Rodent control to fight Lassa fever: Evaluation and lessons learned from a 4-year study in Upper Guinea.

Lassa fever is a viral haemorrhagic fever caused by an arenavirus. The disease is endemic in West African countries, including Guinea. The rodents Mastomys natalensis and Mastomys erythroleucus have been identified as Lassa virus reservoirs in Guinea. In the absence of a vaccine, rodent control and human behavioural changes are the only options to prevent Lassa fever in highly endemic areas. We performed a 4 year intervention based on chemical rodent control, utilizing anticoagulant rodenticides in 3 villages and evaluating the rodent abundance before and after treatment. Three additional villages were investigated as controls. Analyses to assess the effectiveness of the intervention, bait consumption and rodent dynamics were performed. Anthropological investigations accompanied the intervention to integrate local understandings of human-rodent cohabitation and rodent control intervention. Patterns of bait consumption showed a peak at days 5-7 and no consumption at days 28-30. There was no difference between Bromadiolone and Difenacoum bait consumption. The main rodent species found in the houses was M. natalensis. The abundance of M. natalensis, as measured by the trapping success, varied between 3.6 and 16.7% before treatment and decreased significantly to 1-2% after treatment. Individuals in treated villages welcomed the intervention and trapping because mice are generally regarded as a nuisance. Immediate benefits from controlling rodents included protection of food and belongings. Before the intervention, local awareness of Lassa fever was non-existent. Despite their appreciation for the intervention, local individuals noted its limits and the need for complementary actions. Our results demonstrate that chemical treatment provides an effective tool to control local rodent populations and can serve as part of an effective, holistic approach combining rodent trapping, use of local rodenticides, environmental hygiene, house repairs and rodent-proof storage. These actions should be developed in collaboration with local stakeholders and communities.

Palatability and efficacy of bromadiolone rodenticide block bait previously exposed to environmental conditions.

BACKGROUND: In São Paulo city, rodent infestation is considered to be a serious public health problem and is the object of a municipal rodent control programme. One of the most important routine methods involves baiting in sewers, using bromadiolone block bait in a pulsed baiting strategy. It has been observed that, after each pulse, bait is not always consumed, and its appearance is altered, which has led to concerns about efficacy. We assessed whether exposure to sewer conditions influences the palatability and efficacy of rodenticide baits to Norway rats (Rattus norvegicus). Baits containing bromadiolone as active ingredient were placed in sewers, removed after 30 days and offered to rats in a two-choice food trial and a no-choice food trial. RESULTS: The appearance of the rodenticide baits changed after 30 days exposure to sewer conditions, but they continued to be palatable and effective against rats. The level of mortality was considered to be satisfactory, 75% in the two-choice food trial and 100% in the no-choice food trial. CONCLUSION: Results support the reuse of rodenticide block bait in rodent control. It seems to be justified to continue using/reuse baits even when their appearance has changed after 30 days exposure in sewer systems.

Efficacy of methyl nonyl ketone as an in-soil repellent for common voles (Microtus arvalis).

BACKGROUND: Common voles (Microtus arvalis) can cause enormous damage in agriculture. Tests were conducted using an alternative approach to rodenticide-based vole management by developing an in-soil odour repellent based on the secondary plant metabolite methyl nonyl ketone (MNK). Replicated 25 m(2) plots were established in forage grassland to test efficacy and application schemes using a foam application that included MNK. RESULTS: MNK significantly reduced the number of reopened burrow entrances in all field trials compared with untreated control plots, with repeated application for 6 days reducing vole activity by up to 90%. The addition of black pepper oil (BPO) did not enhance the efficacy of the MNK foam. Voles tended to avoid burrows where MNK was applied and rather opened new burrows instead of reopening the treated burrow entrances. The foam application scheme led to a repellent effect that lasted for about 4-5 days. A single additional application of MNK after 4 days can extend the treatment effects for a further 2 days. CONCLUSION: The results indicate that MNK has the potential to repel common voles in the field. However, more studies are needed to enhance the duration of a one-off treatment effect to yield a user-friendly field application to manage vole populations.

The repelling effect of plant secondary metabolites on water voles, Arvicola amphibius.

BACKGROUND: Water voles (Arvicola amphibius Linnaeus 1758) are abundant in most parts of Germany and other European countries. They are known to cause serious damage in fruit and horticulture as well as in agriculture. Currently available repellents, scaring devices and household remedies are mostly inefficient. Tests were conducted to establish whether water voles can be repelled using plant secondary metabolites. These compounds are produced by many plant species as part of their defence against herbivores and pathogens. RESULTS: In this study, 12 volatile substances were tested in T-maze trials. The voles could choose between a test box including a test substance and a control box without odour. The extracts were considered to be repellent if the test box was avoided. Five potential repellents were identified: the essential oils of black pepper oil, Chinese geranium oil and onion, as well as the pure substances methyl nonyl ketone and n-valeric acid. Application of a combination of black pepper oil, Chinese geranium oil and methyl nonyl ketone did not increase efficacy. CONCLUSION: The identification of an effective water vole repellent could help to reduce damage to crops. It may also minimise the use of kill traps and of rodenticides, which will be of benefit for non-target organisms.

Production of UV-light-detectable faeces from house mice (Mus musculus domesticus) after consumption of encapsulated fluorescent pigment in monitoring bait.

BACKGROUND: The authors investigated whether fluorescent pigment in thermoset melamine microcapsules incorporated into monitoring baits would be excreted in the faeces of wild house mice in a quantity and intensity that would be detectable by a human observer. RESULTS: Experimental mice produced 24-116 UV-visible faecal pellets per 24 h; the mean dry weight was 582 mg. The number and weight of the faeces was independent of mouse sex and weight. The defecation of UV-visible faeces began at 2-3 h, peaked at 5-8 h and was complete at 17 h after bait ingestion. The detectability of the highly fluorescent faecal pellets using a small UV flashlight approached 100%, and no false positives were recorded. CONCLUSION: The tested formulation is of significant value for rodent pest monitoring because faeces that are highly visible by UV light are produced for 15 h by mice after ingestion, and their detection is easy and unambiguous.

[Plague control in Madagascar: evaluation of the efficacy of Kartman baitboxes in urban areas]. / Lutte contre ia peste à Madagascar: évaluation de l'efficacité des boîtes de Kartman en milieu urbain.

A method associating an anticoagulant rodenticide and an insecticide called Kartman bait-box aimed both at fighting reservoir and vectors of plague. It was evaluated in two neighbourhoods of Antananarivo (Madagascar) from October 2002 to May 2003. It involved the local community in the control. The study was carried out in Ambodirano-Ampefiloha refered as treated neighbourhood in which the Kartman bait box were laid out with an anticoagulant rodenticide and an insecticide with a rapid action versus a "pilot neighbourhood", Ankorondrano-Andranomahery in which the boxes were provided with non poisoning bait and non insecticidal white powder. The rodenticide used was Baraki (difethialone 25 ppm) and the insecticide was a powder of Propoxur 3%. The evaluation of effectiveness of this method was based on the four following parameters: (1) the number of dead rats collected daily inside and in the vicinity of the houses, (2) the daily number of baits non consumed in the Kartman bait box, (3) the cheopis index of the rats trapped using the BTS trap, and (4) the flea carrier index of the rats captured monthly with BTS trap. The cheopis index and the flea carrier index of the rats were calculated monthly. The number of rats that died in the treated neighbourhood was of 968 versus 3 in the pilot neighbourhood. The other parameters reached a stable level after 3 months. Between days 120 and 180, the mean number of unconsumed baits was 2.79 in the treated neighbourhood versus 0.14 in the pilot neighbourhood, the flea carriage (percentage of parasitized hosts) was 0% versus 61% in the pilot neighbourhood, and the cheopis index was 0.0 versus 5.0 in the pilot neighbourhood. This study demonstrates that Kartman bait-boxes reached the rat borne and the vectors of plague found in urban area. We propose to use this method extensively both during epidemic and inter-epidemic contexts.

[How dangerous are "mouse trap projectile traps"?]. / Wie gefährlich sind "Wühlmausschussfallen"?

The authors research by experiments to define the potency of wounding of a special mouse trap which belongs to the spring-guns. Besides the regular assigned 9 mm blank cartridge also the 9 x 17 mm "green" cattle stunning cartridge is tested. Shots were made on soap, cotton and skin on different conditions. As result the authors found that by close range shots (up to 1 cm) by the blank cartridge badly healing wounds are caused. The 600 Joule cattle stunning cartridge is able to mutilate the hand by contact shots.