By Sola Ogundipe
Gambian sleeping sickness – a deadly parasitic disease spread by tsetse flies – could be eliminated in six years in key regions in the Democratic Republic of Congo (DRC), according to new research by the University of Warwick in the United Kingdom.
Signals from the University indicate that without changing current strategy, elimination if the disease isn’t predicted until the next century, however, if control strategies of the insect vector are well executed, the elimination goal could be achieved within four years when coupled with any screening approach.
Kat Rock and Matt Keeling at the School of Life Sciences, with colleagues in DRC and the Liverpool School of Tropical Medicine, have calculated the impact of different intervention strategies on the population dynamics of tsetse flies and humans – establishing which strategies show the most promise to control and eliminate the disease, a statement issued by the University of Warwick noted.
They found that a two-pronged approach – integrating active screening and vector control – could substantially speed up the elimination of Gambian sleeping sickness in high burden areas of DRC.
But there is a clause. Without changing current strategy, elimination might not happen until the 22nd century.
The research, entitled: “Predicting the Impact of Intervention Strategies for Sleeping Sickness in Two High-Endemicity Health Zones of the Democratic Republic of Congo”, is published in PLOS Neglected Tropical Diseases.
The researchers, who work as part of the Neglected Tropical Disease Modelling Consortium, used complex mathematical models to compare the efficacy of six key strategies and 12 variations within two areas of Kwilu province (within former Bandundu province), DRC.
Previous work by the same group indicates that high-risk people are often missed from active screening. The new model concludes that improved active screening – making sure that all people are screened equally, regardless of risk factor – may allow elimination as a public health problem between 2023 and 2031.
If vector control strategies – using “tsetse targets” coated with insecticide to attract and kill flies – are added, this elimination goal is likely to be achieved within four years when coupled with any screening approach.
If DRC adopts any of the new strategies with vector control, transmission would probably be broken within six years of launching the new programme in these areas – and over 6000 new infections could be averted between 2017 and 2030.
Strategies which rely only on self-reporting of illness and screening of low-risk individuals are unlikely to lead to elimination of sleeping sickness transmission by 2030, and delay elimination until the next century.
Gambian sleeping sickness, or Gambian human African trypanosomiasis, is caused by a parasite called Trypanosoma brucei gambiense, carried by tsetse flies in Central and West Africa.
Without treatment, the disease usually results in death.
In recent years, programmes have performed intense active and passive screening to decrease disease incidence. A few areas have also combined these medical interventions with vector control. But some high prevalence regions of DRC have not achieved the reductions in disease seen in other parts of Africa. Other strategies for elimination will also include reinforced passive screening, new diagnostic tools and improved drugs.
In 2012, the World Health Organization set two public health goals for the control of Gambian sleeping sickness, a parasitic disease spread by the tsetse fly. The first is to eliminate the disease as a public health problem and have fewer than 2000 cases by 2020; while the second goal is to achieve zero transmission around the globe by 2030.
Kat rock said: “We found that vector control has great potential to reduce transmission and, even if it is less effective at reducing tsetse numbers as in other regions, the full elimination goal could still be achieved by 2030.
“We recommend that control programmes use a combined medical and vector control strategy to help combat sleeping sickness.”
What you should know about sleeping sickness
According to the World Health Organisation, Human African trypanosomiasis, also known as Sleeping sickness, is a vector-borne parasitic disease caused by infection with protozoan parasites belonging to the genus Trypanosoma. It is spread by the bite of an infected tsetse fly of the Glossina genus, a species native to the African continent.
Sixty million people who live mainly in rural parts of East, West and Central Africa are at risk of contracting sleeping sickness. Sleeping sickness can be fatal if not treated.
The tsetse fly bite erupts into a red sore and within a few weeks the person can experience fever, swollen lymph glands, aching muscles and joints, headaches and irritability. In advanced stages, the disease attacks the central nervous system and people present with changes in personality, alteration of the biological clock (the circadian rhythm), confusion, slurred speech, seizures and difficulty in walking and talking. These problems can develop over many years and if not treated, the person dies.
The main approaches to controlling African trypanosomiasis are to reduce the reservoirs of infection and the presence of the tsetse fly. Rural populations living in regions where transmission occurs and which depend on agriculture, fishing, animal husbandry or hunting are the most exposed to the tsetse fly and therefore to the disease.
There have been several epidemics in Africa over the last century: one between 1896 and 1906, mostly in Uganda and the Congo Basin; one in 1920 in a number of African countries; and the most recent epidemic started in 1970 and lasted until the late 1990s.
The 1920 epidemic was controlled thanks to mobile teams which carried out the screening of millions of people at risk. By the mid-1960s, the disease was under control with less than 5000 cases reported in the whole continent. After this success, surveillance was relaxed, and the disease reappeared, reaching epidemic proportions in several regions by 1970. The efforts of WHO, national control programmes, bilateral cooperation and nongovernmental organizations (NGOs) during the 1990s and early 21st century reversed the curve.
Since the number of new human African trypanosomiasis cases reported between 2000 and 2012 dropped by 73 per cent, the WHO NTDs roadmap targeted its elimination as a public health problem by 2020.
Transmission of the disease seems to have stopped in some countries but there are still some areas where it is difficult to assess the exact situation because the unstable social circumstances and/or difficult accessibility hinder surveillance and diagnostic activities.