The location of parasites within their hosts: The passage of Nippostrongylus brasiliensis through the lungs of the laboratory rat

This paper examines those factors which determine the emergence of N. brasiliensis from the pulmonary circulation into the alveoli and bronchioles of the rat's lung. After injection into the superior vena cava, larvae were found to be distributed throughout the lobes of the lungs in direct relation to the mass of blood and tissue and it was concluded that this resulted from entirely random forces. Larvae which had been reversibly immobilized in piperazine were trapped in the capillaries of the lungs in the same way as untreated larvae; this accumulation was considered to be passive. Larvae could penetrate surgically collapsed lungs but did so in lower numbers than in functional lungs so host breathing movements may facilitate penetration but are not essential. Larvae could repeat their migrations in a succession of hosts, but only if removed from the lungs within 2 h, by 20 h they could not and were destroyed in the lung tissue. Larvae were passively trapped in the arterioles but can emerge only through their own behavioural efforts. Heavy larval doses (10,000) caused considerable reversible oedema and haemorrhage. This was due to the behaviour of the larvae and not the direct effect of mechanical blockage because the same was not true if 10,000 heat-killed larvae were injected. Larvae of Ancylostomatubae forme, which does not secrete enzymes, also caused haemorrhaging in rat lungs, demonstrating that larval motility alone can lead to emergence through rupturing arterioles. By 20 h larvae were active in the trachea but they showed no directional orientation and were carried passively in the mucus. At this stage they were strongly photonegative.     

Mushroom mycelium and compost substrates in relation to the survival of the larva of the sciarid Lycoriella auripila

The development of sciarids was reduced in old casing and in casing to which a commercial composting additive was added in large amounts. In laboratory tests, adding water, soya bean, cotton seed or oatmeal to finished mushroom composts reduced the mean development time of the larvae of Lycoriella auripila. Soya bean meal significantly increased the number of adult sciarids which matured. While the presence of mushroom mycelium in large quantities inhibited the development of sciarids, smaller amounts increased either the number of larvae maturing or their rate of development in different tests. Larvae were seen to feed on mycelium. The addition of sucrose solution either reduced or prolonged development time in different tests. Nitrogenous additives encouraged the growth of ‘weed moulds’. Both these and the number of sciarids which developed were reduced by adding a solution of calcium nitrate. The results suggested that more selective composts, favouring rapid mycelial colonization, would provide ‘cultural’ control of mushroom sciarids.     

Manipulation of the length of the sensitive period,and the induction of pupal diapause in the flesh-fly,Sarcophaga argyrostoma

Larvae of the flesh-fly Sarcophaga argyrostoma were raised in short-day cycles (LD 12: 12) and at temperatures (18° and 20°C) in which short-day induction of pupal diapause was less than ‘saturated’. The cultures were then subjected to experimental treatments which modified the duration of larval development (the sensitive period). Overcrowding the larvae within a limited quantity of meat, premature extraction of the third instar larvae from their food, or exposure of the mature larvae to pure CO₂ for 24 h, were all found to accelerate puparium formation, thereby curtailing the sensitive period, and reducing the incidence of pupal diapause. Conversely, lengthening the sensitive period by allowing the mature larvae to wander in wet sawdust increased diapause incidence. The results are interpreted in terms of an interaction between the length of the sensitive period and the ‘required day number’, and also in the light of what is known about the endocrinological control of diapause and development in flesh flies.     

The occurrence of Strongyloides ratti in the tissues of mice after percutaneous infection

The migration of infective larvae of Strongyloides ratti has been examined in C57Bl/6 mice after percutaneous infection of the anterior abdominal wall. Lateral migration of larvae through the skin and subcutaneous tissues was not seen. Large numbers of larvae were recovered from the muscles between 2 and 24 hours after infection and larvae were seen in the cerebrospinal fluid 24 and 48 hours after infection. Insignificant numbers of larvae were seen in the blood, serosal cavities, liver, spleen, kidneys, brain or nasopharynx. Larvae arrived in the lungs between 24 and 72 hours after infection and worms were first noted in the small intestines at 48 hours. It is concluded that larvae migrate preferentially to the muscles and CSF before passing to the lungs, but the exact mode of travel is uncertain.     

Structure and development of Austramphilina elongata Johnston, 1931 (Cestodaria: Amphilinidea)

The life cycle and structure of the larva of Austramphilina elongata using light-microscopy, scanning and transmission electron microscopy are described. Eggs are round and non-operculate. Larvae hatch in freshwater and penetrate through the cuticle of juvenile crayfish, Cherax destructor, and of freshwater shrimps, Paratya australiensis and Atya (= Atyoida) sp., shedding their ciliated epidermis. In the last two hosts, development to the infective stage does not occur. In crayfish, larvae grow and reach the infective stage. Turtles, Chelodina longicollis, become infected by eating infected crayfish. Larvae penetrate through the oesophageal wall of the turtle and migrate toward the coelom, where maturation occurs. The free-swimming larva has a syncytial epidermis which covers most of the body except for the posterior region bearing the hooks. It is loosely attached to a thin underlying tegument, which is connected to ‘insunk’ nucleated cell bodies. It forms a thick surface layer in the posterior region. There are three flame cells on each side of the body and two postero-lateral excretory pores. There are no lateral flames. The weir apparatus of the flame cell has the structure typical of parasitic platyhelminths. The smaller capillaries have a smooth surface, that of the terminal ducts is covered by numerous microvilli. Three types of penetration glands open anteriorly. There are five pairs of hooks; one median ‘normal’, two submedian halberd-shaped, and two lateral serrate. Hook are not lost, they are arranged around the gonopore of the adult. Frontal glands opening into the proboscis were found in the anterior part of the body in all stages examined. Infective stages in crayfish have developing reproductive organs and ducts. The tegument of the adult has many microvilli.     

Effect of plant species on the larvae of gastrointestinal nematodes which parasitise sheep

Faeces containing Trichostrongylus colubriformis and/or Ostertagia circumcincta eggs were used to provide four contaminations in each of 2 years on plots of browntop, Yorkshire fog, ryegrass, tall fescue, lucerne, chicory, cocksfoot, white clover, and prairie grass and in the second year a mixed sward of ryegrass/white clover. Third stage larvae were recovered from faeces and from four strata of herbage, 0–2.5, 2.5–5, 5–7.5 and >7.5 cm above the soil surface at 2, 4, 6, 8, 11, and 14 weeks after faeces were deposited on the swards. Herbage species had a significant (P < 0.0001) effect on the number of larvae recovered. Greatest numbers of larvae, as indicated by ranking analysis, were recovered from Yorkshire fog, ryegrass, and cocksfoot and lowest numbers from white clover and lucerne. The difference between herbages in numbers of larvae recovered was due to the ‘‘development success’’, the ability of larvae to develop to the infective stage and migrate on to herbage, rather than ‘‘survival’’, the rate of population decline once on the herbage. Faecal degradation was most rapid from white clover and browntop, intermediate from tall fescue, lucerne, prairie grass, cocksfoot, and ryegrass, and slowest from Yorkshire fog swards. The numbers of larvae recovered from herbages were related (r² = 0.59, P < 0.05) with the faecal mass remaining. A greater proportion of the total larvae recovered from the herbage was recovered from the bottom stratum of Yorkshire fog and prairie grass than from white clover, with the other herbages intermediate, indicating that larvae had greater difficulty migrating up Yorkshire fog and prairie grass than the other herbage species. In most herbage species, despite more larvae being recovered from the lowest stratum, larval density (L₃/kg herbage DM) was highest in the top stratum. This study has demonstrated that herbage species can have a significant impact on the population dynamics and vertical migration of T. colubriformis and O. circumcincta larvae.     

The location of parasites within their hosts: Bile and the site selection behaviour of Nematospiroides dubius

Bile activated and maintained the motility of infective larvae of N. dubius for up to 3 h, compared to the response of only 20 min induced by mechanical stimulation. Larvae accumulated significantly more in bile than in distilled water controls. A dose-response curve showed an exponential increment in the percentage of larvae active after 30 min between aqueous bile concentrations of 0.2–5.0%. Removal or reduction of bile by ligaturing, cannulation or externalization of the bile duct was consistently associated with reduced larval establishment. Larvae established significantly in areas to which the bile had been surgically redirected. The role of bile in larvae habitat selection behaviour is discussed.     

Kinetics of primary and secondary infections with Strongyloides ratti in mice

Dawkins H. J. S. and Grove D. I. 1981 Kinetics of primary and secondary infections with Strongyloides ratti in mice. International journal for Parasitology11: 89–96. The kinetics of infection with S. ratti were quantitated in normal and previously exposed C57B1 /6 mice. In primary infections, larvae penetrated the skin rapidly and were seen in peak numbers 12 h after infection. By 24 h after infection, larval numbers had declined appreciably and there was a slow decrease in numbers thereafter. Larvae were first observed in the lungs at 24 h and maximal recovery occurred at 48 h. It is thought that larval migration through the lungs is rapid. Worms were first seen in the intestines two days after infection. Maximum numbers were seen on the fifth day and worm expulsion was complete by day 10. Two moults took place in the small intestine during days 3 and 4 after infection. Rhabditiform larvae were first noted on the fourth day after infection. Mice exposed to S. ratti four weeks previously had significantly less larvae in the skin 4 and 12 h after infection but by 24 h there was no difference when compared with mice with primary infections. Peak recovery of larvae from the lungs occurred 24 h after infection; significantly less larvae were recovered on days 2 and 3 when compared with normal mice. There was a marked reduction in the adult worm burden in the gut; the number of worms recovered was less than one fifth of that seen in primary infections. Those worms which did mature were less fecund and were expelled from the intestines within 7 days of infection. It is suggested that in previously exposed animals, the migration of larvae from the skin is hastened, many of these larvae are destroyed in the lungs and that expulsion of worms which do mature in the intestines is accelerated.     

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.     

Migration of Gasterophilus intestinalis larvae (Diptera: Gasterophilidae) in the equine oral cavity

Cogley T. P., Anderson J. R. and Cooley L. J. 1982. Migration of Gasterophilus intestinalis larvae (Diptera: Gasterophilidae) in the equine oral cavity. International Journal for Parasitology12: 473–480. Larvae of G. intestinalis pursued a specific migratory pathway within the equine oral cavity en route to the stomach. The larval migration included the following sequence: burrowing in the tongue mucosa, invasion of the interdental spaces, transitory attachment at the root of the tongue and movement to the stomach. The molt from first to second instar did not occur in the tongue, as commonly believed, but between the interdental spaces. Ninety five percent of the larvae invading the interdental spaces were associated with gingiva of the upper molars. SEM analysis revealed further details of the oral migration: (1) air holes excavated in the epithelium which connect with deeper burrows; (2) an intimate association between air holes and posterior spiracles of larvae; (3) precise impressions of larvae in tissue immediately surrounding the most recently formed burrows; and (4) initial larval entry into the tongue through the use of natural disruptions or healing lesions. Factors influencing the development of the oral migration are discussed.     

Infectivity of Strongyloides venezuelensis is influenced by variations in temperature and time of culture

The present research investigated the influence of temperature and time of larvae culture on the infectivity of Strongyloides venezuelensis. Mice were infected s.c. with 1500 larvae of S. venezuelensis maintained at 28 °C for three days of culture (dc), 28 °C for seven dc or 18 °C for seven dc. On days 1, 3, 5, 7, 14 and 21 post-infection the animals were sacrificed and cell numbers in the blood, peritoneal cavity fluid (PCF), broncoalveolar fluid (BALF), cytokines, immunoglobulins, number of parasites and eggs/g of feces were quantified. Results demonstrated an increase in eosinophils and mononuclear cells in the blood, PCF and BALF of infected mice. Larvae at 28 °C/3dc induced earlier eosinophils in the PCF and BALF as opposed to larvae at 28 °C/7dc and 18 °C/7dc. Larvae at 28 °C/7dc induced higher synthesis of IL-4, IL-5 and IL-10 on days 5 and 7 post-infection. Larvae at 28 °C/3dc in culture induced higher synthesis of IL-12 than larvae of seven dc, but time in culture induced better synthesis of IFN-γ after larval migration had ceased and only adult worms were present. Larvae at 28 °C/3dc in culture induced higher synthesis of IgG and IgG1 and expelled less female parasites than larvae cultivated for seven days. In conclusion, it was observed that the infectivity of S. venezuelensis is influenced by variations in temperature and time of culture.     

Symptomless Resistance of Alfalfa to Meloidogyne incognita acrita

Penetration, development and migration of the cotton root-knot nematode, Meloidogyne incognita acrita, in resistant and susceptible alfalfa varieties was compared. Larvae entered both resistant and susceptible plants in approximately the same numbers. After 3 to 4 days, the number of larvae in resistant roots decreased sharply until at 7 days fewer than 5 larvae/seedling and no nematode development could be found. In susceptible roots, larvae became sedentary and developed normally; egg production began as early as 18 days after penetration of the host.     

Hookworm behaviour: larval movement patterns after entering hosts.

Larvae of the cat hookworm, Ancylostoma tubaeforme migrate from the skin to the lungs of both mice and cats. Experiments have examined changes in the basic movement patterns of infective larvae after as long as 5 days within host tissues. Similarly, morphological developments and changes in unbound neutral lipid were investigated. There were no changes in the larvae except for a fall in the concentrations of lipid. Furthermore, it was found that larvae which had successfully completed a migration from the skin of a mouse to its lungs could successfully complete a second migration. The evidence does not support the hypothesis that a distinct series of tissues cr physico-chemical barriers may be sequentially followed in the migration of hookworms in their hosts. The migration route is seen as a much more random, less purposeful series of events.     

Eclosion and hatching in cockroach first instar larvae: A stereotyped pattern of behaviour

Cockroach pharate first instar larvae (Periplaneta americana) spontaneously initiate eclosion and hatch from the oötheca after 30 days' incubation at 29°C. The caudal-to-rostral peristaltic movements involved in both eclosion and hatching are initiated even when the first instar larvae have been removed from the oötheca and incubated separately in organ culture dishes. Therefore, environmental stimuli and conditions in situ are not necessary for the onset of eclosion. However, environmental factors associated with the cuticle control the termination and/or duration of the eclosion behaviour sequence. Larvae which had cuticles glued to their bodies had longer than normal eclosion episodes while larvae which experienced premature cuticle removal immediately ceased the movements. Cuticle removal immediately ‘switched’ behaviour from that of the larva to that of the adult with the characteristic walking gait. Eclosion in larvae removed from the oötheca could be initiated by tactile stimulation. A rôle for this response in synchronizing the eclosion-hatching movements of the many larvae within an oötheca is suggested.     

The effect of osmotic stress on behaviour and water content of infective larvae of Trichostrongylus colubriformis

The role of the cuticle and sheath in the water dynamics of the infective larvae of Trichostrongylus colubriformis under osmotic stress and the effect of osmotic stress on behaviour have been investigated. In hypotonic solutions larvae lose the activity response to mechanical stimulation and there was also some increase in coiling. Larvae can regulate their water content in hypotonic solutions but lose water slowly in hypertonic solutions. Removal of the sheath by exposure to sodium hypochloritc or to a ‘natural’ stimulus had little effect on the water dynamics of infective larvae. The sheath thus appears to be freely permeable to water when hydrated whereas the cuticle has a very restricted permeability.     

Damage and early destruction of Taenia taeniaeformis larvae in resistant hosts, and anomalous development in susceptible hosts: a light microscopic and ultrastructural study

Bortoletti G., Conchedda M. and Ferretti G. 1985. Damage and early destruction of Taenia taeniaeformis larvae in resistant hosts, and anomalous development in susceptible hosts: a light microscopic and ultrastructural study. International Journal for Parasitology15: 377–384. Taenia taeniaeformis larvae in resistant C57 mice have been studied from 5th to 15th day post-infection (L5–L15) both at the light and electron microscopic level. L5 stages were already damaged and total destruction occurred by approx. 15 days post-infection. In stage L5, unlike fertile larvae from C3H mice, the perilarval amorphous layer (PAL) was generally absent, and the host's cells were in close contact with the parasite surface. At this stage eosinophils were already present together with neutrophils and macrophages. Larvae were seen increasing in volume between stages L6 and L8, but remained constant from stages L9 to L14, while both the tegumental distal cytoplasm (TDC) and the subtegumental cellular layer (SCL) gradually decreased. In stages L10–L14 only a narrow TDC separated the larval cavity from host cells. After the larval tegument had been reduced in thickness the eosinophil lytic enzyme release onto the parasite surface contributed to produce a ‘hole’ in the TDC where host cells penetrated and gradually filled the larval cavity of L15, destroying the parasitic residues. Therefore anomalous small larvae (L50 and more) from C3H mice (susceptible host) have been studied: in these the scolex anlagen was absent or greatly reduced; the TDC was very narrow and the SCL greatly damaged. Outside the larva the ‘host tissue’ appeared as an unidentifiable amorphous material. These larvae cannot be considered ‘dead’ but are defined as sterile.     

Trichinella spiralis: vascular recirculation and organ retention of newborn larvae in rats

The recirculation of Trichinella spiralis newborn larvae was studied in inbred AO rats. Newborn larvae collected after in vitro incubation of adult T. spiralis worms for 2 or 24 hr were injected into rats through the tail vein or hepatic portal vein. Blood samples from the femoral vein, hepatic portal vein, and abdominal aorta were collected at intervals from 1 min to 24 hr after larval injection. Newborn larvae of both ages (24 hr or 2 hr old) persisted in femoral vein blood for less than or equal to 5 hr after injection, but they could be detected in portal vein blood by 24 hr after injection. The injection of larvae into a tail vein or the portal vein did not influence the pattern of larval circulation, although there was a 1-5 min delay in newborn larval appearance time after injection into the portal vein. Transcapillary migration through tissue and back to the circulation was evident in the appearance of newborn larvae in the thoracic duct lymph up to 24 (occasionally 48) hr after tail vein injection of newborn larvae. During the course of a natural primary infection, no evidence for trapping of larvae in the mesenteric lymph node could be found despite direct larval migration through this organ. Injected newborn larvae were retained in the lungs, and small numbers could be recovered 24 hr after intravenous injection. We conclude that a proportion of newborn larvae recirculates within the vasculature for several hours; a smaller population extravasates but can reenter the circulatory system via the lymphatics. Furthermore, some newborn larvae are found in organs rich in capillaries up to 24 hr after their entry into the blood.     

The response of lambs to vaccination at weaning with irradiated Trichostrongylus colubriformis larvae: segregation into 'responders' and 'non-responders'

Dineen J. K., Gregg P. and Lascelles A. K. 1978. The response of lambs to vaccination at weaning with irradiated Trichostrongylus colubriformis larvae: segregation into ‘responders’ and ‘non-responders’. International Journal for Parasitology8: 59–63. Groups of colostrum fed and colostrum deprived lambs were vaccinated with irradiated Trichostrongylus colubriformis larvae at weaning (3 months) and challenged with normal infective larvae. As there was no significant difference between the worm counts of these groups after challenge, it was concluded that the failure of lambs, generally, to respond to vaccination as vigorously as mature sheep, was not due to ‘feed-back inhibition’ of the immune response by the action of maternal antibody.However the results showed that the lambs segregated into ‘responders’ and ‘non-responders’. The mean worm count of responders was 1560 whereas for non-responders this was 24,340. A responder was defined as an animal whose worm count was less than the lower limit of the 99 % confidence interval of unvaccinated controls. These results suggest that genetically-determined factors play an important role in the responsiveness of lambs to vaccination.Whereas counts of globule leucocytes in duodenal tissues were negatively correlated with worm counts (i.e. positively correlated with resistance), counts of both eosinophils and neutrophils were positively correlated with worm counts. These findings suggest that either globule leucocytes are involved in the resistance mechanism, or they are by-products of cellular events involved in resistance. On the other hand it is unlikely that either eosinophils or neutrophils are involved in the mechanism of resistance.     

Integrated control of apple pests in New Zealand

In a study at Appleby Research Orchard, Nelson, examination of the fruit from mature ‘Delicious’ apple trees sprayed with ryania over 5 years showed that less than 10% of 5th‐instar larvae of the codling moth (Laspeyresia pomonella) seeking cocooning sites originated from fruit on the ground. In 1972 and 1973 the survival of such larvae was studied by tagging with cobalt‐58 and releasing them beneath mature trees. In both years about 25 % of the tagged larvae returned to the tree to spin cocoons. Larvae released on bare ground 0–1 m from the tree trunks were more successful than those released in the sward 1–2 m away. Once on the trees, most larvae spun cocoons beneath exfoliating bark on the lower parts of the leaders and the trunk. Fifty‐two percent of the cocoons located were formed on the ground, and overwintering mortality of these was estimated to be near 100%. The pre‐cocooning mortality of larvae released on the ground was similar to that of larvae released on the trees in the same year. It was concluded that larvae from windfalls could be ignored in estimating 5th‐instar larval mortality of codling moth on ‘Delicious’ trees. On the cultivars ‘Dunn's Favourite’ and ‘Cox's Orange Pippin’, however, the higher percentage of larvae in windfalls made their inclusion in mortality estimates essential.     

Trichinella spiralis: effect of high temperature on infectivity in pork

Twenty gram samples of homogenized Boston shoulder from swine experimentally infected with Trichinella spiralis were sealed in plastic pouches, pressed to a uniform thickness of 2 mm, and subjected to water bath temperatures of 49, 52, 55, 60, and 63 +/- 0.5 C for intervals of 2 min to 6 hr, especially within the interval of 0 to 15 min. These times included a period of about 1 min at the start and a period of about 1 min at the end for temperature equilibration. Treated samples were rapidly chilled to 25 C and then digested in a 1% pepsin-HCl solution at 37 C for 18 hr to recover T. spiralis larvae. The recovered larvae were suspended in 2 ml saline; 1 ml of this suspension was introduced into the stomach of each of two rats. The linear equation, log (time) = 17.3 -0.302 (temperature), was calculated from the time required at each temperature for the inactivation of T. spiralis larvae. The correlation coefficient for that relationship was r = -0.994. Larvae heated in the meat to 55 C for 4 min retained their infectivity, but were rendered noninfective after 6 min at 55 C. At 60 C, larvae were not infective after only 2 min (zero dwell time); whereas at 52 C, 47 min were required to render the larvae noninfective. Larvae in meat heated to 49 C were infective after 5 hr but not after 6 hr. These data demonstrate that the destruction of infectivity of T. spiralis is time-temperature related.