Strains of myxoma virus associated with a case-mortality rate in wild rabbits of 90—95% can be distinguished from those associated with a case-mortality rate of more than 99% by the use of a standardized virulence test carried out in groups of five laboratory rabbits, and tests carried out on laboratory rabbits are closely correlated with the results obtained with Australian wild rabbits. The test, which attempts to mimic natural mosquito transmission, consists of the intradermal inoculation in one site of about 5 rabbit-infectious doses of the virus, and the subsequent observation of the rate of progress of clinical symptoms and ultimate fate of the rabbit. The mean survival time provides a figure which allows satisfactory classification of all known myxoma virus strains into one of four grades of virulence, very attenuated strains being recognized by their low case-mortality rates.

Using this test, 92 strains of myxoma virus have been compared. These comprised 6 laboratory strains, 62 strains recovered from Australian wild rabbits or from wild caught mosquitoes, between February, 1951 and March, 1955, 19 strains recovered from naturally infected rabbits in Europe between October, 1953 and August, 1955, 3 strains from South America, and 2 from California. Eight types have been described and illustrated, differentiation being based on their virulence and the clinical picture of the disease they cause in laboratory rabbits. The differences are summarized in Text-fig. 2. Four of the virus types produce recognizably different pocks on the chorioallantois of developing chick embryos.

In Australia the repeatedly introduced standard laboratory strain of virus has been replaced by a moderately virulent strain, which appears to be better adapted for survival than either the highly virulent standard laboratory strain, or less virulent variants of which only a few had been recovered up to 1955. Strains of the type dominant in 1953–55 have appeared independently in many widely separated parts of Australia. Examination of these attenuated variants by pure clone techniques showed that the variability in symptomatology associated with them is not due to a mixture of virus strains, but to the expression of differences in innate resistance of the host animals which are obscured by the overwhelming virulence of the highly virulent strains.

Only one introduction of a different strain of virus was made in Europe. All field strains recovered during the first two years after the introduction were of high virulence, but a few attenuated strains appeared in 1955, and they have since become widespread. One of them appears to be a relatively stable mixture of a highly virulent and a greatly attenuated strain.

The collection of the large numbers of strains of virus described in this paper has been made possible only by the generous collaboration of many people. In Australia we would like to acknowledge the great help afforded us by Mr F. N. Ratcliffe, officer-in-charge of the Wildlife Survey Section, Commonwealth Scientific and Industrial Research Organization and his officers, especially Messrs J. H. Calaby, G. Douglas, A. L. Dyce, B. V. Fennessy, E. W. Lines, K. Myers, R. Mykytowycz, W. E. Poole and E. Waterhouse. Messrs B. D. Robinson and T. Pearce of the Lands Department of Victoria have also provided us with specimens, as have Mr G. Edgar, Director of the Veterinary Research Station, Glenfield, New South Wales, Dr D. Surrey Dane of the Institute of Medical and Veterinary Science, Adelaide, Mr D. Gooding, Department of Agriculture, Western Australia, and Messrs T. B. Alexander and A. F. Ryan, Department of Agriculture, Tasmania.

We are indebted to Dr H. de B. Aragão of the Instituto Oswaldo Cruz, Rio de Janeiro, and Dr B. Szyfres, of the Laboratorio de Biologia Animal, Uruguay, for specimens from South America; Dr D. G. McKercher of the University of California School of Veterinary Medicine, Davis, California, for the Californian strains; Drs P. Lépine and H. Jacotot, of the Institut Pasteur, Paris, for strains from France; and Mr J. R. Hudson, of the Veterinary Laboratory, Weybridge, and Dr C. H. Andrewes of the National Institute for Medical Research, Mill Hill, for material from England.

We are grateful to Dr S. Fazekas de St Groth and Dr G. S. Watson of this University for advice on the statistical treatment of the data.

Mr V. Paral took the photographs.

Pernasal and throat swabs taken on 106 newborn babies showed that 99% harboured coagulase-positive Staph. aureus by the time they left the hospital nursery. When the strains isolated from thirty-four of them were phage typed and tested for penicillin sensitivity, it was found that thirty-three (97%) carried at least one penicillin-resistant strain. Phage typing of their subsequent cultures, taken as they became older, demonstrated that they retained these strains for very long periods. Of the twenty-one still under observation at 6 months of age, eleven (53%) were carrying one or more of their original hospital strains, and an additional three (14%) still were consistently yielding an untypable strain believed to be identical to that acquired in hospital. Similarly, of those remaining under observation for the last 6 months of their first year, at least 50% continued to carry their hospital strains.

These babies frequently retained the hospital strains in their throats longer than in their noses. Although their nasal cultures often became negative after the first few months of life, the original hospital strains continued to be recovered from the throats. This would indicate that the throat culture is more accurate than the nasal culture in determining staphylococcal carriers among this age group. Antibiotic-resistant staphylococci in the infant throat may have considerable epidemiological significance, since babies tend to widely distribute their saliva.

The observations suggest that the staphylococci acquired at birth become a normal component of the upper respiratory flora, and may thus prevent new strains of staphylococci from becoming established later. This may explain why newborn babies retain the antibiotic-resistant staphylococci of the hospital much longer than do adult patients. Antibiotic-resistant strains among the general non-hospital population will be increased steadily by babies born in hospitals.

1. Sixteen cases of paralytic poliomyelitis and twenty-four cases of aseptic meningitis (‘non-paralytic poliomyelitis’) occurring in the Sheffield area were studied clinically and by virological methods.

2. Poliovirus was isolated from thirteen of the sixteen cases of paralytic poliomyelitis and from three of the twenty-four cases of aseptic meningitis. In another two of the cases of paralytic poliomyelitis and another six of the cases of aseptic meningitis serological evidence of poliovirus infection was obtained.

3. Serological evidence of Coxsackie virus infection was found in four of the cases of aseptic meningitis; but in one there was also clear-cut evidence of poliovirus Type 3 infection, and in another it seemed that the infection was contracted in hospital. Evidence of Coxsackie virus infection was also obtained in five cases of paralytic poliomyelitis.

4. Serological evidence of Adenovirus infection was found in one case of aseptic meningitis.

5. No acceptable evidence was found of infection with Columbia SK or related viruses, or with the virus of lymphocytic choriomeningitis.

6. From one patient with aseptic meningitis an unidentified virus was isolated.

We wish to thank Dr J. Kennedy for permission to study patients and Prof. C. P. Beattie and Prof. C. H. Stuart-Harris for help in preparing the manuscript.

1. Cultures of tubercle bacilli were obtained from 204 cases of lupus.

2. According to their cultural characters the strains could be divided into two main groups, one containing 102 strains with the characters of human tubercle bacilli and the other containing 102 strains with the characters of bovine tubercle bacilli.

3. Virulence tests were carried out on a large number of animals, and in one instance over 100 animals were used for testing strains from a particular case.

4. Of the 102 culturally human strains 41 were highly virulent for the guineapig, and for the monkey when this was tested, producing progressive and rapidly fatal tuberculosis. The remaining 61 strains (59.8%) showed varying degrees of attenuation.

5. Of the 102 culturally bovine strains 34 were highly virulent for all the animals tested, producing in them severe and rapidly fatal general tuberculosis identical with that set up by standard bovine bacilli. The remaining 68 (66.7%) were of lower virulence for the rabbit, and for the calf and goat when these animals were tested, than standard bovine strains, but they all produced in one, two, or three of these species more extensive tuberculosis than human bacilli. For the guineapig, and for the monkey when tested, these strains fell below the virulence of standard bovine strains, except for a few whose virulence was only slightly lowered for the rabbit.

The primary lesions produced in rabbits by the intradermal inoculation of the virulent French strain of myxoma virus were clearly distinguishable from those produced by the standard laboratory strain or by attenuated Australian field strains. Based on this fact a screening test was developed which allowed classification of large numbers of samples of virus into French or attenuated Australian types.

The virulent French type of virus was introduced into the wild rabbit population at Lake Urana by the inoculation of 242 rabbits over a period of 6 weeks, the attenuated Australian strain of virus having been recovered from a naturally infected rabbit at the beginning of the series of inoculations. A severe outbreak of myxomatosis occurred in which an estimated 70% of cases were caused by the French strain of virus. In spite of the early predominance of cases due to this introduced strain the majority of samples obtained in the latter half of the outbreak were of the attenuated Australian type, and this was probably the only strain which survived through the following winter and caused an intense epizootic in the spring.

A similar picture of early establishment of the artificially introduced virulent French strain, and its subsequent replacement by the naturally occurring attenuated Australian strain, was seen at two other study sites, North Urana Station and Merricumbene.

We are greatly indebted to colleagues on the staff of the Wildlife Survey Section at Albury, especially Mr M. P. Hines, for assistance in the field work, and to Mr P. Bentley, the manager of Cocketgedong Station, on which the experimental site is situated. We have profited from numerous discussions with Mr F. N. Ratcliffe, and are grateful to Dr G. S. Watson for assistance in the statistical treatment of the results.

The relationship of Esch. coli 0.26, 0.55 and 0.111 to the incidence and spread of infantile gastro-enteritis in a defined area has been studied over a period of 5 years in the Public Health Laboratory, Southampton.

In the main, the study was concerned with infants up to 1 year of age suffering from gastro-enteritis, and from this age group faecal specimens from 1234 individuals were examined for three sero-types of Esch. coli (0.55 and 0.111 from the autumn of 1949 until September 1954 and 0.26 from May 1953 until September 1954). Esch. coli O.111 was isolated from 66 infants of whom 56 had enteritis, type 0.55 from 159 infants of whom 126 had acute symptoms, and type 0.26 from 14 infants all but two of whom had enteritis.

During widespread outbreaks there were sometimes multiple foci of infection. The determination of the H-antigen carried by the O sero-types showed, for instance, that the 0.55 outbreak in 1952 was almost entirely due to subtype 0.55 H.2, but that a second subtype 0.55 H.7 was also incriminated. Similarly, an 0.111 outbreak in 1953 was due to a mixture of two subtypes (0.111 H. 2 and 0.111 H. 12), but in 1954 the former subtype was not seen and only O. 111 H. 12 was identified.

During epidemic times Esch. coli 0.55 was isolated from 37·2% of the infants examined, whereas in non-epidemic periods the figure was only 1·2%. In the case of type 0.111 the figureswere 26·9 and 1·4% respectively.

Symptomless excreters were found throughout the period of the study and at all ages, but the proportion as compared with cases was significantly higher in children over 1 year of age. Nevertheless, there were several symptomless excreters less than 4 weeks old. While there was some evidence to suggest that the young child who was a symptomless excreter might be responsible for maintaining a low-grade infection in a community, there was no indication that the rare adult-carrier played any significant part in this.

The specific types of these coliform organisms can survive for long periods outside the body. Naturally infected dust contained viable organisms 12 days after it was first found to be so contaminated; the dust was maintained in a cool shady room.

There is great variety in the clinical severity of the disease as seen in comparable groups of infants, from a very grave illness to the very mildest of diarrhoeas. The very young and those with some other complicating illness are always at a greater risk.

The pattern of the outbreaks as seen in this study suggests a gradual enhancement of virulence of the two main types of Esch. coli with local spread at first and then wide dispersal throughout the district followed by a reversion to the poorly invasive type.

Eleven cases of aseptic meningitis occurred in a Cambridgeshire village between 17 October and 11 November 1955. The syndrome consisted of severe headache, backache, vomiting, fever and neck stiffness together with lymphocytes and frequently some granulocytes in the cerebrospinal fluid. Principally, it affected persons aged between 10 and 30 years. Out of a total population twenty-three at risk, seventeen were infected and eight became ill. A further three contacts who were living in Cambridge became ill.

Identical strains of virus were isolated from the faeces of two patients by inoculation of trypsin-dispersed human amnion cells and from the faeces of another two patients by inoculation of monkey kidney cultures. Bourn virus, which belonged to the ECHO group, Type 9, multiplied readily and produced cytopathogenic effects in human amnion and monkey kidney cultures, but it was not cytopathogenic in HeLa cell cultures. These investigations strongly suggest that Bourn virus caused the epidemic.

We wish to thank Dr M. G. P. Stoker for his advice and criticism and Mrs B. M. Cook for technical assistance.

We are indebted to Dr J. O'H. Tobin and Dr F. K. Sanders for advice on certain technical procedures.

It is a pleasure to acknowledge the assistance given by many colleagues and friends, including Dr D. I. Annear, Miss D. K. Bell, Mrs D. Ditchburn, Dr R. M. Fry, Dr D. Gairdner, Dr J. E. Power, Dr D. Simpson, Dr P. Tyzer and Dr P. J. Wormald.

Of thirty-six babies delivered at home 72% acquired Staph. aureus in their noses and throats within their first fortnight of life. The carrier rate among the twenty-eight who were subsequently followed was 65% during the first fortnight period. Only 18% acquired penicillin-resistant strains, in contrast to the previously observed hospital-born group, 97% of whom acquired strains resistant to penicillin. Phage typing demonstrated that the home-born babies who acquired Staph. aureus during their first fortnight carried the same strains throughout the 15–25 week observation period. As in the hospital-born babies, many of them tended to lose the strains from the nose while retaining them in the throat. Strains having phage patterns of Groups I and II were most common among the home-delivered babies, whereas among the hospital-born babies Groups I, III, or untypable strains were most frequent. There was no evidence that the penicillin sensitive strains acquired from the home are carried for shorter periods than the penicillin-resistant strains of the hospital. Babies failing to acquire Staph. aureus within the first fortnight tended either to acquire it in the throat alone, or to remain non-carriers. It is suggested that babies who do not become carriers within the first two months of life are unlikely to do so later.

I owe thanks to many people: to the late Prof. Sir Alexander Fleming for generously extending the laboratory facilities of The Wright-Fleming Institute; to Prof. Robert Cruickshank for patient guidance and invaluable suggestions; to Dr R. E. O. Williams for providing materials and laboratory space for the phage typing, and to Dr Joan E. Rippon for instruction in the phage typing technique; to Dr Agnes H. W. Smythe for the co-operation of the Marylebone and Lisson Grove Child Welfare Centres, and to Mrs Eastham and Miss MacGilley who took the swabs there; to Dr W. Howard Hughes, Dr W. G. Booth, and Dr K. Hart for arranging co-operation of the Ealing Public Health Department; to the Ealing midwives who collected the swabs from the domiciliary-delivered babies; to members of the Wright-Fleming Institute technical staff.

Also, I am grateful to the following organizations for personal grants while conducting the study: The United States Educational Commission in the United Kingdom for a Fulbright Scholarship, 1951–53; The University of California for a grant from the Student Aid Fund; Sigma Delta Epsilon for a Fellowship Award.

The mouse-protection test is discussed as a routine procedure. It has been shown that the assay is exceptionally subject to variation and that an average slope of 1·47 has been found over a year. With this slope and tests involving 90–180 mice it is possible tobe reasonably sure that a vaccine actually 3 times as potent as needed passes a test which lays down that the lower fiducial limit (P = 0·95) should exceed the specified requirement. For a vaccine only 1·5 times as potent as needed, much more extensive laboratory work would be necessary.

1. An investigation of ninety-eight cases of aseptic meningitis admitted to hospital resulted in the isolation of ECHO virus Type 6 from fifty-one patients.

2. The viruses were cultivated in both human embryonic skin-muscle tissue and human amniotic cell tissue. The latter was found to be more satisfactory.

3. Forty-eight strains were isolated from the stools of patients, six from the cerebrospinal fluid and four from throat-washings.

4. Serological examination of patients from whom the virus was isolated showed that a significant proportion of patients exhibited a specific antibody response. This included three out of six patients with the virus in their cerebrospinal fluid.

5. The clinical picture of aseptic meningitis from which cases ECHO virus was isolated cannot be distinguished from that caused by other known viruses.

6. The evidence presented supports the claim that ECHO virus Type 6 is one of the causes of aseptic meningitis.

Grateful appreciation is acknowledged to Prof. P. M. Holst (Oslo), Prof. Johs. Böe (Bergen), Dr B. Helland-Hanssen (Molde), Dr O. Römcke (Drammen), Dr R. Tingstad (Namsos), and Dr A. H. Brinchmann (Bærum), for providing specimens and case records. I am also grateful to Mrs B. Zapffe and Mrs L. Kohmann for expert technical assistance.

A streptomycin-resistant mutant of a virulent strain of Salm. typhimurium was less virulent to mice than the parent strain. The difference in virulence was only observed when mice were infected with small numbers of organisms. Although the mutant strain caused fewer deaths than the parent strain it remained capable of establishing persistent infection in the majority of animals.

The significant difference in the behaviour of the two strains in vivo was that after clearance from the blood multiplication in the tissues began more rapidly with the virulent strain and was progressive, whereas multiplication of the mutant was delayed, was less in degree and was apparently suppressed within a few days of infection.

The mutant strain was apparently identical antigenically with the parent strain, and was equally toxic. The mice dying of infection with this strain did so when the bacterial population had reached a level similar to that in the terminal stage of infection with the virulent strain.

The essential difference between the two strains was the speed and probability of attaining a critical final population. The mutant strain of Salm. typhimurium, both in vitro and in vivo, had a slower growth rate than the parent strain. A possible hypothesis to explain the importance of this finding in relation to the outcome of infection has been discussed.

I am indebted to the Medical Research Council for the provision of a grant towards the expenses of this investigation and to Mr T. Norris and Miss Italia S. Alderton for technical assistance.

1. Sera from an outbreak of about forty cases of dengue fever due to dengue-1 virus have been studied using the neutralization, haemagglutinin-inhibition, and complement-fixation tests.

2. The neutralization test was the most specific and the complement-fixation test the least so.

3. The neutralization test is essential for clear identification of the causal virus by serological means, and serial serum specimens from each patient must be examined.

4. The haemagglutinin-inhibition test can be used to screen patients in outbreaks where some cases have been fully identified by neutralization tests.

5. Homologous neutralizing antibodies persist in high titre for at least 30 weeks after infection, while heterologous antibodies have disappeared by that time.

6. Both haemagglutinin-inhibiting and complement-fixing antibodies to homologous and heterologous viruses usually persist for at least 30 weeks, although the homologous titres tend to be highest.

7. The implications of these findings in serological surveys are discussed.

8. Some evidence suggesting the occurrence of inapparent infections during the epidemic is presented.

I am greatly indebted to my staff for help with this work: especially to my senior technician, Che Ali bin Mohamed Amin, and to Che Mohamed bin Omar who drew the figures.

Sera of Nigerians aged between 10 and 60 years were tested individually for their antibody to five strains of influenza A virus. The results showed a similar pattern to those which other investigators have found with sera collected in the U.S.A. and in this country. However, antibody to the swine and WS strains was found in younger individuals than was reported previously; and the distribution of antibody titres suggests that this represents antibody to minor antigens of more recent strains, rather than persistence of swine and WS viruses.

We should like to thank Dr C. H. Andrewes F.R.S. for his criticisms and Dr James S. Porterfield who sent the sera.

Four series of tests, A, B, C and D, have been considered in detail. In the first two series, to obtain the values of the ImD 50, percentages of survivors were transformed into probits, and the best-fitting straight lines connecting the probits with the logarithms of the doses were obtained by the method of maximum likelihood. This is the most accurate method to use. These results showed that the error of the test was large, but there were no significant differences in the slope of the probitlog dose relation in the results of tests from any one laboratory. The slope (1·46 ± 0·09) obtained from series A was greater than that from series B (0·79 ± 0·06). with a consequent increase in accuracy.

Mice surviving infection with a strain of Salm. typhimurium of reduced virulence developed a progressive resistance to reinfection with virulent strains.

The degree of resistance was greater than that of vaccinated mice, although the primary infection had not caused any significant degree of natural selection or higher serum titres of O antibody.

The previously infected animals responded to reinfection with a virulent strain of Salm. typhimurium by gradually restraining bacterial growth. Many of the survivors eradicated the reinfecting strain.

The possible reasons for the difference between vaccinated mice and survivors of previous infection have been discussed.

I am indebted to the Medical Research Council for the provision of a grant towards the expenses of this investigation and to Mr T. Norris and Miss Italia S. Alderton for technical assistance.

An analytical method based on survival-time response is described for use in survey neutralization tests with the neurotropic viruses in mice. The method is simple and has been shown to give consistent and comparable results, which enable tests which have been carried out with different doses of virus to be compared.

1. A survey has been made of the serum levels of immuno-conglutinin in apparently healthy persons.

2. The level of immuno-conglutinin is raised in infective diseases and in other diseases where an antigen-antibody interaction is incriminated in the aetiology.

3. The significance of immuno-conglutinin is discussed.

In October, November and early December 1952, an epidemic of poliomyelitis, with an attack rate exceeding 1 %, occurred in Ketchikan, Alaska, a community of approximately 6000 persons. Approximately half of the cases were paralytic.

Type 1 virus was regarded as the principal cause of the epidemic because Type 1 virus was isolated from one patient, and sera from eleven of twelve paralytic patients tested were positive for neutralizing antibodies to Type 1 virus. Three patients had antibodies to Type 2 virus and eight to Type 3.

Serological tests were made to determine the immune status of the general population at the time the epidemic terminated. Approximately one-third of twenty-five children from 6 months to 4 years of age had antibodies to Type 1 virus. Of the 105 children aged 5 to 9 years, approximately three-quarters were positive for antibodies to this virus. All but two of the twenty-six persons more than 9 years of age who were tested were similarly positive.

Spread of Type 2 and Type 3 viruses was more limited in Ketchikan than spread of Type 1 virus. Serological evidence is presented to show that Type 3 poliomyelitis virus was present in Ketchikan some time within the 3-year-period prior to the collection of serum in December 1952. Since the proportion of children showing antibodies to Type 3 virus did not increase with age from 3 to 9 years, it is surmised that virus of this type was not prevalent for a number of years prior to its last occurrence. It is further concluded that spread of Type 3 virus must have terminated when 40 % or less of the children of pre-school age and early school age had been infected and developed antibodies.

Type 2 virus apparently had not been prevalent for several years prior to December 1952. Only one of twenty-one specimens of serum from children under age 5 showed definite evidence of neutralizing antibodies and this child had resided elsewhere during the first 3 months of its life. The proportion of positive results in all ages to 9 years inclusive was well below that obtained in tests with Type 1 virus.

From a review of published data concerning the age distribution of cases in the 1916 epidemic in New York, it is concluded that termination of the spread of Type 1 virus in Ketchikan occurred when the proportion of susceptibles in the general population was comparable to that in New York in each of several non-epidemic years preceding 1916. It is further evident that spread of Type 2 virus in Baltimore during a period of low prevalence of poliomyelitic disease was comparable to that of Type 1 virus in Ketchikan in 1952, in that the proportion of susceptibles in the population at the end of the period of spread of virus was similar.

Serological studies of residents of Metlakatla, an Indian community near Ketchikan, showed evidence of essentially uniform infection with Type 1 virus, a very high incidence of antibodies to Type 3 virus, and a much lower incidence of antibodies to Type 2 virus.

The epidemiological aspects of poliomyelitis in Ketchikan cannot be reasonably attributed to susceptibility resulting from isolation of the community, since travel to and from Ketchikan was considerable and a relatively large proportion of persons with paralytic disease were adults who had travelled extensively, and resided for periods of years in various parts of the United States. It is noted that the municipal water supply showed frequent evidence of faecal pollution.

The willing co-operation and valuable assistance of the following persons is gratefully acknowledged: Mr Alfred Baker, Mrs Dixie M. Baade, Miss Geneva Hubbard and Miss Lorraine Singer of the Ketchikan office of the Alaska Territorial Health Department; and Dr C. Earl Albrecht, Director and Dr Charles R. Hayman, Chief of Section of Preventive Medical Services, of the Alaska Territorial Department of Health.

The National Foundation for Infantile Paralysis financed the initial visits to Ketchikan. Testing of specimens was accomplished through the support of the University of Washington Fund for Biological and Medical Research and the Office of Naval Research.

Calculations have been carried out which indicate that poliovirus vaccine contains sufficient antigen to account for the observed antibody response.

For the purpose of determining the immunogenic potency of polio virus, relatively large amounts of concentrated virus material were prepared which had titres of the order of 1010 T.C.I.D.50 per ml. These were obtained by pervaporating large quantities of tissue culture fluid containing approximately 106.5 T.C.I.D.50 per ml.

We wish to acknowledge the valuable assistance received from Dr P. D. Winter and his staff, of the Poliomyelitis Research Foundation, in carrying out the tissue culture titrations of these materials.