MOLECULAR CHARACTERISATION OF ECHINOCOCCUS GRANULOSUS SPECIES/STRAINS IN HUMAN INFECTIONS FROM TURKANA, KENYA

BACKGROUND

Cystic echinococcosis (CE) or hydatid disease is a neglected, economically important zoonotic disease endemic in pastoralist communities, in particular the Turkana community of Kenya. It is caused by the larval stage of the highly diverse species complex of Echinococcusgranulosus sensu lato (s.l). The situation on the genetic diversity in humans in Kenya is not well established.

OBJECTIVE

To characterise Echinococcus granulosus (s.1) species/strains isolated from humans undergoing surgery in Turkana, Kenya.

DESIGN

A Cross sectional study.

SETTING

The Kakuma Mission Hospital and Centre for Microbiology Research, Kenya Medical Research Institute.

SUBJECTS

Eighty (80) parasite samples from 26 subjects were analysed by Polymerase chain reaction--Restriction fragment length polymorphism (PCR-RFLP) targeting the nad 1 gene for molecular characterization.

RESULTS

Two different genotypes of E. granulosus were identified from the samples analysed: E. granulosus sensu stricto (G1-G3) 85% of the samples analysed and E. canadensis G6/7 (15%). Most of the hydatid cysts (35%) were isolated from the liver. Other sites where cysts were isolated from include: kidney, abdomen, omentum, retroperitonium and the submandibular. Majority of cysts presented as CE1 (50%) and CE3B (42%) images according to WHO ultrasound classification. Both males and females were infected with E. granulosus s.s but only the females showed infection with E. canadensis G6/7. Chi-square test revealed significant difference between age of individuals and cysts classification by ultrasound. In addition, there was an association between cyst presentation (single or multiple) and genotype whereby all the E. canadensis G6/7 cases presented as single cysts in the infected persons.

CONCLUSION

This study corroborates previous reports that E. canadensis G6/7 strain is present in Turkana, a place where initially only E. granulosus s.s (G1-G3) was known to be present and that E. granulosis (G1-G3) remains the most widespread genotype infecting humans in the Turkana community.

Intestinal polyparasitism in a rural Kenyan community

BACKGROUND

Polyparasitism seems to be a common feature in human populations in sub-Saharan Africa. However, very little is known about its epidemiological significance, its long term impact on human health or the types of interactions that occur between the different parasite species involved.

OBJECTIVES

To determine the prevalence and co-occurrence of intestinal parasites in a rural community in the Kibwezi, Makueni district, Kenya.

DESIGN

A cross sectional study.

SETTING

Kiteng'ei village, Kibwezi, Makueni district, between May and September 2006.

SUBJECTS

One thousand and forty five who comprised of 263 adult males, 271 adult females > 15 years of age and 232 boys, and 279 girls <15 years of age.

INTERVENTIONS

All infected members of the community were offered Praziquantel (at dosages of 40 mg/kg body weight) for Schistosomiasis and Albendazole (600 mg) for soil transmitted helminths.

RESULTS

A total of ten intestinal parasite species (five protozoan and five helminth parasite species) were present in this community and polyparasitsm was common in individuals 5-24 years of age with no gendar related differences. Most of the infections were mild. The protozoan parasites of public health significance present were Entamoeba histolytica and Giardia lamblia with prevalence of 12.6% and 4.2%, respectively. The helminth parasites of public health significance in the locality were Schistosoma mansoni with a prevalence of 28%, and hookworms prevalence of 10%. About 53% of the study population harboured intestinal parasite infections, with 31% of the infected population carrying single parasite species infections, and 22% harbouring two or more intestinal parasite species per individual. Significant positive associations (p values <0.05) were observed between S. mansoni and hookworms, hookworms and Hymenolepis. nana and Entamoeba histolytica and Entamoeba coli.

CONCLUSION

Intestinal polyparasitism was common in the Kiteng'ei community, particularly in individuals aged of 5-24 years old. An integrated control programme of approach would be recommended for the control of S. mansoni, hookworms and Entamoeba histolytica for this community.

Genetic diversity and population structure of Schistosoma mansoni within human infrapopulations in Mwea, central Kenya assessed by microsatellite markers

A recently developed high-throughput technique that allows multi-locus microsatellite analysis of individual miracidia of Schistosoma mansoni was used to assess the levels of genetic diversity and population structure in 12 infrapopulations of the parasite, each infrapopulation derived from an infected school child from the Mwea area, central Kenya. The mean number of alleles per locus was in the range 8.22-10.22, expected heterozygosity in Hardy-Weinberg equilibrium was 0.68-0.70, and pairwise F(ST) values ranged from 0.16% to 3.98% for the 12 infrapopulations. Although the genetic diversity within each infrapopulation of S. mansoni in this area was generally high, low levels of genetic structure were observed, suggestive of high levels of gene flow among infrapopulations. Private alleles were found in 8 of the 12 infrapopulation, the highest number of private alleles recorded per infrapopulation was 3. Our data suggest that the level of gene flow among infrapopulations of S. mansoni in Mwea is extremely high, thus providing opportunity for spread of rare alleles, including those that may confer character traits such as drug resistance and virulence.

Genetic structure of Schistosoma mansoni in western Kenya: The effects of geography and host sharing

We examined the spatial structure of Schistosoma mansoni, a parasite of humans, from natural infections at two levels: across the Lake Victoria basin of Kenya and among snail hosts. Using 20 microsatellite markers we examined geographic patterns of relatedness and population structure of cercariae and found weak, but significant structure detected by some, but not all analyses. We hypothesise structure created by aggregations of clonal individuals or adherence of hosts to local transmission sites is eroded by high amounts of gene flow in the region. This finding also supports previous hypotheses concerning the evolution of drug resistance in the region. Intrasnail dynamics were investigated in the context of aggregation and kin selection theory to determine how relatedness and also sex influence host sharing and host exploitation. Cercarial production did not differ significantly between snails with one or two genotypes suggesting that mixed infections resulted in decreased individual fitness and provides a framework for reproductive competition. Coinfection patterns in snails were independent of parasite relatedness indicating that schistosomes were not aggregated according to their relatedness and that kin selection was not influencing host sharing. Additionally, host exploitation in coinfections (measured by cercarial production) was not negatively correlated with relatedness, as predicted by classical models due to increased competition and thus exploitation when parasites are unrelated. Because of the low levels of relatedness within the population, schistosomes may rarely encounter close relatives and kin selection mechanisms that influence the distribution of individuals within snails or the virulence mode of the parasites may simply have not evolved.

A new approach to characterize populations of Schistosoma mansoni from humans: development and assessment of microsatellite analysis of pooled miracidia

OBJECTIVES

To develop and assess a microsatellite technique to characterize populations of Schistosoma mansoni from humans.

METHODS

For each of five patients, we calculated the allele count and frequency at 11 loci for several pools of miracidia (50 and 100), and compared these to population values, determined by amplifying microsatellites from 186 to 200 individual miracidia per patient.

RESULTS

We were able to detect up to 94.5% of alleles in pools. Allele count and frequency strongly and significantly correlated between singles and pools; marginally significant differences (P < 0.05) were detected for one patient (pools of 50) for allele frequencies and for two patients (pools of 100) for allele counts. Kato-Katz egg counts and number of alleles per pool did not co-vary, indicating that further direct comparisons of the results from these two techniques are needed.

CONCLUSIONS

Allele counts and frequency profiles from pooling provide important information about infection intensity and complexity, beyond that obtained from traditional methods. Although we are not advocating use of pooling to replace individual genotyping studies, it can potentially be useful in certain applications as a rapid and cost effective screening method for studies of S. mansoni population genetics, or as a more informative way to quantify and characterize human worm populations.

Microsatellite typing reveals strong genetic structure of Schistosoma mansoni from localities in Kenya

Genetic diversity and population structure of seven populations of Schistosoma mansoni sampled in Kenya were assessed using five microsatellite markers. The mean number of alleles per locus, expected heterozygosity in Hardy-Weinberg equilibrium and pairwise F(ST) values ranged from 5.2 to 10.7, 0.5-0.8 and 3.6-27.3%, respectively. These data reveal that S. mansoni populations in Kenyan have relatively high levels of genetic diversity and is significantly differentiated. Our data combined with information on biogeography support the hypothesis that the strong genetic structure in Kenyan schistosomes is as a result of limited gene flow and large population sizes. Resistance to anthelminthics has not been reported among the Kenyan schistosomes, we hypothesize that this is probably due to the very little gene flow among populations, thereby limiting opportunities for the spread of rare alleles that might confer resistance to the drugs.

<i>Leishmania major-phlebotomus duboscqi</i> interactions: inhibition of anti-LPG antibodies and characterisation of two proteins with shared epitopes

OBJECTIVES

To assess the effect of monoclonal antibodies (MABS) raised against L. major derived LPG on L. major development in vitro and in its natural vector P. duboscqi. Also determine whether LPG molecule and the sand fly the gut lysates have shared epitopes.

DESIGN

A laboratory based study.

SETTING

Colony bred P. duboscqi sand flies and all other experiments were done under laboratory conditions.

METHODS

Laboratory reared sand flies were allowed to feed beneath a blood filled membrane feeder containing 1 x 10(6) amastigotes in 20 microl mixed with 0.5 ml of defibrinated rabbit blood with a 1:100 dilution of anti-LPG MABS. Control blood contained a similar number of amastigotes but no MABS. At least five female previously fed sand flies were later dissected on days two, four, and six post-feeding and examined for promastigote forms and parasite loads in the sand fly mid gut. In vitro, the same number of amastigotes in 100 microl complete Schneider's Drosophila medium was mixed in a 96 well plate with either 100 microl of 1:100 anti-LPG MABS, 1:1000 anti LPG MABS or undiluted sera from L. major infected mice. The control well contained a similar number of amastigotes but no antibodies added. Following an overnight incubation in a CO2 incubator at 37 degrees C and growth at 26 degrees C, parasites were assessed at 3, 6 and 24 hour intervals for changes in their developmental forms.

RESULTS

1:100 dilution of anti-LPG MABS when mixed with amastigotes were effective in reducing L. major development at the early log phase or procyclic stage both in vitro and within the sand fly (p<0.05). The control cultures or sand flies that fed on amastigotes alone and no MABS supported full parasite development up to the metacyclic stage. Results also showed that flies, which had fed on MABS, showed low parasitemia levels of 2+, compared to a high density of 4+ for their controls (p<0.5).

CONCLUSIONS

These findings showed that anti-LPG MABS were effective in reducing sand fly infections. This study also showed that P. duboscqi gut lysates and proteins present in L. major-derived LPG share two common proteins of molecular weights 105 kDa and 106 kDa. Further analysis of these individual proteins from the gut should be studied with a view of determining their vaccine potential.

Leishmania donovani-derived lipophosphoglycan plus BCG induces a Th1 type immune response but does not protect Syrian golden hamsters (Mesocricetus auratus) and BALB/c mice against Leishmania donovani

The efficacy of Leishmania donovani-derived lipophosphoglycan (LPG) plus Mycobacterium bovis Bacille Calmette-Guerin (BCG) as a vaccine candidate against visceral leishmaniosis in susceptible BALB/c mouse and Syrian golden hamster (Mesocricetus auratus) models was investigated. Following a triple vaccination with a total dose of 150 microl BCG plus 60 microg or 30 microg of LPG for hamsters and BALB/c mice respectively, there were no noticeable side effects both locally and systemically; implying that the molecule was safe at this dosage level. Vaccinated animals demonstrated an activation of both the humoral as well as cell-mediated responses to LPG, which correlated with resistance against the disease. Protection by LPG plus BCG, was however, poor as the remaining immunized animals showed disease progression leading to severity of the disease as illustrated by emaciation, mass loss and heavy splenic parasitaemia in hamsters. These data nevertheless suggest that it may be rewarding to further evaluate the potential of LPG as a vaccine candidate in leishmaniosis using other adjuvants, which may enhance its immunogenicity.

Phylogeography of Biomphalaria glabrata and B. pfeifferi, important intermediate hosts of Schistosoma mansoni in the New and Old World tropics

The historical phylogeography of the two most important intermediate host species of the human blood fluke Schistosoma mansoni, B. glabrata in the New World, and B. pfeifferi in the Old World, was investigated using partial 16S and ND1 sequences from the mitochondrial genome. Nuclear sequences of an actin intron and internal transcribed spacer (ITS)-1 were also obtained, but they were uninformative for the relationships among populations. Phylogenetic analyses based on mtDNA revealed six well-differentiated clades within B. glabrata: the Greater Antilles, Venezuela and the Lesser Antilles, and four geographically overlapping Brazilian clades. Application of a Biomphalaria-specific mutation rate gives an estimate of the early Pleistocene for their divergence. The Brazilian clades were inferred to be the result of fragmentation, due possibly to climate oscillations, with subsequent range expansion producing the overlapping ranges. Within the Venezuela and Lesser Antilles clade, lineages from each of these areas were estimated to have separated approximately 740 000 years ago. Compared to B. glabrata, mitochondrial sequences of B. pfeifferi are about 4x lower in diversity, reflecting a much younger age for the species, with the most recent common ancestor of all haplotypes estimated to have existed 880 000 years ago. The oldest B. pfeifferi haplotypes occurred in southern Africa, suggesting it may have been a refugium during dry periods. A recent range expansion was inferred for eastern Africa less than 100 000 years ago. Several putative species and subspecies, B. arabica, B. gaudi, B. rhodesiensis and B. stanleyi, are shown to be undifferentiated from other B. pfeifferi populations.

Schistosoma mansoni and Biomphalaria: past history and future trends

Schistosoma mansoni is one of the most abundant infectious agents of humankind. Its widespread distribution is permitted by the broad geographic range of susceptible species of the freshwater snail genus Biomphalaria that serve as obligatory hosts for its larval stages. Molecular phylogenetic studies suggest that Schistosoma originated in Asia, and that a pulmonate-transmitted progenitor colonized Africa and gave rise to both terminal-spined and lateral-spined egg species groups, the latter containing S. mansoni. Schistosoma mansoni likely appeared only after the trans-Atlantic dispersal of Biomphalaria from the Neotropics to Africa, an event that, based on the present African fossil record, occurred only 2-5 million years ago. This parasite became abundant in tropical Africa and then entered the New World with the slave trade. It prospered in the Neotropics because a remarkably susceptible and productive host, B. glabrata, was widely distributed there. Indeed, a snail similar to B. glabrata may have given rise to the African species of Biomphalaria. Schistosoma mansoni has since spread into other Neotropical Biomphalaria species and mammalian hosts. The distribution of S. mansoni is in a state of flux. In Egypt, S. mansoni has nearly completely replaced S. haematobium in the Nile Delta, and has spread to other regions of the country. A susceptible host snail, B. straminea, has been introduced into Asia and there is evidence of S. mansoni transmission in Nepal. Dam and barrage construction has lead to an epidemic of S. mansoni in Senegal, and the parasite continues its spread in Brazil. Because of competition with introduced aquatic species and environmental changes, B. glabrata and consequently S. mansoni have become less abundant on the Caribbean islands. Control of S. mansoni using praziquantel and oxamniquine has reduced global prevalence but control is difficult to sustain, and S. mansoni can develop tolerance/resistance to praziquantel, raising concerns about its future efficacy. Because of legitimate environmental concerns, snail control is unlikely to be an option in future control efforts. Global warming will impact the distribution of Biomphalaria and S. mansoni, but the magnitude and nature of the effects are poorly understood.

Evolutionary relationships and biogeography of Biomphalaria (Gastropoda: Planorbidae) with implications regarding its role as host of the human bloodfluke, Schistosoma mansoni

The wide geographic distribution of Schistosoma mansoni, a digenetic trematode and parasite of humans, is determined by the occurrence of its intermediate hosts, freshwater snails of the genus Biomphalaria (Preston 1910). We present phylogenetic analyses of 23 species of Biomphalaria, 16 Neotropical and seven African, including the most important schistosome hosts, using partial mitochondrial ribosomal 16S and complete nuclear ribosomal ITS1 and ITS2 nucleotide sequences. A dramatically better resolution was obtained by combining the data sets as opposed to analyzing each separately, indicating that there is additive congruent signal in each data set. Neotropical species are basal, and all African species are derived, suggesting an American origin for the genus. We confirm that a proto-Biomphalaria glabrata gave rise to all African species through a trans-Atlantic colonization of Africa. In addition, genetic distances among African species are smaller compared with those among Neotropical species, indicating a more recent origin. There are two species-rich clades, one African with B. glabrata as its base, and the other Neotropical. Within the African clade, a wide-ranging tropical savannah species, B. pfeifferi, and a Nilotic species complex, have both colonized Rift Valley lakes and produced endemic lacustrine forms. Within the Neotropical clade, two newly acquired natural hosts for S. mansoni (B. straminea and B. tenagophila) are not the closest relatives of each other, suggesting two separate acquisition events. Basal to these two species-rich clades are several Neotropical lineages with large genetic distances between them, indicating multiple lineages within the genus. Interesting patterns occur regarding schistosome susceptibility: (1) the most susceptible hosts belong to a single clade, comprising B. glabrata and the African species, (2) several susceptible Neotropical species are sister groups to apparently refractory species, and (3) some basal lineages are susceptible. These patterns suggest the existence of both inherent susceptibility and resistance, but also underscore the ability of S. mansoni to adapt to and acquire previously unsusceptible species as hosts. Biomphalaria schrammi appears to be distantly related to other Biomphalaria as well as to Helisoma, and may represent a separate or intermediate lineage.

PCR-RFLP analysis of the ITS2 region to identify Schistosoma haematobium and S. bovis from Kenya

Schistosoma haematobium, primarily a human parasite, and the closely related Schistosoma bovis from ruminants, are sympatric in many African countries such as Kenya. Because these two species 1) can inhabit the same Bulinus snails, 2) may be found in the same freshwater habitat, and 3) have morphologically similar cercariae, better means are needed to tell them apart. The second internal transcribed spacer (ITS2) region of the ribosomal gene complex (rDNA) of recent Kenyan isolates of both species was sequenced and found to be a 98% match. The S. bovis sequences were nearly identical (99%) to conspecific sequences from Niger; the S. haematobium sequences were nearly identical (99%) to conspecific sequences from Egypt, Mali, and Niger. Restriction fragment length polymorphism (RFLP) analysis of a 480 base pair (bp) PCR product containing the ITS2 region using two restriction enzymes, Taq1 and Sau3A1, yielded species-specific fragment patterns that allowed successful identification of a single S. haematobium cercaria. The protocol outlined here is useful in providing a rapid, one-day identification of S. haematobium (and likely S. bovis) cercariae (the infective larval stage) and/or other life cycle stages in a basic molecular biology laboratory. By helping to determine whether schistosome-infected bulinid snails in a particular body of water are transmitting a human or an animal schistosome, or both, this analysis will aid in disease control and in ongoing epidemiological studies.

Impact of the crayfish Procambarus clarkii on Schistosoma haematobium transmission in Kenya

The Louisiana red swamp crayfish, Procambarus clarkii, which was introduced into east Africa in the 1950s or 1960s, has since widely dispersed. Previous work by our group has shown that P. clarkii can reduce populations of the molluscan intermediate hosts of human schistosomes through predatory and competitive interactions. Here, we investigate whether crayfish can reduce populations of Bulinus africanus and consequently, Schistosoma haematobium prevalence in school children. Children from 6 primary schools in the Machakos and Kitui Districts of Kenya were selected for study. Schools were divided into 3 experimental-control pairs. At experimental schools, crayfish were introduced into nearby aquatic habitats harboring Bulinus africanus snails and serving as S. haematobium transmission sites. Snail habitats near control schools did not receive crayfish. Six months after crayfish introduction, all infected children were treated with praziquantel. Children were then monitored quarterly for 2 years, at which time infection and reinfection rates were compared statistically between the paired schools. In one such pair, crayfish failed to establish, resulting in neither snail control nor a reduction in transmission. At the second pair of schools, the numbers of snails were decreased by the presence of crayfish, but a clear difference in infection rates in children could not be detected, primarily because drought conditions kept overall transmission rates low. At the third school pair, crayfish established well in experimental habitats, snail numbers decreased precipitously, and children at the experimental school were significantly less likely to acquire S. haematobium infections than children at the control school. Our results indicate that under certain environmental circumstances, P. clarkii exerts a significant impact on the transmission of human schistosomiasis in Kenya. Important questions remain regarding the impact of P. clarkii on Kenyan freshwater ecosystems, not the least of which is its potential to significantly influence the epidemiology of schistosomiasis in east Africa.

Predation of aquatic stages of Anopheles gambiae by the Louisiana red swamp crawfish (Procambarus clarkii)

Laboratory experiments lasting 1-3 days were conducted in 10-liter glass aquaria to evaluate the ability of the Louisiana red swamp crawfish (Procambarus clarkii [Decapoda: Cambaridae]) to consume the aquatic forms of mosquitoes. With Anopheles gambiae as the target species, significantly fewer mosquito larvae or pupae survived in the presence of either juvenile or adult crawfish, relative to conditions without crawfish, regardless of whether crawfish had alternative food or not. When alternative food was excluded, juvenile and adult crawfish had a comparable ability to consume mosquito larvae. However, when alternative food was available, adult crawfish consumed significantly fewer mosquito larvae than did juveniles. In the case of pupae, juvenile crawfish consumed significantly more mosquito pupae than did the adults when alternative food was excluded. No significant difference, relative to controls, was found in the proportion of mosquito pupae surviving when adult crawfish had alternative food. Results of the present study show that P. clarkii has the ability to consume the aquatic forms of anopheline mosquitoes and, therefore, may have an impact on populations of pathogen-transmitting mosquitoes in an area of Kenya where the crawfish has become common.

Experimental control of the schistosome-transmitting snail Biomphalaria pfeifferi by the ampullariid snail Pila ovata

Adults of the African ampullariid snail Pila ovata were examined for their ability to control laboratory populations of the pulmonate snail Biomphalaria pfeifferi, a widespread, intermediate host of the human pathogen Schistosoma mansoni in sub-Saharan Africa. In a 6-week experiment conducted in large (100 x 60 x 60 cm) outdoor tanks containing floating macrophytes (Nymphaea caerula) and initially set up with one adult ampullariid for every three adult pulmonates, the numbers of B. pfeifferi egg masses were always about half those in similar tanks without P. ovata. Although, by week 6, the numbers of B. pfeifferi in the control tanks (without ampullariids) had increased 5-fold, from an initial mean of 30 snails/tank, there was no significant increase in the numbers of B. pfeifferi in the experimental tanks (containing ampullariids). Results of experiments conducted in indoor glass aquaria indicated that adult P. ovata rapidly attacked egg masses or neonates (< 2.5 mm shell diameter) of B. pfeifferi but had no effect on the adults. The adult ampullariids also significantly decreased cover by floating macrophytes over a 6-week period compared with that in similar but ampullariid-free aquaria. This decrease in plant cover is relevant to biological control of the schistosome vectors as macrophytes serve as food, shelter and oviposition sites for pulmonate snails. The present result indicate the ability of P. ovata to inhibit multiplication of B. pfeifferi populations, at least under laboratory conditions, both directly, through predation, and indirectly, by competition for resources. Pila ovata may therefore prove useful in the biological control of medically important, pulmonate snails.

Civil turmoil in Africa: a potential setback in the fight against diseases

Africa continues to face enormous challenges in her efforts to provide health care and to control diseases, particularly in the face of dwindling financial resources, inadequate facilities and supplies, and increased demand for health services. The situation is further compounded by new challenges created by the emergence of new infections, re-emergence of diseases hitherto thought to have been put under control, changes in epidemiological patterns and manifestations of existing diseases. All these factors have an overall effect of increasing disease incidences, morbidity and mortality, thus, hindering efforts to control disease in the continent.A new pattern is also emerging which is likely to be a major setback in the control and fight against infectious diseases in Africa. In recent years, several parts of Africa have experienced civil disruptions that have resulted in the displacement of large numbers of people. The displaced end up in the refugee camps either within their own countries or across the borders, in neighboring countries. Such disruptions are likely to become a setback in the fight against diseases in a number of ways. 1. Besides deaths and injuries resulting from the physical confrontations in such situations, the displaced people, who end up in camps, live under conditions characterized by overcrowding, poor sanitation, inadequate food and water. Such conditions favour disease outbreaks, and the people live under constant threat of contracting diseases. Particularly at risk are vulnerable groups such as children, pregnant mothers, and elderly. Inspite of efforts made, usually through internationally funded agencies, to provide food and health care, diseases outbreaks are common in camps for the displaced people. 2. In many instances, the displaced end up in a neighboring country, far away from the actual focus of trouble. Diseases outbreak affecting people living in camps will most likely spread to the general population of the host country. Infectious diseases spread rapidly from the initial focus of outbreak, often with devastating results. Usually, the already overburdened health care authorities of the host country will be expected to respond to such a crisis. However, because of the meager resources available for health care and diseases control in many countries, it is always difficult to adequately deal with unexpected disease outbreaks. The situation may become even more complicated if the infectious agents display unusual patterns such as high virulence or failure to respond to commonly used drugs. In other words, it is possible that known infections with unusual characteristics or manifestations may be introduced into an area, and spread rapidly to other parts of the country, and probably beyond. Morbidity and mortality associated with such outbreaks is likely to be high and devastating. 3. There are always fear that migration of people from one region to another may lead to the introduction of diseases into geographical areas they did not exist before. Migration of large number of people into a new area may accelerate spread of diseases. As civil turmoil often affects large numbers of people, such an event is likely to have a greater impact in terms of disease spread. 4. The displaced people will have lived in a neighboring country for several months or even years, during which time they will have acquired new infections, most probably, with different characteristics from those in the home country. Thus, they may also introduce new diseases or new strains of disease-causing organisms, acquired from the host country into their home countries on return, once the situation returns to normal. Control of new diseases or strains of infections agent could pose challenges to the health authorities of their home countries. In other words, civil disruptions cold lead to diseases outbreaks and rapid spread of known or new diseases, factors that will increase disease incidences, morbidity and mortality on the continent. This is a major setback in the fight against diseases in Africa, particularly in the face of dwindling resources required for health care and diseases control. One way in which potential spread of diseases could be controlled in situations of turmoil is through rapid response in the provision of food, shelter, medicine and sanitary facilities to the displaced. Adequate knowledge of possible diseases that are likely to be encountered in such communities is essential and health care personnel must be prepared to face these challenges. Research into health issues of the displaced persons in essential in providing solutions associated with turmoil. Health research institutions have a key role to play in this regard. The expertise and facilities available in such institutions could be used, for instance, to accurately identify infectious agents, to detect unusual manifestations of diseases or the infectious agents, both within the refugee camps and beyond. Such initiatives will complement the efforts of health care agencies and the country health care institutions. In this issue, Magambo et al (pp149-156) have attempted to look at health problems of people living in southern Sudan, an area that has, for along time, experienced civil turmoil. Understanding of health problems of southern Sudan will not only provide a basis for instituting diseases control measures in this region, but will also provide a basis for instituting preventing measures within the affected country, and in the neighboring regions.

Enhancement of eosinophil-mediated cytotoxicity to schistosomula of Schistosoma mansoni by autologous mononuclear cells from patients

Adherent mononuclear cells (monolayer), when co-cultured with autologous peripheral blood eosinophils isolated from patients treated for Schistosoma mansoni infections, enhanced the eosinophil-mediated killing of antibody coated schistosomula. The monolayer increased the activity of the eosinophils by 225%, and was observed in 80% of the patients studied. Heat labile factors other than complement, present in immune serum, further enhanced the ability of eosinophils to kill schistosomula in the presence of the monolayer. On their own the adherent cells did not mediate obvious damage to the parasite. Eosinophils that had been pre-incubated with the monolayer (100 mins) and tested separately, killed equal numbers of schistosomula as in the co-culture assay; this excludes the possibility of concurrent schistosomula cytotoxicity by the two cell populations. The ability of the monolayer to activate eosinophils was not altered by inhibitors of protein synthesis. The monolayer was largely consistent of monocytes as demonstrated by an over 96% positive staining for non-specific esterases.

Immune responses after treatment for Schistosoma mansoni infections

The changes in the immune responses of patients before and at 3 weeks after treatment with anti-schistosomal drugs were investigated. Lymphocyte responses to Concanavalin A and to worm antigens were inhibited after treatment, whereas responses to cercarial and egg antigens remained unchanged. Eosinophil levels were significantly elevated after treatment and were positively correlated with the increase in anti-worm antibodies (r = 0.587), and negatively associated with anti-egg antibodies (r = -0.727). Although the eosinophil-dependent cytotoxicity to schistosomula was not significantly enhanced after treatment, some increased killing was evident of half the patients (7/15). On the other hand, the ability of adherent mononuclear cells to stimulate eosinophil functions was markedly enhanced by treatment (P less than 0.001). These studies suggest that treatment may enhance some of the potentially protective host's immune mechanisms.

Control of schistosome-transmitting snails in Kenya by the North American crayfish Procambarus clarkii

Snail-transmitted trematode parasites such as schistosomes and liver flukes assume considerable medical and veterinary significance in tropical Africa. We have observed a strong negative association between the presence of medically important pulmonate snails and the crayfish Procambarus clarkii in freshwater habitats in Kenya. This crayfish, introduced into Kenya around 1970, readily consumes these snails in the laboratory. Field enclosure experiments indicate that crayfish exert a significant negative impact on the abundance of Biomphalaria pfeifferi, the intermediate host of the human blood fluke Schistosoma mansoni. It is likely that P. clarkii will continue to spread naturally in Kenya and that schistosome-transmitting snails will be excluded or reduced in numbers where crayfish are present. Procambarus clarkii may represent an alternative, biological means of snail control in East Africa.

Effect of oltipraz on the susceptibility of adult Schistosoma mansoni to killing by mouse peritoneal exudate cells

Incubation of the adult Schistosoma mansoni with the anti-schistosomal compound oltipraz (OPZ) (40 nM) resulted in a significant decrease in schistosome-reduced glutathione (GSH), a thiol compound which may have a role in protection against oxidant-mediated damage. A significant proportion (20-47%) of worms treated with OPZ became susceptible to in vitro killing by zymosan-stimulated peritoneal exudate cells from mice infected with S. mansoni or inoculated with Bacillus Calmette Guérin (BCG). Killing of the worms was partially inhibited by the addition to the assay system of exogenous glutathione peroxidase with GSH but not by superoxide dismutase. These results suggested that killing of parasites exposed to the drug was partly mediated by cell-generated hydrogen peroxide. They indicate also that depletion of schistosome GSH levels could render the parasites susceptible to killing by oxidative mechanisms, and suggest that there is potential in exploiting schistosome oxidant defense systems and reactive oxygen byproducts in the treatment of schistosomiasis. Inhibition of schistosome oxidant defense systems with drugs may render the parasites susceptible to killing by reactive oxygen byproducts of effector cells.

Glutathione redox state, lipid peroxide levels, and activities of glutathione enzymes in oltipraz-treated adult Schistosoma mansoni

A decrease in reduced glutathione (GSH) levels in adult Schistosoma mansoni exposed in vitro to the antischistosomal drug oltipraz (OPZ) (20-60 nM) was accompanied by a significant increase in oxidized glutathione (GSSG) levels. The total glutathione (GSH + GSSG) levels also diminished in drug-treated parasites. The activities of the parasite glutathione peroxidase (GPO), utilizing cumene hydroperoxide as a substrate, and glutathione S-transferase (GST), measured 18 hr after in vitro incubation with the drug, were elevated significantly, but there were no significant alterations in the activities of the GPO, utilizing H2O2, or glutathione reductase (GR). Drug-treated worms showed increased lipid peroxidation. In vivo, the proportion of the worms recovered from infected mice given OPZ (100 mg/kg body wt) gradually declined with time, to about 30% of that recovered from infected untreated control mice by day 14 after drug administration, and consisted predominantly of male worms. Accompanying this significant decline in the proportion of worms recovered were significant decreases in the activities of the enzymes GR and GST in drug-exposed worms. On the other hand, a slight initial increase in the GPO activity with cumene hydroperoxide was followed by a return to control values, and the GPO activity with H2O2 was decreased only slightly with time. Interestingly, the 4-hydroxyalk-2-enal aldehydes, known products of lipid peroxidation, inhibited the GST reaction with 1-chloro-2,4-dinitrobenzene (CDNB). The OPZ-induced changes in S. mansoni could increase parasite susceptibility to oxidative attack by host phagocytes, and are probably linked with the antischistosomal action of the drug in vivo.

Molluscicidal activity of Solanum aculeatum (family: Solanaceae) berries against Biomphalaria pfeifferi, Bulinus globosus and Lymnaea natalensis

Aqueous suspensions of powder of sun- or freeze-dried berries of the plant Solanum aculeatum (Family Solanaceae), indigenous in Kenya, were tested for molluscicidal activity against Biomphalaria pfeifferi, Bulinus globosus and Lymnaea natalensis under laboratory conditions. One hundred or 50 mg powder L-1 of sun- or freeze-dried berries killed over 60% of the test B. pfeifferi, Bul. globosus and L. natalensis. Whereas 25 mg L-1 of the sun dried material killed less than 60% of the test snails, similar concentrations of the freeze dried molluscicide produced 60-80% mortality in the snails, under similar conditions. Using L. natalensis as the target snail, it was shown that the freeze dried material was more potent than the freeze-dried berries of S. incanum, S. nigrum or leaves of Polygonum senegalensis (Family Polygonaceae), all present in Kenya, and known to possess molluscicidal properties. The powdered material retained molluscicidal activity even after several months storage at room temperature. These findings suggest that S. aculeatum is a potent plant molluscicide, and has the potential for the control of vectors of schistosomiasis and fascioliasis in Kenya.

Depression of hydrogen peroxide dependent killing of schistosomula in vitro by peritoneal exudate cells from Schistosoma mansoni infected mice

Peritoneal exudate cells from mice infected with Schistosoma mansoni (S-PEC) can kill a small proportion of schistosomula in vitro in the presence of immune serum. S-PEC produce a low level of respiratory burst. However, schistosomula mortality in their presence is not reduced when exogenous antioxidants are added, suggesting that with S-PEC, oxidative killing may not be important. Hydrogen peroxide (H2O2) and superoxide production by S-PEC, and cells from Bacillus Calmette-Guerin (BCG) and thioglycollate (THGL) injected mice, nonspecifically stimulated with opsonized zymosan, were measured. Levels of H2O2 produced by S-PEC were significantly lower than BCG or THGL PEC, and were below the threshold for schistosomula killing. This correlated with lower levels of cell-mediated killing of schistosomula in vitro by S-PEC than by BCG-PEC. Superoxide levels, however, were similar between the 3 cell populations. It therefore appears that the efficiency of PEC to kill schistosomules in vitro correlates with H2O2 rather than superoxide levels. It was found that there was a sharp concentration threshold in H2O2 mediated killing of schistosomula. A depression in the levels of H2O2 produced may be a mechanism by which the parasite can partially evade the host immune system.