Impact of aerial humidity on seasonal malaria: an ecological study in Zambia

Background

Seasonal patterns of malaria cases in many parts of Africa are generally associated with rainfall, yet in the dry seasons, malaria transmission declines but does not always cease. It is important to understand what conditions support these periodic cases. Aerial moisture is thought to be important for mosquito survival and ability to forage, but its role during the dry seasons has not been well studied. During the dry season aerial moisture is minimal, but intermittent periods may arise from the transpiration of peri-domestic trees or from some other sources in the environment. These periods may provide conditions to sustain pockets of mosquitoes that become active and forage, thereby transmitting malaria. In this work, humidity along with other ecological variables that may impact malaria transmission have been examined.

Methods

Negative binomial regression models were used to explore the association between peri-domestic tree humidity and local malaria incidence. This was done using sensitive temperature and humidity loggers in the rural Southern Province of Zambia over three consecutive years. Additional variables including rainfall, temperature and elevation were also explored.

Results

A negative binomial model with no lag was found to best fit the malaria cases for the full year in the evaluated sites of the Southern Province of Zambia. Local tree and granary night-time humidity and temperature were found to be associated with local health centre-reported incidence of malaria, while rainfall and elevation did not significantly contribute to this model. A no lag and one week lag model for the dry season alone also showed a significant effect of humidity, but not temperature, elevation, or rainfall.

Conclusion

The study has shown that throughout the dry season, periodic conditions of sustained humidity occur that may permit foraging by resting mosquitoes, and these periods are associated with increased incidence of malaria cases. These results shed a light on conditions that impact the survival of the common malaria vector species, Anopheles arabiensis, in arid seasons and suggests how they emerge to forage when conditions permit.

Diagnostic urinary cfDNA detected in human cystic echinococcosis

Cystic echinococcosis (CE) is a major neglected tropical zoonotic disease caused by the tissue-dwelling larval stage of the cestode parasite Echinococcus granulosus. For individuals suspected of CE, the diagnostic standard is imaging using ultrasonography, X rays, or computed tomography. These resource-demanding and expensive procedures are rarely available in endemic rural areas where CE is most prevalent. There is a critical need for a new approach to identify CE patients so that they can be managed early in the course of their infection. This study reports on the results of a diagnostic approach that identifies E. granulosus-derived cell-free DNA (cfDNA) in the urine of CE patients. Utilizing PCR to amplify a fragment of a major tandem repeat element found in E. granulosus nuclear DNA, urine samples from all seven imaging-confirmed CE patients who harbored active liver cysts were positive. In addition, the urine samples from 2/4 patients who presented with non-viable/calcified liver cysts were also PCR positive for the repeat fragment. To our knowledge, this is the first report of using parasite cfDNA from urine to diagnose CE. This approach provides an easy to implement and cost-effective method to survey for the prevalence of E. granulosus in humans populations.

Transrenal DNA-based diagnosis of Strongyloides stercoralis (Grassi, 1879) infection: Bayesian latent class modeling of test accuracy

For epidemiological work with soil transmitted helminths the recommended diagnostic approaches are to examine fecal samples for microscopic evidence of the parasite. In addition to several logistical and processing issues, traditional diagnostic approaches have been shown to lack the sensitivity required to reliably identify patients harboring low-level infections such as those associated with effective mass drug intervention programs. In this context, there is a need to rethink the approaches used for helminth diagnostics. Serological methods are now in use, however these tests are indirect and depend on individual immune responses, exposure patterns and the nature of the antigen. However, it has been demonstrated that cell-free DNA from pathogens and cancers can be readily detected in patient’s urine which can be collected in the field, filtered in situ and processed later for analysis. In the work presented here, we employ three diagnostic procedures—stool examination, serology (NIE-ELISA) and PCR-based amplification of parasite transrenal DNA from urine–to determine their relative utility in the diagnosis of S. stercoralis infections from 359 field samples from an endemic area of Argentina. Bayesian Latent Class analysis was used to assess the relative performance of the three diagnostic procedures. The results underscore the low sensitivity of stool examination and support the idea that the use of serology combined with parasite transrenal DNA detection may be a useful strategy for sensitive and specific detection of low-level strongyloidiasis.

As international bodies focus efforts on control of the world’s neglected tropical diseases, the critical importance of accurate and sensitive diagnosis becomes a key factor. The problem arises when the infection load in a community is reduced to a level where the standard diagnostic methodologies are insufficiently sensitive to detect the residual infection in the community. There is a need to develop improved diagnostic strategies for many parasitic diseases. One of the more difficult to diagnose helminth parasites is the nematode Strongyloides stercoralis. We have introduced a new approach that detects parasite-specific cell free DNA in urine as a sensitive measure of parasite presence. In the work presented here, we compare the performance of parasitological, serological and urine/DNA-based diagnosis of S. stercoralis infection. Using a Bayesian Latent Class Analysis approach, we provide evidence for the enhanced utility of using both urine and blood for the diagnosis of this parasite.

Point of care diagnosis of multiple schistosome parasites: Species-specific DNA detection in urine by loop-mediated isothermal amplification (LAMP)

Schistosomes are easily transmitted and high chance of repeat infection, so if control strategies based on targeted mass drug administration (MDA) are to succeed it is essential to have a test that is sensitive, accurate and simple to use. It is known and regularly demonstrated that praziquantel does not always eliminate an infection so in spite of the successes of control programs a residual of the reservoir survives to re-infect snails. The issue of diagnostic sensitivity becomes more critical in the assessment of program effectiveness. While serology, such as antigen capture tests might improve sensitivity, it has been shown that the presence of species-specific DNA fragments will indicate, most effectively, the presence of active parasites. Polymerase chain reaction (PCR) can amplify and detect DNA from urine residue captured on Whatman No. 3 filter paper that is dried after filtration. Previously we have detected S. mansoni and S. haematobium parasite-specific small repeat DNA fragment from filtered urine on filter paper by PCR. In the current study, we assessed the efficacy of detection of 86 urine samples for either or both schistosome parasites by PCR and loop-mediated isothermal amplification (LAMP) that were collected from a low to moderate transmission area in Ghana. Two different DNA extraction methods, standard extraction kit and field usable LAMP-PURE kit were also evaluated by PCR and LAMP amplification. With S. haematobium LAMP amplification for both extractions showed similar sensitivity and specificity when compared with PCR amplification (100%) verified by gel electrophoresis. For S. mansoni sensitivity was highest for LAMP amplification (100%) for standard extraction than PCR and LAMP with LAMP-PURE (99% and 94%). The LAMP-PURE extraction produced false negatives, which require further investigation for this field usable extraction kit. Overall high positive and negative predictive values (90% - 100%) for both species demonstrated a highly robust approach. The LAMP approach is close to point of care use and equally sensitive and specific to detection of species-specific DNA by PCR. LAMP can be an effective means to detect low intensity infection due to its simplicity and minimal DNA extraction requirement. This will enhance the effectiveness of surveillance and MDA control programs of schistosomiasis.

Comparison of a PfHRP2-based rapid diagnostic test and PCR for malaria in a low prevalence setting in rural southern Zambia: implications for elimination

Background

Rapid diagnostic tests (RDTs) detecting histidine-rich protein 2 (PfHRP2) antigen are used to identify individuals with Plasmodium falciparum infection even in low transmission settings seeking to achieve elimination. However, these RDTs lack sensitivity to detect low-density infections, produce false negatives for P. falciparum strains lacking pfhrp2 gene and do not detect species other than P. falciparum.

Methods

Results of a PfHRP2-based RDT and Plasmodium nested PCR were compared in a region of declining malaria transmission in southern Zambia using samples from community-based, cross-sectional surveys from 2008 to 2012. Participants were tested with a PfHRP2-based RDT and a finger prick blood sample was spotted onto filter paper for PCR analysis and used to prepare blood smears for microscopy. Species-specific, real-time, quantitative PCR (q-PCR) was performed on samples that tested positive either by microscopy, RDT or nested PCR.

Results

Of 3,292 total participants enrolled, 12 (0.4%) tested positive by microscopy and 42 (1.3%) by RDT. Of 3,213 (98%) samples tested by nested PCR, 57 (1.8%) were positive, resulting in 87 participants positive by at least one of the three tests. Of these, 61 tested positive for P. falciparum by q-PCR with copy numbers ≤ 2 x 10³ copies/μL, 5 were positive for both P. falciparum and Plasmodium malariae and 2 were positive for P. malariae alone. RDT detected 32 (53%) of P. falciparum positives, failing to detect three of the dual infections with P. malariae. Among 2,975 participants enrolled during a low transmission period between 2009 and 2012, sensitivity of the PfHRP2-based RDT compared to nested PCR was only 17%, with specificity of >99%. The pfhrp gene was detected in 80% of P. falciparum positives; however, comparison of copy number between RDT negative and RDT positive samples suggested that RDT negatives resulted from low parasitaemia and not pfhrp2 gene deletion.

Conclusions

Low-density P. falciparum infections not identified by currently used PfHRP2-based RDTs and the inability to detect non-falciparum malaria will hinder progress to further reduce malaria in low transmission settings of Zambia. More sensitive and specific diagnostic tests will likely be necessary to identify parasite reservoirs and achieve malaria elimination.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0544-3) contains supplementary material, which is available to authorized users.

Malaria vector control at a crossroads: public health entomology and the drive to elimination

Vector control has been at the core of successful malaria control. However, a dearth of field-oriented vector biologists threatens to undermine global reductions in malaria burden. Skilled cadres are needed to manage insecticide resistance, to maintain coverage with current interventions, to develop new paradigms for tackling 'residual' transmission and to target interventions as transmission becomes increasingly heterogeneous. Recognising this human resource crisis, in September 2013, WHO Global Malaria Programme issued guidance for capacity building in entomology and vector control, including recommendations for countries and implementing partners. Ministries were urged to develop long-range strategic plans for building human resources for public health entomology and vector control (including skills in epidemiology, geographic information systems, operational research and programme management) and to set in place the requisite professional posts and career opportunities. Capacity building and national ownership in all partner projects and a clear exit strategy to sustain human and technical resources after project completion were emphasised. Implementing partners were urged to support global and regional efforts to enhance public health entomology capacity. While the challenges inherent in such capacity building are great, so too are the opportunities to establish the next generation of public health entomologists that will enable programmes to continue on the path to malaria elimination.

Remotely-sensed, nocturnal, dew point correlates with malaria transmission in Southern Province, Zambia: a time-series study

BACKGROUND

Plasmodium falciparum transmission has decreased significantly in Zambia in the last decade. The malaria transmission is influenced by environmental variables. Incorporation of environmental variables in models of malaria transmission likely improves model fit and predicts probable trends in malaria disease. This work is based on the hypothesis that remotely-sensed environmental factors, including nocturnal dew point, are associated with malaria transmission and sustain foci of transmission during the low transmission season in the Southern Province of Zambia.

METHODS

Thirty-eight rural health centres in Southern Province, Zambia were divided into three zones based on transmission patterns. Correlations between weekly malaria cases and remotely-sensed nocturnal dew point, nocturnal land surface temperature as well as vegetation indices and rainfall were evaluated in time-series analyses from 2012 week 19 to 2013 week 36. Zonal as well as clinic-based, multivariate, autoregressive, integrated, moving average (ARIMAX) models implementing environmental variables were developed to model transmission in 2011 week 19 to 2012 week 18 and forecast transmission in 2013 week 37 to week 41.

RESULTS

During the dry, low transmission season significantly higher vegetation indices, nocturnal land surface temperature and nocturnal dew point were associated with the areas of higher transmission. Environmental variables improved ARIMAX models. Dew point and normalized differentiated vegetation index were significant predictors and improved all zonal transmission models. In the high-transmission zone, this was also seen for land surface temperature. Clinic models were improved by adding dew point and land surface temperature as well as normalized differentiated vegetation index. The mean average error of prediction for ARIMAX models ranged from 0.7 to 33.5%. Forecasts of malaria incidence were valid for three out of five rural health centres; however, with poor results at the zonal level.

CONCLUSIONS

In this study, the fit of ARIMAX models improves when environmental variables are included. There is a significant association of remotely-sensed nocturnal dew point with malaria transmission. Interestingly, dew point might be one of the factors sustaining malaria transmission in areas of general aridity during the dry season.

Detection of parasite-specific DNA in urine sediment obtained by filtration differentiates between single and mixed infections of Schistosoma mansoni and S. haematobium from endemic areas in Ghana

Differential diagnosis of Schistosoma mansoni and S. haematobium, which often occur sympatrically in Africa, requires both urine and stool and the procedures are low in sensitivity. The standard diagnostic tests, such as Kato-Katz (KK) for S. mansoni eggs and presence of haematuria for S. haematobium both lack sensitivity, produce false-negative results and show reduced accuracy with decreasing intensity of infection. The need for a single diagnostic test with high sensitivity and specificity for both parasites is important as many African countries are implementing Mass Drug Administration (MDA) following recommendations of the World Health Organization (WHO). Eighty-six samples of urine sediment obtained by filtration were collected from a group of 5–23 years old people from an endemic area of southern Ghana. DNA was extracted from the urine sediment on filter paper from which a species-specific repeat fragment was amplified by polymerase chain reaction (PCR) with specific primers for S. mansoni and for S. haematobium. Additionally, all participants were tested by KK (stool) and dipstick for haematuria. Diagnostic parameters for all three tests were analyzed statistically. Amplification of species-specific DNA by PCR showed much higher sensitivity (99%–100%) and specificity (100%) compared to KK and haematuria (sensitivity: 76% and 30% respectively) for both schistosome species. The same pattern was observed when the data were stratified for age group and sex specific analysis. In addition PCR amplification detected DNA from 11 individuals infected with both parasites who were negative by KK and haematuria. This approach of detecting parasite specific DNA from either or both species in a single urine specimen is a practical advantage that avoids the need for two specimens and is more effective than standard tests including those based on serology. This promises to improve the effectiveness of surveillance of MDA control programs of schistosomiasis.

Evaluating local vegetation cover as a risk factor for malaria transmission: a new analytical approach using ImageJ

BACKGROUND

In places where malaria transmission is unstable or is transmitted under hypoendemic conditions, there are periods where limited foci of cases still occur and people become infected. These residual "hot spots" are likely reservoirs of the parasite population and so are fundamental to the seasonal spread and decline of malaria. It is, therefore, important to understand the ecological conditions that permit vector mosquitoes to survive and forage in these specific areas. Features such as local waterways and vegetation, as well as local ecology, particularly nocturnal temperature, humidity, and vegetative sustainability, are important for modeling local mosquito behavior. Vegetation around a homestead likely provides refuge for outdoor resting of these insects and may be a risk factor for malaria transmission. Analysis of this vegetation can be done using satellite information and mapping programs, such as Google Earth, but manual quantification is difficult and can be tedious and subjective. A more objective method is required.

METHODS

Vegetation cover in the environment is reasonably static, particularly in and around homesteads. In order to evaluate and enumerate such information, ImageJ, an image processing software, was used to analyse Google Earth satellite imagery. The number of plants, total amount of vegetation around a homestead and its percentage of the total area were calculated and related to homesteads where cases of malaria were recorded.

RESULTS

Preliminary results were obtained from a series of field trials carried out in South East Zambia in the Choma and Namwala districts from a base at the Macha District Hospital.

CONCLUSIONS

This technique is objective, clear and simple to manipulate and has potential application to determine the role that vegetation proximal to houses may play in affecting mosquito behaviour, foraging and subsequent malaria incidence.

Diagnosis of Schistosoma mansoni without the stool: comparison of three diagnostic tests to detect Schistosoma [corrected] mansoni infection from filtered urine in Zambia

Diagnosis for intestinal Schistosoma mansoni lacks sensitivity and is arduous to conduct. The standard diagnostic tests, Kato-Katz (KK) and circulating cathodic antigen (CCA) both lack sensitivity and with KK, require obtaining, transporting, and examining fresh stool. We compared diagnostic efficacy of KK, CCA, and polymerase chain reaction (PCR) to detect S. mansoni infection (species-specific DNA) from 89 filtered urine samples collected in Zambia. The PCR was the strongest indicator of positive cases with sensitivity and specificity of 100% in comparison to CCA (67% and 60%) and KK (50% and 100%). High positive and negative predictive values (100%) were also indicative of robustness of PCR. The same pattern was observed when stratified for sex and age group-specific analysis. Diagnosis of S. mansoni from filtered urine samples by PCR is an effective means to detect low intensity infection and would enhance the effectiveness of surveillance and control programs of schistosomiasis.

Measuring malaria by passive case detection: a new perspective based on Zambian experience

Most measurements of malaria are based on cross-sectional data and do not reflect the dynamic nature of transmission, particularly when interventions require timely data for planning strategies. Such data can be collected from local rural health centres (RHCs) where the infrastructure is sufficiently developed and where rapid diagnostics are in use. Because in rural areas, the population served by RHC is reasonably static, the regular use of malaria rapid diagnosis in RHCs can provide data to assess local weekly incidence rates, and such data are easily dispersed by cell phones. Essentially each RHC is a potential sentinel site that can deliver critical information to programme planners. Data collected during this process of passive case detection over a five-year period in the Macha area of Zambia show the importance of ecological zones and refugia in the seasonal fluctuation of malaria cases. If this process is implemented nationally it can assist in planning efficient use of resources and may contribute to local management and even elimination of malaria in this region.

Malaria antifolate resistance with contrasting Plasmodium falciparum dihydrofolate reductase (DHFR) polymorphisms in humans and Anopheles mosquitoes

Surveillance for drug-resistant parasites in human blood is a major effort in malaria control. Here we report contrasting antifolate resistance polymorphisms in Plasmodium falciparum when parasites in human blood were compared with parasites in Anopheles vector mosquitoes from sleeping huts in rural Zambia. DNA encoding P. falciparum dihydrofolate reductase (EC 1.5.1.3) was amplified by PCR with allele-specific restriction enzyme digestions. Markedly prevalent pyrimethamine-resistant mutants were evident in human P. falciparum infections--S108N (>90%), with N51I, C59R, and 108N+51I+59R triple mutants (30-80%). This resistance level may be from selection pressure due to decades of sulfadoxine/pyrimethamine use in the region. In contrast, cycloguanil-resistant mutants were detected in very low frequency in parasites from human blood samples-S108T (13%), with A16V and 108T+16V double mutants (∼4%). Surprisingly, pyrimethamine-resistant mutants were of very low prevalence (2-12%) in the midguts of Anopheles arabiensis vector mosquitoes, but cycloguanil-resistant mutants were highly prevalent-S108T (90%), with A16V and the 108T+16V double mutant (49-57%). Structural analysis of the dihydrofolate reductase by in silico modeling revealed a key difference in the enzyme within the NADPH binding pocket, predicting the S108N enzyme to have reduced stability but the S108T enzyme to have increased stability. We conclude that P. falciparum can bear highly host-specific drug-resistant polymorphisms, most likely reflecting different selective pressures found in humans and mosquitoes. Thus, it may be useful to sample both human and mosquito vector infections to accurately ascertain the epidemiological status of drug-resistant alleles.

Clinical utility of squamous and transitional nuclear structure alterations induced by Schistosoma haematobium in chronically infected adults with bladder damage verified by ultrasound in Ghana

OBJECTIVE

To evaluate the clinical utility of quantitative nuclear morphometry--i.e., alteration in nuclear size/shape, DNA content and chromatin structure-of intact cells obtained from the sediment of urine specimens collected from people living in an area highly endemic for Schistosoma haematobium in Ghana.

STUDY DESIGN

Digital images of Feulgen-DNA-stained squamous cell (SC) and transitional cell (TC) urothelial nuclei were captured using the AutoCyte imaging system, and nuclear morphometric descriptors (NMDs) were calculated. A total of 3,495 and 4,523 SC and TC nuclei from normal bladder ultrasound subjects (n =21) and 3,465 and 3,064 SC and TC nuclei from severely abnormal bladder ultrasound subjects (n = 20) were captured.

RESULTS

Univariate logistic regression analyses of pooled SC and TC nuclei training sets showed that 27/40 NMDs and 24/40 NMDs were univariately significant for differentiating between SCs and TCs of subjects with normal and severely abnormal bladder ultrasound. Multivariate models constructed using NMDs with > or = 50% inclusion frequency yielded AUC-ROCs of 75.23% and 74.42% in the SC training and validation, and 69.90% and 66.70% for TC training and validation. Further, a squamous cell patient-specific model predicted severe bladder damage with an AUC-ROC of 86.90%, yielding the sensitivity, specificity and accuracy of 85.00%, 76.19% and 80.49%, respectively.

CONCLUSION

Quantitative nuclear structure alterations can be used to make a noninvasive assessment of cytologic changes observed in both SC and TC bladder epithelia due to S haematobium infection.

Urinary schistosomiasis in Zimbabwean school children: predictors of morbidity

BACKGROUND

The morbid effects of urinary bilharziasis are becoming more evident with the advent of sophisticated diagnostics such as ultrasound. However, such diagnosis of Schistosoma haematobium morbidity is often hampered by lack of funds, proper equipment, or training.

OBJECTIVE

We performed a cross-sectional investigation of schoolchildren in a highly endemic area of east central Zimbabwe in order to assess the utility of a number of simple clinical indicators to predict Schistosoma haematobium morbidity.

METHODS

Prevalence and intensity of S. haematobium infection was determined in 551 schoolchildren, with ultrasound examination of the kidneys and bladder performed on 222. The association of a number of demographic, parasitological, and clinical parameters with clinical outcome was evaluated.

RESULTS

Overall, 60% of the children were infected with S. haematobium . Although lacking specificity, proteinuria and parasite eggs count best predicted bladder pathology. Presence of kidney dilation was associated with fatigue and pain upon urination, but these variables were not very sensitive.

CONCLUSIONS

None of the variables assessed were ideal predictors of morbidity. However, the results suggest that a combination of inexpensive, simple indicators may allow for improved targeting of S. haematobium treatment to those with severe morbidity and better monitoring of the progress of control campaigns when more expensive diagnostic methods are not available.

Urinary tract pathology attributed to Schistosoma haematobium: does parasite genetics play a role?

Disease outcome in persons infected with Schistosoma haematobium varies dramatically, ranging from mild symptoms to severe damage of the kidneys and/or bladder. We used ultrasonography to characterize the extent of urinary tract pathology of infected children in Zimbabwe, and random genetic markers to examine the relationship between genetic diversity of S. haematobium and clinical outcome. One hundred thirty-three parasite isolates from 12 students with mild lesions and 13 with severe lesions were compared. Using four randomly amplified polymorphic DNA (RAPD) markers, we scored parasite allelic frequencies at 53 loci. Although parasite heterogeneity did not differ, allelic frequencies at eight loci differed significantly between the mild and severe groups. Parasite isolates were analyzed further using a modified cluster analysis that segregated the population into 13 clusters of associated genotypes. Three clusters were significantly over-represented in children with severe lesions. Our findings, although preliminary, suggest that parasite genetic associations may be important in clinical outcome.

Epidemiological assessment of Schistosoma haematobium-induced kidney and bladder pathology in rural Zimbabwe

Clinical outcome of Schistosoma haematobium infection may vary significantly, ranging from mild symptoms to severe damage of urinary tract organs. This present study was undertaken to assess the relationship of a number of epidemiological and parasitological parameters with disease outcome in children from rural Zimbabwe. We surveyed 551 primary school students from three schools in the Chikwaka Communal Lands for schistosomiasis; 59.7% were infected with S. haematobium. Ultrasound examination of 189 of the infected students revealed that 50% had pathological changes of their bladder and 36% had abnormal pyelon dilation of at least one of their kidneys. Intensity of infection, certain water contact behaviours, male gender, proteinuria, and self-perceived haematuria were associated with increased bladder damage. Strenuous playing was negatively associated with pathology, especially for those with the highest grade of bladder damage. Kidney pathology was significantly linked with fatigue and pain upon urination and was more prevalent in students from schools closest to the major river systems. Our findings suggest that pathology due to urinary schistosomiasis is widespread and symptomatic in this population. The associations with bladder and kidney pathology can be used to predict disease severity and may be useful in targeting treatment to those most at risk.

Genetic diversity of a population of Schistosoma haematobium derived from schoolchildren in east central Zimbabwe

To characterize the extent of genetic diversity of Schistosoma haematobium within and among its definitive host (intra- and interhost parasite diversity), 133 individual isolates from 25 infected schoolchildren were compared using randomly amplified polymorphic DNA markers. With 4 primers, 53 unambiguous loci were identified, and of these, 22 were polymorphic. Mean heterozygosity in the population was 0.116 +/- 0.043. Analysis of molecular variance showed the majority of variance occurred within, rather than between, hosts. Frequencies of certain alleles segregated the parasite population into 13 distinct clusters of associated genotypes, with 4 of these first appearing 10 mo after the initial survey. Considering the level of diversity within this limited geographical area and the possibility of rapid turnover of genotypes, parasite variance may impact acquired immunity and clinical outcome of the infection.

Recovery of avian schistosome cercariae from water using penetration stimulant matrix with an unsaturated fatty acid

Avian schistosome cercariae that emerge from aquatic snails can penetrate human skin causing cercarial dermatitis resulting in serious skin disease in sensitized and immunocompromised people. A trap developed for Schistosoma mansoni cercariae was tested for recovery of avian schistosome cercariae. A matrix with an unsaturated fatty acid, linoleic acid stimulates attachment and penetration of Trichobilharzia spp. cercariae, and the immobilized larvae can be subsequently visualized. The number of trapped cercariae exceeded by 3 to 7 times the number of larvae expected on the surface of the trap, based on their random distribution in the water. Recognition, attachment, and penetration of Trichobilharzia spp. cercariae led to injection of more secretory products into the stimulant matrix than by Schistosoma mansoni cercariae. This method can assist in the identification of waters infected with avian schistosome cercariae so that human exposure to these parasitic larvae can be minimized.

Environmental and geographical factors contributing to watershed contamination with Cryptosporidium parvum oocysts

Cryptosporidium parvum is a waterborne parasite which infects cattle and produces life-threatening zoonosis in people with impaired immune systems. Digital maps of 100-year floodplain boundaries, land use/cover, and livestock operations were used to select and characterize cattle farms in the floodplain area in Lancaster County, Pennsylvania, U.S.A. Over 21% of the cattle farms were located within 100-year floodplain boundaries. On average, a single farm comprised 12.8 ha of pasture (including buildings and farmyard) at risk of inundation. In all farms cattle had unlimited access to the creek. Manure samples collected from closed-in calf pens, cow/heifer yard runoff, and cattle paths through the creek were tested for C. parvum. On 64% of the farms (n=50) at least one sample was positive for C. parvum, and 44% of the farms had oocysts in all manure samples. Concentration varied from 90 to 371 oocysts/g and was significantly higher (P<0.02) in calf samples than in manure from cow and cow/heifer.

Social and cultural factors affecting rates of regular retreatment of mosquito nets with insecticide in Bagamoyo District, Tanzania

Insecticide-treated mosquito nets have an impact on mortality and morbidity in young children under controlled conditions. When integrated into larger control programs, there is the danger that rates of regular retreatment of the nets with insecticide will drop, greatly limiting their effectiveness as a public health intervention. In Bagamoyo District, Tanzania, rates of retreatment dropped significantly when payment for the insecticide was introduced. A series of neighbourhood (hamlet) meetings were held in all study villages to discuss people's concerns about the insecticide and ways to increase rates of retreatment. Although changes were made in the procedure for retreatment, rates of retreatment remained lower than expected and showed marked variation within as well as between villages. We then conducted unstructured key informant interviews as well as informal discussions in a village with strong variation between different sectors of the villages in rates of retreatment. While logistical problems were most frequently cited as reasons not to bring nets for retreatment, political and social divisions within the community provided a better explanation. This is borne out by the low response to rearrangements in logistics which made retreating the nets significantly easier for households, and the higher response when changes were made in the channels of communication as well as the logistic features. It is clearly more difficult for villagers to appreciate the benefits of the insecticide than those of the nets. Great emphasis needs to be placed on the insecticide and its beneficial effects from the outset for any large-scale programme to be sustainable.

Post treatment sensitivity studies with the ParaSight-F test for malaria diagnosis in Zimbabwe

The post-treatment diagnostic performance of the Plasmodium falciparum histidine-rich protein (HRP-II) antigen detection test, ParaSight-F test, was assessed on 55 falciparum malaria cases treated with chloroquine during in vivo drug sensitivity studies. The post-treatment sensitivity of the test remained high, except for an insignificant decline on day 1. However, specificity dropped sharply by day 1, subsequently increasing linearly with time to satisfactory values by day 10. As expected, from its inverse relationship to specificity, the false positive rate was high on day 1 and decreased linearly to low level by day 10. The temporary increase in false positive rate-following treatment was due to persistent parasite antigen, rather than subpatent parasitaemia. Thus findings showed that positive readings by the test within 10 days post-treatment may occur in cured cases and will not necessarily imply treatment failure. Furthermore it will be important to take patient antimalarial history into consideration during routine usage of the test for malaria diagnosis. The trend of Youden's J-index for the ParaSight-F test showed that from 10 days post-treatment, the test was generally reliable, with positive readings indicating active infection. It was concluded that the ParaSight-F test was not only valuable at confirming malaria diagnosis on clinical cases in seasonal transmission areas, but had potential for application to detect recrudescent infections within 2 weeks of chloroquine treatment.

Trial of the ParaSight-F test for malaria diagnosis in the primary health care system, Zimbabwe

Rapid diagnosis of Plasmodium falciparum malaria remains one of the main limitations to prompt treatment. Diagnosis based on clinical symptoms is decidedly unreliable, especially in areas of seasonal transmission like Zimbabwe. In view of this, the Plasmodium falciparum histidine rich protein (HRP-II) antigen detection assay (ParaSight-F test) was tried at 10 health centres in 3 malaria endemicity zones of Zimbabwe, as a malaria diagnostic tool for primary health care. Parasitological evaluations were conducted using thick and thin film microscopy as gold standard, and ease of test operation and practicability to nurses were ascertained by questionnaire. The sensitivity of the test did not vary substantially by endemicity zone and was approximately 93%. Specificities were 85, 72 and 92% in the hyperendemic, mesoendemic and hypoendemic zones, respectively. Positive predictive values varied considerably with endemicity, the lowest being in the hypoendemic zone (56%). However, negative predictive values did not change significantly, with a mean of 94%. It was found that the ParaSight-F test reduced mistreatment for malaria, relative to clinical diagnosis, by up to 81%, especially in the hypoendemic region. Test acceptability evaluations were good.

Schistosoma mansoni: the immune response against cercarial glycocalyx

Schistosoma mansoni cercarial glycocalyx was separated and purified by Sephacryl-300 SR. It was found to stimulate the humoral immune response in mice injected with it. Antiglycoalyx antibodies raised in CD/1 mice were found to be cytotoxic to schistosomula in vitro. But conversely, no protective effect was demonstrated in vivo. Eosinophil-mediated cytotoxicity was found to have no effector function in the murine immune response against schistosomes. A monoclonal antiglycocalyx IgM was prepared during our study. It was found to have no cytotoxic effect on schistosomules in vitro. However, it was found to have an inhibitory activity blocking the cytotoxic effect of other antiglycocalyx isotypes in the immune mouse. The contradiction between the result of antiglycocalyx antibody-mediated cytotoxicity obtained in vivo and that obtained in vitro is in itself revealing and suggests that the effect is crucially dependent upon factors as yet poorly understood.

Treatment practices for degedege, a locally recognized febrile illness, and implications for strategies to decrease mortality from severe malaria in Bagamoyo District, Tanzania

Malaria remains one of the chief causes of mortality among young children in sub-Saharan Africa. Verbal autopsies for cases of childhood mortality in Bagamoyo District, Tanzania demonstrated that degedege, a locally defined illness of children characterized by fever and convulsions, is frequently treated by traditional healers. To investigate this further, an ethnographic study was carried out in one village that included in-depth interviews with 14 traditional healers and 3 focus groups with parents. Parents and traditional healers were unanimous in their conviction that degedege requires traditional treatments, at least initially, and that these treatments are effective. While traditional healers do refer cases that are not improving to the District Hospital, this frequently occurs late in the course of the illness, after one or more stages of traditional treatments. The prognosis will thus be poor for those children who are suffering from severe malaria. Consideration should be given to enlisting the support of traditional healers in efforts to improve treatment for severe malaria, including teaching them how to distinguish febrile convulsions from cases of severe malaria.

The polymerase chain reaction method as a tool for identifying members of the Anopheles gambiae complex (Diptera:Culicidae) in northeastern Tanzania

Polymerase chain reaction (PCR) primers developed at the Centers for Disease Control in Atlanta for the identification of members of the Anopheles (Cellia) gambiae Giles complex were tested on material collected in the Bagamoyo and Muheza districts of northeastern Tanzania. Part of the sample from Bagamoyo was chromosomally identified and correlated with the PCR identifications. This sample contained 170 Anopheles arabiensis, 328 An. gambiae, and 58 Anopheles merus, of which 121, 237, and 54 specimens, respectively, were identified with both PCR and chromosomes. Three specimens identified chromosomally as An. merus gave only the PCR fragment characteristic for Anopheles quadriannulatus, but on retesting gave the correct result. The Muheza sample consisted of 771 An. arabiensis, 852 An. gambiae, 43 An. merus, and 4 specimens producing the fragment characteristic for An. quadriannulatus. Because An. quadriannulatus has never been recorded from mainland Tanzania and due to the high number of specimens that produced no result (193), it is probable that DNA degradation led to misidentification of An. merus specimens as An. quadriannulatus. The overall probability of correct identification by PCR was 99.685% at first testing, which compares favorably with other genetic methods currently in use.

Local terminology for febrile illnesses in Bagamoyo District, Tanzania and its impact on the design of a community-based malaria control programme

This paper reviews results of several ethnographic studies that have examined the issue of local terminology for malaria in Africa, then presents findings from an on-going study in Bagamoyo District, Tanzania. The study used a mixture of qualitative and quantitative interview methods to examine local perceptions of malaria and malaria treatment practices. Although the local term homa ya malaria or malaria fever appeared on the surface to correspond closely with the biomedical term malaria, significant and often subtle differences were found between the two terms. Of perhaps greatest importance, common consequences of malaria in endemic areas such as cerebral malaria in young children, severe anaemia and malaria in pregnancy were not connected with homa ya malaria by many people. A set of guidelines are described that were used to determine how best to promote acceptance and use of insecticide-impregnated mosquito nets, given these results. It is demonstrated that the position of the term used to denote malaria in the local taxonomy of febrile illnesses has important implications for the design of health education interventions.

Comparison of sampling anopheline mosquitoes by light-trap and human-bait collections indoors at Bagamoyo, Tanzania

The mosquito sampling efficiency of CDC miniature light-traps, relative to night-biting collections, was evaluated indoors at two sites in coastal Tanzania. We found that the total number of anophelines captured overnight by light-traps (hung beside a bednet in use) was 1.23 times the number of anophelines captured by human-bait collections. This relationship was not affected significantly by changes in the mosquito density, order of trapping method, date of sampling, or number of household occupants. Malaria sporozoite rates were twice as high among mosquitoes captured by light-trap as compared to those captured by night-biting collection. This was attributed to the tendency of light-traps to capture a larger proportion of gravid mosquitoes, which also had high sporozoite rates. The differences in sporozoites rates according to abdominal stage indicates that unfed mosquitoes captured by light-traps may define more precisely the human-biting activity and sporozoite rates as seen by night-biting collections. Our study shows that light-traps, when used in combination with night-biting collections, can be an effective and sensitive means for measuring human-biting activity and the sporozoite rate.

Malaria infection potential of anopheline mosquitoes sampled by light trapping indoors in coastal Tanzanian villages

Anopheline mosquito populations were studied during 1992 in seven villages south of Bagamoyo, coastal Tanzania, prior to malaria control intervention using insecticide treated bednets. To collect mosquitoes, CDC light traps were used in ten houses per village fortnightly for 12 months. Anopheles females were identified and checked by ELISA for the presence of malaria sporozoite antigen and source of bloodmeal. An.funestus peaked in June-July after the long rains. Three members of the An.gambiae complex had different seasonality: An.arabiensis, An.gambiae and small numbers of An.merus were collected. In most villages transmission was extremely high and perennial with the entomological inoculation rate reaching three to eleven infective bites per person per night in July and persisting at around 0.1 and 1 for most of the remainder of the year. Sporozoite infection rates within the An.gambiae complex ranged from 2% to 25%, with the peaks in January and July following the two rainy periods. An.funestus showed a similar pattern. The light traps were reliable, simple to operate, and proved to be satisfactory to study the mosquito vector population.

A chemokinetic response in Schistosoma mansoni cercariae

Schistosoma mansoni cercariae have been shown to aggregate in the presence of glass slides treated with clear nail varnish and linoleic acid. In choice chambers cercariae move toward the stimulant, but this behavior is not seen when linoleic acid is omitted. After 30-45 min, the cercariae were concentrated near the end of the choice-chamber containing the linoleic acid slide. When the cercariae were added in the center of the choice chamber, they formed a diffuse cloud that dispersed slowly in both directions in the absence of linoleic acid. Cercariae aggregating in the vicinity of a stimulant surface are not immediately stimulated to commence penetration; this appears to be time and dose related.

Extraction of Haemoproteus columbae (Haemosporina: Haemoproteidae) antigen from rock dove pigeons (Columba livia) and its use in an antibody ELISA

Erythrocytic stages of Haemoproteus columbae were extracted from the cytoplasm of nucleated red blood cells (RBC) of Rock dove pigeons (Columba livia) using cationic detergent (N,N',N'-polyoxyethylene(10)-N-tallow-1,3-diaminopropane [EDTA-20]) and discontinuous Percoll gradient density. Crude RBC extract (CRBCE) antigen was prepared. Parasitized RBCs were more resistant to EDTA-20 action than unparasitized cells. An enzyme-linked immunosorbent assay (ELISA) was developed for detection of anti-H. columbae immunoglobulins in 30 wild-captured C. livia. Whole blood, serum, and dried blood on filter paper gave similar results; the latter was selected for sampling convenience. Optimal antigen concentration was 5 micrograms/ml, and anti-H. columbae immunoglobulins were detectable at a 10(-4.11) dilutions. The binding efficacy of anti-chicken IgG to the pigeon immunoglobulins was significantly higher than anti-duck IgG or anti-turkey IgG. Parasitemia by Giemsa-stained thin blood smears ranged from 20.0 to 47.5%, mean = 32.4 +/- 8.3%; 17 of 30 birds had multiply infected RBCs with a mean parasitemia of 2.4 +/- 1.1%, range 0.7-4.9%; 27 birds were positive by the ELISA. No clinical signs of infection were observed. ELISA absorbance values were not correlated with the level of parasitemia in individual birds. All pigeons were negative for anti-Plasmodium relictum and anti-P. elongatum immunoglobulins as determined by ELISA. The pigeons were not subclinically infected with Plasmodium spp. as determined by inoculation of domestic ducklings with blood from dexamethasone-immunosuppressed pigeons.

Seasonal variation in the perceived risk of malaria: implications for the promotion of insecticide-impregnated bed nets

Bed nets (mosquito nets), impregnated every 6 months with pyrethroid insecticides, are a simple, low-cost malaria control method well suited to conditions in sub-Saharan Africa. As large seasonal variations in levels of net usage may seriously limit the potential impact of the nets on malaria transmission, a study was conducted on local definitions of seasons, perceptions of seasonal variation in mosquito populations and incidence of febrile illnesses in Bagamoyo District, Tanzania, to aid in the design of a communication strategy for promoting sustained use of the nets. Both the diagnosis and treatment of febrile illnesses are affected by what season people think it is, by what illnesses they think are common in each season, and also by their perceptions of how abundant mosquitoes are. During dry seasons when mosquitoes are scarce and malaria is thought to be unlikely, it will be difficult to attain high rates of net usage. It will be necessary to develop locally-appropriate messages and communication materials that explain how it is possible that malaria can be a threat even when mosquitoes are few. Cultural consensus analysis was found to be a particularly valuable tool for understanding the reasons behind large variations in local perceptions of seasonality.

Chloroquine resistant Plasmodium falciparum in coastal Tanzania. A challenge to the continued strategy of village based chemotherapy for malaria control

An in vivo study to assess Plasmodium falciparum sensitivity to chloroquine was conducted in two villages of the Bagamoyo District, Tanzania in December 1992. The WHO standard field test (7 days) and the extended test (28 days) were carried out on symptom free children. The presence of chloroquine resistance was confirmed with 59% of infections being found resistant. Fifty-three percent were RI, 2% were at RII and 4% at RIII levels of resistance. Dosage was 25 mg/kg chloroquine base delivered over three days.

Molluscan defence mechanisms: Immunity or population biology?

In recent studies of associations between host and parasite, there has been a tendency to consider the internal defence mechanisms of the mollusc as pivotal in the relationship. However, evolution is a population-based phenomenon, and it is by considering populations rather than individuals that the success of these associations can best be appreciated. Among susceptible host species within the biocoenosis, truly resistant strains appear to be remarkably rare. Clive Shiff here examines mechanisms of defence or avoidance among molluscan hosts of tremotodes from both the internal and ecological perspective.

Viability of Notocotylus attenuatus (Trematoda: Notocotylidae) metacercariae under adverse conditions

The viability of Notocotylus attenuatus metacercariae was 80% at 20 wk post-encystment (PE) and decreased to 10% at 24 wk PE. Cyst viability was influenced by the duration of cercarial swimming activity prior to encystment, by the occurrence of cyst associations, and by the type of cyst storage. This is the first report on cyst associations formed by Notocotylidae cercariae. Cyst associations were formed only by cercariae encysting shortly after their emergence from snails. In cyst associations metacercariae did not overlap, but were separated by regular distances ranged from 20.4 to 24.5 microns mean = 22.3 microns, SE = 0.41. The mucoid materials which formed the external cyst wall covered the areas between parasites seven if distances were comparable with the cyst size. In cyst associations, metacercariae in the water and those located close to the water were viable up to 24 wk PE. Cercariae with extended swimming activity did not form associations even when present in numbers, < or = 50 cercariae per cm3. The cysts established by these cercariae had a thin external cyst wall, and were not viable by 12 wk PE.

The ParaSightR-F test: A simple rapid manual dipstick test to detect Plasmodium falciparum infection

A rapid diagnostic for Plasmodium falciparum based on an antigen capture has been incorporated in a simple, easily interpreted dipstick by Becton Dickinson Advanced Diagnostics. In this article Clive Shiff, Japhet Minjas and Zul Premji discuss its evaluation in rural Tanzania and the implications of such a test in handling malaria cases under field conditions.

ELISA method for detecting anti-Plasmodium relictum and anti-Plasmodium elongatum antibody in infected duckling sera using Plasmodium falciparum antigens

An enzyme-linked immunosorbent assay (ELISA) with 3 Plasmodium falciparum NF-54 antigens, R32tet32, P.F.R27, and crude red blood cell extract (CRBCE), was tested for detection of anti-Plasmodium relictum and anti-Plasmodium elongatum antibodies in sera from experimentally infected ducklings. Whole blood, serum, and dried blood on filter paper gave similar results. The latter was selected for convenience. All birds infected by experimental blood challenge, but not exposed to sporozoites, had detectable antibody (up to 1.0 x 10(-3.8) dilution) reactive with R32tet32, P.F.R27, and CRBCE antigens. Ducklings infected with P. elongatum had higher antibody levels than those infected with P. relictum. In a blind trial, the described ELISA accurately distinguished sera taken from infected and uninfected ducklings. This study provides the first evidence on cross reactivity in the ELISA format between P. falciparum antigens and antibodies induced by P. relictum and P. elongatum in experimentally infected ducklings. The proposed ELISA is fast, easy to perform, reproducible, and requires a minimal amount of equipment. The assay can be used for the detection of P. relictum and P. elongatum antibodies in captive or wild ducks, along with monitoring the level of antibody in selected groups of birds or for surveys of laboratory experiments where evidence of infection is required.

The rapid manual ParaSight-F test. A new diagnostic tool for Plasmodium falciparum infection

A rapid manual test for Plasmodium falciparum, the ParaSight-F test, has been used on a series of patients in a holoendemic malaria area of coastal Tanzania. The test, which is an antigen capture test detecting trophozoite-derived histidine rich protein-II, is simple to perform and provides a definitive answer in about 10 min. It requires no special equipment and is read using a single drop of blood. When compared with 272 thick blood films examined microscopically by 2 observers and confirmed by the QBC malaria test, the ParaSight-F test had 88.9% sensitivity and 87.5% specificity. Detectable antigenaemia in a group of 40 people declined following treatment with Fansidar and by 10 d after treatment all but 4 individuals were antigen free. The remaining 4, although clear of peripheral parasitaemia, remained antigenaemic for 14 d. The test shows great promise for rapid effective diagnosis of P. falciparum in clinics and village health centres where there is no facility for microscopy. Because of its accuracy and rapid action it may even obviate the need for microscopical examination of blood films to diagnose P. falciparum malaria.

Experimental infection of domestic ducks and rodents by Notocotylus attenuatus (Trematoda: Notocotylidae)

In order to study transmission patterns of Notocotylus attenuatus five 3-wk-old domestic ducks, five 8-wk-old rats and ten 4-wk-old mice were infected with the parasite. All ducks became infected and all flukes were recovered from the intestinal ceca. Worms moved down the length of the cecum during development and as the parasites grew they changed their method of attachment. Flukes became gravid by day 16 post-infection, after which growth ceased. Egg filaments appear to play a role in the formation and movement of worm egg clusters from the distal portion of the cecum to the lumen of small intestine. Rodents also became infected with the parasite producing granulomatous nodular lesions in the lower small intestine but all flukes in the granulomata were dead. It is unlikely that transmission of this trematode can depend on mice and rats.

Excystment in vitro of Cotylurus cornutus (Trematoda: Strigeidae) metacercariae

An acid-medium pretreatment appeared to be essential for in vitro excystation of Cotylurus cornutus metacercarial cysts. Both acid-pepsin or acid-saline were effective but optimum excystation occurred after 15 min acid-pepsin pretreatment and subsequent 2 hr treatment at 41.5 C in an alkaline bile salt-trypsin medium. The rate of excystation was rapid, reaching 78.1% by 1 hr and increasing to 84.3% after 2 hr. Storage of metacercarial cysts up to 16 wk at 4 C in sterile Locke's 1:1 solution did not alter cyst viability.