Antibiotic resistance plasmids from organisms that had caused serious epidemics, including those responsible for epidemics of chloramphenicol-resistant typhoid fever and dysentery in Central America, were transferred to a strain of Salmonella typhimurium and of Salmonella gallinarum. The virulence and infectivity of these R+ forms were then compared with the R− parent forms in orally inoculated chickens.

None of the R+ forms were more virulent than their R− parent forms. The mortality rates they produced were either the same as or less than that of their R− parent forms. The mortality rates were not increased by feeding the chickens on diets containing antibiotics against which the plasmids provided resistance.

The removal of the plasmids from some R+ forms of decreased virulence was not accompanied by any alteration in virulence, indicating that they were less virulent mutants of the parent strain that had conjugated preferentially. In other cases their virulence was increased, indicating that the very possession of the plasmid was involved in their decreased virulence. Of four forms of the S. gallinarum strain harbouring the plasmid that had been incriminated in the Central American dysentery outbreak, one was as virulent as the parent R− form and the other three were less virulent. Preferential conjugation by an avirulent mutant was responsible for the lack of virulence of one of them but the very possession of the plasmid appeared responsible for the decreased virulence of the other two. The decreased virulence of de-repressed F+ and I+ forms of the S. typhimurium strain was increased to that of repressed F+ form and of the parent form by plasmid removal.

Organisms of the R+ forms of the S. typhimurium strain were not excreted in larger amounts or for longer periods of time by infected chickens than organisms of the R− parent form were. Neither did organisms of the R+ forms of this strain or the S. gallinarum strain spread more rapidly or more extensively from infected chickens to in-contact chickens than organisms of the R− parent forms did. When antibiotics against which the infecting R+ organisms provided resistance were included in the diet of these chickens the R+ organisms were usually excreted in greater amounts, for longer periods of time and spread more rapidly and more extensively from the infected chickens to the in-contact chickens.

A total of 4551 sera from 863 Strain 19 vaccinated and non-vaccinated adult cattle, independent of disease status, were tested by five serological methods to detect the presence of antibodies to B. abortus. Results from Standard Agglutination Tube (SAT), Buffered Brucella Antigen or card (CT), Complement Fixation (CF), Enzyme Linked Immunosorbent Assay (ELISA) and Rivanol (Riv) methods were compared.

There was a 95% probability for agreement among CT negative sera, between serological methods, for all groups of vaccinated and non-vaccinated cattle. The agreement between tests with Riv Positive sera, excluding the calfhood and adult vaccinated group tested by the CF method, was 91–100%. The probability of a serum which was serologically negative by other methods being Riv negative was 98%. The usefulness of serological results from Riv (≥ 1/50) tests for classifying the reactor status of cattle are of doubtful supplemental value to confirm card test positive results.

Vaccination history is an important consideration when evaluating serological data on cattle sera particularly from SAT and CF methods.

Two temperature-sensitive mutants of the Ukg 27/72 strain of swine vesicular disease virus were isolated in tissue culture and a third was derived following adaptation in mice. All three were found to have similar growth restrictive temperatures, but varied considerably in their virulence when administered to pigs. The route of inoculation appeared to exert a considerable influence on the apparent degree of attenuation, the antibody titre engendered and the transmission of disease to pigs held in contact with inoculated animals. One strain appeared almost totally attenuated when inoculated into pigs but spread to animals in contact causing severe disease. Virus re-isolated from one such animal was found to have retained its temperature sensitive phenotype, suggesting that virulence in this case was not directly related to temperature sensitivity. Pigs with high antibody titres were found to be susceptible when placed in contact with challenge animals, although the lesions which developed were mild.

Water pollution was monitored in six Gambian village wells over a period of 8 months spanning the 5-month monomodal rains and the pre- and post-rains dry periods. Faecal coliform (FC) and faecal streptococci (FS) counts were high throughout and there was a massive increase associated with the onset of the rains, maximum counts exceeding 5 x 105/100 ml. This pattern was largely sustained throughout the rainy season. Some individual variations in patterns of pollution could be ascribed to well design, in particular lining of the shaft, but no well was protected from the seasonal increase in faecal pollution. The source of the increased pollution appeared to be a flushing in of faecal material of indeterminate or mixed human and animal origin, probably over considerable distances. Peaks of pollution not associated with rainfall episodes could have resulted from the practice of communal laundering in the near vicinity of the wells. Specific pathogens including Salmonella spp. were isolated only intermittently. Attention has been drawn to a problem complicating the standard method for assessing FC counts.

The infusion of 10 μg of endotoxin lipopolysaccharide from Escherichia coli into the mammary gland of four cows 16 h before inoculation with ureaplasmas did not prevent, or even diminish, the subsequent ureaplasmal mastitis. There was no reduction in the severity or duration of the inflammatory cell response in milk or in the clinical appearance of the resulting mastitis. Also, the excretion of ureaplasmas was not reduced.

A similar experiment with Mycoplasma dispar in two cows demonstrated that endotoxin was again ineffective in preventing the mastitis. Furthermore, there was some indication that the proliferation and excretion of this mycoplasma was enhanced in endotoxin-treated quarters.

High titres of endotoxin as measured by the Limulus test were usually found in burned patients who had raised body temperatures, and were colonized with gram-negative bacteria; also some infected patients showed raised endotoxin without a raised temperature.

Patients vaccinated with an antipseudomonas vaccine rarely showed endotoxin in their plasma but occasional plasma samples from vaccinated patients had a high titre of endotoxin which appeared unrelated to infection or to a raised temperature in the patient.

Sixty-seven isolates of citrate-positive variants of Escherichia coli were isolated from human, domestic animal, feral bird and environmental sources. With the exception of citrate utilization, all isolates were identified as typical E. coli by their biochemical reactions. The transmission of the ability to utilize citrate on Simmons' citrate agar was demonstrated in 53 (79·1%) out of the 67 citratepositive E. coli variants obtained from various sources. Drug resistance determinants and citrate utilizing character were co-transmitted into E. coli K-12 by conjugation among citrate-positive E. coli isolates carrying R plasmids except for that isolated from horses. The other characters (haemolysin or colicin production, raffinose or sucrose fermentation) were not transmitted together with the citrate utilizing character. These facts suggested that the structural gene responsible for citrate utilizing ability in citrate-positive variants of E. coli was located on a conjugative plasmid.

A blastogenic test to detect peripheral blood leukocytes specifically sensitized to foot-and-mouth disease virus antigen is described. The test is carried out in microtitre plates and optimum conditions were found by titration. These employed 7.5 × 105 cells/well and 20 complement fixing units of antigen. Peak [3H]thymidine incorporation was found to take place at 2–3 days.

Laboratory feeding tests were carried out to assess the efficacy of seven rodenticides against Mastomys natalensis. The poisons (warfarin, coumatetralyl, difenacoum, brodifacoum, bromadiolone, calciferol and zinc phosphide) were all toxic at the concentrations normally used against Rattus norvegicus (Berk.), although several were unpalatable. Trials are now needed to demonstrate the relative efficacy of these poisons in the field, but it is likely that, given suitable bait formulations, they would all be useful as practical control agents.

An injection of influenza vaccine was offered to approximately 60 000 Postal and Telecommunications staff at the beginning of five successive winters. The sickness absence of this group, which included those who accepted the offer of vaccine as well as those who did not, was compared throughout the winter with that of a similar number of employees who were not offered vaccine. The two groups, ‘vaccinated’ and control, comprised the staff of nearly 400 Post Office units scattered throughout Great Britain, the units of the two groups being matched as far as practicable for numbers employed, type of work, region and type of location.

The proportion who accepted vaccine fell from 42% in the first year (when only 26 000 Telecommunications employees were offered vaccine) to 35% in the second year, and 25% by the fifth year.

With the exception of Telecommunications employees in 1972–73, the sickness absence rate of the group offered vaccine was less than that of the group not offered vaccine, and the difference was evident during the winter observation periods both when influenza was prevalent and when it was not. In the last four years of the study the average difference in sickness absence between the ‘vaccinated’ and control groups was 1.26 days per 100 employees per week during and 1.12 days outside the influenza periods. Moreover, the difference during the influenza periods was greater than could be expected from the acceptance rate of vaccine and the estimated attack rate of influenza. The apparent reduction in sickness absence of the group offered vaccine in comparison with the groupnot offered vaccine represented an appreciable saving in cost.

It is suggested than an annual influenza vaccination campaign in industry may produce financial benefit, but that only a proportion of the benefit is due to an improvement in health.

An indirect enzyme linked immunosorbent assay (ELISA) was applied to the detection and identification of foot-and-mouth disease (FMD) virus types. The test proved successful for the specific detection of virus from infected tissue culture, and from epithelial tissues from bovines suspected of having FMD. The ELISA compared favourably with the complement fixation (CF) test, being more sensitive and unaffected by anticomplementary factors.

As mentioned in Chapter 1, the Brown Institution was staffed by a remarkable series of Superintendents, seven out of eight of whom were, or became, Fellows of the Royal Society. Much of the research work they undertook has already been referred to in preceding chapters, but it seems only fitting that something should be said about their personalities and careers. In preparing the short accounts that follow, I am greatly indebted to obituary notices in the various scientific journals, especially those in the Proceedings of the Royal Society; to the pen sketches given by Professor Sharpey-Schafer (1927) in his History of the Physiological Society;and to the Memoirs in book form of Sir John Burdon-Sanderson by his wife (1911)and of Sir Victor Horsley by Sir Stephen Paget (1919).

A method is described for the laboratory breeding of the rabbit flea in which the immature stages are reared at constant temperature and humidity.

Eggs are obtained by confining fleas taken from a rabbit and her nest shortly after parturition with two of her nestlings in an incubator for 24 h. The eggs are transferred to an artificial diet medium on which the immature stages are reared. On average a female flea produces 50 eggs during the first six days post-partum. At 25 °C, 95% of eggs hatched at 79% RH and 98% at 84% RH. Most eggs hatched on the third day after laying and hatching was completed by the fourth day. Significantly more fleas of both sexes were obtained when larvae were reared at 25 °C on a medium containing powdered 41B rodent diet than on one containing terrier meal. Both diets also contained yeast and dried rabbit blood. There was no significant difference between the numbers of fleas obtained at 79% RH and 84% RH. Significantly more fleas were also obtained when larvae were reared at 27 °C, 84% RH, than at 25 °C. Female fleas emerged sooner than males at both 27 °C and 25 °C. Fleas from the laboratory culture were heavier than those from wild nests. Female fleas were heavier than male fleas in both cases.

A solid phase radioimmunoassay (RIA) has been successfully developed to measure both African swine fever virus (ASFV) antigen and antibody. Studies show that the assay is reproducible and will detect limiting antigen concentrations equivalent to 50–500 HAD50/ml. Both direct and indirect antibody RIA have been developed and have proved to be approximately 100 times more sensitive than the complement fixation test at present available and 1000 times more sensitive than the immuno-electro-osmophoresis test for the detection of ASFV antibody.

A solid-phase enzyme-linked immunosorbent assay was developed to measure both African swine fever virus (ASFV) antigen and antibody. Experiments showed it to be reproducible and able to detect limiting antigen concentrations of 50–500 HAD50/ml. The assay was more sensitive than those used at present to detect ASFV antibody and it is suggested that it might be of great diagnostic use in countries where African swine fever has recently appeared.

Twenty-three of 89 enterotoxigenic strains of Escherichia coli were resistant to one or more antimicrobial agents. Eleven strains transferred resistance directly and five transferred resistance after mobilization. In three cases a resistant recipient was enterotoxigenic. One of these strains contained a conjugative plasmid carrying genes for both drug resistance and enterotoxin production. In the two other strains genes for drug resistance and enterotoxin production were carried on separate co-transferable plasmids.

To determine the presence and prevalence of bluetongue (BT) infection in a variety of domestic animal species in different geographical regions of the Sudan, a serological study using the agar gel precipitation technique was initiated. A total of 2142 serum samples were examined. Of the numbers tested approximately 28% of sheep, 11.2% of goats, 8% of cattle and 4.9% of camels were positive for group-specific antibodies to BT virus antigen, indicating previous exposure to BT infection. None of the samples tested from horses or donkeys were positive. The findings suggest that the disease is widely distributed in most parts of the Sudan where possible insect vectors prevail and may be endemic in sheep in Juba District, Equatoria Province, Southern Region. Goats appeared to have some degree of resistance to infection compared with sheep, and there seemed to be no significant differences in positive rates between farm and free-range cattle.

It is concluded that BT infection may cause clinical disease in sheep, while it is probably subclinical or inapparent in goats, cattle and camels of the Sudan.

A sudden increase in the incidence of ampicillin resistance was observed among Salmonella species isolated within New Zealand in 1973–4. This increase was due mainly to the appearance and proliferation of Salmonella newington and Salmonella anatum serotypes resistant to ampicillin. The plasmid complements of 14 ampicillin-resistant S. newington and S. anatum isolates obtained from widely separated geographical areas within New Zealand between 1973 and 1974 were characterized by agarose gel electrophoresis. Each contained one or more plasmids ranging in molecular weight from 1·4 to 42 Mdal. Eleven isolates contained a self-transmissible plasmid of 33 Mdal which encoded resistance to ampicillin. After transfer to Escherichia coli, the 33 Mdal R-plasmids from each of these isolates were shown to be identical by restriction endonuclease analysis. The remaining three strains contained ampicillin R-plasmids having molecular weights of 35, 37·5 and 42 Mdal. These plasmids were shown by restriction endonuclease analysis to be related to the 33 Mdal R-plasmid. We conclude that the 33 Mdal plasmid and its derivatives were responsible for the increase in the incidence of ampicillin-resistant S. newington and S. anatum serotypes among the total Salmonella population.