Tsetse flies (genus Glossina) can threaten health and agriculture by transmitting the parasites that cause the potentially fatal diseases of sleeping sickness in humans and nagana in livestock. The fact that only parts of sub-Saharan Africa are infested is attributable to many causes, including the temperature in the area. This raises the possibility that climate change will affect the abundance and distribution of tsetse – the leading questions being how great and how rapid the effects will be. SACEMA is addressing these questions by a combination of field work and simulation modelling.
Other infectious diseases
Africa and Asia have the highest prevalence of Hepatitis B virus (HBV) worldwide. Mother-to-child transmission (MTCT) is the most common route of transmission in high prevalence areas. There are three different prevention strategies available to prevent HBV MTCT: Vaccine, Hepatitis B Immunoglobulin and Antiviral therapy during pregnancy. Strategic investment now could see the eradication of HBV MTCT in Africa and ultimately potentially the elimination of this major public health problem.
The evolutionary origin of Ebolaviruses is not very clear. The simple notion that these viruses have been circulating for many millennia in wildlife in tropical parts of Africa, occasionally spilling over into human populations, often brought on by human activities, may not be correct or at least incomplete. Over time a number of Ebola disease outbreaks reported and a pattern in the outbreak response seemed to have been established. A lot was also learnt about Ebola viruses, their epidemiology and ecology.
However, the 2014 Ebola outbreak challenges our understanding in many respects.
Once more we are hearing about ‘exponential growth’ – popularly some sort of synonym for ‘rapid growth’ or ‘explosive growth’ – but actually a technical term with a quite specific meaning. This time the talk is about the ongoing Ebola outbreak in West Africa, understandably causing increasing disruption (is devastation too strong a word?) in the region, and alarm much further afield.
Kaposi sarcoma (KS) is the most common tumour in HIV-infected individuals in Africa and is preceded by infection with Kaposi sarcoma herpes virus (KSHV). The influence of KS on response to ART is not well defined in resource-limited settings. Additionally, it is unclear if co-infection with oncogenic viruses such as KSHV places untreated HIV-infected patients at increased risk even without clinically apparent illness. The analysis presented here aimed to determine the effect of clinical disease due to KS and also to estimate the impact of co-infection with KSHV among HIV-1 infected adults receiving ART.
T. b. rhodesiense is the acute form of African human trypanosomiasis or sleeping sickness which is common in East and Southern Africa. Trypanosomiasis is caused by the parasite Trypanosoma brucei and transmitted by tsetse flies (genus Glossina spp). Treatment of livestock in sub-Saharan Africa with trypanocidal drugs has been hindered by drug resistance and proves to be too expensive for many farmers. Tsetse control methods include aerial and ground spraying, sterile insect technique, and bait technology, including the use of insecticide-treated cattle (ITC). We compared two techniques of application of insecticides on cattle using a mathematical model: whole-body (WB), where insecticides are applied on the entire animals body and restricted application (RAP), where insecticides are applied on the legs, belly and ears of the animal.
All models are imperfect, but unless the model both accounts for the known biology of the disease and is challenged with data this might not be detected.
One of the articles in this edition concerns the modelling of the control of the tsetse-borne disease trypanosomiasis using trypanocides or insecticide-treated livestock. SACEMA has been short-listed for WHO/TDR funding of a project focussing on modelling the way in which various climate change scenarios might affect the population dynamics of tsetse flies and the trypanosomes that they transmit. For this study we have access to large, long-term, unique archives of data of the type required to address these questions. These data will be augmented during the study through field studies in Zimbabwe and Tanzania, aimed at understanding the spatiotemporal variability of disease threat and how this is likely to change at different locations and altitudes in the context of climate change. Field studies will address particularly the problem of the interface between humans and tsetse, and suggest optimal methods of disease control.
Across sub-Saharan Africa, several species of trypanosome, transmitted by tsetse flies (Glossina spp), cause human and animal trypanosomiasis. While interventions can be directed against either the vector or the parasite, emphasis has usually been on the use of drugs to treat the disease both in humans and in livestock. Several advances in our understanding of tsetse biology and ecology and improvements in the cost-effectiveness of tsetse control have revived interest in the vector control approach to disease management. This article discusses and compares two different approaches to the control of trypanosomiasis in cattle: either we can control the disease by treating cattle with insecticides that kill the tsetse vectors without having any direct effect on the trypanosomes. Or we can inject the cattle with trypanocides that kill the parasites but leave the tsetse flies unharmed.
Outbreaks of cholera are ongoing, with recent outbreaks in Zimbabwe and Haiti highlighting the devastation this disease can cause. In response, several mathematical models of cholera transmission have been proposed, with the aim of comparing the impact of interventions including provision of clean water, antibiotics, and vaccination. In this piece, we provide a brief summary of how uncertainty in parameters and the spatial heterogeneity of cholera incidence argue for cautious interpretation of quantitative predictions about the impact of interventions.