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1. The availability of Nematodirus infection to sheep was followed by grazing successive pairs of worm-free lambs on a contaminated plot. It was shown that lambs did not become infected during the summer following pasture contamination in the spring, but became infected when they were grazed on the plot the following spring.2. The development and hatching of the eggs and larval stages of N. battus and N. filicollis were followed by the periodical examination of infected faeces set out during May-November. The results showed that development to the infective larval stage occurred during the summer, taking normally about 3 months, but that the larvae then remained dormant within the egg membranes until the following spring.3. Laboratory studies confirmed the hypothesis that the hatching of the infective larvae was a response to a rise in temperature in the spring, following sensitization by exposure to low temperature during the winter. A rise in temperature to 50° F. was necessary before a high percentage hatch occurred.4. The epidemiology of Nematodirus infection is discussed in relation to these observations.

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In February 1989 the largest reported outbreak to date in the United Kingdom of Salmonella enteritidis phage type 4 (PT4) infection occurred following a wedding reception at a hotel. One hundred and seventy-three people met the case definition of illness of whom 118 had the organism isolated from their stools. A further 17 were found to be S. enteritidis PT4 positive, but were asymptomatic. Lightly-cooked, egg-based sauces were the epidemiologically proven vehicles of infection. Investigations showed this outbreak to be the first to implicate imported European eggs as the source of infection. An unusual feature of this outbreak was a reported incubation period of less than 3 h for some of the confirmed cases of salmonellosis.

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