M. D. Yates

Zoonotic aspects of Mycobacterium bovis infection

The bovine tuberculosis eradication campaigns in many industrially developed countries have led to a huge reduction in the incidence of human tuberculosis caused by Mycobacterium bovis. Overt disease in man may, however, manifest decades after the initial infection and the occurrence of such disease raises several important questions. In particular, it is important to determine whether man-to-man transmission occurs, thereby rendering man a continuing reservoir of infection, and whether, if this is the case, man develops infectious forms of tuberculosis that enable M. bovis to be transmitted back to cattle. Epidemiological studies in South East England indicate that human tuberculosis due to M. bovis is rare and that the incidence is declining. In contrast to earlier days, the lung is now involved in many cases, raising the possibility of transmission of bacilli to other human beings and to cattle by the aerogenous route. No direct evidence of man-to-man transmission of overt disease was found but it is possible that inapparent primary pulmonary infections are occurring and these may proceed to overt post-primary disease in the future. The genito-urinary tract is now the most prevalent site of non-pulmonary lesions and there is firm evidence that this form of tuberculosis poses a hazard to cattle. Though uncommon, human tuberculosis due to M. bovis is still a public health problem of concern to both the medical and veterinary professions and there is a need to maintain careful bacteriological surveillance.

Mycobacterium marinum infections in man

Mycobacterium marinum , formerly known as ‘Mycobacterium balnei’, is a free-living organism which causes disease in fish and occasionally in man. When such infections occur in man they are usually associated with some aquatic activity, e.g. swimming, fishing, boating and keeping tropical fish. For this reason, the organism has been called a ‘leisure-time pathogen’ by Feldman, Long & David (1974) and the disease a ‘hobby hazard’ by Heineman, Spitzer & Pianphongsant (1972).

Subdivision of Mycobacterium tuberculosis into five variants for epidemiological purposes: methods and nomenclature.

Virulent strains of Mycobacterium tuberculosis isolated from humans are divisible into five variants by using four tests: oxygen requirement (aerobic or microaerophilic), nitrate reductase activity, susceptibility to pyrazinamide (60 micrograms/ml) and susceptibility to thiophene-2-carboxylic acid hydrazide (5 micrograms/ml). The five variants are referred to as Classical human, Asian human, bovine, African I and African II. The relation of these variants to previously described types is discussed. This simple division has been shown to be useful in epidemiological studies.

Incidence and nature of human tuberculosis due to bovine tubercle bacilli in South-East England: 1977-1987.

A total of 201 new cases of tuberculosis due to bovine tubercle bacilli was confirmed in South-East England between 1977 and 1987 inclusive. This represents about 1% of all cases of tuberculosis in this region. Most cases occurred amongst older individuals of indigenous white British origin, although some younger patients of Southern European and Indian subcontinent ethnic origin were also diagnosed. The lung was the most frequent site of disease, followed by the genito-urinary tract. In view of the known risk of transmission of disease from man to cattle via the respiratory and urinary tracts, continued surveillance of this relatively uncommon form of tuberculosis is still indicated.

Bacteriological survey of tuberculous lymphadenitis in South-east England: 1973-80.

During the eight years 1973-80 the Public Health Laboratory Service Regional Centre for Tuberculosis Bacteriology received cultures of mycobacteria from 2339 patients with tuberculous lymphadenitis. Of these, 2272 were M tuberculosis (2207 human and 65 bovine strains) and 67 were other mycobacterial species, usually M avium and its intracellulare variant. Disease due to the human strains of M tuberculosis occurred most often in young women of Asian ethnic origin. Many bovine strains isolated from Asian patients differ from the classical bovine type in being sensitive to pyrazinamide: the origin of these strains, whether from other people or from cattle, is unknown. Lymphadenitis due to bovine strains tended to occur in an older age group than the human strains and probably include relatively more cases of reactivation diseases. Infection caused by the other mycobacterial species occurred mainly in young children of European origin. Tuberculosis, therefore, remains an important cause of lymphadenopathy in Britain.

Bacteriological survey of tuberculous lymphadenitis in southeast england, 1981-1989

STUDY OBJECTIVE--The aim was to detect any changing trends in the nature and incidence of tuberculous lymphadenitis in southeast England and to determine whether there is any evidence for an increase in this disease that could be related to HIV infection. DESIGN--Mycobacteria isolated from patients with lymphadenitis in the years 1981 to 1989 were identified. Information was available on the age, sex, and ethnic origin of the patients and the anatomical site from which the mycobacterium was isolated. SETTING--The Public Health Laboratory Service Regional Tuberculosis Centre at Dulwich, which receives over 95% of mycobacteria isolated in southeast England. MAIN RESULTS--From 1980 to 1989, cultures were received from 1817 patients with mycobacterial lymphadenitis: 1677 were M tuberculosis, 25 M bovis, 21 M africanum, and 94 were other (environmental) species. In comparison with a survey conducted in the same region in 1973-80, the number of ethnic Indian subcontinent patients with lymphadenitis due to M tuberculosis had dropped by 30% and the number of European patients had dropped by 43% and showed a continuing decline and a shift towards an older age group. By contrast, there was a 20% increase in the number of cases due to environmental mycobacteria. The number of species causing such infections had increased and a greater proportion of patients were adults. Three patients infected by environmental mycobacteria were known to be HIV positive. CONCLUSIONS--The incidence of lymphadentis due to M tuberculosis is declining but cases due to environmental mycobacteria are increasing, with a greater diversity of species and more adult patients. There is no conclusive evidence for an impact of HIV infection on the incidence and nature of mycobacterial lymphadenopathy in southeast England, but this cannot be ruled out.

A bacteriological survey of tuberculosis due to the human tubercle bacillus (Mycobacterium tuberculosis) in south-east England: 1984-91.

The occurrence and nature of bacteriologically confirmed tuberculosis due to Mycobacterium tuberculosis in South-East England in the period 1984-91 is reported and compared with the results of a study for 1977-83. Registered new cases reached a low of 1028 in 1988 but increased to 1252 in 1991. This appeared to be due to a halt in the previous decline in new cases of European patients, a small increase in the number of Indian subcontinent (ISC) patients and an increase in patients from Africa. A total of 122 patients, mostly of European ethnic origin, were known to be HIV positive. As in the 1977-83 study, disease in the ISC group affected younger patients than in the European group, tubercle bacilli were more frequently isolated from a non-pulmonary site in the ISC group (45%) than in the European group (19%) and there was a higher incidence of the South Indian variant of M. tuberculosis in the former group (17%) than in the latter (9%). The overall incidence of drug resistance has not altered significantly since the 1977-83 study but 46 strains resistant to 3 or more drugs were isolated from 4099 ISC patients, compared with 3 of 4594 strains from European patients. Six of the 122 isolates from HIV positive patients were drug-resistant but none was multi-drug resistant. The slight rise in registered bacteriologically proven cases of tuberculosis, the presence of multi-drug resistant strains, the occurrence of HIV-related tuberculosis and reports of the emergence of multi-drug-resistant HIV-related tuberculosis in other countries strongly indicate the need for continued careful surveillance.

Names for mycobacteria.

To the founding fathers of bacteriology the nomenclature of pathogens was straightforward. Tuberculosis was caused by the tubercle bacillus and leprosy was caused by the leprosy bacillus and when these pathogens were allocated to the genus Mycobacterium this posed no problem, they merely became M tuberculosis and M leprae. This golden age of simplicity in nomenclature was, however, short lived as it soon became apparent that tubercle bacilli were not all identical and that

Differentiation of bcg from other variants of Mycobacterium tuberculosis isolated from clinical material

BCG isolated from clinical material may be reliably differentiated from other variants within the species Mycobacterium tuberculosis by means of a few simple cultural and biochemical tests and by bacteriophage typing. Animal pathogenicity tests may therefore be avoided.

Molecular epidemiology of Mycobacterium avium complex isolated from patients with and without AIDS in Brazil and England

Mycobacterium avium complex (MAC) is ubiquitous throughout the world. It is an opportunistic pathogen in AIDS patients but the number of cases in HIV negative patients is also increasing. The aim of this study was to determine whether patients were being infected with different MAC strains or whether one strain was dominant. DNA obtained from isolates in Brazil and England were compared using pulsed field gel electrophoresis (PFGE). Strains from 22 Brazilian patients clustered into 7 groups but 68/90 patients had a unique strain. In all patients, Brazilian and English, the same strain was isolated repeatedly over time, some over several years. This study shows that it is most likely that Man is infected from the environment and that one strain can survive without change for many years both in the environment and in Man.