Genetic distinction between contiguous urban and rural multimammate mice in Tanzania despite gene flow.

Special conditions are required for genetic differentiation to arise at a local geographical scale in the face of gene flow. The Natal multimammate mouse, Mastomys natalensis, is the most widely distributed and abundant rodent in sub-Saharan Africa. A notorious agricultural pest and a natural host for many zoonotic diseases, it can live in close proximity to humans and appears to compete with other rodents for the synanthropic niche. We surveyed its population genetic structure across a 180-km transect in central Tanzania along which the landscape varied between agricultural land in a rural setting and natural woody vegetation, rivers, roads and a city (Morogoro). We sampled M. natalensis across 10 localities and genotyped 15 microsatellite loci from 515 individuals. Hierarchical STRUCTURE analyses show a K-invariant pattern distinguishing Morogoro suburbs (located in the centre of the transect) from nine surrounding rural localities. Landscape connectivity analyses in Circuitscape and comparison of rainfall patterns suggest that neither geographical isolation nor natural breeding asynchrony could explain the genetic differentiation of the urban population. Using the isolation-with-migration model implemented in IMa2, we inferred that a split between suburban and rural populations would have occurred recently (<150 years ago) with higher urban effective population density consistent with an urban source to rural sink of effective migration. The observed genetic differentiation of urban multimammate mice is striking given the uninterrupted distribution of the animal throughout the landscape and the high estimates of effective migration (2Ne M = 3.0 and 29.7), suggesting a strong selection gradient across the urban boundary.

Host range and distribution of fruit-infesting pestiferous fruit flies (Diptera, Tephritidae) in selected areas of Central Tanzania.

The host range of major fruit fly pests in Central Tanzania was evaluated from October 2004 to October 2006. Samples of 48 potential hosts were collected and incubated for fruit fly emergence. Bactrocera invadens was the dominant species in incidence expressed as the ratio of infested to total number samples collected, as well as infestation rate, expressed as number of flies emerging per unit weight. Eight new host fruits are reported. Infestation by native pests, such as Ceratitis capitata and C. cosyra, was minor compared to B. invadens. Ceratitis rosa was the dominant species in temperate fruits, and Cucurbitaceae were mainly infested by Bactrocera cucurbitae, a specialized cucurbit feeder. Among commercial fruits, high infestation incidences were observed in mango and guava, but they decreased throughout the fruiting season. Low infestation rates were observed in all Citrus species and in avocado, indicating these fruits as poor hosts for the studied fruit fly pests in this region. Widespread availability and abundance of fruit species studied here ensures year-round breeding of B. invadens. Seasonal infestation differs, with mango being the most important host in October to January, while guava being important from February to August. Tropical almond showed very high incidence and infestation rate for B. invadens and might act as an important reservoir host, bridging the fruiting seasons of mango and guava. Soursop acts as an important host for C. cosyra after the mango season. Ceratitis capitata is a pest of minor importance of the commercial fruits studied in this region.

Demographic and spatio-temporal variation in human plague at a persistent focus in Tanzania.

Human plague in the Western Usambara Mountains in Tanzania has been a public health problem since the first outbreak in 1980. The wildlife reservoir is unknown and eradication measures that have proved effective elsewhere in Tanzania appear to fail in this region. We use census data from 2002 and hospital records kept since 1986 to describe the temporal, spatial and demographic variation in human plague. A seasonal peak in cases occurs from December to February with the numbers of cases during this peak varying between 0 and 1150. Variation in incidence, calculated for each village as the mean number of cases per thousand inhabitants per year, indicates that human plague is concentrated around a group of three neighbouring, relatively isolated, high-altitude villages; Nywelo, Madala and Gologolo. However, there was no evidence that these villages were acting as a source of infection for the remainder of the focus. The likelihood of becoming infected with plague is highest between the ages of 5 and 19 and lowest for adult men. This was most clear in the ward encompassing the three high-incidence villages where the risk of plague among children aged 10-14 was 2.2 times higher than for adults aged 30-34, and among adults aged 30-34, the risk was 2.4 times higher for women than men.

Plague in Lushoto district, Tanzania, 1980-1988.

Rodents were live-trapped in selected plague-inflicted villages from June 1980 to March 1988. Flea infestation rates were determined and the animals were serologically tested for plague. Clinically suspected and clinically healthy people in the affected areas were similarly tested for plague antibodies. Of 1596 rodent sera tested, 91 (5.7%) were positive for plague. These were mostly from Rattus rattus, Mastomys natalensis, Otomys spp. and Pelomys fallax. A total of 1772 fleas, of which Dinopsyllus lypusus, Xenopsylla brasiliensis and Ctenophthalmus calceatus comprised the largest proportion, was collected from the captured rodents. Total flea indices ranged from 0.67 to 1.12 fleas per rodent. A total of 2809 human cases and a mortality rate of 10.2% were recorded in 1980-1988. It was concluded that most rodent species in the area were suitable reservoirs of plague and that D. lypusus, X. brasiliensis and C. calceatus were probably responsible for transmitting the pathogen. Lack of effective quarantine measures during outbreaks was partly responsible for the spread of the disease to many villages, while inadequate rodent and flea control and poor sanitary measures could be responsible for continued outbreaks of plague in the area.

A decade of plague epidemiology and control in the western Usambara mountains, north-east Tanzania.

Outbreaks of human plague have been occurring in the Western Usambara mountains since 1980, involving many cases and deaths. Epidemiological surveys and control activities were carried out from June 1980 to May 1990. Rodents were trapped live, identified and serologically tested for plague, using the passive haemagglutination and passive haemagglutination inhibition tests. Rodent fleas were collected, processed, identified and counted. House fleas were caught with light traps and similarly treated. People and domestic carnivores were serologically tested for the disease. Various plague control measures were undertaken. A total of 2433 animals, 2254 rodent fleas and 1366 house fleas were collected. Average indices of rodent and house fleas were 0.93 and 5.38 respectively. Rattus rattus and Mastomys natalensis were the most abundant rodent species. Xenopsylla brasiliensis and Dinopsyllus lypusus were their commonest flea ectoparasites while Pulex irritans was the major house flea. Of 2044 rodent, 1880 human and 176 dog sera tested, 5.5%, 0.5% and 6.3% respectively were positive. It was concluded that plague was active in the focus despite the control measures and that common reservoirs and efficient vectors were present. It was suggested that dogs were probably involved in the epidemiology of the disease, that P. irritans was not susceptible to the insecticide used and that the flea was probably involved in murine plague transmission. Bacteriological research on the causative agent to establish the nature of its long persistence in the area and maintenance of a surveillance service are recommended.