Biocontrol of rats in an urban environment in Southeast Asia using Sarcocystis singaporensis.

BACKGROUND: Upon request of the local administration a control campaign targeting commensal rats (Rattus rattus, R. exulans) was conducted in 30 sub-districts (villages) of the World Heritage town Luang Prabang, Northern Laos, using rat bait containing lethal quantities of the parasitic protist Sarcocystis singaporensis. The associated investigations assessed the short-term control efficacy, willingness of residents to co-operate (community approach), and temporal and spatial changes of the urban rat population in response to treatment. RESULTS: Biological rodent control significantly reduced rodent activity (percentage of positive tracking patches) in the town, from a mean of 25.3% (±12.8% SD) before (January-February) down to 8.0% (±4.4%) after (June) treatment. Reduction of rodent activity relative to three untreated villages was 83%. Similarly, residents observed significantly fewer rats on their properties after the campaign (mean percentage of households (HHs) per village with sightings), whereby reduction of sightings amounted to 57%. There was significant correlation between residents' observation rates and rodent activity. Among 94 rats trapped before and after treatment each, proportions of adult R. exulans and juvenile R. rattus were higher after rodent control, suggesting that a considerable part of the adult house rat population had been removed. Furthermore, a 5% post-campaign incidence of infection suggested that few rats had survived bait uptake. CONCLUSION: S. singaporensis may be used successfully as tactical biocontrol agent for culling of rats in urban environments. We propose additional components of a long-term rodent management strategy for the town, without which the impact of culling campaigns would be limited. © 2019 Society of Chemical Industry.

Factors explaining the abundance of rodents in the city of Luang Prabang, Lao PDR, as revealed by field and household surveys.

A field and a household survey, the latter of which included inspections and interviews with the residents of a total of 1370 properties, were conducted in 2004 in 30 villages of the city of Luang Prabang, Lao PDR, in order to assess the degree of rodent infestation and to identify potential factors influencing infestations. Roof rats, Rattus rattus, and the Polynesian rat, Rattus exulans, were the only rodents found in the city, and trapping results showed a clear dominance of roof rats (80-90% of all individuals). Measurements of rodent activity using tracking patches correlated positively with the trapping data, and revealed a significantly higher degree of rat infestation during the rainy season (September) than during the dry season (November). If households in the vicinity of the sampling locations were considered, villagers' accounts of indoor rodent infestations recorded during the household survey correlated positively with measurements of rodent activity. At least every second household reported indoor infestations. Using explorative statistical analyses (classification trees, factor analysis) we checked the predictive or explanatory value of up to 28 variables assessed during household inspections for villagers' observations on rodent infestation as the dependent variable. Trophic factors such as exposed food (indoors) and garbage (outdoors), and structural features such as open ceilings (indoors) and rat harborage in gardens (outdoors) ranked highest as explanatory variables. Assessment of a small sample of roof rat droppings collected inside houses revealed the presence of the potential disease agents Salmonella javiana, Cryptosporidium parvum, Giardia duodenalis and the parasitic nematode Calodium hepaticum (syn. Capillaria hepatica). These results underline the need for an appropriate rodent management strategy for the city, whereby simple sanitation and rodent-proofing measures could be cheap means of reducing rat infestation rates.