Countries Of Tropical Africa Research Articles

Exploring the diversity of flies (Diptera)

ABSTRACT Flies (Diptera) are an important but underappreciated part of our planet's biodiversity. With over 124,000 described species, and countless more awaiting discovery, they are one of the most diverse groups of organisms on Earth. This series of ten papers explores the diversity of Diptera. Several authors describe the diversity of dipteran lifestyles and behaviours, both as larvae and adults. They also reveal the various roles that these animals play in the ecological interactions of the planet—countless numbers of flies feed on plants, control pest arthropods (including other flies!), break down rotting vegetation and excrement, pollinate flowers, provide food for other species, and of course, spread diseases. Indeed, because of their role as vectors of disease, flies have almost single-handedly prevented the economic development of countries in tropical Africa and South America. But flies are used in positive ways by humans, too, and several authors describe their use in forensic science, molecular research, and even as “main attractions” in the tourism industry. The intent of this series of papers is to encourage a broader interest in Diptera that, ideally, will lead to further research and conservation efforts.

Commentary: Mortality decline in Senegal

Sub-Saharan Africa has become associated in the minds of many with news stories about famine, civil war, or hospitals overwhelmed by terminally ill AIDS patients. The continent’s success stories receive less news attention. Delaunay et al. present results from a study documenting the reductions in infant and child mortality achieved in rural Senegal since the 1960s. 1 In the Niakhar area, the probability of a child dying in the first five years of life in the mid-1960s remained 485 per 1000. Nationally, this proportion was around 300 per 1000. 2,3 The former statistic, at least, represents a level of mortality among infants and children more characteristic of 19th century Asia or 18th century Europe than of the second half of the 20th century. The improvement in child survival achieved since the 1960s is impressive. By the late 1990s under-5 mortality in Niakhar had fallen to about 213 per 1000, while estimates of the proportion of all Senegalese children dying before their fifth birthday fall in the range 115‐130 per 1000. 4,5 Senegal is now one of the lowest mortality countries in tropical Africa. Despite its relative proximity to the capital, Niakhar lies in the region of Senegal with the highest mortality. 3 In particular, in the 1960s the study area combined high mortality in infancy with exceptionally high mortality of children aged 1‐4. This pattern has been found in many parts of Africa and some other tropical regions but it seems to be most pronounced in the Sahel. 6 It was more extreme in Niakhar in the 1960s than in any other population that has been investigated in detail. 3,6,7 In this population, mortality rates rose in the second half of infancy, reaching a peak at about age 12 months, but remained very high right through the second year of life and into the third. This unusual age pattern of mortality was underlain by seasonal variation in numbers of births and deaths. Detailed analysis of the early data from Niakhar demonstrates that the age at which the risk of dying was highest differed according to season of birth: children were experiencing heavy excess mortality during their first two rainy seasons. 8 The overall pattern arose because the peak in mortality was particularly severe for those children aged 9‐15 months during the rains and because this was a relatively large group of children, as the birth rate also peaked at this time of the year. Delaunay et al. propose that under-5 mortality has been declining at a steady rate throughout the 37 years under study. Visual inspection of the relevant Figure in their paper suggests that one could argue equally plausibly that much of the decline in the risk of death occurred during the 1980s, with slower advances being made before and since. It would perhaps be asking too much of the data from a relatively small study, however, to attempt to differentiate between these accounts. It is clear though that it was children aged 6‐30 months that benefited from the early part of the mortality decline. Although mortality in this age range is still higher than is usual, the peak in mortality around one year of age had disappeared by the end of the 1970s. In contrast, the survival of children of all ages has improved during the past two decades. Thus, the explanations of the age pattern of mortality and of mortality decline in this population are closely inter-linked and the causes of mortality decline may differ between the two periods. Two diseases are emphasized in accounts of the age pattern of mortality in childhood in Senegal, of seasonal variations in mortality and of the reduction of mortality: measles and malaria. 1,3,9 The former disease figures prominently in the discussion by Delaunay et al. of the changing age pattern of mortality and the latter in their discussion of the disappearance and re-emergence of the seasonal peak in mortality. Apart from isolated campaigns in the 1960s, however, vaccination coverage in Niakhar began to rise only with the establishment of an EPI programme in the 1980s. 3 It therefore seems unlikely that measles and its sequellae played a significant role in the elimination of the 6‐30 month peak in the risk for dying in Niakhar, which occurred before this date. Moreover, others have argued that more than half the drop in mortality up to 1980 resulted from declining rainfall rather than from human intervention. 9 It was deaths from malaria, and perhaps also diarrhoea, that fell. During the 1980s though, when mortality may have fallen particularly rapidly, the crucial factor does seem to have been improvements in health care, perhaps buttressed by improve

Rôle des oiseaux migrateurs dans l'épidémiologie du virus West Nile

West Nile (WN) virus, first isolated from a human in Uganda, is a common arboviral disease in sub-Saharan Africa and India. The viral cycle of transmission, which involves mosquitoes and birds, usually inducing a non-symptomatic disease, was extensively studied in Egypt 50 years ago. Humans and horses are sensitive to WN virus infection. Most cases are non-symptomatic, but encephalitis cases are also reported as well as some fatalities, mostly in old patients. For a few years, West Nile has appeared as a reemerging virus with several outbreaks recorded in the Mediterranean region and Southern and Eastern Europe (Algeria 1994, Romania 1996, Israel and France 2000). West Nile anti-bodies were detected in many bird species, and the virus was isolated from birds like a turtle dove in Slovakia, a barred warbler in Cyprus, a rock pigeon in Egypt or a dead white stork in Israel. Birds are suspected for multiple introductions of WN virus in Europe from endemic countries in tropical Africa. Usually outbreaks occurred in temperate countries during the summer period, and mostly in humid regions (deltas, etc.) where large colonies of migrating and resident birds and populations of potential vectors like Culex modestus are present. Several factors are necessary for an outbreak to occur: the arrival of migrating infected birds presenting a high viremia susceptible of infecting potential vectors, replication in mosquitoes and amplification of the virus within susceptible birds and mosquitoes, and transmission to humans and/or horses. West Nile virus emergence for the first time in the Americas in 1999 in New York was revealed by the death of several thousand native birds, mostly crows and blue jays. However, bird migrations do not seem to be involved in the recent WN introduction in the United States. A better knowledge of the different factors involved in the WN virus transmission cycle are needed, especially the possible persistence of viral infection in birds and the role of ticks in WN virus dissemination. Combinations of surveys of potential regions of reemergence of WN virus in Europe in connexion with other places in the Middle East, North Africa and tropical Africa would be important for a better understanding of the epidemiology of this arbovirosis.

The public health impact of chloroquine resistance in Africa.

Between 1978 and 1988 Plasmodium falciparum resistance to chloroquine has been reported in all countries of tropical Africa. Despite the intensification of resistance during the last 2 decades, chloroquine remains in 2000 the first-line treatment for malaria in most of these countries. Here we review published data on the public health impact of antimalarial drug resistance in Africa. These data show that since the late 1980s convincing evidence of a major public health impact of the spread of chloroquine resistance has been available. Hospital studies in various African countries have documented a 2- or 3-fold increase in malaria deaths and admissions for severe malaria, an increase temporally related to the emergence of chloroquine resistance. Data from sentinel demographic surveillance systems in Senegal indicated that mortality attributable to malaria in children increased by as much as 6-fold among populations where low levels of malaria mortality had been achieved because of efficient health services before the emergence of chloroquine resistance. Increasing incidence of severe malarial anemia also contributed to human immunodeficiency virus dissemination. The dramatic impact of chloroquine resistance on malaria mortality has long been underestimated because only a low proportion of malaria attacks are potentially lethal among persons continuously exposed since birth to high levels of transmission. There is an urgent need to change treatment policies in Africa.

Development of a species-specific PCR-restriction fragment length polymorphism analysis procedure for identification of Madurella mycetomatis.

Madurella mycetomatis is the commonest cause of eumycetoma in Sudan and other countries in tropical Africa. Currently, the early diagnosis of mycetoma is difficult. In attempting to improve the identification of M. mycetomatis and, consequently, the diagnosis of mycetoma, we have developed specific oligonucleotide primers based on the sequence of the internal transcribed spacer (ITS) regions spacing the genes encoding the fungal ribosomal RNAs. The ITS regions were amplified with universal primers and sequenced, and then two sets of species-specific primers were designed which specifically amplify parts of the ITS and the 5.8S ribosomal DNA gene. The new primers were tested for specificity with DNA isolated from human mycetoma lesions and DNA extracted from cultures of M. mycetomatis reference strains and related fungi as well as human DNA. To study the genetic variability of the ITS regions of M. mycetomatis, ITS amplicons were obtained from 25 different clinical isolates and subjected to restriction fragment length polymorphism (RFLP) analysis with CfoI, HaeIII, MspI, Sau3AI, RsaI, and SpeI restriction enzymes. RFLP analysis of the ITS region did not reveal even a single difference, indicating the homogeneity of the isolates analyzed during the current study.

Isozyme Diversity in Bambara Groundnut

Bambara groundnut [Vigna subterranea (L.) Verde.] is an important crop in many countries of tropical Africa. Compared with other leguminous crops, little is known about the organization of its genetic diversity. Our goal was to investigate its population structure and the partitioning of genetic diversity between domesticated and wild accessions. Seventy‐nine accessions of domesticated and 21 wild Bambara groundnut populations were evaluated for genetic diversity at 41 isozyme loci, representing 23 enzyme systems. Domesticated accessions were characterized by very low genetic diversity (Ht = 0.052) with only 7 polymorphic loci. Wild populations were characterized by higher genetic diversity (Ht = 0.087), with 14 polymorphic. This suggests a marked bottleneck between wild and domesticated forms. Intrapopulation diversity was comparatively high (Hs = 0.033 for domesticated and Hs = 0.025 for wild populations) despite the near absence of heterozygous individuals, which suggests a predominantly selfing mode of pollination in both wild and domesticated Bambara groundnut High genetic identity between wild and domesticated forms suggests that wild Bambara groundnut is the true progenitor of domesticated Bambara groundnut. Both morphological and isozyme data show a gradient between true wild and domesticated Bambara groundnut through weedy populations. The improved understanding of the organization of genetic diversity of Bambara groundnut provided by our data will allow a better conservation of its genetic resources.

Rabies – risk of exposure and current trends in prevention of human cases

According to official WHO data more than 2.5 billion people are at risk in over 100 countries reporting the disease. Rabies mortality ranks ten in all infectious diseases worldwide. There are still about 50,000 to 60,000 human deaths annually although effective vaccines for post-exposure treatment are available. Most affected are the tropical countries in Africa, Asia, South America, and Oceania. The mortality figures range from about 0.001 per 100,000 for the US to 18 per 100,000 in Ethiopia. The vast majority (95–98%) of the 60,000 annual human death cases worldwide occur in canine (dog rabies) endemic regions with large stray dog population. Control of the disease is hampered by cultural, social and economic realities. In the rabies infested developing countries modern cell culture vaccines are hardly affordable. Dangerous neural tissue derived vaccines are still used. Three dose-saving treatment schedules have been developed: The reduced dose intramuscular 2-1-1 regimen, the two-site intradermal and the 8-site intradermal regimen. There is a critical shortage of human and purified equine rabies immunoglobulins, which are essential biologicals in the treatment of severe exposures.

New communication technologies in tropical African development

New communication technologies may be a mixed blessing for tropical African states. They could foster development, by promoting health, education, agriculture, entertainment, business and tourism; and also enhance international trade and regional cooperation. However, these technologies might accentuate the gap between the rich and poor, creating a society characterised by an information-rich elite and an information-poor under-class. In an age when information is power, this could devastate countries that are facing the problems of poverty, disease, hunger, and political instability. Ultimately, these technologies might also jeopardise the sovereignty, security, human rights, and, consequently, the development of countries in tropical Africa.

Analyse multiparamétrique de la composition minérale des pollens d'une population deBactris gasipaes(Arecaceae)

Abstract Bactris gasipaes Kunth is important both economically and as a food resource in several countries of tropical Africa. The profitability of cultivation can be increased by genetic amelioration of natural morphotypes. We observed that pollen characteristics influence the morphological and physiological features of the fruits. This prompted us to undertake a study based upon ten morphotypes from the Yurimaguas (Peru). We here complete the morphological and ultrastructural investigation of pollen, previously started by one of us, with an analysis of the elements with respect to the importance of the role they play in relation to pollen function. A determination of the 8 major elements, which corresponds to a precise analysis of the exine, was performed by micro-X-Ray diffraction analysis using an electron probe coupled with a scanning electron microscope. At the same time, the determination of calcium, magnesium and twelve oligo-elements by inductive coupled plasma spectrometry (ICP) provided a complete mineral analysis of the pollen. A comparison of the element patterns of the morphotypes, obtained by both was carried out through a number of numerical data reduction techniques (Factor analysis and clustering). This led us to suggest two classifications: (1) that of pollen based upon mineral elements (2) that of mineral elements based upon pollen and further to look for possible multiple correlations between elements and pollens. From the results obtained the following conclusions may be drawn: (1) the sequence of elements in descending order of concentration in the exine is an indication of the functional integrity of pollen and depends upon conservation and storage; (2) further, this sequence is a good fertility criterion; (3) variations in oligo-element concentrations in one cultivar allows infraspecific groups to be distinguished. This multiparametric approach also allow the location of an unknown pollen sample of Bactris gasipaes in the population under investigation. Bactris gasipaes Kunth, ressource économique et alimentaire importante pour plusieurs pays d'Amérique tropicale, fait actuellement l'étude de recherches intensives. La rentabilité de sa culture pourra être augmentée par l'amélioration génétique des morphotypes naturels. Les caractéristiques du pollen ayant montré leur influence sur les caractères morphologiques et physiologiques des fruits, nous avons entrepris une étude sur la base de dix morphotypes originaires de Yurimaguas, au Pérou. Nous avons compléte l'étude morphologique et ultra-structurale du pollen, réalisée précédemment par l'un de nous, par une analyse des éléments minéraux qu'il contient en raison de l'importance qu'ils revêtent dans les différentes fonctions du pollen. Ainsi, la teneur en huit éléments minéraux majeurs, qui correspond à une analyse ponctuelle de l'exine, a été déterminée par micro-analyse X par sonde électronique couplée au microscope à balayage. De même, le dosage du calcium, du magnésium et de douze oligoéléments, effectué par spectométrie à plasma à couplage inductif (ICP), correspond à l'analyse minérale globale du pollen. L'étude comparative des profils en éléments minéraux des différents morphotypes, obtenue par chacune de ces deux méthodes d'analyse, a été réalisée par différentes techniques d'analyse mathématique de réduction de données multidimensionnelles (analyse factorielle et classifications automatiques). Nous avons ainsi pu proposer une double classification: (1) celle des pollens sur la base des éléments minéraux, (2) celle des éléments minéraux sur la base des pollens, puis rechercher les corrélations multiples éléments minéraux/pollens. Les résultats obtenus ont montré: (1) que la séquence des éléments minéraux dans l'ordre de concentration décroissante dans l'exine est caractéristique de l'intégrité fonctionnelle du pollen et dépend de ses conditions de conservation et de stockage, (2) que çette même séquence constitue un bon marqueur de la fertilité de pollen, (3) que la variabilité entre les concentrations en oligoéléments observée entre les différents cultivars permet la constitution d'un marqueur chimiotaxonomique satisfaisant pour discriminer sur la base du pollen les groupes d'individus au sein même de l'espèce végétale considérée. Cette approche multiparamétrique offre également la possibilité de positionner a priori un nouvel échantillon de pollen de Bactris par rapport à la population initiale étudiée.

Continuous rearing of the maize stem borer Busseola fusca on an artificial diet

AbstractBusseola fusca (Fuller) (Lepidoptera: Noctuidae) is a major pest of maize and sorghum in many countries of tropical Africa. Hitherto, research on this important pest has been hampered by the occurrence of a six‐month long diapause in the last larval stage and the lack of an artificial diet for rearing the insect in the laboratory. Incorporating 4 to 8‐week‐old sorghum powder in a nutritionally adequate diet and rearing larvae individually in vials at ambient laboratory conditions (25–30 °C, 50–80% r.h., and L12: D12) have made it possible to rear 15 successive non‐diapausing generations of B. fusca capable of producing between 35 to 40 healthy pupae/litre of diet and upto 70% pupation without loss of vigour or reproductive capacity. Five to six generations were completed per year and the overall mean developmental period (egg‐egg) was 68 days (egg 6, larval 45, pre‐pupal 1, pupal 14 and pre‐oviposition 2 days). Larval period lasted 70 days in the first generation compared to 32.3 days in the fifteenth generation. Average fecundity increased from 158.0 to 394.6 eggs per female with a concomitant increase of egg hatch from 44.8 to 79.6% in the first and fifteenth generation, respectively.

Isozyme Diversity in the Cowpea Species Complex

The cowpea [Vigna unguiculata (L.) Walp] is an important crop in many countries of tropical Africa, Asia and South America. Compared with other leguminous crops, little is known about the population structure of the cowpea and the partitioning of genetic diversity between cultivated and wild cowpea. One hundred and twelve accessions of cultivated cowpea (V. unguiculata ssp. unguiculata) and 43 of wild cowpea (V. unguiculata ssp. dekindtiana) were evaluated for genetic diversity at 26 isozyme loci. Cultivated accessions were characterized by very low genetic diversity (Ht = 0.029), with only six polymorphic loci. Four of these polymorphic loci displayed one very common allele and one rare allele. Accessions possessing these rare alleles were dispersed throughout Africa and a geographical center of isozyme diversity was not evident. Cultivated groups biflora (the catjang) and sesquipedalis (the yard‐long bean) could not be differentiated from the cowpea. Wild cowpea, on the other hand, were highly diverse (Ht = 0.168), with 19 out of 26 loci polymorphic. Our data indicate introgression from wild to cultivated must be very rare. Six wild accessions displayed high identity with the cultivated cowpea. Wild cowpea may, therefore, be the progenitor of the cultivated cowpea. Because these wild accessions were dispersed throughout equatorial Africa, there is no isozyme evidence for a narrowly defined center of domestication.

Out of Africa: observations on the histopathology of Mycobacterium ulcerans infection.

Introduction Mycobacterium ulcerans infection produces progressive skin ulceration in man and other mammals. The disease was first described in 1948 in patients from the Bairnsdale district in Australia' but was known in Africa well before this time.2 It has since been recorded in many, mostly tropical countries in Africa, Central and South America, and South East Asia.3 The infection characteristically occurs in defined areas which are associated with river or lacustrine systems draining tropical or warm-temperature rain forest. Like the flora to which it is related, the mycobacterium shows a Gondwanian distribution which is evidence of its great antiquity.4 The disease usually begins as a skin papule (stage IA) which later ulcerates (stage 2) (fig 1)5; less commonly the infection may first appear as a subcutaneous nodule (stage 1B)6 which subsequently affects the dermis and then ulcerates, or sometimes the disease may produce diffuse oedema of a limb (stage 1 C),7 due to a necrotising panniculitis, which clinically mimicks cellulitis. The infection is usually on extremity but, particularly in children, it may affect the face or trunk.8 Occasionally, the necrotic process extends through deep fascia with involvement of muscle9 and even bone.'0 Metastatic infection may occur. The features of the pathology ofM ulcerans infection have been described'; additional characteristics of the disease, as observed in Zaire (Belgian Congo), have been detailed in the papers by Janssens et al.7 l Infection in Uganda has been described by Dodge,'2 13 and later by Connor and Lunn,'4 15 and infection in Papua New Guinea by Lytton and Lavett. 6 Hayman and McQueen described the pathology in additional Bairnsdale district patients in 1985.1' Burchard and Bierther'8 briefly described the pathology of the disease as seen in Gabon; their paper was illustrated with electron photomicrographs of M ulcerans. The earlier descriptions of the pathology of the disease have been comprehensively reviewed. '9 In the original paper' MacCallum detailed the clinical and macroscopic appearances of the ulcers with straight or undermined edges, subcutaneous spread producing nodules of induration and eventual ulceration at a distance from the initial lesion (fig 1), and the development in the subcutaneous tissue of an abundant gelatinous mass like blubbery granulation tissue which could be readily wiped off with gauze. Histologically, necrotic tissue lined the ulcer wall and floor and extensive necrosis of fatty tissue extended beneath the Figure 1 Clinical appearances of Mycobacterium ulcerans infection, on the posterolateral aspect of the left leg in a 64 year old man. The photograph demonstrates the undermining of skin and the development of a satellite lesion associated with extensive necrosis of subcutaneous fat. (Photograph, courtesy ofMr Kendall Francis, FRACS.).

Some phytoseiid mites (Acari: Phytoseiidae) from tropical africa with description of a new species

Abstract New records of 19 phytoseiid mites collected mostly from cassava (Manihot esculenta Crantz) habitat in countries of tropical Africa are given. Euseius beninensis Moraes and McMurtry is described and illustrated.

Agricultural development and the size distribution of personal income: The tropical African experience

We use data from a sample of countries in Tropical Africa to investigate the relationship between relative income and growth rate of the agricultural sector and income inequality. We find that an increase in the income of the agricultural sector relative to that of the non-agricultural sector decreases income inequality. The growth rate of agricultural production and the proportion of the labor force in the non-agricultural sector were also found to be negatively correlated with income inequality.

Partnership with nursing mothers: an interim strategy for combating childhood enteric diseases in Nigeria.

Five hundred and fifteen homes of nursing mothers in Ile-Ife, Nigeria, who had earlier brought their children for treatment of diarrhoeal diseases at the IUTHC infant child welfare clinics were visited between January 1982 and June 1984. The mothers' perceptions as to causes, prevention and control of childhood enteritis were elicited: 49.7% of the mothers attributed the cause of the disease to evil spirits; and 9.5% believed enteritis in children to be due to contamination of children's feeds. Modern medicine was perceived to be the ideal method for treating this disease by only 7.4% of the mothers, while 88.8% opted for any of the traditional methods. In order to reduce the devasting effects of enteric diseases among children born to mothers in tropical countries of Africa and Asia, it is imperative that all health workers understand the cultural and social perceptions of their clients towards the disease in question. Illiteracy, and unsanitary and unhygienic environmental conditions were found to be the main factors precipitating enteritis. Implications and strategies for minimizing diarrhoea and other childhood enteric diseases are discussed in the text.

Bird species richness in tropical Africa: Some comparisons

Species richness provides a simple measure of diversity, and high diversity is commonly considered a desirable attribute of an area. To determine factors favouring high species richness, we obtained data for 18 countries in tropical Africa, and for comparison, 12 in tropical America. We also considered data from smaller areas in Africa. Species richness for African countries depends upon their area, but latitude is even more important. When considering areas of all sizes, separation into moist and dry was found useful. Species richness is similar in both moist and dry areas up to about 10 4 km 2, but increases much more steeply for larger moist than larger dry areas. Species richness of breeding species is higher for moist than for dry areas of all sizes, and is higher for tropical countries of America than for Africa. Comparison of species totals in particular reserves (or countries) with the predictions given by the lines in the various figures provides a means of assessing their relative values in terms of species richness.

Sexually transmitted diseases in tropical Africa. A review of the present situation.

At present very little information is available on the prevalence and pattern of sexually transmitted diseases (STDs) in many countries of tropical Africa. The available evidence does, however, suggest that these diseases are highly prevalent and that a considerable reservoir of infection exists among the female population. Gonorrhoea is probably the most commonly recognised STD in tropical Africa, frequently causing epididymitis and urethral stricture in men and salpingitis and pelvic inflammatory disease in women. The prevalence of a infectious syphilis is still high, particularly the late manifestations of the disease. The prevalence of the other STDs is also high. Thus, the problem is clearly very serious and the need for improving facilities for diagnosis and treatment urgent; some attempt also must be made to initiate control measures.

Breeding cassava for resistance to cassava mosaic disease

Cassava mosaic disease (CMD) is one of the most serious and widespread diseases throughout cassava growing areas in Africa, causing yield reductions of up to 90%. Early research on breeding of cassava (Manihot esculentaCrantz) for resistance to CMD in Africa is reviewed. Changes in population size and in activity of the white-fly vector to CMD (Bemisia tabaciGenn.) in relation to changes in environmental conditions such as amount and distribution of rainfall, light intensity and temperature are discussed in relation to screening for resistance to CMD. Over the past eight years, significant progress has been made at the International Institute of Tropical Agriculture (IITA). Resistance to CMD has been successfully incorporated into high yielding cultivars of acceptable quality. The CMD resistant material has been evaluated and many promising clones have been selected in various countries in tropical Africa and India. The resistance has been effective in those countries.

Diagnostic radiology: geography of a high technology.

A survey was made of the manpower employed, facilities available and utilization of radiology in countries in tropical Africa and Southeast Asia. The data obtained are compared with those from industralized societies in temperate climates. The level of use of radiographic services varied by a factor as high as 40. The differences between the level of radiology manpower available could be over a hundredfold and for x-ray technologists, many hundred times. The concentration of services in capital cities is characteristic of many tropical societies. Measures to improve radiologic health care in tropical countries, with particular emphasis on rural areas, are discussed. The main need is for availability of radiodiagnosis close to the primary care level in rural areas to deal with the important clinical problems of trauma, chest infections, and obstetrics. Simplification of equipment and employment of technicians with short training can help relieve maldistribution of services.

Toxins and carcinogens in the environment: an observation in the tropics.

The incidence of primary liver cancer in the countries of tropical Africa is the highest in the world. There is a growing belief that the relatively high prevalence of hepatocellular carcinoma in Nigeria may have a multiple chemical factor etiology in such forms as food contaminants, herbal teas, and environmental chemicals. Major chemical toxins and carcinogens that have been identified so far in the tropical environment include sapotoxin, cycasin, mushroom toxin, capsaicin, oxalic acid, prussic acid, fluorooleic acid, N-nitroso compounds, aflatoxin, palmotoxin, pyrrolizidine alkaloids, quinine, DDT, and cyclamate.