Verandah-Design Experimental Huts

Experimental hut sites are located 15km from KCM College and 800m above sea level in an area between the Masai savannah and 5,896m high Mount Kilimanjaro. The surrounding area is dominated by agriculture and irrigated rice farming is the major activity close to the experimental huts. Japanese aid in this area of semi-arid savannah began in 1978 and has resulted in a system of irrigation canals and agricultural training. Paddy fields cover an area of more than 1,100 hectares. The irrigated fields are a major breeding site for the predominant malaria vector species in the area Anopheles arabiensis.

Fig. 1 Experimental huts are located next to irrigated rice fields (with Mt. Kilimanjaro in the background) which provide ideal breeding sites for An. arabiensis

The nuisance biting and filariasis vector Culex quinquefasciatus is also present at certain times of the year, breeding mainly in latrines and a sewage disposal plant situated approximately 1km away. Over the years three suites of experimental huts have been constructed in the Lower Moshi area as demand for Phase 2 trials of bed nets and IRS has increased.

Mabogini Field Station (Est. 2002)

Mabogini was the first site used for experimental huts trials and was constructed as part of the Gates Malaria Partnership in 2002. Six experimental huts are located at Mabogini Field Station which has rice fields 10 metres away on one side and semi-arid scrub the other side.

In addition to the experimental huts there is an office used for data recording of mosquito collections, a mosquito holding room, and a field insectary. A weather station is housed at the field station to record both external conditions and conditions within the huts.

Harusini Field Station (Est. 2007)

After conducting a series of trials in the experimental huts at Mabogini expansion was needed to meet demand. Harusini field station is located 8km from Mabogini in the same rice irrigation scheme. Seven experimental huts were built in 2007 to the same specifications as previous.

As in Mabogini there is an office for data recording and a mosquito holding room.

“Simple huts”

To bridge the gap between laboratory testing of IRS insecticides and experimental hut testing a suite of 4 “simple huts were built. These huts can be used to spray multiple insecticides on a variety of surfaces; such as mud, concrete, wood, and thatch; and monitor decay under natural conditions using WHO cone bioassays.

Kaloleni Field Station (Est. 2010)

Kaloleni field station is the latest addition to our experimental hut testing facilities. Initially we have constructed 4 verandah huts with space to expand upon demand. This area is situated at the start of the rice irrigation scheme 2km from Moshi centre. While our sites at Harusini and Mabogini have rotational rice cropping this site has the added benefit of continual rice cycles ensuring mosquito breeding sites the whole year round.

Mosquitoes
Anopheles arabiensis in this area are largely susceptible to most insecticide classes but show pyrethroid tolerance (as defined by WHO 80-100% mortality in susceptibility tests), due to metabolic mechanisms, and resistance to dieldrin. Culex quinquefasciatus in the area show resistance to pyrethroids, carbamates, and dieldrin.

Rainfall is concentrated in March-May accounting for 60% of the annual total 800mm in Moshi town (10km North). The remainder falls during October-December. Between the two rainy seasons are a hot, dry season January-February and a cool, dry season June-September. Rice is grown in 2 cycles at Mabogini and Harusini with the sowing being done in mid-June, and November. Irrigation of rice fields during the early growing season coincide with peak An. arabiensis populations. Lower Moshi area

is hyperendemic for falciparum malaria with an entomological inoculation rate (EIR) of 0-10.

Fig. 2 Seasonal population dynamics of An. arabiensis at Mabogini field site. Showing mean number caught in the untreated control hut p/night.

Fig. 3 Seasonal population dynamics of Cx. quinquefasciatus at Mabogini field site. Showing mean number caught in the untreated control hut p/night.

Nb. Indoor recording device was moved from the office to an experimental hut in May 2009