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.

Total iron concentrations in waters and fish tissues in the Nam Theun 2 Reservoir area (Lao PDR).

Data on total iron concentrations in waters and freshwater fish tissues in man-made reservoirs are scarce, especially in Southeast Asia. Changes in total iron concentrations in water and in fish tissues were studied after the impoundment of the Nam Theun 2 Reservoir (central Lao PDR). Water quality parameters were monitored at 11 stations (reservoir, upstream area and downstream areas) from 2008 to 2010. In 2009 and 2010, total iron concentrations were measured in three different fish tissues (viscera, gills and flesh) from 14 species belonging to the omnivorous and carnivorous feeding groups. The results indicated that iron concentrations in the water were influenced by the reservoir impoundment during the first year after the creation of the reservoir. Intra-annual variations of the total iron concentration in these waters appeared to be driven by the soil leaching processes mainly during the wet season. In fish, total iron accumulated preferentially in viscera, followed by gills and flesh. Iron concentration was highly species dependant and related to the ecology of the species whereas feeding habits (omnivorous or carnivorous) did not influence total iron concentration in fish tissues. Finally, reservoir impoundment did not affect iron concentrations in fish from the reservoir and from both downstream areas.