An assessment of rural women's knowledge, constraints and perceptions on cervical cancer screening: the case of two districts in Zimbabwe

This paper gives a sociological and anthropological insight into the rural women's perceptions and understanding of cervical symptomatology, screening and cancer. Qualitative data was collected through in-depth interviews and focus group discussions with women and health personnel. Quantitative data was obtained through questionnaires administered to 356 women from Mutoko and Shurugwi districts. The study revealed that cervical cancer is a disease that is of concern among health practitioners and women. 95.78% of the interviewed women had never gone for screening and had little knowledge about the various aspects of the disease in terms of causes, prevention and treatment. The study made four recommendations: the need for national screening policy and programme to be put in place, health education to women about cervical cancer, use of VIA in low resource settings and sensitisation of women about the availability of screening facilities in the districts where programmes are in place.

HIV infection and reproductive health in teenage women orphaned and made vulnerable by AIDS in Zimbabwe

AIDS has increased the number of orphans and vulnerable children (OVCs) in sub-Saharan Africa who could suffer detrimental life experiences. We investigated whether OVCs have heightened risks of adverse reproductive health outcomes including HIV infection. Data on HIV infection, sexually transmitted infection (STI) symptoms and pregnancy, and common risk factors were collected for OVCs and non-OVCs in a population survey of 1523 teenage children in eastern Zimbabwe between July 2001 and March 2003. Multivariate logistic regression was used to test for statistical association between OVC status, adverse reproductive health outcomes and suspected risk factors. Amongst women aged 15-18 years, OVCs had higher HIV prevalence than non-OVCs (3.2% versus 0.0%; p = 0.002) and more common experience of STI symptoms (5.9% versus 3.3%; adjusted odds ratio = 1.75, 95% CI 0.80-3.80) and teenage pregnancy (8.3% versus 1.9%; 4.25, 1.58-11.42). OVCs (overall), maternal orphans and young women with an infected parent were more likely to have received no secondary school education and to have started sex and married, which, in turn, were associated with poor reproductive health. Amongst men aged 17-18 years, OVC status was not associated with HIV infection (0.5% versus 0.0%; p = 1.000) or STI symptoms (2.7% versus 1.6%; p = 0.529). No association was found between history of medical injections and HIV risk amongst teenage women and men. High proportions of HIV infections, STIs and pregnancies among teenage girls in eastern Zimbabwe can be attributed to maternal orphanhood and parental HIV. Many of these could be averted through further female secondary school education. Predicted substantial expanded increases in orphanhood could hamper efforts to slow the acquisition of HIV infection in successive generations of young adults, perpetuating the vicious cycle of poverty and disease.

Contrasting cellular responses in Schistosoma haematobium infected and exposed individuals from areas of high and low transmission in Zimbabwe

The study compared cytokine profiles of individuals from two areas with different transmission patterns for Schistosoma haematobium. One area was a high transmission (HT) while the other was a low transmission (LT) area for S. haematobium. Observations on cellular immune responses were made on stimulated peripheral blood mononuclear cells (PBMC), which were collected pre-treatment, then at 12 and 18 months post treatment. Stimulation was with schistosome worm and egg antigens and a mitogen, phaetohaemaglutinin (PHA). Observations were made on PBMC proliferation and the profiles of cytokine produced over a 5-day incubation period. The two distinct areas showed significant differences on both levels of proliferation and cytokine production for all the measured classes (IL-4, IL-5, IL-10 and IFN-gamma). PBMC from individuals from the LT area had high levels of proliferation but low cytokine production to both antigen stimulants while PBMC from individuals from the HT area showed low levels of proliferation but high cytokine production levels. Prior to treatment, individuals not excreting schistosome ova in the HT area had higher levels of proliferation to the stimulants, than the infected individuals. However, after treatment re-infected individuals showed high levels of proliferation. Before treatment, both infected and uninfected groups showed low and similar ratios, respectively, of IL-4:IFN-gamma, IL-5:IFN-gamma and IL-10:IFN-gamma, while IFN-gamma was high in the infected individuals. After treatment the non re-infected had higher levels of IL-4, IL-5 and IL-10, with the infected having high levels of IFN-gamma. Th1-like response dominated during infection with the Th2-like responses dominating post treatment and in uninfected individuals. The results indicated that the cytokine balance determines, in part, susceptibility or resistance to S. haematobium infection.

T cell clones from Schistosoma haematobium infected and exposed individuals lacking distinct cytokine profiles for Th1/Th2 polarisation

T cell clones were derived from peripheral blood mononuclear cells of Schistosoma haematobium infected and uninfected individuals living in an endemic area. The clones were stimulated with S. haematobium worm and egg antigens and purified protein derivative. Attempts were made to classify the T cell clones according to production of the cytokines IL-4, IL-5 and IFN-gamma. All the T cell clones derived were observed to produce cytokines used as markers for the classification of Th1/Th2 subsets. However, the 'signature' cytokines marking each subset were produced at different levels. The classification depended on the dominating cytokine type, which was having either Th0/1 or Th0/2 subsets. The results indicated that no distinct cytokine profiles for polarisation of Th1/Th2 subsets were detected in these S. haematobium infected humans. The balance in the profiles of cytokines marking each subset were related to infection and re-infection status after treatment with praziquantel. In the present study, as judged by the changes in infection status with time, the T cell responses appeared to be less stable and more dynamic, suggesting that small quantitative changes in the balance of the cytokines response could result in either susceptibility or resistant to S. haematobium infection.

The impact of repeated treatment with praziquantel of schistosomiasis in children under six years of age living in an endemic area for Schistosoma haematobium infection

Praziquantel was given every eight weeks for two years to children aged under six years of age, living in a Schistosoma haematobium endemic area. Infection with S. haematobium and haematuria were examined in urine and antibody profiles (IgA, IgE, IgM, IgG1, IgG2, IgG3, and IgG4) against S. haematobium adult worm and egg antigens were determined from sera collected before each treatment. Chemotherapy reduced infection prevalence and mean intensity from 51.8% and 110 eggs per 10 ml urine, respectively, before starting re-treatment programme to very low levels thereafter. Praziquantel is not accumulated after periodic administration in children. Immunoglobulin levels change during the course of treatment with a shift towards 'protective' mechanisms. The significant changes noted in some individuals were the drop in 'blocking' IgG2 and IgG4 whereas the 'protecting' IgA and IgG1 levels increased. The antibody profiles in the rest of the children remained generally unchanged throughout the study and no haematuria was observed after the second treatment. The removal of worms before production of large number of eggs, prevented the children from developing morbidity.

A rural HIV epidemic in Zimbabwe? Findings from a population-based survey

The aim of the study was to use population-based data from 689 adults to describe the socio-demographic, behavioural and biomedical correlates of HIV infection and aid identification of effective HIV control strategies for rural Zimbabwe. Dried blood spot and urine samples were collected for HIV and sexually transmitted disease (STD) testing and participants were interviewed on socio-demographic characteristics, sexual behaviour and experience of STD symptoms. HIV seroprevalence was 23.3% and was higher in females, divorcees, widows, working men, estate residents, and respondents reporting histories of STD symptoms. Female HIV seroprevalence rises sharply at ages 16-25. A third of sexually-active adults had experienced STD-associated symptoms but there were delays in seeking treatment. Herpes simplex virus type 2 (HSV-2) and Trichomonas vaginalis are more common causes than syphilis, gonorrhoea, and chlamydia, and are strongly associated with HIV infection. Local programmes promoting safer sexual behaviour and fast and effective STD treatment among young women, divorcees and working men could reduce the extensive HIV transmission in rural communities.

Quality of life evaluation in patients with HIV-I infection: the impact of traditional medicine in Zimbabwe

OBJECTIVES

To evaluate the impact of phytotherapy (traditional medicine) in persons with HIV infection and to assess the quality of life of those persons with respect to HIV disease progression, including sociodemographic characteristics.

DESIGN

A community based open label non-intervention and uncontrolled cohort study.

SETTING

Blair Research Institute Clinic.

SUBJECTS

A total of 105 HIV infected persons at various stages of HIV infection. Seventy-nine percent were on phytotherapy (PT) and 21% on conventional medical care (CMC).

MAIN OUTCOME MEASURES

(a) Assessment of quality of life of HIV infected persons on phytotherapy using the WHOQol instrument, and (b) assessment of quality of life of those persons in relation to the HIV disease progression using CD4 cell counts and viral load as measure of disease progression.

METHODS

We interviewed 105 patients with various stages of HIV-I infection in a community based cohort study from June 1996 to May 1998, in Harare. The 96 (91.4%) asymptomatic and six (8.6%) symptomatic patients underwent regular physical examinations and had blood drawn for laboratory tests at the baseline afterwards at three month intervals over a period of two years.

RESULTS

The mean (s.d.) age was 34.9 (7.3) years; 64.4% were women and 60.3% were married. In multi variate analyses, age was significantly correlated with the level of independence domains (p = 0.032), whereas, gender was significantly correlated with social relationships' domains (p = 0.034). The type of treatment received was significantly correlated with spiritual domains (p = 0.045). Proportions of scores on five domains measuring different aspects of quality of life for patients on phytotherapy were much lower than those on conventional therapy (p < 0.0001, for all variables).

CONCLUSION

Our data support the role of phytotherapy in improving the quality of life of HIV-I infected patients, yet its pharmacological basis is unknown. The WHOQol instrument is a good measure of quality of life for patients with HIV infection.

Dissociation of interleukin-4 and interleukin-5 production following treatment for Schistosoma haematobium infection in humans

Infection with Schistosoma haematobium, the causative agent of urinary schistosomiasis is characterized by high levels of specific immunoglobulin (Ig) E and eosinophilia. The primary cytokines driving production of IgE and eosinophilia are IL-4 and IL-5, respectively. In this study, IL-4 and IL-5 production in children from a schistosome endemic area of Zimbabwe were investigated. Blood samples were taken, stimulated in vitro with either mitogen or schistosome antigens and assayed for IL-4 and IL-5 production. These samples produced either IL-4 or IL-5 but rarely both cytokines when blood was cultured in vitro for 24 or 48 h. After 72 h culture in vitro, both cytokines were detected in most samples. These data imply that while IL-4 and IL-5 are both produced by schistosome infected people, they are not necessarily coproduced.

Exposure, infection and immune responses to Schistosoma haematobium in young children

Behavioural, parasitological and immunological data were obtained from 48 children up to 6 years old, resident in a Schistosoma haematobium endemic area in Zimbabwe. The children averaged more than 1 contact with infective water bodies every 3 days and all showed immunological evidence of exposure (an anti-cercarial and/or anti-egg antibody response). IgM was the dominant isotype and appeared in the youngest children, followed by IgA, IgE and IgG3. However, only 38 children showed evidence of infection (an anti-egg response or eggs in urine) and only 14 were excreting eggs. The best estimates from these data are that less than 1 in 100 contacts results in infection and less than 1 in 1000 result in egg output. This suggests that there may be substantial attrition of invading cercaria even in naïve individuals.

Alcohol consumption in HIV-I infected persons: a study of immunological markers, Harare, Zimbabwe

OBJECTIVE

To examine the effect of alcohol use in relation to the age, gender and plasma levels of HIV-I RNA and CD4 cells count in HIV-I infected persons as a prognostic indicator for the disease progression to AIDS.

DESIGN

A community based cohort study.

SETTING

The study was conducted at the Blair Research Institute Clinic from June 1996 to May 1998.

SUBJECT

We interviewed 105 volunteers, at a baseline and then followed them up on a three monthly basis. They underwent physical examinations and had blood drawn for laboratory tests. AUDIT Core was used to gain an indication of how much dependence there was on alcohol by patients in relation to demographic and immunological variables.

MAIN OUTCOME MEASURES

Frequency of alcohol use and HIV-I disease progression to AIDS using viral loads and CD4 cells counts as measures of immune impairment.

RESULTS

The volunteers had a mean (s d) age of 34.9 (7.3) years. Prevalence of alcohol use was 30.5% (n = 34.95% CI = 21.7 to 39.3). Most of the patients with CD4 cells count less than 200 mm3 did not use alcohol (p = 0.023) by the six months follow ups. There were no significant mean differences between users and nonusers of alcohol regarding the levels of both plasma viremia and CD4 cells count.

CONCLUSION

Our finding is consistent with previous findings that found no relationship between alcohol use in persons with HIV-I infection and progression of disease to AIDS.

Apostles and Zionists: the influence of religion on demographic change in rural Zimbabwe

Religion has acted as a brake on demographic transition in a number of historical and contemporary populations. In a study in two rural areas of Zimbabwe, we found substantial differences in recent demographic trends between Mission and Independent or "Spirit-type" churches. Birth rates are higher in some Spirit-type churches and, until recently, infant mortality was also higher. Recent increases in mortality were seen within Mission churches but not in Spirit-type churches. Missiological and ethnographic data indicate that differences in religious teaching on healthcare-seeking and sexual behaviour and differences in church regulation could explain this contrast in demographic patterns. More restrictive norms on alcohol consumption and extra-marital relationships in Spirit-type churches may limit the spread of HIV and thereby reduce its impact on mortality. These contrasting trends will influence the future religious and demographic profile of rural populations in Zimbabwe.

People's perceptions about malaria transmission and control using mosquito repellent plants in a locality in Zimbabwe

OBJECTIVE

To assess peoples' perceptions and knowledge about malaria transmission and control with special reference to the use of plants as mosquito repellents.

DESIGN

Cross sectional study.

SETTING

Mandeya ward "A" (33 degrees E and 18 degrees 30' S), Honde Valley, Zimbabwe.

SUBJECTS

226 household heads present when interview was conducted.

MAIN OUTCOME MEASURES

Mosquito control methods, spraying coverage, plants used to repel mosquitoes and reasons for using them.

RESULTS

215 (95.0%) of the respondents' homes had been sprayed and their understanding of malaria transmission was not related to compliance with the National Malaria Control Programme (NMCP). Taking mosquito control measures was related to knowledge of malaria transmission, with 24 (75.0%) of those who did not know, taking no measures of their own. The use of plants was mentioned by 50 (23.5%) of the respondents and the reasons given were that they were cheap 43 (86.0%), effective five (10.0%) and locally available two (4.0%). The plant which was mentioned as being used by all age groups was L. javanica 25 (50.0%) and the other plants were used to a lesser extent. Forty six (92.0%) of the people said that they had used plants for mosquito control. The leafy part of the plant was used by 43 (86.0%) and a fresh preparation 43 (86.2%) gave better protection than a dry one. The plants were crushed and applied on the skin by eight people (14.6%), burnt by 36 people (72.8%) and used in their original form by six people (12.6%) and used once per by day 42 people (84.0%).

CONCLUSIONS

One of the important points to emerge from this study is that, despite widespread knowledge about the morbidity of malaria, understanding about its prevention was generally low and this has negative implications on an integrated control programme.

Heterogeneities in schistosome transmission dynamics and control

We review the theoretical framework for exploring the impact of individual and spatial heterogeneities in patterns of exposure and contamination and on the basic reproduction number, R0, for human schistosomes. Analysis of water contact data for 5 communities in Zimbabwe and Mali suggests that the impact is substantial, increasing R0 by factors of up to 6.5, mostly due to highly overdispersed distributions of contact rates among individuals. Several practical conclusions emerge: concentration of contacts at a single site should be avoided; the impact of control targeted at certain sites cannot be predicted without knowledge of how individuals' contacts are distributed among sites; control programmes targeted at individuals or sites contributing most to transmission can be very efficient but, conversely, will be ineffective if any of these individuals or sites are missed.

Status of chloroquine efficacy against falciparum malaria in the Mola area of Kariba district, Zimbabwe

The therapeutic efficacy of chloroquine was assessed, during the 1997 transmission season, using 64 cases of uncomplicated, falciparum malaria originating from 18 villages in the Mola area of Kariba district, Zimbabwe. Chloroquine effected a modest reduction in asexual parasite density and clinical symptoms. The mean density of asexual parasites on day 3 post-treatment was 24.94% (95% confidence interval = 13.59%-36.30%) of that on day 0, and 78% of the patients followed-up for at least 1 week were free of parasitaemia on day 7. However, there was appreciable therapeutic failure. The early treatment failure rate (i.e. by day 3) was 21% and about 6% of the cases exhibited increasing asexual parasitaemia despite treatment. Late treatment failures (i.e. by day 14) occurred in 32% of the malaria cases, and 52% of the patients were ultimately considered failures. All the failures were successfully treated with sulfadoxine-pyrimethamine or quinine. Chloroquine therefore has declining parasitological and clinical value as the first-line, presumptive treatment for uncomplicated, falciparum malaria in the study area, necessitating strategies to cope with resistant cases. The proportion of the patients failing to be treated successfully with chloroquine, one of the largest reported in Zimbabwe to date, may-force major policy reviews in the near future. It is recommended that the second-line antimalarial, sulfadoxine-pyrimethamine, be distributed to health-centre level in the study area, backed up by the decentralised confirmation of diagnosis. Measures to deal with treatment failures at local health centres are proposed.

Chemotherapy accelerates the development of acquired immune responses to Schistosoma haematobium infection

Treatment of 41 Schistosoma haematobium-infected children, 5-16 years old, with the drug praziquantel induced a switch from a predominantly IgA-specific antibody response to a predominantly IgG1 response within 12 weeks. A cross-sectional survey suggests that the same switch occurs naturally, but over several years, as children age (n = 251). The switch may be driven by alterations in cytokine levels in response to the release of antigens by dead or damaged parasites. Adults are more resistant to schistosome infection than children, and the switch to an "adult" response suggests that praziquantel treatment may have an immunizing effect, with benefits extending beyond a transient reduction in levels of infection.

Efficacy of mosquito coils containing 0.3% and 0.4% pyrethrins against An.gambiae sensu lato mosquitoes

OBJECTIVE

To investigate the efficacy of a formulation containing 0.4% pyrethrins against registered mosquito coil containing 0.3% pyrethrins.

DESIGN

Non intervention analytical study.

SETTING

Four villages in Mashonaland East province, Mumurwi, Chitengu, Katiyo and Nyagande.

SUBJECTS

Biological efficacy of Doom and IT mosquito coils.

MAIN OUTCOME MEASURES

To measure insecticidal, knock down and inhibition of biting activities of the coils in the presence of mosquitoes.

RESULTS

A two hour exposure of mosquitoes to both coils results in a 99% and 98.5% mortality rate for a 0.4% and a 0.3% formulation respectively. The KT50 and KT90 of a formulation containing 0.4% pyrethrins were half those of a 0.3% formulation, suggesting that a 0.4% formulation has a rapid knock down effect. A formulation containing 0.4% pyrethrins inhibited 92.5% from biting as compared to a 0.3% formulation (80%).

CONCLUSION

A formulation containing 0.4% pyrethrins is more effective in repelling mosquitoes than a 0.3% formulation.

Effect of human immigration on the age distribution of schistosome infections in Siavonga community, Lake Kariba, Zambia

A study on the distribution of schistosomiasis in the community at Siavonga revealed Schistosoma haematobium infection in 35.5% of 338 subjects and a geometric mean egg count (GMEC) and (S.D.) of 13.7 (7.2) eggs/10 ml urine. The prevalence of S. mansoni infection among 323 subjects was 60.1%, with a GMEC of 336.8 (4.8) eggs/g stool. Among the infected, 69.5% carried both schistosome species. Although prevalence of infection with either species was highest in those aged 10-14 years, high prevalences of infection were found in older age groups and egg intensities were uniformly distributed throughout all age-groups. The observed diversion from the typically age-dependent distribution of schistosome infections probably reflects exposure to infection relatively late in life, as the result of immigration from non-endemic areas.

Is there evidence for behaviour change in response to AIDS in rural Zimbabwe?

This article reports on evidence for behaviour change in response to AIDS among women in two rural areas of Manicaland Province, Zimbabwe. It examines self-reported data on two overlapping areas of behaviour: (1) actions taken to avoid HIV-1 infection; and (2) fertility practices. The latter were used to assess the validity of the former, given that self-reported behaviour data are notoriously problematic. It is concluded that while self-reported behaviour change is exaggerated, the true level of change has nonetheless been significant and includes delayed onset of sexual relations, increased use of condoms and, possibly, increased monogamy. Reported actions taken to avoid HIV-1 infection and differentials in fertility practices were correlated with data on demographic, social and psychological factors. Differentials in fertility practices were associated with heightened risk perception--particularly when based on personal acquaintance with AIDS patients--but not with greater knowledge of HIV-1/AIDS. Results from the study suggest that effective behaviour change in Manicaland is facilitated by greater knowledge, experience and personal risk perception but obstructed by low female autonomy, marital status and economic status, and by male labour migration and alcohol consumption. Gaps in knowledge included misconceptions about the distinction between HIV-1 and AIDS, the influence of STDs, perinatal transmission, and incorrect modes of transmission. Better knowledge was associated with education, religion, travel and media exposure Personal risk perception was quite high (42%) and correlated with non-marriage, media exposure and contact with medical services. Few respondents knew close relatives with HIV/AIDS (4%) but nearly a quarter of those who felt in danger of infection said this was because friends and relatives were dying of AIDS. Many reported credible behavioural responses, some of which would only be effective given their partner's co-operation. Intensified behaviour interventions are needed which should include peer-education initiatives targeting men and individuals without access to modern media. The epidemic may accelerate fertility decline in rural Zimbabwe through behavioural as well as biological change.

Risk factors for HIV infection in a rural cohort in Zimbabwe: a pilot study

OBJECTIVE

To identify demographic, sexual behavioural and cultural risk factors for human immunodeficiency virus (HIV) infection in a rural community in Zimbabwe.

DESIGN

Prospective study.

SETTING

Rural area in Zimbabwe.

SUBJECTS

207 subjects (81 males, 126 females) mean age 31.6 years (SD 15.3), range 12 to 76 years living in the area.

MAIN OUTCOME MEASURES

HIV seropositivity and seroconversion, exposure or no exposure to risk factor.

RESULTS

Prevalence of HIV was 7.7% and was associated with being divorced or widowed [Odds ratio (OR) 4.26, 95% confidence interval (CI) 1.17 to 14.97] and past history of sexually transmitted diseases (STDs) [(OR 3.54, 95% CI 1.31 to 9.89)]. Seroconversion rate was 3.6% per year and was associated with history of STD [Relative Risk (RR) 13.22, 95% CI 1.15 to 156.1)] during the follow up period. Individuals over 20 years of age, those reporting one or more sexual partners, those reporting irregular use of condoms and those scarified were at greater risk than their counterparts. Individuals who reported being circumcised were at slightly lesser risk than those who did not report circumcision.

CONCLUSION

STDs were major determinants of HIV transmission in the study area. In addition being divorced or widowed was a risk factor for HIV infection. Scarification, tattooing and circumcision require further investigations.

Recent upturn in mortality in rural Zimbabwe: evidence for an early demographic impact of HIV-1 infection?

OBJECTIVES

To describe recent mortality trends in rural Zimbabwe and to assess the impact of HIV-1 infection.

METHOD

Comparative, cross-sectional, retrospective, demographic survey with 1-year follow-up. Parallel HIV-1 surveillance. Comparison of results with 1992 national census and vital registration data and results from mathematical model-based population projections.

SETTING AND PARTICIPANTS

Residents of 929 (745 revisited in 1995) households in two rural areas of Manicaland Province, Zimbabwe, with contrasting HIV-1 prevalence: Honde and Rusitu valleys. Subjects gave information on parental survival for 2320 resident children. Female residents aged 13-49 years (n = 1237) provided information on birth histories and child survival. Consenting women attending local antenatal clinics (n = 487) provided blood samples for HIV-1 screening and demographic information.

MAIN OUTCOME MEASURES

HIV-1 prevalence in pregnant women; per capita death registration rates; incidence of parental death for children aged under 8 years; infant mortality and age-specific death probabilities.

RESULTS

HIV-1 prevalence was high in each study area. Death registration and age-specific mortality have begun to rise. The largest increases were seen in the area of higher HIV-1 prevalence (Honde) and among younger adults, particularly men. Incidence of parental death was observed to be rising. Increases in registered deaths were concentrated among HIV-1-associated causes.

CONCLUSIONS

The observed increases in mortality by age, sex and cause of death were consistent with those expected early in a severe HIV-1 epidemic, on the basis of mathematical model projections and observations elsewhere in Africa. Further rises in mortality, particularly among women and young children, and consequent increases in orphanhood, are to be expected in rural areas of Zimbabwe.

Heterogeneities in the transmission of infectious agents: implications for the design of control programs

From an analysis of the distributions of measures of transmission rates among hosts, we identify an empirical relationship suggesting that, typically, 20% of the host population contributes at least 80% of the net transmission potential, as measured by the basic reproduction number, R0. This is an example of a statistical pattern known as the 20/80 rule. The rule applies to a variety of disease systems, including vector-borne parasites and sexually transmitted pathogens. The rule implies that control programs targeted at the "core" 20% group are potentially highly effective and, conversely, that programs that fail to reach all of this group will be much less effective than expected in reducing levels of infection in the population as a whole.

On estimating the basic reproduction number for Schistosoma haematobium

Existing estimates of the basic reproduction number, Ro, for human schistosomes are mostly in the range 1-4, implying that schistosomes should be relatively easy to eliminate from endemic areas, which is contrary to practical experience. An estimate of Ro for a site in Zimbabwe is obtained here using a mathematical model explicitly incorporating two features believed to be epidemiologically significant; age-dependent exposure and acquired immunity. Parameter estimates are, as far as possible, obtained independently, but the coefficients representing man-snail and snail-man transmission, as well as parameters representing effects of acquired immunity, must be estimated indirectly by fitting the model to field data. Heterogeneity in human exposure and contamination is crudely incorporated by considering "wormy' and non-wormy' fractions of the population. The results suggest Ro to be in the range 4-5 or more, higher than previous estimates and despite only moderate levels of infection at this site. It is shown that this estimate is sensitive to the form of the underlying model. The application of less realistic models may lead to less reliable estimates of Ro.

Retrospective study on the criteria for diagnosis of HIV infection in adults in Zimbabwe

OBJECTIVE

To review the criteria for diagnosis of HIV infection in adults in order to improve upon the Zimbabwe Adult AIDS case definition.

DESIGN

A descriptive study which involved the analysis of "Request fo r HIV Antibody Test" forms which had been submitted by clinicians to Masvingo Public Health Laboratory, between June 1990 and December 1992.

SETTING

Masvingo Public Health Laboratory, Zimbabwe.

SUBJECTS

627 adult patients.

MAIN OUTCOME MEASURES

HIV seroprevalence; specific, sensitivity and positive predictive values of the Adult AIDS case definition.

RESULTS

The HIV seroprevalence in 627 adult patients whose forms had been submitted to Masvingo Public Health Laboratory was 79pc. The criterion for the diagnosis of HIV infection had a very high specificity value of 93pc but low sensitivity of 53pc. The positive predictive value of the case definition was very high (97pc). The positive predictive values of individual symptoms were calculated and only weight loss and persistent generalized lymphodenopathy had high values of 99pc and 72pc respectively.

CONCLUSIONS

This study has shown that the criterion used in the diagnosis of HIV infection in Zimbabwe is highly specific but relatively insensitive at identifying seropositive patients. This shows the ability of clinicians to identify HIV positive patients irrespective of the stage of the disease (i.e. HIV related symptoms, AIDS related complex or full blown AIDS). There is also a need for constant monitoring of the clinical manifestations of AIDS patients to keep abreast with newer disease manifestations.

Age-related antibody profiles in Schistosoma haematobium infections in a rural community in Zimbabwe

Antibody responses to soluble Schistosoma haematobium egg (SEA) and worm (SWA) antigens in a rural Zimbabwean study population were examined by ELISA. One hundred and sixteen S. haematobium infected and 124 non-infected individuals representing individuals greater than five years old, were included. Non-endemic control sera were obtained from a schistosomiasis non-endemic part of Zimbabwe and from Norwegian blood donors. A possible association between IgE antibody responses and resistance to S. haematobium infection was indicated by a negative correlation between IgE anti-SEA levels and intensity of S. haematobium infection, and by a positive correlation between IgE responses to SEA and SWA and age. Similarly, an association between IgA and anti-SWA and resistance to S. haematobium was suggested by a negative correlation to intensity of infection and a positive correlation with age. A probably association between IgM and IgG4 with susceptibility to S. haematobium infection was described; intensity of S. haematobium infection correlated positively with IgG, IgG4 and IgM responses to SEA and with IgG4 and IgM responses to SWA, also age correlated negatively with IgG4 and IgM responses to SEA and with IgG4 responses to SWA. These findings support the concept of IgG4 and IgM as blocking antibodies. Significant positive correlations between antibody responses to SEA and SWA suggests cross-reactivity between eggs and adult worms. In addition, the recognition by IgE and IgG4 of the same schistosomulum antigens in immunoblotting suggests competitions for the same antigens.

Genetic structure and parasite compatibility of Bulinus globosus (Gastropoda: Planorbidae) from two areas of different endemicity of Schistosoma haematobium in Zimbabwe

A comparative study of the genetic structure of 8 populations of B.globosus from 2 areas of different endemicity of Schistosoma haematobium was done. Five populations were from Chiweshe (high endemicity) and three were from Plumtree (low endemicity). Genetic structure, as determined by allozyme genetics, revealed high levels of genetic variability in Chiweshe populations (Ho = 0.12-0.26) and low levels in Plumtree (Ho = 0.06-0.12). Populations from Chiweshe were genetically heterogeneous whereas in Plumtree the populations were uniform. There were significant deviations from Hardy-Weinberg proportions at different loci in Chiweshe populations. The observed excess of homozygotes was probably caused by partial selfing. The compatibility studies showed variation between allopatric and sympatric combinations of snails and parasites, and the Plumtree parasite had a significant influence on the compatibility parameters. This strain had a positive correlation (P < 0.01) of its infection rate with allele frequency of Est-2(100) and a negative correlation (P < 0.05) with allele Idh100.

Optimization of the Magnetic Bead Antigen Capture Enzyme Immuno Assay for the detection of circulating anodic antigens in mixed Schistosoma infections

In the present study, simplification and adaptation of the Magnetic Bead Antigen Capture Enzyme Immuno Assay (MBAC-EIA) technique for detection of circulating anodic antigens (CAA) under field conditions was achieved. It was shown that the assay could be performed successfully within the broad temperature range of 18-37 degrees C. The slightly lower sensitivity observed at low temperatures could be adjusted for by prolonging the incubation period. Shaking the plate by hand was as good as automatic mechanical shaking, aspiration of the supernatant before the addition of conjugate was not necessary, and the use of whole blood and serum offered similar assay sensitivity. Furthermore incubation times could be considerably shortened without loss of sensitivity. A major advantage of the MBAC-EIA was that the beads, after elution of bound components, were found to be reusable. The study also showed that the sensitivity of the MBAC-EIA technique in diagnosis of schistosomiasis in a Zimbabwean community endemic for both urinary and intestinal schistosomiasis, was 94%.

Schistosomiasis around Siavonga, on the shores of Lake Kariba, Zambia

A schistosomiasis prevalence survey was carried out at Lake Kariba, Zambia--only the second since the creation of the lake more than 30 years ago. In the 20 or so years since the first study the prevalence of Schistosoma mansoni has increased from 16% to 56% while that of S. haematobium has dropped from 69% to 17%. There was variability in the infectivity of contact sites (P < 0.001) and this had an impact on prevalence. In contrast, sex, age (within the range 5-19 years), residential area (distance from the lakeshore) and activity at the contact site had no significant effect on prevalence (P > 0.05). The population at Matinangala was more at risk of infection by both S. haematobium (P < 0.001) and S. mansoni (P < 0.05) than the Siavonga population. Both Biomphalaria pfeifferi and Bulinus globosus were present in the area and factors which may be influencing their distribution are discussed.

A trap for the detection of schistosome cercariae

A simple trap for schistosome cercariae has been developed using clear nail varnish as a matrix and linoleic acid as stimulant affixed to a 75 x 25-mm glass slide. Schistosoma mansoni cercariae will attach to the surface and easily can be visualized either stained or unstained. The trap works well under laboratory and field conditions where the retrieval rate varies from 30% to 100%. Under laboratory conditions there appears to be some form of affinity for cercariae to the surface.

The epidemiology and control of hookworm infection in the Burma Valley area of Zimbabwe

An integrated hookworm control programme, involving mass chemotherapy and improvements in public health, was conducted in the Burma Valley and Vumba areas of Zimbabwe between 1985 and 1990. Three sequential annual mass chemotherapy programmes were implemented. Infection status was monitored annually throughout. Initial observations indicated asymptotic age prevalence and intensity profiles, with peak infection levels in adults. Mass chemotherapy was shown to have immediate and medium term benefits for community health. Reinfection was slow to develop, and average intensity had not returned to pre-intervention levels 39 months after the cessation of chemotherapy. The results support the existence of age-dependency in reinfection. Despite a marked increase in the number of sanitation units, no relationship was found between latrine availability and reinfection intensity on individual farms. This result is consistent with observations that the effect of sanitation is slow to develop, and indicates that repeated anthelmintic intervention should be maintained until sanitation has an impact on transmission.

Bilharzia in a small irrigation community: an assessment of water and toilet usage

A questionnaire study was conducted in the Mushandike small scale irrigation schemes in Zimbabwe to investigate the following: 1) to establish whether field latrines are used or not; 2) to find out why people visit natural water bodies for bathing and laundry instead of using water from boreholes for these purposes; 3) to assess people's knowledge on the transmission and control of schistosomiasis. Results of the study indicated that the field latrines are utilised and that the borehole water is not preferred for bathing and laundry because of its hardness and oily nature. The results further indicated that the community was aware of schistosomiasis but their knowledge on transmission and control of the disease was limited. Possible reasons for the observations made are discussed in the paper and recommendations emanating from the study are stated.

Progress in the control of schistosomiasis in Zimbabwe since 1984

Schistosomiasis remains the second most important parasitic disease in Zimbabwe. In terms of its combined morbidity and prevalence, schistosomiasis is thought to be the most important helminth infection of man. Since 1984, a number of control programmes have commenced around the country and a national control programme aimed at reducing morbidity is being implemented. The strategy adopted in Zimbabwe is a community based approach integrated in the primary health care system.

Development of Health Systems Research and National HSR networking in Zimbabwe

Health Systems Research (HSR) aims at improving the quality of health care delivery through health managers with a management tool for decision making. Since 1988, over 100 health cadres from provincial and district health teams, central hospitals and municipalities have received training in HSR methodology. This training has resulted in the implementation of 12 research projects with the results being used to solve immediate problems identified. The development of HSR in Zimbabwe has focused on training priority setting for essential health research and the development of infrastructure and local resource groups to sustain the initiative. The HSR unit in conjunction with the Medical Research Council of Zimbabwe (MRCZ) have developed a computerised databank for keeping track of all health and medical research conducted in the country. The databank is a mechanism for co-ordinating and promoting research through minimising duplication of research effort in the dissemination and utilisation of research findings. Prospects for HSR in Zimbabwe are good; further development requires adequate funding, networking of all research groups and a national commitment to build a critical mass of trained health research manpower at all levels.

A further model for temporal patterns in the epidemiology of schistosome infections of snails

The prevalence of Schistosoma mansoni infections of Biomphalaria pfeifferi shows seasonal variation. Field data from Zimbabwe show annual ranges from 0 to 7%. In this paper a mathematical model of B. pfeifferi population dynamics and S. mansoni epidemiology is used as a framework for analysis of these patterns. Snail fecundity is a function of snail age and of temperature, and is apparently affected by other seasonal factors. The pre-patent period is dependent on temperature. Infection affects snail fecundity and mortality. Parameter values are derived from previous field and laboratory studies. The force-of-infection is estimated from the analysis of size-prevalence data. Using observed temperatures, model output agrees well with field data on snail abundance and prevalence of infection over a 14-month period. Seasonal variation in prevalence largely reflects variation in the pre-patent period and in snail population age structure. The possible role of seasonality in the force-of-infection is discussed. Prevalence patterns are not greatly affected by year-to-year differences in temperature. Significant seasonal variation in snail-man transmission rates is expected.

The epidemiology and population biology of Necator americanus infection in a rural community in Zimbabwe

Baseline data from an epidemiological study of hookworm infection in a rural community in Zimbabwe are presented. The infection status of an age-stratified sample of the community was assessed using anthelmintic expulsion techniques. Necator americanus was the only helminth parasite found to be present. The age-prevalence and intensity profiles rose asymptotically to an adult prevalence of about 80% and adult mean burden of 7.7 worms per host. The overall mean burden was 4.8 worms per host. The frequency distribution of N. americanus was overdispersed and well described by the negative binomial distribution with a value for the aggregation parameter, k, of 0.346. Separate estimates of k were lower in males and older hosts. The distribution patterns were difficult to reconcile with any simple process of age-dependent acquisition of an effective immune response. A significant negative correlation was recorded between per caput fecundity and worm burden, providing evidence for a density-dependent regulation of female worm fecundity. The basic reproductive rate (R0 congruent to 2) was found to be similar to estimates from other geographical areas.

Heterogeneities in water contact patterns and the epidemiology of Schistosoma haematobium

Variations in the amount of water contact made by individuals and in the amount of water contact made at different sites may have significant impacts on patterns of human schistosome infection. Previous studies have reported variations in the rate of water contact and differences in the sites used between age/sex classes, but there is limited information on variations in individual water contact behaviour. In this paper we report and analyse observations of essentially all water contacts made over a two week period by all individuals in a rural community in eastern Zimbabwe. The mean rate of water contact was 0.43 contacts/person/day. These data were over-dispersed, ranging from zero to 3.3 contacts/person/day; 90% of contacts were made by only 37% of the population. Contact rates were related to age (highest in 8 to 10-year-olds) but not sex, with substantial variation unaccounted for by these variables. Age and sex classes differed in types of water-related activities and the time of day of contact. A greater diversity of sites was used by children than by adults and by males than by females. Individual contact rates were correlated with intensities of infection, although the risk of infection per contact was estimated to be highest in 2 to 4-year-old children and higher for males than females. Five contact sites were used during the study period, with more than 50% of contacts occurring at just 2 sites. Different age and sex classes used different sites and there were additional site-related differences in types of activity and the time of day of use. The implications of these water contact patterns for schistosome epidemiology are discussed. In particular the results provide strong quantitative support for control programmes aimed at heavily used sites (e.g. focal mollusciciding) or at the minority of individuals making most water contacts (e.g. targeted chemotherapy).

Heterogeneities in transmission rates and the epidemiology of schistosome infection

Previous theoretical studies have suggested that heterogeneities in transmission rates can have significant effects on the epidemiology of parasite infections. However, the magnitude of these effects in practice remains uncertain because of the difficulty of quantifying such heterogeneities under natural conditions. In this paper we consider the effects of heterogeneous rates of contact with infective water bodies on the basic reproductive rate, R0, of human schistosomes. In particular, we examine the theoretical effects of differences in the distribution of contacts among individuals and among sites. We find that an individual's contribution to R0 depends not only on the net contact rate but also on how these contacts are distributed among sites--the contact pattern. Our analysis of field data suggests a substantial impact of heterogeneous contact rates on R0 in practice. Significant reductions in R0 may be possible if schistosomiasis control efforts are targeted at certain sites and, especially, certain individuals.

Acquired immunity and epidemiology of Schistosoma haematobium

Human immune responses to schistosome infection have been characterized in detail. But there has been controversy over the relative importance of ecological factors (variation in exposure to infection) and immunological factors (acquired immunity) in determining the relationships between levels of infection and age typically found in areas where infection is endemic. Independent effects of exposure and age on the rates of reinfection with Schistosoma haematobium after chemotherapy have been demonstrated in the Gambia and Zimbabwe. This age effect could be the result of acquired immunity to infection. Indeed, allowing for variation in exposure and age, low rates of reinfection in the Gambia are correlated with high amounts of specific IgE antibodies--human IgE can kill S. mansoni schistosomulae in vitro. Further, animals can acquire immunologically mediated resistance to S. mansoni infection, although nonimmunological factors could also be involved. Acquisition of this immunity seems to be related to the cumulative effects of repeated infection and provides only partial protection. These characteristics are consistent with immuno-epidemiological data for both S. mansoni and S. haematobium infections of humans. We have now analysed age-prevalence data for human infection with S. haematobium, and find patterns of variation that are indeed consistent with the epidemiological effects of acquired immunity predicted by mathematical models.

Community control of schistosomiasis in Zimbabwe

The community-based primary health care approach to control schistosomiasis morbidity is the strategy adopted in Zimbabwe. The paper outlines the results of such a control strategy in a rural community with over 30,000 people in the Madziwa area of Zimbabwe from 1985 to 1989. The community-based control strategy involved diagnosis of infection in school children (seven-15 years of age) using reagent strips followed by treatment with praziquantel. The treatment was linked to programmes aimed at improved sanitation, better water supplies and health education. Following chemotherapy, there was a marked reduction in schistosomiasis prevalence (urinary and intestinal forms combined) (from 60 to 20pc) in the affected groups. Of even greater importance was the significant reduction of 90pc in heavy infections (greater than 50 S. haematobium eggs per 10 ml of urine of greater than 100 S. mansoni eggs per gram of faeces). Progress made through chemotherapy was consolidated by the implementation of intervention measures aimed at reducing human water contact with cercariae infested water. In the last three years of the community-based programme, 2,152 improved ventilated pit latrines were constructed and 104 hand pumps installed at new or existing water points. Drama competitions at schools showed great potential in communicating health education messages. However, technical and organisational difficulties limited the impact of the health education to the general population. A single application of the synthetic molluscicide Bayluscide was carried out in the main streams at the beginning of the programme in support of the initial chemotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)

The epidemiological implications of a multiple-infection approach to the control of human helminth infections

It has been suggested that there is economic advantage in using a single community therapy programme to deliver multiple treatments against several parasitic infections. This preliminary study estimates the occurrence of concurrent helminth infection in Africa and Brazil to determine whether such an approach is justified epidemiologically. The results indicate that the occurrence of geohelminthiasis with schistosomiasis is sufficiently frequent in some areas of both Africa and Brazil for a combined approach to control to be appropriate, but that the relatively low frequency of occurrence of onchocerciasis with other infections would justify a multi-infection approach to control at specific foci only.

Factors affecting the intensity of reinfection with Schistosoma haematobium following treatment with praziquantel

Infection with Schistosoma haematobium was studied in a rural community of approximately 500 persons in eastern Zimbabwe. The overall prevalence of infection, as determined by urine egg counts, was 40.1%, and of heavy infections (greater than or equal to 50 eggs/10 ml urine) was 11.0%. The prevalence of both heavy and all infections was highest in the 8 to 10-year-old age class. During 1987-88 data were obtained from 102 individuals on intensity of reinfection 14 weeks after treatment with praziquantel, the efficacy of treatment having been determined after 4 weeks. The water contact made by these individuals during 2-week periods immediately following treatment was recorded. The relative abundance of patent infected intermediate host snails, Bulinus globosus, was also monitored. An index of exposure was developed which weighted each water contact by its duration, the type of activity, the time of day, and the abundance of infected snails at the site used. The relationships between rates of reinfection, rates of exposure, and age were examined. Although only 13 individuals showed positive rates of reinfection, there were statistically significant and independent effects of both exposure and age on reinfection rate. Quantitative estimates of reinfection rates suggested that individuals aged 12 years or less acquired substantially more infection (measured as egg output) than individuals more than 12 years old.

Age-dependency in predisposition to hookworm infection in the Burma valley area of Zimbabwe

We examined hookworm re-infection intensities (measured as faecal egg count by the Kato technique) following anthelmintic treatment of farm workers resident on 15 large-scale commercial farms in Zimbabwe. All individuals examined were treated with albendazole (400 mg). Hookworm reinfection intensities of individuals examined, treated and reexamined were compared with the intensities of infection before treatment. Adults had higher than average infection intensities both before and after reinfection. Predisposition to hookworm infection was marked in adults, and absent from younger, less heavily infected hosts. The observations suggest that acquired immunity is unlikely to be an important determinant of hookworm infection and that behaviour may play a major role in determining the observed infection patterns in this community.

On the distribution of schistosome infections among host snails

The distribution of Schistosoma haematobium infections in a population of Bulinus globosus snails collected from a field site in Zimbabwe is described. Cercariae of both sexes emerged from a proportion of patent infected snails, as was demonstrated by the detection of paired schistosomes in hamsters each exposed to cercariae from a single snail. These snails must have been infected by two or more miracidia. Analysis showed that the proportion of mixed-sex infections was higher than expected if infections were distributed at random among snails. An index of overdispersion was calculated. Overdispersion of infections results from heterogeneities in the exposure and/or susceptibility of snails to infection. The implications for the epidemiology and control of schistosomiasis haematobium are discussed.

Temporal patterns in the epidemiology of schistosome infections of snails: a model for field data

The prevalence of patent schistosome infections of intermediate host snails often shows seasonal variations. For schistosome, mainly Schistosoma haematobium, infections of Bulinus globosus field data from Zimbabwe show annual ranges in prevalence from 2% to 30%. In this paper a mathematical model is developed for B. globosus population dynamics and the epidemiology of schistosome infection. The model is a discrete-time analogue of a catalytic model, with an added recruitment term. Snail fecundity and survival are functions of age, infection, and temperature. The pre-patent period of infection is dependent on temperature. Parameter values, and relationships with temperature, are taken from earlier field and laboratory studies. The force-of-infection is estimated from analysis of age-prevalence data. Model predictions, making use of temperature data recorded in the field, are in good agreement with observations over a 2-year period at a study site in Zimbabwe. The key features of interest are a fall in the prevalence of patent infections during the cold season and a rapid rise to a peak early in the hot season. This pattern results from the accumulation of pre-patent infections which fail to develop at low temperatures, but mature en masse, together with new infections, after a few weeks at higher temperatures. Model analysis demonstrates that seasonal patterns in the prevalence of patent infections may be due largely to the influence of temperature on the pre-patent period. Seasonal and year-to-year variations in temperature may therefore have significant epidemiological effects.

The epidemiology of schistosome infections of snails: taking the theory into the field

Most field studies of the epidemiology of schistosome infections of snails have been essentially descriptive in nature. Although much use has been made of epidemiological models in the interpretation of experimental studies of schistosome-snail interactions, the models have had restricted application outside the laboratory. Here, Mark Woolhouse and Steve Chandiwana make use of a theoretical framework in discussing current understanding of schistisome-snail epidemiological patterns in the field, and then consider the implications of the analysis for the control of schistosomiasis.

Population dynamics model for Bulinus globosus, intermediate host for Schistosoma haematobium, in river habitats

A mathematical model is developed that describes the population dynamics of the freshwater snail Bulinus globosus, an intermediate host of Schistosoma haematobium. The model is developed from field data recording abundance changes, recruitment rates, and mortality rates for adult snails in river habitats in Zimbabwe. Rate of recruitment into the adult population is dependent on temperature, incorporating a time lag to allow for growth to adult size. Mortality rate is also a function of temperature. A temperature-dependent model provides a useful description of changes in abundance during the dry season. Long-term population fluctuations are greatly affected by spates (flooding) associated with heavy rainfall. An estimate is made of the frequency and effects of spates. A simulation model that allows variable annual rainfall predicts fluctuations in snail abundance over two orders of magnitude over timescales of ten or more years. The role of density-dependent factors and the long-term persistence of the population are discussed. B. globosus population dynamics can be described as 'density vague'.