The spermatogenesis of Dictyocaulus filaria (Nematoda, Trichostrongyloidea)

A cytological study was carried out, using male Dictyocaulus filaria, that revealed the diploid number of chromosomes was 2n = 11 and the sex determining mechanism was XO. The behaviour of the chromosomes in the different stages of meiosis was also investigated. Cross, open ring and rod bivalents were observed in diakinesis. The chromosomes appeared to be acrocentric since they acquired a radial disposition in Metaphase-II. The chiasma frequency was 1 and the nucleolus-organizing region was located at the ends of the chromosomes.     

Morphology of inhibited larvae of the bovine lungworm Dictyocaulus viviparus.

Some morphological features of inhibited fourth stage (L4) and fourth moult larvae (4M) of the bovine lungworm Dictyocaulus viviparus are described. Inhibition was induced by maintaining the third stage larvae (L3) for 6 weeks at 4 degrees C. Inhibited fourth stage (L4) and fourth moult larvae (4M) were collected by perfusion of the lungs of experimentally infected calves after necropsy at 15 and 68 days post infection (d.p.i.), respectively. Inhibited 4M, isolated at 68 d.p.i., were about ten times larger than inhibited L4 isolated at 15 d.p.i.     

Observations on the bionomics of the free-living stages of Trichostrongylus vitrinus

Eggs of Trichostrongylus vitrinus in faecal pellets deposited on grass plots each month from April 1981 to March 1982 developed into infective larvae. From October to March development was slow and mortality of the pre-infective stages was very high. From April to September development was more rapid. The weather was generally dry and mortality of the pre-infective stages was high on plots with short herbage but was lower on most of the plots with long herbage, especially in July and August. In the laboratory, development of eggs into infective larvae was completed at temperatures ranging from 4 degrees C to 27 degrees C in faecal pellets which were either kept moist or dried out slowly, but not in faecal pellets which dried out rapidly. The rate of development increased as the temperature rose. Infective larvae survived for up to 16 months on the herbage of grass plots; some survived during very cold weather in the winter of 1981/82. In the laboratory, infective larvae suspended in tap water survived even longer at 4 degrees C and 10 degrees C but not at higher temperatures. They were rapidly killed by continuous freezing. They survived for up to 8 weeks when subjected to desiccation. The relationship between climatic conditions and the development and survival of the free-living stages is discussed.     

Field studies on the bionomics of the free-living stages of St. Lucian Schistosoma mansoni.

Densities of Schistosoma mansoni miracidia and cercariae in natural habitats in three St. Lucian valleys were monitored over a 3-year period by exposure of sentinel snails, Biomphalaria glabrata, and a cercariometric technique, supplemented by sampling of field snails. Separate measures for control of S. mansoni transmission were under evaluation in two of the valleys. Sentinel snails became infected sporadically and their infection rates per valley ranged from 0·12% to 4·99%. S. mansoni miracidial inoculation rates ranged from 1 to over 4 per infected sentinel snail. Combined rainfall of more than 3 in on the day before any day of sentinel snail exposure interfered with miracidium-snail interaction. Densities of S. mansoni cercariae ranged from 0·05 to 21 per litre of water sampled. The number of cercariae detected in a habitat by cercariometry was directly proportional to the number of infected field snails. Sentinel snail infection rates exhibited a downward and an upward trend, respectively, in the controlled and uncontrolled areas, although the changes were not significant statistically.     

Phospholipid and fatty acid content of the blood of sheep infected with the nematode Dictyocaulus filaria

The results of analysis of phospholipids (PL) and fatty acid content in the blood of sheep infected with the nematodes Dictyocaulus filaria are displayed. A significant increase of lysophosphatidylcholine and arachidonic acid as well as a decrease of docozagexaenic acid in PL of infected sheep have been recorded. That points out to structural and functional disorders of cellular membranes during the infection. These disorder could be used as a metabolic criterion to estimate the relationships within the host-parasite system examined.     

Osmotic fragility of sheep erythrocytes and alterations in their membrane constituents in Dictyocaulus filaria infection

Alterations in the sheep erythrocyte membrane constituents during the course of Dictyocaulus filaria infection were studied in 4–6 month old Nali lambs. During the acute course of infection, plasma cholesterol, membrane cholesterol, cholesterol: phospholipid ratio and acetylcholinesterase activity fell significantly when compared with uninfected controls. The onset of the fall in the values of these parameters was observed 1–2 weeks prior to an increase in the osmotic fragility of erythrocytes. The altered values persistently remained at sub-normal levels during the chronic stage of the infection. However, the membrane proteins and phospholipids of sheep erythrocytes remained unaffected during the entire period of study. The clinico-parasitological picture of the disease, as judged by the clinical course of disease, faecal larval output and necropsy worm recovery, was typical of ovine dictyocauliosis.     

C'3 polymorphism of human complement in North-East England.

The C'3 polymorphism of human complement was investigated in a sample of 268 unrelated individuals in North-East England. The two common genes were comparable in frequency with other European populations investigated so far. Two individuals were found to have rare variant C'3 types.     

Efficacy of eprinomectin pour-on treatment in sheep naturally infected with Dictyocaulus filaria and Cystocaulus ocreatus

The efficacy of eprinomectin on Dictyocaulus filaria and Cystocaulus ocreatus in naturally infected sheep was evaluated in the present study. In total, 30 infected sheep were randomly divided into two groups: treated (n?=?15) and untreated (n?=?15). A single pour-on dose of eprinomectin (0.5?mg/kg) was administered to the treated group. No medication was used in the untreated group. Faecal larval counts were performed on pre-treatment (day 0) and post-treatment (days 7, 14, 21 and 42) days. Eprinomectin was found to be 100% effective against D. filaria on day 7 post-treatment when compared with the untreated group and it maintained this effect on days 14, 21 and 42. However, the decrease in faecal larval count of C. ocreatus was found to be 86, 86 and 91%, on days 14, 21 and 42, respectively.     

宽额螯蜂的幼期形态及生物学特性研究

宽额螯蜂Dryinus latus Olmi在山东商河寄生恶性席瓢蜡蝉Sivaloka damnosus Chouet Lu若虫,具有捕食和寄生的双重控制作用。首次明确该蜂寄主,记述其幼期形态特征、生活史、生活习性。在山东商河1年发生2代,以4龄老熟幼虫在茧内越冬。翌年4月下旬至5月上旬为化蛹盛期,5月中旬越冬代成虫开始出现,捕捉寄主若虫补充营养。成虫主要产卵于恶性席瓢蜡蝉3～5龄若虫前后翅芽下紧贴体背的淡绿色组织上。第1代卵历期平均78.1h,幼虫孵化至脱囊平均历时209.5h,产卵至脱囊平均历时280.0h,蛹期平均386.4h。幼虫作茧于枝条、叶片或地面枯叶上,茧外缀有枝条表皮或叶片碎屑。7月下旬至8月上旬出现第1代成虫,第2代幼虫8月上旬开始脱囊结茧越冬。野外寄生率27.8%～45.7%,控制作用显著。     

Chromosome C-banding techniques in Dictyocaulus filaria (Rudolphi, 1809) Railliet and Henry, 1907

C-banding has been performed on Dictyocaulus filaria using both original and modified techniques. The karyotype is reported based on C band observations. The existence of large heterochromatic blocks appears to be the cause of the low chiasmata frequency.     

Molecular identification and prevalence of Dictyocaulus spp. (Trichostrongyloidea: Dictyocaulidae) in Swedish semi-domestic and free-living cervids

Lungs of 102 roe deer (Capreolus capreolus), 136 moose (Alces alces), 68 fallow deer (Dama dama), and six red deer (Cervus elaphus) were examined during hunting seasons from 16 September 1997 to 1 March 2000. The aim was to determine the species composition and prevalence of Dictyocaulus lungworms in these hosts in Sweden. Worms were identified following polymerase chain reaction (PCR) amplification of the internal transcribed spacer of ribosomal DNA (ITS2), followed by hybridization with four species-specific oligonucleotides. In addition, 50 lungworms from five reindeer (Rangifer tarandus) from Norway were similarly analyzed. A total of 399 worms were recovered and analyzed representing a range of 29-128 worms per host species. All specimens from roe deer were identified as Dictyocaulus capreolus, whereas those from red deer and reindeer were identical with D. eckerti. From moose, 73 (81.1%) of the worms were identified as D. capreolus whereas 17 (18.9%) were D. eckerti. The ITS2 sequence of fallow deer lungworms differed significantly when compared with the ITS2 of D. viviparus, D. capreolus, and D. eckerti. This indicated that fallow deer in Sweden may be infected with a new genotype of Dictyocaulus spp. Consequently, a specific probe designed for the ITS2 from this Dictyocaulus sp. hybridized exclusively with samples from lungworms of fallow deer. Interestingly, no D. viviparus were found in any of these hosts. The prevalence of infection in each host was as follows: D. capreolus in roe deer (14.7%) and moose (10.6%); D. eckerti in moose (0.7%) and red deer (33.3%); and Dictyocaulus sp. in fallow deer (10.3%). Regardless of lungworm species, the overall prevalence of Dictyocaulus spp. in these hosts was 12.2%. Prevalence between male and female animals and among the different age groups did not differ significantly. Finally an enzyme linked immunosorbent assay (ELISA) specific for patent D. viviparus infection in cattle was utilized to analyze lung tissue fluids from infected animals. All samples from roe deer, red deer, and fallow deer were negative in the ELISA. However, three out of twelve (25%) samples from moose and 17 of 40 (43%) samples from cattle were positive. This indicated that moose anti-D. capreolus antibodies recognized the D. viviparus antigen and that anti-cattle immunoglobulin cross-reacted with moose antibodies.     

The development and overwintering survival of free-living larvae of Haemonchus contortus in Sweden

Five complimentary studies were undertaken with the overall aim to examine the ability of free-living stages of Haemonchus contortus to over-winter and tolerate cold stress. Two studies deal with the development and long-term survival of eggs and infective larvae of two geographically different isolates (Kenya and Sweden). Eggs and larvae were monitored in climatic chambers at temperatures that fluctuated daily between -1 degrees C and 15 degrees C, or at constant temperatures of 5 degrees C and 15 degrees C. The development from egg to larvae was dependent on temperatures over 5 degrees C. The long time survival was favoured at lower temperatures. Furthermore, the overwintering capacity of the free-living stages of these isolates was estimated under Swedish field conditions. Two groups of lambs were experimentally infected with different isolates, and kept separated on previously ungrazed plots. In early May the following year, two parasite-naive tracer lambs were turned out on each of the plots to estimate the pick up of overwintered larvae. This experiment was replicated in central and southern Sweden. In addition, two experiments were performed in 2003 on pasture previously grazed by naturally infected sheep. One trial was on a pasture in southern Sweden grazed by a commercial flock, where extreme numbers of H. contortus were found towards the end of the grazing season 2002. The other study was on a pasture plot in central Sweden grazed by a hobby flock in 2002, where three of six lambs died due to haemonchiasis. Overwintered H. contortus was recorded on three of four experimental sites. Worm burdens were in all instances extremely low. No differences in development and survival were found between the isolates. Consequently, overwintering on pasture is of no practical significance in the transmission of H. contortus between grazing-seasons in Sweden.     

The role of biotic factors in the transmission of free-living endohelminth stages

The transmission success of free-living larval stages of endohelminths is generally modulated by a variety of abiotic and biotic environmental factors. Whereas the role of abiotic factors (including anthropogenic pollutants) has been in focus in numerous studies and summarized in reviews, the role of biotic factors has received much less attention. Here, we review the existing body of literature from the fields of parasitology and ecology and recognize 6 different types of biotic factors with the potential to alter larval transmission processes. We found that experimental studies generally indicate strong effects of biotic factors, and the latter emerge as potentially important, underestimated determinants in the transmission ecology of free-living endohelminth stages. This implies that biodiversity, in general, should have significant effects on parasite transmission and population dynamics. These effects are likely to interact with natural abiotic factors and anthropogenic pollutants. Investigating the interplay of abiotic and biotic factors will not only be crucial for a thorough understanding of parasite transmission processes, but will also be a prerequisite to anticipate the effects of climate and other global changes on helminth parasites and their host communities.     

In vitro migration of Dictyocaulus viviparus larvae: migration of the infective stage inagar gel.

The infective stage of the cattle lungworm, Dictyocaulus viviparus, was able to migrate in agar gel when activated by bile. The number of larvae which penetrated the upper surface of a 2 mm thick agar layer was counted and found to be independent from the agar concentration. Larvae which had migrated out of the agar remained on the surface and did not re-enter. The agar migration process was temperature dependent. Influence of time as well as dependency of agar thickness was investigated. The significance of these findings is discussed.     

The duration of passive protection against Taenia ovis larvae in lambs

In an attempt to induce passive protection in lambs against Taenia ovis larvae that would last for the 15-20 weeks from birth to slaughter as fat lambs, one group of ewes was immunized by a series of injections of 2000, 4000, 8000, 16 000 and 32 000 activated oncospheres of Taenia ovis prior to parturition. Another group of ewes was not immunized. All ewes had previously grazed pasture lightly infected with T. ovis eggs. Most lambs from non-immunized ewes developed cysts after oral infection with T. ovis eggs. However, no lambs from immunized ewes developed cysts up to and including 6 weeks after birth. Between 8 and 16 weeks after birth a proportion of lambs were found to be susceptible to infection. By 18 weeks after birth all lambs were apparently susceptible. The 99% confidence band for the mean duration of demonstrable complement-fixing antibody titres was 6.2-7.8 weeks for lambs from immunized ewes. The persistence of maternal protective antibody in some lambs could possibly preclude successful active immunization of all lambs against T. ovis larvae before 18 weeks of age.     

Studies on the cryopreservation of Dictyocaulus viviparus (Nematoda) third-stage larvae

Various cooling (0.1-5,100 degrees C min-1) and warming (20-6,800 degrees C min-1) rates, stepped cooling schedules and four cryoprotective additives (dimethyl sulphoxide, methanol, ethanediol and glycerol) were investigated in cryopreservation studies with Dictyocaulus viviparus third-stage larvae. Exsheathment with sodium hypochlorite was essential to achieve significant survival. With uninterrupted cooling, highest survival (30% normally motile) was achieved with rates of 10-70 degrees C min-1. Survival was higher (50-75%) using 1 degree C min-1 to -10 degrees C followed by plunging into liquid nitrogen. The optimum warming rate was 6,800 degrees C min-1. The use of cryoprotectants led to marginally lower survival while varying the suspending media had no significant effect on survival. X-irradiated, exsheathed third-stage larvae cryopreserved by the optimum protocol yielded 38.3 +/- 4.2% survival. Two calves each infected with 45,000 (15,000 viable) exsheathed, unirradiated, cryopreserved third-stage larvae harboured 494 worms (1.1% infectivity) and 355 worms (0.8%) at necropsy. Numbers of first-stage larvae in the faeces reached 420/g and 105/g respectively 27 days after infection.