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.
Other infectious diseases
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.
Randomised trials show that male circumcision reduces the prevalence and incidence of high-risk human papillomavirus (HPV) infection in men (1). However, the question was whether it also reduces the prevalence and incidence of high-risk HPV in the female partners of these men. In Rakai, Uganda, two randomised controlled trials of male circumcision where conducted between Read More
In Etosha National Park, Namibia, the plains zebra and other herbivores experience outbreaks of anthrax. Anthrax is generally not considered to be a problem in Etosha but rather a natural regulating force in the ecosystem. However, the extent to which anthrax plays this role remains poorly understood. Estimating how many carcasses there really are will help us understand the extent to which anthrax regulates zebra and other host populations. The general approach we take is to think about all the factors that affect the probability any carcass is detected (distance from road, time since death, if and when that road was driven, how long carcasses are scavenged for) and then estimate the number of carcasses that were missed. Keeping track of both how we collect data, in addition to the items of interest themselves, can thereby allow us to tease much more information out of our data as well as avoid biasing our results. And with better estimates of anthrax incidence we can learn more about the role anthrax plays in Etosha and elsewhere.
II. Glyn Vale and the birth of the “artificial cow” In a recent poll of British university academics the cracking of the DNA-based genetic code was cited as the most important advance by British scientists during the past 60 years. More surprisingly, voted into eighth-place, just ahead of work on stem cell research, was the Read More
Cervical cancer is the second most common cancer among women worldwide, with an annual incidence of approximately half a million cases. Over 80% of these occur in developing countries. It is firmly established that persistent infection with one of the so-called high-risk human papillomavirus (hrHPV) types is a prerequisite for the development of cervical cancer. Estimating the impact of HPV vaccination on the reduction in the rate of cervical cancer requires an understanding of the determinants that govern the prevalence of the various hrHPV types prior to vaccination. The fact that hrHPV is sexually transmitted partly explains the age-specific patterns in hrHPV prevalence data and the geographic variation in hrHPV infection risk. However, it is unclear why some high-risk types are more widespread than others.
An article published in the June 2009 edition of the SACEMA Quarterly reported on the positive association between genital herpes (most often caused by Herpes Simplex Virus type 2 (HSV-2)) and HIV acquisition (1). It has been argued that HSV-2 could have a major role in fuelling the spread of HIV and that significant numbers Read More