A computer model was constructed to mimic the 1967–8 foot-and-mouth epizootic in Shropshire and Cheshire, but the daily spatial distribution of outbreaks was randomized. This pattern of outbreaks was then examined to determine what percentage of outbreaks would fulfil an arbitrary set of criteria for milk-lorry-borne disease, or the primary movement of milk. Some 21% of herds visited subsequent to a ‘source farm’ were affected, as were 4% of herds visited after any infected herd. The relevance of these results to the true risk of disease through the primary movement of milk off affected farms is discussed.

Between 1961 and 1974, 11934 samples of serum were tested by the Sabin- Feldman Dye test for the presence of antibodies to Toxoplasma gondii.

Analysis of high-titred sera suggested that a 6-year cycle of high disease prevalence occurred across Canada. In addition, a decline in the percentage of positive reactions occurred each year in the Fall. The suggestion that this decline was due to dry conditions during the summer months was supported by the observation that differences in the prevalence of toxoplasma infection in ten Canadian cities were related to their average summer rainfall. The significance of these observations in relation to the epidemiology of toxoplasmosis in this country is discussed. The influence of patient age on the prevalence of infection was also investigated; the results obtained suggested that at least 75% of infants with high antibody titres against T. gondii had obtained these antibodies by placental transfer from their mothers.

Enterobacteria are more resistant to nalidixic acid than the majority of other Gram-negative organisms isolated from river water, so allowing their selection on MacConkey agar containing nalidixic acid. Selection is further improved by anaerobic incubation which, with nalidixic acid, virtually eliminates oxidase-positive strains such as Pseudomonas or Aeromonas.

A modified haemagglutination inhibition test for rubella antibodies, using standardized freeze-dried reagents, was developed and compared with haemagglutination inhibition tests using fresh erythrocytes. This comparison was made in collaboration with six European laboratories. A total of 4205 serum samples were tested. The results show that:

(1) Sensitivity and reliability of the modified test are good;

(2) the modified test can be performed in glass tubes as well as in polystyrene microtitration plates.

Ninety-eight samples of pig slurry from 54 farms were examined for the presence of salmonellas, porcine enteropathogenic strains of haemolytic Escherichia coli and mycobacteria. Salmonellas were isolated from 12 farms (22 %) and enteropathogenic E. coli from 13 farms (24%). Pathogenic mycobacteria were not isolated.

Salmonellas were isolated from 7 of 16 farms (44%) stocked with ‘minimal disease’ pigs compared with only 5 of 38 farms (13%) stocked with conventionally reared pigs. Conversely enteropathogenic coliforms were isolated from 3 of 16 farms (19%) stocked with ‘minimal disease’ pigs compared with 10 of 38 farms (26%) stocked with conventionally reared pigs.

One thousand two hundred and sixty-nine freeliving, wild mammals, representative of 16 species from estates in Berkshire, Oxfordshire and Surrey, were examined for the presence of salmonellas. Salmonella typhimurium was isolated from 1 and S. dublin from 7 house mice (Mus musculus). There were no isolations from the other species examined. It was concluded that the house-mice infected with S. dublin acquired the organism from experimentally infected cattle.

The wild mammal population does not at present appear to constitute a reservoir for infection of domestic animals.

The effectiveness of the single-dose poison treatments of farm rat infestations, analysed by comparing the weights of the post-treatment census bait takes in covariance with the weights of the prebait takes, showed that treatments with 2·5% zinc phosphide, 0·3% thallium sulphate or 0·3% gophacide were equally effective and significantly better than were treatments with 1% zinc phosphide or 0·1% thallium sulphate. The methodology and sensitivity of different analyses are also considered.

This study was carried out to investigate the effect of desert conditions on the pattern of delayed hypersensitivity to mycobacteria in school children aged 6–10 and 11–18 years. A new range of tuberculins prepared from ultrasonic lysates of living mycobacteria belonging to 12 different species was employed. Three centres were chosen for study, a sea port and two desert towns differing greatly from each other. The results obtained were compared with those of a previous study using the same reagents in Kenya.

As expected both the range of mycobacterial species to which the children reacted, the rate of acquisition of specific hypersensitivity with age and the total percentage of children reacting to individual reagents differed from centre to centre. The harsh desert conditions of Ajdabia produced the least, and the proximity of the people's dwellings to those of their farm animals in Kufra produced the most positive reactors to essentially environmental species. The greatest number of reactors to our Tuberculin were found in Benghazi where the cosmopolitan urban conditions probably lead to a high contact with open cases of tuberculosis. As assessed by skin test reactivity, immunization with BCG in Libya was much less effective than in Kenya. The interpretation of the differences between the results from the different test centres and between those for Libya and Kenya are discussed.

Foot-and-mouth disease virus (FMDV) survived in skim milk, cream and the pelleted cellular debris components of milk obtained from FMDV-infected cows after pasteurization at 72°C for 0·25 min. Virus was recovered from whole milk of infected cows after that milk was heated at 72°C. for 5 min. and from the skim milk component after it was heated at the same temperature for 2 min. Evaporation of the whole milk samples after they were heated at 72°C. for 3 min. did not inactivate the virus, but evaporation of infected skim milk samples after they were heated at 72°C. for 0·5 min. did inactivate the virus. FMDV survived in the cream component after it was heated at 93°C. for 0·25 min.

In many countries, the prevalent serotypes of Bordetella pertussis have changed from a mixture of types 1,2,3 and 1,2 (organisms possessing antigen 2) to a predominance of type 1,3. The timing of the change in different countries is shown to be related to the introduction of mass-vaccination with material rich in antigens 1 and 2 but weak in, or devoid of, antigen 3. In several parts of the world, there have been outbreaks of type 1,3 infection in fully vaccinated children.

Non-vaccinated communities in various parts of the world still show the pattern of serotypes which existed elsewhere before mass-vaccination.

In order to avoid the disappointments experienced in the past, it is essential that pertussis vaccine for use in previously non-vaccinated communities, like that for any other country, should be rich in each of the three antigens.

More organisms were found on the paralysed hands of hemiplegic patients than on their unaffected ones. However, both showed considerably higher bacterial counts than did geriatric patients without paralysis. An infection rate for Cl. welchi of 15% was found in the paralysed hands.

Two tests for the estimation of Vi antibody in sera were studied and their validity in the screening of typhoid carriers was assessed. One was a modified Vi haemagglutination test in which Vi-coated glutaraldehyde-fixed erythrocytes were used as the antigen and Vi antibody resistant to treatment with 2-mercaptoethanol was titrated. The other was a fluorescent Vi antibody test in which acetone-fixed bacterial Vi cells were used as the antigen and the total Vi antibody was titrated. In both tests, the antigens used were stable so that standardization of the tests would not be difficult. The modified Vi haemagglutination test was found equally sensitive but more specific in giving less false positives than the conventional Vi haemagglutination test. The fluorescent Vi antibody test was however found superior to both tests not only in giving less false positives but also in detecting more typhoid carriers.

Restrained American cockroaches, Periplaneta americana L., were fed graded doses of Salmonella typhimurium ranging from 1·6 × 103 to 2·0 × 106, and their faeces assayed daily for the pathogen. Only 4 specimens out of 117 demonstrated multiplication of salmonellas, which was unrelated to size of input. When data of persistence regardless of actual numbers were expressed as percentage Salmonella-positive faecal-days, and these transformed to probits, a graph of percentage-positive faecal-days versus log dose allowed a calculation of the CD 50, or contaminative dose required for 50% of the faecal-days to be infective. The CD 50 for this cockroach species was 1·4 × 106Salmonella.

Two interesting new phenomena have been observed in suspensions of T4Bo bacteriophage which were frozen to temperatures below the eutectic temperature of the salt (sodium chloride) in the suspending medium. Approximately 10% of the phage appeared to survive such a phase change as determined by plaque titre. However, exposure of these survivors to ultrasonic vibration or repeated freezing showed them to be hypersensitive and thus latently injured. The hypersensitivity was lost on incubating the phage at 37° C. for 3 hr. Furthermore, following a eutectic phase change, the surviving phage could be inactivated by rapid cooling to — 90° C. followed by slow rewarming. Such inactivation cannot be accounted for by accepted theories of freezing injury.

Electron microscopic observation of negatively stained preparations of frozen and thawed suspensions of T4Bo phage clearly separated the morphological changes produced by low-temperature salt denaturation from those produced by eutectic phase changes. Salt denaturation caused contraction of tail sheaths. Eutectic phase changes appeared to cause two separate lesions. Firstly the tail sheath was disjointed 18–22 nm. below the collar and the tail core was disjointed at 40–60 nm. below the collar, giving rise to separated heads with a small tail remnant, and separated tails in which the sheath remarkably remained in its extended form. Secondly, tears were seen in the head membranes of particles with collapsed empty heads. In all the experiments the percentage of normal phage particles counted electron-microscopically was close to the percentage of viable phage as determined by plaque assay.

Escherichia coli was found in a similar proportion of stool specimens from infants who were breast-fed and from others fed on three different artificial-milk preparations. When E. coli was present its mean colony count in the stools of breast-fed infants was within the range of the mean counts for infants receiving the artificial-milk feeds.

There was no consistent relation between high counts of bifidobacteria (Lacto-bacillus bifidus) and low counts of E. coli. This suggests that measures aimed at implanting or stimulating the growth of bifidobacteria in the large intestine of artificially fed infants may not greatly influence the E. coli population therein.

The results are discussed in relation to the protection of artificially fed infants from E. coli enteritis.