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A breeding programme, based on selection for faecal egg counts, has produced lines of sheep which demonstrate either increased resistance (high responder) or susceptibility (low responder) to challenge infection with T. colubriformis after vaccination with irradiated larvae. Circulating blood eosinophilia, a hallmark of helminth infections, was examined in third generation lambs from two separate selective matings and random bred control lambs. Numbers of eosinophils were higher in high responder lambs when compared to low responders after vaccination and challenge infections. Analysis of eosinophil counts confirmed a strong line effect and there was no evidence of a sex effect. Random bred lambs showed wide individual variations in eosinophil numbers and their response to infection. It was concluded that peripheral eosinophilia was more a measure of host responsiveness to infection than an indicator of helminthiasis. As such the eosinophil may serve as an indicator of the hosts ability to respond to T. colubriformis vaccination and infection.

The course of infection with a Malaysian dog strain of Ancylostoma ceylanicum was investigated in 15 inbred strains of mice, in outbred and inbred mice immunosuppressed with prednisolone, and in immunodeficient hypothymic mice. Oral, percutaneous and subcutaneous routes of infection, in both sexes of mice, were assessed. In only one instance was a single small adult male worm found. Following oral infection, larvae migrated from the stomach to the large bowel and then a proportion of worms penetrated the perianal skin. This was followed by the appearance of larvae in the lungs. Living 3rd-stage larvae were seen in the anterior small intestine, perianal skin and lungs for the 6 weeks of the study, with peak recoveries being at 12 h, 8 days and 3 weeks, respectively. It is clear that systemic migration of larvae occurs after oral infection, and it is possible that recirculation may occur. Only a small percentage of larvae penetrated the abdominal skin after being administered percutaneously. In subcutaneous infections, a small proportion of larvae moved rapidly from the site of injection and were recovered from the lungs 2 h after infection. Most larvae, however, migrated from the injection site over the ensuing few days. Living 3rd-stage larvae were seen in the lungs and in the small intestine for the 4 weeks of observation. The strain of A. ceylanicum employed does not complete its development in mice. Nevertheless, this model offers significant potential for studying the immune responses, as well as investigating the means by which these parasites evade host defences.

The scanning electron microscopical appearances of infective larvae of Strongyloides ratti and Ancylostoma caninum have been described. Particularly noteworthy was the tail of S. ratti which was found to have a distal aperture surrounded by a row of eight projections. The penetration of larvae through newborn mouse skin was investigated. S. ratti larvae forced its way rapidly and directly through the stratum corneum. No larvae of A. caninum were observed in stages of partial penetration but the occasional empty sheath was seen.

C57Bl/6 mice were infected with Strongyloides ratti. Susceptibility to infection was ascertained by quantifying the numbers of larvae in the faeces 1 week after infection. Resistance to infection was transferred by pooled immune serum and mesenteric lymph node (MLN) cells obtained 2 and 3 weeks after infection. There was no additive effect when immune serum and MLN cells were given together. Protection was not conferred by MLN cells 1, 4 or 6 weeks after infection nor by spleen cells taken 1--6 weeks after infection. There was, however, a mild non-specific reduction in larval excretion after transfer of either normal or immune spleen cells. These data indicate that both humoral and cell-mediated immune responses may confer resistance to infection in murine strongyloidiasis.

As parasitology increasingly becomes the domain of molecular biologists, it is important to keep in mind that a fundamental understanding of the whole parasite, its structure and behaviour can help to solve complex problems of molecular biology. Hugh Dawkins and Terence Spencer discuss the preparation of DNA from filaform larvae of Trichostrongylus colubriformis and Ostertagia circumcincta and how a detailed knowledge of the morphology and life cycle of each parasite helps in this process.

The changes in numbers of 6 cell populations in the intestine of mice at various intervals after primary and challenge infections with Strongyloides ratti have been quantified. The number of lamina propria mast cells increased 8 days after primary infection and reached a peak at 12 days. After secondary infection, there was a transient fall in mast cell numbers followed by a slow increase. Globule leucocytes showed a similar trend early in the primary infection and had reached normal levels after 28 days. After challenge infection, there was an early and rapid increase in their numbers. Granular intraepithelial lymphocytes did not alter significantly during the first 14 days, but were significantly greater 28 days after primary infection; they did not vary significantly after challenge infection. However, numbers of non-granular intraepithelial lymphocytes increased 10 days after infection, were elevated prior to the secondary infection at 28 days, then declined in numbers nearly 2 weeks after challenge infection. Goblet cells increased significantly 12 days after primary infection then declined rapidly. After challenge infection, there was an accelerated increase in numbers. Eosinophil numbers increased 4 days after infection, reached a peak at 12 days and then declined. After challenge infection, there was an augmented and accelerated increase in eosinophil numbers followed by rapid decline. The role of the various cells types in host defences against worms or in containment of the inflammatory responses evoked by these parasites are discussed.

The techniques for large DNA separation have developed from a seminal idea for field alternation which has transformed the field of DNA electrophoresis. This single innovation of pulsed field-gradient electrophoresis (PFGE) and the subsequent modifications have made a significant impact on molecular biology, eukaryote genetics, biopolymer research and diagnostic research. The apparatus types used for large DNA separation are depicted and critically compared with relation to molecular mass separation capabilities, straight-lane migration of samples, band sharpness and ease of operation. With these criteria in mind PFGE and orthogonal field alternation gel electrophoresis systems had a number of drawbacks, the principle one being the inability of these systems to give straight-lane migration. To a large extent this has restricted the widespread use of these systems. Field inversion gel electrophoresis produces straight-lane migration but was subject to an upper molecular mass limitation of 2 megabase pairs and tended to produce broader bands in the higher-molecular-mass areas. Transverse alternating field electrophoresis, rotating gel electrophoresis and contour-clamped homogeneous electric field electrophoresis systems where superior to all the other systems. They gave straight-lane migration, separation of chromosomes up to 10 megabase pairs, good resolution of bands and were all relatively simple to operate. Very little was found to separate these three electrophoresis systems. Field alternation electrophoresis has enabled a 500-fold increase in the size of DNA molecules that can be resolved in agar gels. Consequently, electrophoretic karyotypes of a number of organisms have been produced, while genome maps, gene locations and sequences of large areas of mammalian genomes are now being undertaken. The ability to separate entire chromosomes or large DNA fragments has, in conjunction with novel molecular biology techniques, enabled scientists to work backwards from large purified fragments or entire chromosomes to construct long-range genetic maps. The time saving alone when compared with the old techniques of using very small fragments to construct a picture of the gene or gene complex is commendable. The diagnostic role of large DNA separation and electrophoretic karyotyping is beginning to be explored, while the use of this technique for clinical studies of genetic disorders is well advanced. Very few innovations in nucleic acid separation have had as marked an influence on as many areas as field alternation electrophoresis. These techniques have brought mapping of the mammalian genome into the realms of possibility and is contributing in many sphere

In an outbreak of Salmonella ealing infections in November and December, 1985, the proportion of infants infected was in excess of the normal distribution pattern and the cases were geographically widespread. All the infected infants had been fed with a dried-milk product from one manufacturer. Despite intensive efforts to isolate S ealing from packets of the product, it was found only in low numbers in 4 of 267 sealed packets. The source of infection was traced to the factory spray-drier, which had a hole in its inner lining, allowing escape of powder and its return from contaminated insulation material. The plant was closed and the equipment scrapped and later replaced. It is recommended that raw milk and whey, which frequently contain salmonellae, should not be allowed onto the site of milk-drying plants.

Gel electrophoresis has many applications in parasitology, especially for the separation of enzymes, immunoglobulins and DNA, but the ability to separate molecules based on size is usually restricted to within the upper and lower ranges o f molecular weight. These limitations are particularly evident in mocromolecular DNA electrophoresis, although recent innovations in ogorose gel electrophoresis have substantially reduced these boundaries and are permitting the separation of very large DNA molecules and intact chromosomes of many organisms. In this article, Hugh Dawkins explains these techniques and their principle variants.

The immunological changes occurring after primary and challenge infections with Strongyloides ratti in C57B1/6 mice are described. Serum IgM and IgG antibodies against Strongyloides antigen appeared one week after primary infection. The levels of antibody in both immunoglobulin classes increased markedly after secondary infection and persisted for at least 6 weeks. Immediate hypersensitivity (15 min footpad) reactions were transient after a primary infection, but were marked and persistent after a secondary infection. Arthus (5 h footpad) reactions were mild and very transient after a primary infection, but a persistent anamnestic response was seen after challenge infection. Cell-mediated immune (24 h footpad) reactions were marked 1 week after both primary and secondary infections but were not sustained in either case. Antigen-reactive cells were present in the mesenteric lymph nodes 1 week after primary infection and 1-4 weeks after challenge infection. No antigen-reactive cells were noted in the spleen. Mesenteric lymph node (MLN) cells and spleen cells from infected or uninfected animals were stimulated with phytohaemagglutinin (PHA) or lipopolysaccharide (LPS) but did not differ significantly in their 3H thymidine incorporation. A transient eosinophilia was observed after primary infection and an anamnestic response was noted after challenge infection. The possible roles of these immunological responses to worm rejection and immunopathology are considered.

The course of infection with Strongyloides ratti was examined in congenitally hypothymic CBA/H, C57Bl/6 and BALB/c nude mice. The intensity of infection and the duration of faecal larval excretion were both increased in nude mice when compared with intact mice. Adult worms persisted in the small intestine of nude mice for at least 6 weeks. Greater worm burdens were found in such mice after subcutaneous injection as compared with percutaneous infection. Hypothymic mice did not acquire resistance to re-infection. It is concluded that both the spontaneous expulsion of worms in primary infection and resistance to challenge infection are T cell-dependent events. Autoinfection was not seen.

When Strongyloides ratti free-living infective larvae were incubated with peritoneal exudate cells from normal or previously infected mice, cell attachment occurred only in the presence of normal (NMS) or immune mouse serum (IMS). This non-specific effect was transitory with larvae being alive and free of cells 24 h after incubation. Cell attachment was mediated by complement. When incubated with infective larvae which had penetrated mouse skin, both normal and immune cells attached to larvae in the absence of serum. This effect was again transitory except when immune cells or immune serum were present, indicating a specific immunological mechanism. Again, larvae remained viable. When incubated with isolated parasitic adult worms, persistent cell attachment occurred in the presence of immune serum, immune cells or both, but all worms remained viable. This system provides a means for investigating the mechanisms of resistance to reinfection in strongyloidiasis.

ELISA and immunoblotting techniques were used to examine the humoral immune response to Pasteurella multocida, in bovine sera from Indonesia and Malaysia. Elevated levels of antibody to a crude lipopolysaccharide preparation were found in vaccinated animals. In addition to the response to lipopolysaccharide, antibodies from the vaccinated cattle strongly labelled five to six of the 40 protein bands in this organism.