Allele-specific antibodies to Plasmodium falciparum merozoite surface protein-2 and protection against clinical malaria.

IgG and IgG3 antibodies to merozoite surface protein-2 (MSP-2) of Plasmodium falciparum have been associated with protection from clinical malaria in independent studies. We determined whether this protection was allele-specific by testing whether children who developed clinical malaria lacked IgG/IgG3 antibodies specific to the dominant msp2 parasite genotypes detected during clinical episodes. We analysed pre-existing IgG and IgG1/IgG3 antibodies to antigens representing the major dimorphic types of MSP-2 by ELISA. We used quantitative real-time PCR to determine the dominant msp2 alleles in parasites detected in clinical episodes. Over half (55%, 80/146) of infections contained both allelic types. Single or dominant IC1- and FC27-like alleles were detected in 46% and 42% of infections respectively, and both types were equally dominant in 12%. High levels of IgG/IgG3 antibodies to the FC27-like antigen were not significantly associated with a lower likelihood of clinical episodes caused by parasites bearing FC27-like compared to IC1-like alleles, and vice versa for IgG/IgG3 antibodies to the IC1-like antigen. These findings were supported by competition ELISAs which demonstrated the presence of IgG antibodies to allele-specific epitopes within both antigens. Thus, even for this well-studied antigen, the importance of an allele-specific component of naturally acquired protective immunity to malaria remains to be confirmed.

Index of potential contamination: Schistosoma haematobium infections in school children in the Ashanti Region of Ghana.

BACKGROUND: Children are acknowledged as the most vulnerable group to urinary schistosomiasis. OBJECTIVE: To determine the age group(s) of school children considered as the major contributor(s) to the spread of the disease. DESIGN: Observational/Prospective (concurrent) studies. SETTING: Barekuma, Aninkroma and Hiawo Besease, riparian communities in the Ashanti Region of Ghana. SUBJECTS: Hundred children each were randomly selected from Barekuma and Hiawo Besease basic schools with population age profiles between 4 and 18 years. They were then categorised into 4-6, 7-9, 10-12, 13-15 and 16-18 years, respectively. However, at Aninkroma, the entire school population of 119 pupils, aged between 4 and 15 years were used. They were similarly grouped into 4-6, 7-9, 10-12 and 13-15 years, respectively. Urine filtration method was used for isolation and enumeration of S. haematobium eggs from the subjects. The subjects were monitored through repetition of the experiment at fortnightly intervals over four weeks. MAIN OUTCOME MEASURES: Corrected relative Index of Potential Contamination (IPC) expressed as percentage after calculating the crude IPC. RESULTS: The age groups with the highest relative IPCs at Barekuma, Aninkroma and Hiawo Besease were 7-9, 10-12 and 13-15 years, registering 35.6%, 53.9% and 57.7%, respectively. The age group 4-6 years consistently had the lowest IPC in all the communities. CONCLUSION: The age groups 7-9,10-12 and 13-15 years were considered to be the major transmitters of the disease in the communities.

Management of incomplete abortion in South African public hospitals.

OBJECTIVE: To describe the current management of incomplete abortion in South African public hospitals and to discuss the extent to which management is clinically appropriate. DESIGN: A multicentre, prospective descriptive study. SETTING: South African public hospitals that manage gynaecological emergencies. SAMPLE: Hospitals were selected using a stratified random sampling method. All women who presented to the above sampled hospitals with incomplete abortion during the three week data collection period in 2000 were included. METHODS: A data collection sheet was completed at the time of discharge for each woman admitted with a diagnosis of incomplete, complete, missed or inevitable abortion during the study period. Information gathered included demographic data, clinical signs and symptoms at admission, medical management, surgical management, anaestetic management, use of blood products and antibiotics and complications. Three clinical severity categories were used for the purpose of data analysis and interpretation. MAIN OUTCOME MEASURES: Detail of medical management, detail of surgical management, use of blood products and antibiotics, methods of analgesia and anaesthesia used, and use of abortifacients. RESULTS: There is a trend towards low cost technology such as the use of manual vacuum aspiration and sedation anaesthesia; however, this is mainly limited to the better resourced tertiary hospitals linked to academic units. The use of antibiotics and blood products has decreased but much of the use is inappropriate. The use of abortifacients does include some use of misoprostol but merely as an adjunct to surgical evacuation. CONCLUSIONS: The management of incomplete abortion remains a problem in South Africa, a low income country that is still managing a common clinical problem with costly interventions. The evidence of a trend towards low cost technology is promising, albeit limited to tertiary centres. This study has given us information as how to best address this problem. More training in low cost methods is needed, targeting in particular the district and regional hospitals, and reinforced by skills training focussed mainly on undergraduates and midwife post-abortion care programmes.

Working with public sector clinics to provide adolescent-friendly services in South Africa.

Health care facilities can play an important role for adolescents in preventing health problems, in promoting sexual and reproductive health and in shaping positive behaviours. Extensive research has established that South African public health facilities are failing to provide adolescent-friendly health services. The National Adolescent-Friendly Clinic Initiative (NAFCI) is an accreditation programme designed to improve the quality of adolescent health services at the primary care level and strengthen the public sector's ability to respond to adolescent health needs. The key objectives of the programme are to make health services more accessible and acceptable to adolescents, establish national standards and criteria for adolescent health care in clinics throughout the country, and build the capacity of health care workers to provide quality services. One of the indicators for success of NAFCI will be increased utilisation of public sector clinics by adolescents. NAFCI is an integral component of the largest, most innovative, public health programme ever launched in South Africa, loveLife. Achieving NAFCI accreditation involves clinic self-appraisals, quality improvements, external assessments and award of achievement stars. NAFCI is currently being piloted in ten government clinics in South Africa.

Structural integrity of the female condom after multiple uses, washing, drying, and re-lubrication.

Establishing the safety of re-using the female condom could significantly increase women's access to barrier methods especially in poorer countries. In this study, the structural integrity of female condoms was tested (n = 295) after multiple acts of vaginal intercourse. Fifty women were recruited to the study. Each woman re-used one condom up to eight times and washed, dried, and re-lubricated between each use. Structural integrity was measured using standard quality control testing; water-leakage, air-burst, and seam tensile strength. All results were compared to the United States Food and Drug Administration (US FDA) standards for an unused female condom. The results of the structural integrity tests for all cycles were above the FDA minimum standards for seam strength and burst tests. There was no deterioration detected in condoms used 8 times when compared to new female condoms in these tests. Five holes were detected by the water leakage test across all cycles, of which three were detected by the subjects themselves and reported to the investigators, therefore, giving a breakage rate of 1.7%. The holes were not associated with increased number of uses. This study provides further evidence that suggests the structural integrity of the female condom after multiple use is still within FDA minimum standards, although random holes resulting from handling occur infrequently with the re-use procedure.

Frequent and persistent, asymptomatic Plasmodium falciparum infections in African infants, characterized by multilocus genotyping.

To determine the duration and complexity of naturally acquired Plasmodium falciparum infections in small children, a longitudinal cohort study of 143 newborns was conducted in coastal Ghana. On average, children experienced 2 episodes of infection in their first 2 years of life, the median duration of an asymptomatic infection was <4 weeks, and estimates of the mean number of parasite genotypes per infection were 1.15-2.28. Nevertheless, 40% of the children experienced infections lasting 5 months old. The ability of very young children to clear or control malaria infections indicates the presence of effective innate or immune antiparasite mechanisms.

The acceptability of reuse of the female condom among urban South African women.

This study assessed whether reuse of the female condom was acceptable among two groups of women in central Johannesburg, South Africa, who were taking part in two separate studies of female condom reuse. The first group consisted of women (aged 17 to 43 years) attending a family planning/sexually transmitted infections (STIs) clinic who were participating in a cross-sectional survey of the acceptability of female condoms reuse (n = 100). The second group included women (aged 18-40 years) at high risk for STI (80% self-declared sex workers) who were taking part in an ongoing cohort study to investigate the safety of reuse of the female condom through a structural integrity and microbial retention study (n = 50). Among women participating in the acceptability study, 83% said that they would be willing to reuse the female condom, and 91% thought the idea of reuse of the female condom was acceptable. All women taking part in the safety of reuse study and who reused the female condom up to seven times (n = 49) reported that the steps involved in reusing the device were easy to perform and acceptable. All 49 women said they would reuse the female condom at least once, while 45% said they would use it a maximum of seven or eight times. From the results of the interviews with both study groups, it can be concluded that, among women in a South African urban environment who have used a male and/or female condom, the concept of reuse of the female condom is acceptable and thought to be a good idea.

Lack of association between maternal antibody and protection of African infants from malaria infection.

Maternally derived antibodies are believed to protect infants against infection, but there is little direct evidence for a protective role of passively acquired antibodies against malaria. A longitudinal study of malaria infection in 143 infants was conducted in a region of southern Ghana where Plasmodium falciparum is endemic. Infants born in the high-transmission season were less likely to become infected in the first 20 weeks of life than children born in the low-transmission season. Plasma, obtained at birth, was tested for immunoglobulin G (IgG) and IgG subclasses to P. falciparum schizonts and recombinant circumsporozoite antigen, MSP-1(19), MSP-2, AMA-1, and Pf155 (also called ring-infected erythrocyte surface antigen). Antibody levels at birth were not associated with resistance to malaria infection. On the contrary, antibodies at birth were positively associated with infection, indicating that high levels of maternally derived antibodies represent a marker for intensity of exposure to malaria infection in infants. However, all five children who experienced high-density infections (>100 parasites/microl of blood) were seronegative for MSP-1(19) at the time of infection.

A family of secreted mucins from the parasitic nematode Toxocara canis bears diverse mucin domains but shares similar flanking six-cysteine repeat motifs.

Infective larvae of the parasitic nematode Toxocara canis secrete a family of mucin-like glycoproteins, which are implicated in parasite immune evasion. Analysis of T. canis expressed sequence tags identified a family of four mRNAs encoding distinct apomucins (Tc-muc-1-4), one of which had been previously identified in the TES-120 family of glycoproteins secreted by this parasite. The protein products of all four cDNAs contain signal peptides, a repetitive serine/threonine-rich tract, and varying numbers of 36-amino acid six-cysteine (SXC) domains. SXC domains are found in many nematode proteins and show similarity to cnidarian (sea anemone) toxins. Antibodies to the SXC domains of Tc-MUC-1 and Tc-MUC-3 recognize differently migrating members of TES-120. TES-120 proteins separated by chromatographic methods showed distinct amino acid composition, mass, and sequence information by both Edman degradation and matrix-assisted laser desorption ionization/time of flight mass spectrometry on peptide fragments. Tc-MUC-1, -2, and -3 were shown to be secreted mucins with real masses of 39.7, 47.8, and 45.0 kDa in contrast to their predicted peptide masses of 15.7, 16.2, and 26.0 kDa, respectively. The presence of SXC domains in all mucin products supports the suggestion that the SXC motif is required for mucin assembly or export. Homology modeling indicates that the six-cysteine domains of the T. canis mucins adopt a similar fold to the sea anemone potassium channel-blocking toxin BgK, forming three disulfide bonds within each subunit.

Toxocara canis: genes expressed by the arrested infective larval stage of a parasitic nematode.

Toxocara canis is a widely distributed nematode parasite which reaches maturity in dogs. However, eggs voided by canid animals are infective to a very wide range of paratenic hosts including humans. In noncanid hosts, infective larvae emerge from the eggs and invade the soft tissues, often entering the brain and musculature. Such larvae may remain for many months or years in these tissues without further growth or differentiation, and yet appear to evade inflammatory reactions or other modes of immune attack. To understand the ability of T. canis larvae to survive in the immunocompetent host, we have undertaken a molecular analysis of the major genes expressed at this stage. By a combination of protein sequencing, gene identification, and expressed sequence tag (EST) analysis we have characterised a range of potentially important gene products from this parasite. Some of these are homologues of prominent mammalian proteins such as C-type lectins (represented by the secreted products TES-32 and TES-70), and mucins (TES-120), and additional products show strong similarities to known cysteine proteases, phosphatidylethanolamine-binding proteins and other ligands. A number of these proteins include a conspicuous 36-amino acid motif containing six cysteines. This domain (termed NC6 or SXC) appears to be an evolutionarily mobile module, which in T. canis is combined with a spectrum of diverse functional domains in different genes. In addition, we have identified a set of novel gene sequences that show no resemblance to any genes encoded by the free-living nematode C. elegans. Four of these are designated abundant novel transcripts, and collectively these account for nearly 20% of the cDNA isolated from the arrested infective stage. Such parasite-specific genes expressed at a high level by a stage that shows remarkable endurance may represent critical products necessary for the success of the parasitic mode of life.

A novel C-type lectin secreted by a tissue-dwelling parasitic nematode.

Many parasitic nematodes live for surprisingly long periods in the tissues of their hosts, implying sophisticated mechanisms for evading the host immune system. The nematode Toxocara canis survives for years in mammalian tissues, and when cultivated in vitro, secretes antigens such as TES-32. From the peptide sequence, we cloned TES-32 cDNA, which encodes a 219 amino-acid protein that has a domain characteristic of host calcium-dependent (C-type) lectins, a family of proteins associated with immune defence. Homology modelling predicted that TES-32 bears remarkable structural similarity to mammalian immune-system lectins. Native TES-32 acted as a functional lectin in affinity chromatography. Unusually, it bound both mannose- and galactose-type monosaccharides, a pattern precluded in mammalian lectins by a constraining loop adjacent to the carbohydrate-binding site. In TES-32, this loop appeared to be less obtrusive, permitting a broader range of ligand binding. The similarity of TES-32 to host immune cell receptors suggests a hitherto unsuspected strategy for parasite immune evasion.

Identification of abundantly expressed novel and conserved genes from the infective larval stage of Toxocara canis by an expressed sequence tag strategy.

Larvae of Toxocara canis, a nematode parasite of dogs, infect humans, causing visceral and ocular larva migrans. In noncanid hosts, larvae neither grow nor differentiate but endure in a state of arrested development. Reasoning that parasite protein production is orientated to immune evasion, we undertook a random sequencing project from a larval cDNA library to characterize the most highly expressed transcripts. In all, 266 clones were sequenced, most from both 3' and 5' ends, and similarity searches against GenBank protein and dbEST nucleotide databases were conducted. Cluster analyses showed that 128 distinct gene products had been found, all but 3 of which represented newly identified genes. Ninety-five genes were represented by a single clone, but seven transcripts were present at high frequencies, each composing >2% of all clones sequenced. These high-abundance transcripts include a mucin and a C-type lectin, which are both major excretory-secretory antigens released by parasites. Four highly expressed novel gene transcripts, termed ant (abundant novel transcript) genes, were found. Together, these four genes comprised 18% of all cDNA clones isolated, but no similar sequences occur in the Caenorhabditis elegans genome. While the coding regions of the four genes are dissimilar, their 3' untranslated tracts have significant homology in nucleotide sequence. The discovery of these abundant, parasite-specific genes of newly identified lectins and mucins, as well as a range of conserved and novel proteins, provides defined candidates for future analysis of the molecular basis of immune evasion by T. canis.