambs with 2 doses of Oncosphere Secretory Antigen (OSA) 4 weeks apart, at either 4-8 and 8-12 weeks or at 12-16 and 16-20 weeks of age, was equally effective in protecting them against infestation with the larval stage of Taenia multiceps. In this trial, the lambs of ewes, vaccinated with OSA when they were 90 and again 120 days pregnant, were as susceptible to infestation as the lambs of untreated control ewes. Another trial to provoke passive immunity in lambs gave inconclusive results. In a 3rd trial 2 doses of regular OSA and 2 doses of freeze-dried OSA protected all the lambs in each group, while a single dose of regular OSA protected 9 out of 10 lambs against cerebral lesions.     

Influence of adjuvants on immunity in rabbits vaccinated with infective larval somatic proteins of Trichostrongylus colubriformis

Adult New Zealand rabbits were vaccinated at 2-week intervals with three doses of 100 micrograms of infective larval somatic proteins (L3SP) administered subcutaneously with Freund's complete adjuvant (FCA) or beryllium hydroxide and then challenged orally with 10,000 L3. Groups of rabbits immunized orally with three doses of 5000 or 2000 L3 served as vaccination controls. Intestinal worm burdens on Day 21 after challenge revealed that beryllium hydroxide effectively potentiates the protective immunogenicity of L3SP. The level of protection obtained using the beryllium adjuvant (94.8%) was nearly as high as that in rabbits immunized with three doses of 5000 L3 (99.8%). Rabbits vaccinated using FCA showed very poor immunity (29.5%). Local and systemic antibody levels detected by radioimmunoprecipitation tests using 125I-L3SP showed very little correlation with the degree of protection. The beryllium hydroxide-treated group demonstrated significantly higher bile IgA antibody levels than other experimental rabbits. FCA-treated rabbits developed a much higher serum precipitating antibody response, detectable using gel double diffusion tests, than the beryllium group. Also, mucosal IgA antibody levels detected on Day 21 after challenge were significantly higher in the FCA group than in other groups.     

Field evaluation of a mixture of albendazole sulphoxide and levamisole against Ostertagia and Trichostrongylus spp in sheep

The efficacy of a mixture of albendazole sulphoxide and levamisole, 3.6 and 8.25 mg/kg respectively, at single and double dose rates, was compared with the recommended dose rate of each anthelmintic alone. The comparison was conducted on groups of 6 to 14-week-old lambs on 22 farms, 16 of which had evidence of multiple resistance to benzimidazole and levamisole. A single dose of the mixture reduced mean egg counts by 95% on half the farms with multiple resistance and on all the remaining farms. Consequently, the mixture should be included in an assessment of effective anthelmintics on farms to determine its value for nematode control. A double dose rate of mixture was effective on all but 4 farms. Reductions caused by the mixture were due to the additive actions of the drugs on 18 of 22 farms; synergistic action was noted on only 3 farms. It was concluded that the mixture of albendazole sulphoxide and levamisole offered many farmers an effective anthelmintic for use in preventive control programs. Recommendations for such programs include annual rotation of effective anthelmintics as a means of delaying selection for drug resistance.     

Synergistic influence of Ostertagia ostertagi and Trichostrongylus axei on Ostertagia ostertagi larval inhibition and abomasal lesions in cattle

Parasite-free 4-month-old calves were inoculated with Ostertagia ostertagi and/or Trichostrongylus axei followed 6 weeks later by increasing doses of O ostertagi for 8 weeks. Clinical signs of parasitism, fecal egg counts, and plasma pepsinogen concentrations were monitored, and gross lesions and parasite burdens were determined postmortem. Clinical signs of parasitism were not observed and weight gains were not affected in experimentally infected calves. In calves infected with O ostertagi, mean plasma pepsinogen concentrations were greater than for control calves and were diagnostically significant 4 weeks after inoculation and during the last 4 weeks of serial inoculations with O ostertagi. In calves that were given O ostertagi and T axei, abomasal pH was significantly increased, and abomasal lesions were more pronounced than in control calves or in calves inoculated with only O ostertagi or T axei. Abomasal lymph nodes were enlarged in all parasitized calves; other lymph nodes in the calves inoculated with both O ostertagi and T axei were usually smaller than in calves inoculated with only O ostertagi or T axei. Numbers of O ostertagi-inhibited larvae were small in all inoculated calves, but the percentage inhibition was significantly greater in calves inoculated with both O ostertagi and T axei. The percentage inhibition was 3.53% for the O ostertagi-inoculated calves and 7.07% for calves inoculated with both O ostertagi and T axei. These percentages indicated a synergistic effect of concurrent abomasal parasitism, whereas a synergistic effect on T axei worm burden was not observed. The low percentage of larval inhibition indicated that factors other than host resistance are involved in naturally occurring pretype II ostertagiosis.     

A dog with alveolar echinococcosis: the larval stage of the fox tapeworm

In this report we describe the first case of alveolar echinococcosis and leukemic malignant T-cell lymphoma in a dog presented to a general practice in the Netherlands. The owner and the dog moved from Switzerland to The Netherlands a few weeks before. The clinical aspects, diagnostics, pathology, therapy and public health aspects of this severe parasitic zoonosis are described.     

Inhibited development of cyathostominae in the horse in the early third stage

Inhibited early third stage larvae of Cyathostominae were found in the digested mucosa of the large intestine of 12 yearling, female Shetland ponies, which were used in two grazing experiments. The ponies were killed in late autumn. In some ponies the inhibited larvae were very abundant and in most animals the majority of the Cyathostominae populations consisted of these early third stage larvae, suggesting that the phenomenon has an epidemiological significance.     

Measurement in vitro of a larval migration inhibitory factor in gastrointestinal mucus of sheep made resistant to the roundworm Trichostrongylus colubriformis

Lambs were challenged by dosing with 2500 T. colubriformis larvae per day for 34 weeks, rested for 4 weeks and then re-challenged with the infective larvae for a further 10 weeks. A technique for the measurement of inhibition of larval migration from agar gels was used to investigate the antiparasitic activity of mucus, obtained from the small intestine and abomasum of the lambs, at the end of the re-challenge period. Measurements were also made on ileal digesta samples collected at different times during the development of the initial resistance, the rest period and the re-challenge period, and on faeces collected during the re-challenge infection. The mucus from the small intestine and abomasum paralysed and inhibited larval migration from agar gels significantly more (P less than 0.01 and P less than 0.05, respectively) than corresponding mucus from parasite-free control animals. This inhibitory activity was also detected (P less than 0.01) in the ileal digesta of infected animals from Week 6 of primary dosing. The magnitude of the inhibition in the ileal digesta increased with time during the infection period and was again detected during re-infection (P less than 0.01). It was not detectable in resistant sheep towards the end of the rest period. Slight inhibitory activity was detected in faeces after 2 weeks of re-infection. These observations suggest that substances secreted into the lumen of the small intestine of infected animals are responsible for resistance against ingested larvae.