This review examines the relationship between severe pulmonary disease caused by respiratory syncytial virus (RSV) infection in infancy and later development of asthma or reactive airway disease (RAD). RSV infection accounts for 70% or greater of all cases of infantile bronchiolitis and has been linked to subsequent asthma or RAD, either directly or through a shared common predisposition. Several studies suggest that RSV bronchiolitis is an important factor in the development of asthma and possibly atopy, although the association is lost by the age of 13 years. The mechanism is as yet unclear, but murine models of RSV disease have identified many plausible causal explanations. Further study is necessary to determine the relative roles of RSV infection and genetic predisposition in explaining the association between RSV infection and asthma/RAD.

Bovine tuberculosis caused by Mycobacterium bovis is a worldwide animal health problem and remains a major threat to public health in the countries in which people live in close contact with their cattle and milk is not pasteurized (7, 11). Early experimental studies (5, 15) suggested that the principal route of M. bovis transmission is most likely to be aerogenous (rather than oral). These experiments indicated that lower doses of M. bovis could be used to infect cattle intranasally compared with the larger doses required when an oral route of delivery was used. Furthermore, tuberculous lesions in the gut, a relatively rare event in naturally infected animals, were common only in cattle that were experimentally infected via the oral route (10, 15). Observations from more recent experimental infections confirmed that infection of cattle via the intranasal route results in pathology that is largely confined to the upper respiratory tract, while intratracheal infection tends to cause lesions in the lower respiratory tract. Naturally infected field reactor cattle most commonly have lesions in the lower respiratory tract and pulmonary lymph nodes, while involvement of the upper respiratory tract occurs more rarely (2,6,17,19,30).Bovine tuberculosis may spread by cattle-to-cattle transmission and also through the involvement of wildlife reservoirs (16). However, experimental intranasal and intratracheal M. bovis infections in cattle have shown that bacterial shedding (the presence of viable M. bovis in the nasal mucus) is, at best, transient and involves extremely low numbers (approximately 70 CFU) of bacilli (14). Such a low dose of M. bovis has not previously been considered relevant in the bovine model of tuberculosis, even though a low infection dose for Mycobacterium tuberculosis in humans has been accepted for many decades (21, 24, 25, 27). These historical studies showed that the numbers of primary calcified M. tuberculosis lesions in otherwise healthy people were low (between one and three lesions per individual) and also established that the infectious dose of M. tuberculosis could be as low as 1 to 10 bacilli.Previous experimental infections of cattle with M. bovis have suggested that the infective dose can have a profound influence on the severity of the disease that follows. For example, in the intranasal model, 5 ϫ 10 5 to 10 6 CFU resulted in multiple respiratory lesions, while 5 ϫ 10 2 to 10 4 CFU resulted in a more variable pathology (some animals had multiple lesions, and some animals had no lesions) and 10 2 CFU resulted in no visible lesions at all. Although the latter group remained skin test negative, M. bovis was isolated from the nasal mucus of one animal 100 days after infection (17). We and other workers have shown that in the intratracheal model low doses of M. bovis (800 to 6 ϫ 10 3 CFU) can result in animals that are skin test negative, have no visible lesions at post mortem, and are M. bovis culture negative (2,4,20,23). Interestingly, Rhodes et al. (23) also measured specific cytokine re...

SUMMARYThe development of novel vaccine strategies to replace or supplement bacille Calmette-Gue´rin (BCG) is urgently required. Here we study, in cattle, the use of heterologous prime-boost strategies based on vaccination with BCG and the mycobacterial mycolyl transferase Ag85A (Rv3804c) expressed either in recombinant modified vaccinia virus Ankara (MVA85A) or attenuated fowlpox strain FP9 (FP85A). Five different vaccination schedules were tested in the first experiment: MVA85A followed by BCG (group 1); BCG followed by MVA85A (group 2); BCG followed by FP85A and then MVA85A (group 3); MVA85A followed by MVA85A and then FP85A (group 4); and FP85A followed by FP85A and then MVA85A (group 5). Vaccineinduced levels of cellular immunity were assessed by determining interferon-c (IFN-c) responses in vitro. Prime-boost protocols, using recombinant MVA and BCG in combination (groups 1-3), resulted in significantly higher frequencies of Ag85-specific IFN-c-secreting cells than the two viral vectors used in combination (P = 0AE0055), or BCG used alone (groups 2 and 3, P = 0AE04). The T-cell repertoires of the calves in all five groups were significantly broader following heterologous booster immunizations than after the primary immunization. In a second experiment, the effects of BCG/MVA85A heterologous prime-boost vaccination were compared with BCG/ BCG homologous revaccination. The results suggested a higher Ag85A-specific response with a wider T-cell repertoire in the MVA85A-boosted calves than in the BCG/BCG-vaccinated calves. In conclusion therefore, the present report demonstrates the effectiveness of heterologous prime-boost strategies based on recombinant MVA and BCG to induce strong cellular immune responses in cattle and prioritise such vaccination strategies for rapid assessment of protective efficacy in this natural target species of tuberculosis.