The 4th International Glossina Genomics Initiative (IGGI) Meeting, Welcome Trust Genome Campus, Cambridge, UK, 15 – 16 December 2006

  POPULATION GENETIC STUDIES IN SUPPORT OF TSETSE ERADICATION

EFFORTS IN TANZANIA

  Msangi A. R., TTRI Tanga, Tanzania

1. Background

• Tanzania has a total area of 945,000 km2

• It has a human population of 34.5 million that is heavily dependent on Agriculture with 17 million Cattle

• Tsetse & Trypanosomiasis having a devastating effect on Human and Livestock

The Tsetse Fly • Seven tsetse (Glossina) spp

– G. morsitans,

– G. pallidipes,

– G. swynertonni,

– G. austeni,

– G. brevipalpis,

– G. longipennis,

– G. fuscipes.

• In Tanzania the distribution of tsetse & cattle are the converse of one another

• Tsetse have excluded cattle from a large portion of good grazing lands thus separating livestock maintenance from farming

Disease in cattle - Nagana • AAT in cattle is caused by T. congolense, T. vivax & T. b. brucei

• It is wide spread & ranks very high in hampering cattle productivity.

• About 60 - 80% of cattle are infected with trypanosomes

• AAT & Tick borne diseases account for 70% of all cattle deaths

Disease in Man - Sleeping sickness

• HAT caused by T.b.rhodesiense

• It is localized & is one of the major public health problems

• About 4 mill people are risk of contracting HAT

Tsetse Control Efforts

• Tsetse control in Tanzania has a long history but with minimal success due to various reasons including:

1. Improper co-ordination & co-operation

2. Control operations were– Without regard for the biological

distribution limits of the target tsetse populations

– Not area-wide based • leading to problems of the controlled

areas being re-infested (i.e. Problems of sustainability).

AU/PATTEC

• Following the successful eradication tsetse fly on Zanzibar Island, a campaign to eradicate tsetse in Africa (PATTEC) was initiated by African Heads of State & Government

• PATTEC intends to get rid of the scourge of tsetse-transmitted diseases from the African continent more effectively & more expeditiously

 

PATTEC approach

• PATTEC proposes – a phased, systematic creation of tsetse-free zones,

involving the • identification of individual zones of tsetse fly

infestation at a time, and• tackling by applying principles of the area-wide

approach, by• employing appropriate tsetse suppression and

eradication methods

• Therefore, feasibility study is conducted before attacking (eradication), so that data obtained is used to assists in the decision-making on type of intervention strategy, i.e. means of tackling

2. National Strategy for T&T Eradication

• Recently Tanzania finalized a “National Strategy for Tsetse & Trypanosomiasis Control & Eradication”.

• The long-term goal of this strategy is to Eradicate Tsetse and Trypanosomiasis in the Country in line with the PATTEC initiative.

Population Genetic Studies

• Tanzania realizing that tsetse distribution is

NOT CONTINUOUS and that• geographical isolation may cause GENETIC

CHANGE between isolated populations and that• techniques like SIT requires MATING (genetic)

COMPATIBILITY for its successful application • then understanding of the GENETIC PROFILES

of target tsetse populations became an integral part of feasibility studies in Tanzania

Proposed Sites for Tsetse Eradication

• Three identified sites in Tanzania:

– Mafia Island targeting G. brevipalpis

– Northeastern Tanzania targeting G. swynnertoni

– Kagera river basin bordering Tanzania & Rwanda targeting G. pallidipes

Site 1: Mafia Island Tanzania - G. brevipalpis

• The island has an area of approximately 700 km2, and situated about 20 km off the Tanzania coastline

• It has a human population of about 50,000 & a cattle population of about 15,500

Results of a Feasibility Study - Mafia

• A preliminary disease survey conducted in north - western part of the island between 1988 and 1990– identified T. congolense as a causative agent of AAT

• A recent disease survey revealed that– G. brevipalpis is the only cyclical vector with apparent

density of 9.5 flies per trap per day – AAT prevalence is very low (2%)

• Further epidemiological studies using molecular tools will be conducted to investigate the link between the vector, its feeding habit (hosts) and the trypanosomes found in tsetse flies and cattle population.

Site 2: NE Tanzania targeting G. swynnertoni

• G. swynnertoni occurs in Tanzania & a major cyclical vector of AAT & HAT

• The fly is more restricted in distribution and unlike other tsetse species it invades more arid thorn bushes

• The fly belt was estimated to cover more than 40,000km2 but expanding human agriculture may have greatly reduced the area infested

NE Tanzania - G. swynnertoni Cont…

• The belt is confined to a large extent in northeastern part of Tanzania with a small extension into southwestern Kenya

• The northeastern parts of Tanzania is economically important because it has a high concentration of cattle, large farms for cash crops, and fast-developing tourism industry.

Results of a Feasibility Study - G. swynnertoni Area

• Previous limited surveys indicated that G. swynnertoni– is a dominant

tsetse species – it overlaps to a

small extent with other tsetse species: G. pallidipes, G. Brevipalpis, G. m. centralis, G. longipennis

Results of a Feasibility Study - G. swynnertoni Area cont…

• In another collaborative work with Prof E. S. Krafsur lab, Iowa State University, USA, – Nucleotide diversity at two mitochondrial loci

in four geographically separate samples of G. swynnertoni was examined

– It was found that the overall mean diversity was only 0.09

• indicating that the genetic differentiation among sampled G. swynnertoni populations were small

Results of a Feasibility Study - G. swynnertoni Area cont..

• The surveys conducted so far have been limited to a certain localized areas.

• A more systematic, grid-based entomological survey will be conducted with technical assistance from IAEA. Relevant ecological information will be collected such as:– absolute population densities and limits, – tsetse blood meal on spatial scale, – trypanosome infection rates in tsetse flies. – population genetic studies will be performed to identify

potential isolated fly pockets and to assess the degree of gene flow between the different populations.

Site 3: Kagera river basin G. pallidipes

• The basin is shared by

• Rwanda on the east

• Tanzania on the west

• Tanzania has more than two third of the basin

Kagera River Basin cont..

• The Majority of economic activities of the people in the basin comprises livestock production and some cultivation.

• In both Rwanda and Tanzania, livestock sub-sector could contribute more to national GDP but is hampered by diseases of which animal and human trypanosomiasis ranks very high.

Kagera River Basin Cont…

• The entire basin is occupied by tsetse fly, mainly G. pallidipes, which transmits trypanosomiasis.

• To address the problem of trypanosomiasis and their impact in the economy, Tanzania and Rwanda have joined other African countries in the implementation of PATTEC by initiating a regional PATTEC project to be executed in the Kagera river basin where the two countries share a common tsetse belt.

• A feasibility study will be initiated with funding from ADB.

3. OUTCOME OF FEASIBILITY STUDY

• The outcome of this study will

– provide a better understanding of the distribution, ecology and population dynamics of the target tsetse species.

– assist in the decision making on the type of intervention strategy to be used,

– build TTRI capacity in molecular techniques

THANKS