This edition of “Websites of Interest” is dedicated to those Culinarians and foodies alike who appreciate opportunities to develop their repertoire of new food and beverage experiences. In 2008, in...
Tsetse-transmitted trypanosomiasis is unique to sub-Saharan Africa, affecting 9 million km2. As it precludes the keeping of livestock in areas of high challenge, trypanosomiasis severely disrupts the development of sustainable mixed farming over large and potentially productive areas, rendering the region one of the most agriculturally impoverished in the world. Where agriculture and trypanosomiasis do coincide, livestock production is reduced by 20–40%, depending on the degree of agricultural activity and rainfall 1. It is estimated that direct effects of trypanosomiasis include the deaths of >100 people and ∼10 000 cattle daily. A recent study estimated that annual losses in agricultural production are in the region of £3 billion, and that the removal of this burden through concerted control actions 2 would require a 10–15-year investment of £12–15 billion.
Part of current evolutionary theory – the Red Queen hypothesis – predicts that parasites should become better adapted to exploit sympatric rather than allopatric host populations. Reciprocal cross-infection experiments of sympatric and allopatric host–parasite combinations have been the foundation of this hypothesis. New work by Krist et al. 1. Krist A.C et al. Spatial variation in susceptibility to infection in a snail-trematode interaction. Parasitology. 2000; 121: 395-401 Crossref PubMed Scopus (28) Google Scholar follows this theme and continues from a preceding study that was at odds with the Red Queen theory – previously, Microphallus sp., a trematode that infects ducks and snails, appeared better adapted to an allopatric population of its freshwater snail host Potamopyrgus antipodarum than to a sympatric one. Krist et al. have now resampled snails from essentially the same, single locality but from two differing ecological zones, shallow- or deep-water habitats. Microphallus was initially collected from natural infections present in either shallow- or deep-water snails. Wild-caught snails from shallow- and deep-water habitats were later collected and exposed to this parasite material, after laboratory passage. To monitor existing Microphallus infections, a sentinel control group was used. Throughout the experiment, groups of snails were inspected to monitor snail growth, parasite development and patency of Microphallus infections.
It is entirely natural that molecular biologists should enthuse about the prospects that their science proffers 8xHurrah for genome projects. Ivens, A. Parasitol. Today. 2000; 16: 317–320Abstract | Full Text | Full Text PDF | PubMed | Scopus (6)See all References8. Economists have, however, indicated that, with the cold war at an end, it is technology not ideology that now divides the world. Tropical diseases are among the greatest problems of technologically excluded regions but, because of the overall poverty of these regions, technological solutions are beyond their means. Sometimes, the technologies required are available abroad, but the countries are too poor to buy or license them on the necessary scale. Often, the technologies do not exist in appropriate forms, and poor-country markets offer scant incentives for research and development 9xSee all References9. These economic arguments are particularly relevant to the control of African trypanosomiasis, which affects only the rural poor.We can see this technology trap in action in the case of sleeping sickness treatment in Africa. The sleeping sickness drug Suramin is now also used for the treatment of HIV in the developed world, and its price has correspondingly increased. Cost might not be the only problem – persuading pharmaceutical companies to continue to produce drugs for the limited market that African trypanosomiasis represents is also difficult. Eflornithine is such a drug, developed originally as an anti-cancer therapeutic, but found to be effective treatment for T. b. gambiense sleeping sickness, particularly in those patients who failed to respond to Melarsoprol. In the West Nile sleeping sickness focus in northern Uganda, over 30% of T. b. gambiense cases now fail to respond to the Melarsoprol and, in these circumstances, despite its cost, Eflornithine would be the drug of choice. Sadly, Eflornithine is no longer deemed sufficiently commercially viable to merit its continued production.Africa has been subject to a difficult period of structural adjustment forced on its governments by the World Bank and the International Monetary Fund (IMF) 10xSahn, D.E. et al. See all References10. Africa now faces the problems of globalization, which include technological exclusion – genomics is a technology from which Africa could easily be excluded. What impact, in the present economic climate, can we expect genomics research to have on the lives and health of rural Africans in the foreseeable future? Suppose, for example that, as a result of the T. brucei Genome Project, a drug target is identified and this is developed commercially by the pharmaceutical industry. The likelihood is that such a drug will also be effective for other conditions, such as cancer, and, therefore, will be marketed in the developed world – the chances of it being made available to sleeping sickness patients (or more likely, to WHO acting on their behalf) at a price they can afford are minimal.How can poor people in technologically excluded countries benefit from globalization? Sachs 9xSee all References9 has suggested that the developed world should respond in the following ways: (1) recognise the technologically driven character of the global economy; (2) broaden international assistance; (3) engage multinational firms, first-world universities and scientific establishments; and (4) reform global development agencies (IMF, the World Bank and the various United Nations agencies).A new strategy is needed for technological promotion involving scientists, government and industry, with participation from rich and poor countries. The international community should make a firm commitment to promote scientific and technological capacity in poor countries, and rich countries should exercise restraint in the use of property rights. A better balance needs to be struck between incentives for innovation on one hand, and the interests of the poorest on the other.These points are particularly relevant to genomics initiatives. Rich countries are claiming rights of private ownership over genetic sequences. Genomics is so seductive a subject scientifically and, when we are dealing with diseases affecting the very poorest in the world, can surround itself with an altruistic halo that almost guarantees research funding. Parasitologists, in particular, might be expected to have a deeper understanding of the problems of controlling diseases in developing countries and it is perhaps within the power of the parasitological community not only to ensure free access, but also true benefit for the developing world from such parasite genome initiatives.
Sleeping sickness presents clinically as two distinct diseases, reflecting the fact that two very different trypanosomes are responsible. The African Rift separating East and West Africa defines the distribution of the two diseases. In this review, Susan Welburn, Eric Fèvre, Paul Coleman, Martin Odiit and Ian Maudlin discuss the biology and distribution of these two diseases in relation to the evolution of hominids in Africa.
To celebrate the 100th anniversary of the Bernhard Nocht Institute for Tropical Medicine, a European Filariasis Conference was held 28–30 September 2000, in Hamburg, Germany, covering aspects of the immunology, genetics, biochemistry and chemotherapy of filariasis.Filarial nematodes infect more than 150 million humans worldwide and threaten one billion individuals in Africa, India, South East Asia and the Americas. Filarial diseases are still far from being extinct, and thus pose a challenge for multiple areas of research.
Neospora caninum, a protozoan parasite of cattle and other animals, is at the center of several scientific debates. On the one hand, N. caninum infection is one of the most common findings in aborted bovine fetuses. On the other hand, infections in cattle are so common that it has been suggested that N. caninum could often be an innocent bystander in cases of abortion. A further cause of confusion is the observation that N. caninum-associated abortion losses primarily occur at four months or later in gestation. This raises a question: do cows protect fetuses from N. caninum transmission in early gestation, or are the earliest infections simply not noticed because the embryo is absorbed and the loss undetected? Controversy also surrounds the practical implications of the fact that N. caninum is frequently transmitted across the placenta from one generation to the next. This linear transmission (or vertical propagation) has prompted recommendations that infected female cattle be removed from breeding herds, which implies the belief that infections are permanent and that post-natal infection is a rare event; however, these assumptions are not universally accepted.
will always be ascariasis (not ascariosis),filariasis (not filarilidosis or filarioidosis),schistosomiasis (not schistosomosis) etc.’ In my opinion, there is no rationalewhatsoever for using different terms inparasitology, for example echinococcosis,toxoplasmosis and trichinellosis on theone hand and filariasis andschistosomiasis on the other.Furthermore, a new system of uniformnomenclature for parasitic diseases hasbeen officially adopted and recommendedfor general use by the World Associationfor the Advancement of VeterinaryParasitology (WAAVP)
The use of geographical information systems (GIS) in the management of African animal trypanosomosis in sub-Saharan Africa offers potential in assisting decisions on allocation of resources, prioritization of control areas, and planning and management of field operations. Here, Guy Hendrickx and colleagues review approaches being used to develop reliable data-layers and to incorporate these data into GIS models. They argue that techniques should be further refined to produce more-detailed data layers and to include a dynamic element, a problem rarely addressed until now.
The three trypanocides used to control tsetse-transmitted trypanosomiasis in domestic animals in Africa have been in use for over 40 years and, not surprisingly, resistance of trypanosomes to these drugs has emerged. Because of the relatively limited market in Africa and the high costs of developing and licensing new drugs, international pharmaceutical companies have shown little interest in the development of new trypanocides for use in either animals or humans. Therefore, the current challenge is to achieve optimal use of the relatively old existing drugs, and it is in this context that the problem of drug resistance has to be quantified - as discussed here by Stanny Geerts, Peter Holmes. Oumar Diall and Mark Eisler.
The target dose rate for DDT sprayed on house walls is generally 2 g a.i. m−2 (grams of active ingredients per square metre), so that a typical house with 200 m2 of wall and roof surface will require application of 400 g a.i., equivalent to 534 g of 75% formulated product. Bulk freight and distribution costs vary greatly, but would typically sum to ≈US$ 1200 per metric tonne – representing about 64 cents per 534 g per house. So the total product cost (TPC) for each sprayed house can be approximated as: TPC=(0.534×cost per kilo)+0.64. By contrast, a pyrethroid such as lambda-cyhalothrin is applied at a target dose of 30 mg a.i. m2−2, so that the typical house would require 6 g a.i., equivalent to 60 g of 10% formulated product. Applying the same bulk freight and distribution costs would add just 7.2 cents per 60 g per house, so that the TPC in this case becomes: TPC=(0.06×cost per kilo)+0.072. From this, we can derive the price equivalence curve shown in Fig. IFig. I, below.Fig. IView Large Image | Download PowerPoint SlideFrom this example, and assuming that application costs were equivalent for the two products, a DDT price of US$ 6 per kilo of 75% formulated product would be equivalent in operational terms to a lambda-cyhalothrin price of US$ 63 per kilo of 10% formulated product. So if the purchaser knows the offer price of either product, then the acceptable price equivalent threshold can be read from the curve. If DDT is offered at US$ 6 per kilo, then any lambda-cyhalothrin price below US$ 63 per kilo would be preferable, whereas if the DDT were offered at US$ 5 per kilo, then the lambda-cyhalothrin price should be below US$ 54 per kilo to be preferred on cost alone.
Chemotherapy of human African trypanosomiasis is problematic because of the high frequency of severe adverse events, the long duration and high cost of treatment, and an increasing number of treatment-refractory cases. New cost-efficient, easy-to-use drugs are urgently needed. Whereas basic research on potential drug targets is anchored in academia, the complex, highly regulated and very expensive process of preclinical and clinical drug development is almost exclusively in the hands of pharmaceutical companies. Jennifer Keiser. August Stich and Christian Burri here review, from the angle of industrial drug research and development, the past ten years of research activities at different stages of the development of trypanocidal drugs, and assess future prospects. The absence of compounds in clinical development Phases I-III indicates no new drugs will become available in the next few years.
Tsetse control technology, as well as the science of environmental impact and risk assessment, has come a long way over the past 20 years. The application of science to tsetse control has significantly reduced impacts on the environment, and the costs of environmental monitoring and assessment have reduced dramatically. Environmental impacts are encountered with all insecticide-based techniques, but they appear to be relatively minor and short-lived. Despite a wealth of ecotoxicological information, conflict between real and imagined risks is hampering decision making. As discussed here by Ian Grant, public confidence in control technologies is being undermined by political viewpoints, fears (often based on misinformation) and poor communication of the environmental issues.
Two visitors to the Serengeti National Park in Tanzania were infected with Trypanosoma brucei rhodesiense. As reported to the ProMED-mail list, an American tourist, there for only 2 days in May, in Nepal a week later was found to have acute trypanosomiasis; a British man there for 3 days also acquired the parasite. Both had a chancre at the site of infection, both had noticed tsetse bites. These cases, unusual after such brief exposure, were presented at the recent ASTMH meeting. David Freedman (GeoSentinel Network, University of Alabama at Birmingham, USA) commented that its database covering 26 global sites since 1997 contains no other cases of East African trypanosomiasis in travellers. [A.Sinha et al., African trypanosomiasis in two travelers from the United States.Clin. Infect. Dis. 29, 840–844, 1999 includes reviews of 29 other published cases.]
Recent research 1. Bentwich Z Good worms or bad worms: do worm infections affect the epidemiological patterns of other diseases?. Reply. Parasitol. Today. 2000; 16: 312 Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar appears to support the concept that mass deworming might help to control the incidence and/or progression of HIV/AIDS and tuberculosis (TB) 1. Bentwich Z Good worms or bad worms: do worm infections affect the epidemiological patterns of other diseases?. Reply. Parasitol. Today. 2000; 16: 312 Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar , 2. Bentwich Z et al. Can eradication of helminthic infections change the face of AIDS and tuberculosis?. Immunol. Today. 1999; 20: 485-487 Abstract Full Text Full Text PDF PubMed Scopus (179) Google Scholar , 3. Fincham J.E Markus M.B HIV/AIDS, helminths and eosinophilia. HIV and AIDS: Current Trends. 1999; 5: 9-11 Google Scholar , 4. Fincham J.E et al. Could non-selective anthelmintic treatment programmes contribute to control of the spread of HIV infection and AIDS?. Trans. R. Soc. Trop. Med. Hyg. 1999; 93: 536 Abstract Full Text PDF PubMed Scopus (7) Google Scholar , 5. Bundy D et al. Good worms or bad worms: do worm infections affect the epidemiological patterns of other diseases?. Parasitol. Today. 2000; 16: 273-274 Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar , 6. Markus M.B Fincham J.E Mbeki and AIDS in Africa. Science. 2000; 288: 2131 Crossref PubMed Google Scholar .
Tsetse control has long been an important option for reducing the impact of African trypanosomiasis but, although many effective methods have been used, the results have seldom proved sustainable. Developments to reduce cost and environmental impact increasingly limit the choices available for control and the scale of operations has declined. Conversely, human trypanosomiasis has reached epidemic proportions in some countries. Here, Reg Allsopp argues that those tasked with managing trypanosomiasis or committed to poverty alleviation in Africa should consider large-scale, area-wide tsetse control involving all proven methods, including aerial spraying and the sterile insect technique.
