Are local plague endemicity and ecological characteristics of vectors and reservoirs related? A case study in north-east Tanzania

The pattern of plague endemicity in Tanzania is characterized by continuous re-appearance of the disease in some locations,while in other neighbouring villages the disease has never or seldom been observed.To understand the reasons for this pattern,we studied small mammal and flea species composition,diversity and relative abundances in two plague-endemic and two plague-free locations.We asked(a)whether fleas more abundant in plague-endemic locations differ in their characteristic abundance and the degree of their host specificity from fleas more abundant in plague-free locations and(b)whether hosts most abundant in plague-endemic locations differ in the diversity of their flea assemblages from hosts most abundant in plague-free locations.We characterized(a)each host species by species richness and degree of taxonomic relatedness of its flea assemblages and(b)each flea species by its mean abundance and size,and degree of taxonomic relatedness of its host spectrum and compared their relative abundances between locations.No significant difference between plague-endemic and plague-free locations in either host density or any variable related to flea abundance or diversity was found.However,there was marginally significant effect of taxonomic distinctness of a flea assemblage harboured by a host on its probability to be more abundant in either plague-endemic or plague-free locations.Furthermore,hosts more abundant in plague-endemic locations tended to harbour closely-related fleas.Finally,while opportunistic and specialist fleas were equally distributed in both sets of locations,fleas exploiting distantly-related hosts were found mainly in plague-free locations during the rainy season.We suggest that the observed patterns might arise due to seasonal and spatial differences in local microclimatic conditions and landscape connectivity.

Distribution and ecology of lesser pouched rat,Beamys hindei,in Tanzanian coastal forests

The lesser pouched rat,Beamys hindei,is a small rodent that is patchily distributed in the Eastern Arc Mountains and coastal forests in East Africa.The ecology of this species and its current distribution in coastal forests is not well known.Therefore,we conducted a study in selected coastal forests to assess the current distribution of the species and to investigate the population ecology in terms of abundance fluctuations and demographic patterns.Assessments of the species distribution were conducted in 5 forests through trapping with Sherman live traps.Data on ecology were obtained from monthly capture–mark–recapture studies conducted for 5 consecutive nights per month in two 1 ha grids set in Zaraninge Forest over a 2-year period.The results indicate the presence of B.hindei in 3 forests where it was not previously recorded.The population abundance estimates ranged from 1 to 40 animals per month,with high numbers recorded during rainy seasons.Reproduction patterns and sex ratios did not differ between months.Survival estimates were not influenced by season,and recruitment was low,with growth rate estimates of 1 animal per month.These estimates suggest a stable population of B.hindei in Zaraninge Forest.Further studies are recommended to establish the home range,diet and burrowing behavior of the species in coastal forests in East Africa.

Impact of contraceptive hormones on the reproductive potential of male and female commensal black rats (Rattus rattus)

The black rat is considered one of the world’s top pests.With increased restrictions on rodenticides,new alternatives to manage rats are urgently needed.Research on the use of contraceptive hormones,levonorgestrel(LE),and quinestrol(QU),have been evaluated against some rodent species,and this research is thefirst study to assess these on black rats.Hormones were incorporated into rodent bait at 10 and 50 ppm concentrations singly and in combination(EP-1).Groups of 10 animals of each sex were fed the baits over 7 days.Lower bait consumption was observed with slight body mass reductions.On dissection,it was observed that the uterus was in a state of edema and male reproductive organs weighed less with reduced sperm counts/motility.The 2 most promising baits,50 ppm QU and EP-1,were used to assess impact on pregnancy and litter size.Pregnancy was reduced from 70%success when both males and females consumed untreated bait,down to 30%when males had consumed contraceptive bait but females had not,and down to 0%when females had consumed contraceptive bait,regardless of whether they had paired with a treated or untreated male.Litter size in the untreated pairs was 8 pups,but only 4 pups in those cases where the male only had consumed the contraceptive.Further studies should investigate how long the effect lasts and its reversibility.Field studies at the population level may also shed light on the practicality of using contraceptive baits for black rats in different habitats.

Comparative assessment on rodent impacts and cultural perceptions of ecologically based rodent management in 3 Afro-Malagasy farming regions

Rodents generate negative consequences for smallholder farmers in Africa that directly impact household and livestock damage,food security,and public health.Ecologically Based Rodent Management(EBRM)seeks sustainable solutions for the mitigation of rodent damage through assessments of rodent population dynamics,agro-ecosystems,and socio-cultural contexts.We adopt a comparative approach across 3 rural Afro-Malagasy smallholder farming regions in South Africa,Tanzania,and Madagascar to assess the household impacts of rodent pests and current perceptions and preferences associated with several rodent control measures.We conducted focus group questionnaires and interviews in different study site locations.Rodents assert multiple impacts on Afro-Malagasy farmers demonstrating recurrent and emerging agricultural and household costs,and public health impacts.We identify a significant knowledge gap in educating communities about the application of different EBRM approaches in favor of acute poisons that are perceived to be more effective.Cultural issues and taboos also have a significant impact on the social acceptance of rodent hunting as well as biological control using indigenous predators.We advocate for an enhanced investigation of the socio-cultural beliefs associated with different rodent practices to understand the factors underlying social acceptance.A collaborative approach that integrates the perspectives of target communities to inform the design of EBRM initiatives according to the specific agro-ecosystem and socio-cultural context is necessary to ensure programmatic success.

Demography, reproductive biology and diet of the bushveld gerbil Tatera leucogaster (Rodentia: Gerbillinae) in the Lake Rukwa valley, south-western Tanzania

Seasonal abundance, reproductive biology and feeding ecology of the bushveld gerbil Tatera leucogaster (Peters,1852) were investigated in small-scale maize field–fallow land mosaics in south-western Tanzania. The gerbilswere collected over a 2-year period using Sherman live and Victor hold-fast snap traps in permanent 4.5-ha grids. Atotal of 664 individuals were captured over 13 650 trap nights, giving an overall trap success rate of 4.9%. Trapsuccess varied between seasons with and without crops in the field but not between habitat types. At this site, thebreeding activity of this species is seasonal. All individuals whose stomachs were analyzed ate a wide range ofitems, indicating omnivory in this species at this site;however, seeds were the most preferred diet category, with amean contribution of 50.4%, followed by arthropods, with a mean contribution of 25.7%. Other plant materialsbecame important during the very dry periods.

Relationship between sampling intensity and precision for estimating damage to maize caused by rodents

In this study we aimed to determine the relationship between sampling intensity and precision for estimating rodentdamage. We used the systematic row sampling technique to provide data to achieve precision and accuracy inestimations of rodent damage in maize fields at the planting and seedling stages. The actual rodent damage to maizein 15 fields, each 0.5 ha in size, in Morogoro, Tanzania, was established at the seedling stage. These data were usedto simulate the sampling intensities that would provide precision and accuracy. The variations between estimateswere plotted against the sampling intervals. The results of this study show that the relationship between averagestandardized variances and sampling intervals is linear. The heterogeneous distribution of damage in some plotscaused variations in the accuracy of the estimates between plots, but a sampling interval of five rows consistentlyproduced estimates with a variance of less than 10%. We provide a standard curve that will allow a decision to bemade on the sampling intensity as a function of required precision using the systematic row sampling technique inmaize fields.

Soil type limits population abundance of rodents in crop fields:case study of the multimammate rat Mastomys natalensis Smith,1834 in Tanzania

Studies of populations of the multimammate rat Mastomys natalensis in Morogoro, Tanzania, show that soil textureappears to influence the population abundance and distribution of these rats in agricultural fields. The lowest rodentpopulation abundance was found on sandy clay soils (F(2, 5) = 8.42;P = 0.025). The population abundances of M.natalensis on sandy clay loam and sandy loam soils did not differ significantly (P ≤ 0.05), possibly because thesesoils have a very similar texture. The results of this study suggest that M. natalensis prefers loam-textured soilswith a high percentage of sand, which are probably better than clay soils for burrowing and nesting, particularly inthe rainy season. The lower preference for clay soils is probably related to the poor aeration in these soils and thewaterlogging that occurs during the wet season.

Reproduction and population dynamics of Mastomys natalensis Smith, 1834 in an agricultural landscape in the Western Usambara Mountains, Tanzania

The multimammate rat,Mastomys natalensis Smith 1834,is a dominant species in agro-ecosystems in Sub-Saharan Africa,but adapts quickly to changes in non-agricultural landscape,particularly woodlands and forests.In this study we report on reproduction and population dynamics of M.natalensis in deforested high elevation localities in the Usambara Mountains,north-east Tanzania.We conducted Capture-Mark-Recapture studies in 2002-2004,and established that reproduction of M.natalensis takes place in the extended wet season between February and June,and the population density peaks in June-August.Reproduction cease in July to January and population density drops from July onwards.Reproduction and population density fluctuations are linked to the duration and amount of rainfall.In years when rainfall was below average and the wet season was short,the population density was significantly lower(below 10 animals/ha and 60 animals/ha in 2003 and 2004 respectively,compared to>100 animals/ha in 2002 when rainfall was above the seasonal average)(Fdf 2,13=9.092,p<0.01 for in between years variations and Fdf_(12,15)=5.389,p<0.01 for effect of cumulative annual rainfall on population density).These densities were much lower than in the lowland savannah habitats in central and southwest Tanzania.A comparison between the farmland/fallow mosaic fields and agro-forestry areas showed higher population densities in the former,which have similarities to the preferred habitats in the lowland savannahs.The increasing abundance of M.natalensis in the Usambara could have some consequences:M.natalensis is major pest and is involved in the plague cycle in the western Usambara Mountains.Mastomys natalensis is also a strong competitor and the impact on endemic rodent species,e.g.Lophuromys flavopunctatus and Praomys delectorum is unknown.