Rattus norvegicus infestations on six farmsteads were poisoned with 0.5% 5-p-chlorophenyl silatrane and those on another six with 2.5% zinc phosphide. Both poisons were applied in pinhead oatmeal bait containing also 5% corn oil, after pre-baiting. The result of each treatment was assessed by comparing the take of pre-bait with that of a census bait (wheat) laid after the poisoning.

The zinc phosphide treatments were generally more effective than those done with 5-p-chlorophenyl silatrane, but the latter were somewhat detrimentally affected by cautious baiting on the part of one of the operators.

The results are discussed and it is concluded that although they indicate that 0.5% 5-p-chlorophenyl silatrane may have approached zinc phosphide in effectiveness under the conditions of the trial, it would in most circumstances be significantly less effective and possibly less safe to use than the latter, well-tried poison.

The degree of immunity due to cross-reactions between antibody to influenza virus A/Hong Kong/1/68 and A/England/42/72 was studied in ferrets. Ferrets were immunized with the viruses by either live infection or by inoculation with inactivated virus vaccines. The vaccines were given with Freund's incomplete adjuvant or were given to ferrets previously infected with influenza virus A/PR/8/34. As a result of these immunizations the animals all produced similar titres of serum HI antibody to the immunizing virus, although the degree of crossreaction with the other virus strain was variable. After immunization the animals were challenged by infection with an A/Eng/42/72-like virus and their degree of immunity was measured. It was found that the greatest immunity was in ferrets previously infected with the homologous A/Eng/42/72 virus. Animals previously infected with A/HK/68 virus also showed a measurable degree of immunity to A/Eng/42/72 infection, and this was greater than that found in animals given inactivated virus vaccines. The immunity produced by the vaccines was approximately equal, regardless of which vaccine or method of immunization was used. Thus, live infection produced a more effective, broader immunity than did the use of inactivated virus vaccines.

The performance of the rodenticide 5-p-chlorophenyl silatrane at 0.5% in a wholemeal flour/pinhead oatmeal/corn oil bait was compared with that of zinc phosphide at 3% in the same base in poison treatments carried out against urban infestations of the house mouse (Mus musculus L.). Each poison treatment was conducted for 1 day and after 3 days' pre-baiting. The success of the treatments was assessed from census baitings conducted before and after treatment. Treatment success varied considerably with both poisons used but in general 5-p-chlorophenyl silatrane proved to be at least as effective as zinc phosphide, a commonly used acute rodenticide for the control of mice.

A comparison was made of the incidence of foot-and-mouth disease virus 'carrier' cattle in an unvaccinated enzootic area and an area where routine 6-monthly vaccination with an inactivated vaccine had been carried out for 3–4 years. The incidence of carriers in the vaccinated area was 0·49% as compared to 3·34% in the non-vaccinated area. The results indicate that, provided the immune status of the vaccinated herd is maintained at a level sufficient to prevent outbreaks of clinical disease and the re-introduction of virus is prevented through livestock movement controls, it should be possible to eradicate the disease from an enzootic area through vaccination.

The subtype variants found in Kenya in the past ten years have been studied. The type O and type SAT 2 subtypes have a distinct geographical distribution which appears to be associated with livestock movement patterns. The type A viruses have a greater tendency to antigenic variation and their geographical distribution is less distinct. In type C only minor differences exist between the three viruses studied.

An analysis was made of the dose-response of several populations of Rattus norvegicus fed upon baits containing 0·005% warfarin for various numbers of days. Warfarin-susceptible populations fell within a narrow range, with LFP50s and LFP98s (lethal feeding periods in days to obtain 50% and 98% mortalities respectively) of up to 3·0 and 5·0 days respectively. The probability of an individual rat from these populations surviving a six-day feeding period was estimated at 0·003 or less. Populations with responses falling beyond these limits were regarded as warfarin-resistant.

Six of nine populations of R. norvegicus, from England, Germany and the United States, were determined to be warfarin-susceptible within the narrow limits given above. In all six cases, no animals survived the six-day WHO feeding test for anticoagulant susceptibility. In three populations from the United States, where rats survived six days feeding, their population responses clearly fell outside the measures given above. It is suggested, tentatively, that anticoagulantresistant Norway rat populations be defined as those whose LFP50 and LFP98 exceeds 3·0 and 5·0 days respectively, and in which the probability of an individual animal surviving a six-day feeding upon 0·005% warfarin is 0·01 or more.

Statistical methods are described in detail for the calculating and comparing of cross-infection rates. In addition the use of these rates has been extended to study the influence of age and of different virus types on susceptibility to cross-infection in children's wards.

This paper contains an assessment of the physical performance of a permanently installed down-flow laminar-flow operating room at the London Hospital. This system employs partial walls extending 0.76 m (2.5 ft.) from the ceiling, from which the air is allowed to issue freely downwards at an initial velocity of about 0.4 m./sec. (80 ft./min.).

The usefulness of the partial wall, as compared with a free issuing system, was demonstrated and a comparison made with a fully walled system. It was shown that a fully walled system would be more efficient than a partial-walled system as there was a loss in air velocity of about 20–25% with the partial wall due to the nonconstrained flow of air. This loss would be reflected in an increase in airborne bacterial count and would mean that an increase of 20–25% in the air volume would be required to obtain the same conditions as with the full-walled system. Entrainment of contaminated air was demonstrated but it was concluded that this would be of little consequence in the centre of the clean area, i.e. at the wound site. Sterile instruments, etc., however, on the outside of the clean area, would be more liable to airborne contamination.

Bacterial and dust airborne counts taken during total hip operations gave a very low average figure (0.3 bacteria/ft.3 or 10.5/m.3) from which we conclude that the system was about 30 times cleaner in terms of airborne bacteria than a well ventilated conventional operating-room. We concluded that although the partial-walled system was slightly less efficacious than a normal full-walled system, the freedom of movement and of communication for the operating team could in some circumstances outweigh this disadvantage.

Sound levels were such that normal conversation was possible with little or no awareness of background noise.

The distribution and serotype of strains of Escherichia coli from a poultry packing station and an abattoir are described. The results indicated that animal faecal strains contaminated the environment and the animal carcasses.

Using 150 O antisera, a high proportion of the E. coli strains were non-typable. This suggests that the serotype distribution of E. coli in animals is different from that in man.

Strains with single antigenic differences were isolated, and the possibility of genetic transfer of these antigenic structures is suggested.

The clearance of neomycin and kanamycin from the intestines after stopping oral supply has been determined in mice. Both antibiotics, although given in different doses, were excreted in essentially the same way; the clearance being a little faster than logarithmically in both cases. The importance of this observation with regard to isolation and the moment of reconventionalization is discussed.

The incidence of infections caused by Pseudomonas aeruginosa did not increase significantly among general surgical and medical patients between 1967 and 1972, and the majority of such infections were trivial. Serious infections were virtually confined to the intensive care unit and the renal transplant unit, and were usually associated with major trauma, surgical mishap or immunosuppression. The majority of these patients had received prior antibiotic therapy. Persistent isolation of Ps. aeruginosa from surgical wounds was often associated with severe intra-abdominal sepsis, and antibacterial therapy was commonly ineffective in these cases. Apparently susceptible patients did not necessarily acquire infection, though the organism was present in their environment. It is suggested that this may reflect a variation of virulence among environmental strains of Ps. aeruginosa, and that further study of this aspect may contribute to improved control of infection.

Active protection against Pseudomonas aeruginosa could be induced in mice by immunization with either the phenol killed cells or the alcohol precipitated fraction of the slime layer, or the ribosomal vaccine preparation. Passive protection could also be induced by injecting into mice antisera prepared in rabbits against these bacteria. This protection was due to the production of antibodies in reaction to the slime layer; the absorption of these antibodies by the slime caused the loss of protection. The fact that mice were also protected by vaccination with strains other than those used for challenging was attributed to the presence of an antigenically similar slime. Passive protection towards a heterologous strain, even one with an antigenically similar slime layer, was dependent on the dose of the challenging injection.

Normal bovine milk and whey was mycoplasmacidal for 6 of the 13 strains of bovine T-mycoplasmas examined. The in vitro assay used also demonstrated no killing of the human, canine and simian T-mycoplasma strains after 4 hr. incubation. However, there appeared to be some cow-to-cow variation in possession of this activity, and following E. coli endotoxin stimulation of the mammary gland the activity was considerably reduced.

Whey from three normal cows was fractionated on a Bio-Gel A 1·5 m. column and the mycoplasmacidal activity of the resulting five peaks assayed. Only the second peak, peak B, contained activity and was characterized as the only peak containing bovine IgA. The active component in whey, however, was found to be heat stable at 60° C. for 60 minutes and to pass through a dialysis membrane. This is inconsistent with it being immunoglobulin.

Despite the existence of a close serological relationship between the entero-viruses Swine Vesicular Disease (SVD) and Coxsackie type B5 (Cx B5), the administration of this Coxsackie virus type to susceptible pigs by various routes failed to produce clinical disease.

Viraemia was not detected after exposure but virus was recovered intermittently from faeces and buccal swabs. A mixed virus population was demonstrated in faecal cultures from some pigs, including Coxsackie virus type B5 and other agents, presumably native pig enteroviruses. The Coxsackie virus persisted in faeces in declining amounts for up to 8 days after primary exposure.

Serum neutralizing antibody showed a transient rise to Coxsackie virus, reaching a peak at 14 days and declining below demonstrable titres by 28 days after exposure. The antibody titres attained were proportional to the dose of virus administered and the degree of neutralization was very similar to both SVD and Cx B5 viruses.

On cross challenge by exposure to SVD virus 28 days after exposure to Cx B5 virus, most animals (5/6) succumbed with typical vesicular lesions, although the serum neutralizing antibody titres showed a characteristically anamnestic response to both viruses.

The nature of the antibodies detectable by the microscopic agglutination test for bovine leptospirosis was examined. Density gradient ultracentrifugation, gel filtration and disulphide-bond-reduction experiments indicated that antileptospiral agglutinating activity was present in both IgM and IgG immunoglobulin fractions. This was confirmed by selective precipitation of specific antibody classes and ion-exchange chromatography.

Enterotoxin production by strains of Staphylococcus aureus isolated from routine samples of foods and from human beings was investigated. Twenty-one to 26% of 112 strains isolated from raw meat, sausages and poultry and 32–36% of 183 strains isolated from cooked foods, e.g. meat, chicken and frozen seafoods, produced enterotoxins A, B, C, D or E. Staph. aureus isolated from raw meat and chicken less frequently produced enterotoxins A, B, C or E and more frequently enterotoxin D, than those from cooked meat and seafoods. Of the 113 strains isolated from cheese and raw milk 6–11% produced enterotoxin and most of these produced enterotoxin D. Only a few strains isolated from foods produced enterotoxin E. Results of enterotoxin tests on Staph. aureus from human beings resembled those on strains from cooked foods.

A dengue epidemic due to type 2 virus involving some 3,400 cases began in Fiji early in 1971, had a peak during May, June and July, and cases have continued to occur with a low incidence during 1972 and 1973. Many of the notified cases showed classical dengue fever symptoms and there were no confirmed cases of haemorrhagic fever. A serological survey indicated that there had been at least 20,000 subclinical infections. It is probable that the virus was introduced to Fiji either through the port of Lautoka or Nadi international airport in February 1971. The normal travel patterns of residents must have spread the virus to all the more accessible localities but, with the exception of Rotuma, it caused infections only in areas where Aedes aegypti was available as a vector. There was no evidence that pre-existing dengue type 1 serum antibody gave any protection during this epidemic.

A number of outbreaks of food poisoning attributed to Bacillus cereus have been reported recently and all have been associated with cooked rice usually from Chinese restaurants and ‘take-away’ shops.

Tests were made to assess the heat resistance of B. cereus spores in aqueous suspension, the growth of the organism in boiled rice stored at temperatures in the range 4–55° C., and the effect of cooking and storage on the growth of the organism in boiled and fried rice. The spores of B. cereus survived cooking and were capable of germination and outgrowth. The optimum temperature for growth in boiled rice was between 30° and 37° C. and growth also occurred during storage at 15° and 43° C.

To prevent further outbreaks it is suggested that rice should be boiled in smaller quantities on several occasions during the day, thereby reducing the storage time before frying. After boiling the rice should either be kept hot (> 63° C.) or cooled quickly and transferred to a refrigerator within 2 hr. of cooking. Boiled or fried rice must not be stored under warm conditions especially in the range 15–50° C.

Two published methods for the maximum likelihood estimation of a common relative potency from a series of parallel-line assays are shown to be equivalent.

Cattle and sheep were housed with infected pigs for 11 days. Small amounts of virus were recovered intermittently from the pharynx, milk and rectal swabs of the cattle, but no evidence of subclinical infection was found. Some indication of virus growth in the sheep was obtained in that large amounts of virus were recovered from the pharyngeal region 4 to 7 days after exposure and six of the eight sheep developed significant titres of neutralizing antibody which were maintained in four animals for at least 6 weeks.