Persistence of salmonella gallinarum under simulated environmental conditions

Abstract

Fowl typhoid caused by ~. gallinarum has been reported from all the parts of the world. In Kenya, it is widely reported, recurrent and apparently resistant to eradication. Little detailed work had previously been undertaken to determine the ability of the causative agent to persist in materials associated with husbandry namely soil, litter and layers mash. More work on the ability of the organism to persist on poultry pens was also necessary. The details of such work could then explain the observed recurrences and resistance to eradication, and could be used to draw suggestions on useful measures for eradication. Twelve isolates of ~. gallinarum were obtained from .clinical cases and one was used to artificially infect the forenamed materials and also sawdust-wood shavings mixture-to represent unused but pre-contaminated litter. The same isolate was also dispensed onto concrete walls and floor of a chicken pen. The ability of ~. gallinarum to persist in water under defined conditions of light and temperature was also investigated in detail. Three isolates were used to infect tap· and trough water. Survival in all materials was monitored by quantitative culture for ~. gallinarum followed by selenite enrichment. In the chicken pen, monitoring was also done before and after disinfection with user recommended dilutions of four locally available disinfectants. The organism survived in used litter for 5 days when moisture content was 25% v/wt and 10 days when moisture content was 50% v/wt. In unused but pre-contaminated sawdustx woodshavings mixture, ~. gallinarum organisms were not recovered after one day despite increasing the moisture content to over five times the natural content of 10% wt/wt. In soil and layers mash respectively, 107 and 108 organisms per gram survived for 2 days even when the moisture content was increased to 4 times the natural level of 6% and 12% wt/wt, respectively.' owing to preliminary studies indicating persistence of ~. gallinarum in water, a further detailed study on this aspect was neccesitated. Three isolates of ~. gallinarum were used, subjected to defined conditions of light and temperature likely to be encountered in the field in tap and trough water. Persistence in water varied from 5 days to over 79 days depending on physical conditions. The longest survival duration recorded was 79 days but two isolates in trough water kept in the dark survived 77 days. The longest duration for the same isolates in light was 15 days only. Analysis of viable counts to compare effects of light and of temperature could not give statistical significance in each and every case. On pen surfaces, recovery from the floor was higher than from wall but the counts were not statistically significant. When inoculated with 105 organisms per 25cm2, no recoveries from both sites were possible, 3 days post inoculation. Persistent infections could not therefore be established. When decontamination and hygiene user dilutions of 4 disinfectants were tested in the laboratory, the most locally used disinfectants were found to be ineffective. Establishment of organisms in wat~r may give rise to recurrent outbreaks of disease in flocks with access to such water. The results of this work could not point at persistence of §.. qallinarum in soil, litter, layers mash and on premises. They show active reduction of the organisms and therefore rule out establishment of §.. qallinarum infections in such materials and on concrete surfaces as a sole cause of recurrent outbreaks of fowl typhoid.