The occurrence of Mycobacterium bovis infection in cattle in and around an area subject to extensive badger (Meles meles) control

The occurrence of Mycobacterium bovis infection in cattle herds during the period 1966-92 in two geographically related areas in South-West England is compared. In one area comprising 104 km2 all badgers were systematically destroyed from 1975-81, after which recolonization was allowed; in the other, comprising 116 km2, small scale, statutory badger removal operations were undertaken from 1975 onwards where specific herds were detected with M. bovis infection. In the area with total clearance, no further incidents with M. bovis isolation occurred from 1982-92. Survival analysis and proportional hazards regression indicated that the risk of herds being identified with infection was less once badgers had been cleared from their neighbourhood, whereas it was greater in herds with 50 or more animals, and once cattle in a herd had responded positively to the tuberculin skin test, even though infection with M. bovis was not confirmed subsequently. The study provides further evidence that badgers represent an important reservoir of M. bovis infection for cattle and that badger control is effective in reducing incidents of cattle infection with M. bovis if action is thorough and recolonization is prevented.

Thresholds and stability analysis of models for the spatial spread of a fatal disease

A simple two-class (susceptibles and infectives) model describing the dynamics of a fatal disease in a variable-size population is presented and analysed. Spatial dependence is introduced into the model by considering two different mechanisms for the geographic spread of the disease: nonlocal interaction between susceptibles and infectives, and migratory spread of the animals. The steady states and their stability for these spatially dependent models are deduced; no spatially heterogeneous steady states were possible. For nonlocal interaction, there were two spatially uniform steady states: the trivial state (no infectives or susceptibles), which was unstable, and the endemic state (constant proportion of the population infected), which was locally asymptotically stable. With migratory spread, the number of spatially uniform steady states was dependent on the boundary conditions imposed. With hostile (Dirichlet) boundary conditions, only the trivial steady state was possible and its local stability found to depend on the rate of diffusion of the total population. With no-flux (Neumann) boundary conditions, the steady states are the trivial and endemic states; these were unstable and locally asymptotically stable, respectively.

Effect of systemic BCG infection in syrian golden hamsters

The response of Syrian golden hamsters to systemic infection with several doses of Mycobacterium bovis (strain BCG) was assessed. Large numbers of organisms (10(7)), injected intravenously, were lethal for hamsters, whereas all animals survived infection with 10(4) colony-forming units of BCG. Animals responded immunologically to purified protein derivative as assessed by increased footpad swelling and splenic lymphocyte proliferation. The immediate cause of death was a diffuse granulomatous interstitial pneumonia.

Restoration of T-cell responsiveness by thymosin: development of antituberculous resistance in BCG-infected animals

T-cell-depleted (adult thymectomized, lethally irradiated, bone marrow-reconstituted [THXB]), sham-thymectomized (XB) and normal control mice were injected daily with 3 mg of calf thymosin for 16 days. On day 8 of the treatment, the mice, together with untreated controls, were infected intravenously with 4 X 10(6) viable Mycobacterium bovis (BCG Montreal). Growth of the BCG in the lungs and spleens was compared quantitatively for up to 100 days. Thymosin treatment reversed the progressive weight loss seen in BCG-infected THXB mice and prevented their death due to the ongoing mycobacteriosis that developed in the T-cell-depleted animal. There was a late-developing anti-mycobacterial response in the thymosin-treated THXB mice, which resulted in a progressive decline in viability for the lung and spleen populations over the 40- to 80-day period, when the corresponding counts for the untreated THXB mice remained relatively constant. The histopathology of the lung and the increased antibacterial activity seen in the thymosin-treated THXB mice correlated with decreased [3H]deoxyribonucleic acid levels seen in the lungs and spleen compared with that present in the T-cell-depleted controls.