CHANGING TRENDS IN THE DIAGNOSIS OF MALARIA AND TYPHOID FEVER

Malaria In tropical Africa, fever is commonly associated with malaria that was known variously as Roman fever,   marsh fever(Rocco 2003),  and whose name was derived from the Italian ‘Mal=bad, Aria=air.’(Prakash et al. 2013).    Malaria is caused by five species of the plasmodium parasite: P. falciparum, P. vivax, P.ovale, P. malariae and P. knowlesi all of which are transmitted by the female anopheles mosquito, which is the vector of the parasite. Over 2.4 billion people are at risk of P. falciparum infection, which results in about 300 to  500 million clinical episodes and 1million deaths annually (Bousema & Drakeley 2011). While about 2.9 billion persons are at risk for P. vivax infection with up to 300 million clinical episodes per year(Bousema & Drakeley 2011). A vast proportion of malaria morbidity occurs in sub-Saharan Africa, (SSA). However, there is substantial evidence that the intensity of malaria transmission in Africa is declining (Snow et al. 2012, Graz et al. 2011), and rapid malaria parasitemia tests are well distributed in endemic countries and easy to use (Graz et al. 2011).    Certain recent developments, however, are worth considering when assessing malaria burden and control.First, the discovery of Plasmodium falciparum with deleted histidine-rich repeat region of the histidine-rich-protein 2 and the evidence that parasites not detected by HRP2 lateral flow immunoassay(LFI) cause latent infection(Koita et al. 2012), is of extreme importance in endemic countries such as Sierra Leone, where HRP2  LFIs are predominantly used. LFIs have made malaria testing ubiquitous in sub-Saharan Africa, including in very remote areas. However, false negatives resulting from deleted hrp2 in certain P.falciparum may result in lower prevalence reports. The alternative dipstick to HRP2 LFIs is the Plasmodium lactate dehydrogenase (pLDH)-based LFI. However, in Sierra Leone, the use of pLDH LFIs is less common, and a similar trend exists in the other parts of Sub-Saharan Africa. LFIs were intended to be used primarily in resource-limited locations where expert microscopists are unavailable. So the use of LFIs is not routinely duplicated with smear results in many developing countries. This could be a setback for resource-poor settings.The use of point of care, multiplex molecular detection methods have been highlighted as a means of salvaging diagnosis in resource-poor countries, but cost remains a major limitation. Notwithstanding, PCR is emerging as most sensitive malaria diagnostic apart from rapid antigen tests. Antigens and DNA may persist in blood after parasite clearance through treatment.  A plausible alternative has sought sexual stages of malaria parasites representing a small fraction of parasites during infection(Tao et al. 2014), but which can also be detected in body fluids such as saliva. Prior evidence indicates that saliva is an excellent non-invasive candidate for rapid malaria testing (Fung et al. 2012), but this aspect of malaria diagnostics is still under development including rapid tests based on nano trap technology.There has been a renewed global commitment for malaria elimination and both symptomatic and asymptomatic malaria infections are critical for the elimination of malaria. Novel diagnosis of subclinical malaria targeting sexual stages of the parasite are emerging, but the best candidate for such diagnostics are those that could be adaptable to the resource-poor settings in Africa. One such candidate is the nano trap, saliva-based, malaria rapid test that is under development by Johns Hopkins(http://www.jhsph.edu/news/news-releases/2015/johns-hopkins-bloomberg-school-of-public-health-researchers-receive-grant-to-evaluate-malaria-detection-test.html). Typhoid Fever In the case of typhoid fever, there seems to be an over-diagnosis.  The gold standard for the diagnosis of typhoid is by blood culture, which has a sensitivity of 40-60%(Parry et al. 1999), but low-cost tests, mainly the widal test, are more adaptable to resource-poverty and are commonly used in resource-poor settings such as Sierra Leone. Widal tests have been in use for over 110 years, but the results are very controversial(Olopoenia & King 2000, Nga et al. 2012),  and the test suffers from low specificity in endemic countries probably as a result of an increase in population antibody levels (Clegg et al. 1994).A positive Widal test does not always denote the presence of typhoid fever. Apart from increased population antibody levels, there exist up to 40 cross-reacting antigens between Salmonella enterica serotype Typhi and other Enterobacteriaceae(Parry et al. 1999). Cross-reacting antigens could also be from malaria, brucellosis, dengue fever, chronic liver disease or endocarditis(Colle et al. 1996).Blood culture which is the gold standard is time-consuming and may delay treatment apart from its inherently low sensitivity.  Several typhoid dipsticks have been reported, but side-by-side independent assessments in endemic countries do not always yield the expected outcome.Polymerase chain reaction is currently a better option for diagnosing typhoid fever with same day result, but cost remains a big issue in countries that could be most in need. While suitable alternatives based on economic conditions of countries are sought, the cut-off value for the widal test requires evaluation and standardization. Having a wrong diagnosis at the point of care could lead to wrong clinical outcomes.

Attitudes toward home-based malaria testing in rural and urban Sierra Leone

Background The purpose of this study was to examine malaria testing practices and preferences in Bo, Sierra Leone, and to ascertain interest in and willingness to take a home-based rapid diagnostic test administered by a community health volunteer (CHV) or a trained family member rather than travelling to a clinical facility for laboratory-based testing. Methods A population-based, cross-sectional survey of 667 randomly-sampled rural households and 157 urban households was conducted in December 2013 and January 2014. Results Among rural residents, 69% preferred a self/family- or CHV-conducted home-based malaria test and 20% preferred a laboratory-based test (with others indicating no preference). Among urban residents, these numbers were 38% and 44%, respectively. If offered a home-based test, 28% of rural residents would prefer a self/family-conducted test and 68% would prefer a CHV-assisted test. For urban residents, these numbers were 21% and 77%. In total, 36% of rural and 63% of urban residents reported usually taking a diagnostic test to confirm suspected malaria. The most common reasons for not seeking malaria testing were the cost of testing, waiting to see if the fever resolved on its own, and not wanting to travel to a clinical facility for a test. In total, 32% of rural and 27% of urban participants were very confident they could perform a malaria test on themselves or a family member without assistance, 50% of rural and 62% of urban participants were very confident they could perform a test after training, and 56% of rural and 33% of urban participants said they would pay more for a home-based test than a laboratory-based test. Conclusion Expanding community case management of malaria to include home testing by CHVs and family members may increase the proportion of individuals with febrile illnesses who confirm a positive diagnosis prior to initiating treatment

Surveillance of Vector-Borne Infections (Chikungunya, Dengue, and Malaria) in Bo, Sierra Leone, 2012–2013

Malaria remains a significant cause of morbidity and mortality in West Africa, but the contribution of other vector-borne infections (VBIs) to the burden of disease has been understudied. We used rapid diagnostic tests (RDTs) for three VBIs to test blood samples from 1,795 febrile residents of Bo City, Sierra Leone, over a 1-year period in 2012–2013. In total, 24% of the tests were positive for malaria, fewer than 5% were positive for markers of dengue virus infection, and 39% were positive for IgM directed against chikungunya virus (CHIKV) or a related alphavirus. In total, more than half (55%) of these febrile individuals tested positive for at least one of the three VBIs, which highlights the very high burden of vector-borne diseases in this population. The prevalence of positives on the Chikungunya IgM and dengue tests did not vary significantly with age (P > 0.36), but higher rates of malaria were observed in children < 15 years of age (P < 0.001). Positive results on the Chikungunya IgM RDTs were moderately correlated with rainfall (r 2 = 0.599). Based on the high prevalence of positive results on the Chikungunya IgM RDTs from individuals Bo and its environs, there is a need to examine whether an ecological shift toward a greater burden from CHIKV or related alphaviruses is occurring in other parts of Sierra Leone or the West African region

Prevalence of markers of HIV infection among febrile adults and children in Bo, Sierra Leone, 2012-2013.

The goal of this study was to examine the prevalence of HIV among febrile patients seeking care in Mercy Hospital, Bo, Sierra Leone, in 2012-2013. A total of 1207 febrile persons were tested for HIV with Determine™ and SD Bioline rapid diagnostic tests kits that detect the presence of HIV antibodies and HIV p24 antigens. The overall prevalence of HIV among the tested patients was 8.9%, which is considerably higher than the < 2% prevalence of HIV reported previously in the general population. While these results are not sufficient to prove a causal relationship, the obtained data imply that HIV positive individuals may be more likely to suffer from febrile infectious diseases than individuals without HIV infection. Increasing the availability and use of HIV testing services will allow antiretroviral therapy to be accessed in a timely manner and improve health status among people living with HIV

Reemergence of chikungunya virus in Bo, Sierra Leone.

We diagnosed 400 possible IgM-positive cases of chikungunya virus in Bo, Sierra Leone, during July 2012-January 2013 by using lateral flow immunoassays. Cases detected likely represent only a small fraction of total cases. Further laboratory testing is required to confirm this outbreak and characterize the virus

Ebola in Freetown Area, Sierra Leone — A Case Study of 581 Patients

Schieffelin et al. (Nov. 27 issue)1 reported on 106 patients with Ebola virus disease who were treated in Kenema, Sierra Leone, in May and June 2014. Here we report similar data on the 631 patients with Ebola virus disease, as confirmed by polymerase-chain-reaction assay, who were admitted to the Ebola treatment center at the Hastings Police Training School near Freetown, Sierra Leone, on or after September 20, 2014 (the date on which the first patients were admitted to that center). The 31% case fatality rate at Hastings is lower than the 74% rate reported by Schieffelin et al

Estimating the size of urban populations using Landsat images: a case study of Bo, Sierra Leone, West Africa

Background This is the third paper in a 3-paper series evaluating alternative models for rapidly estimating neighborhood populations using limited survey data, augmented with aerial imagery. Methods Bayesian methods were used to sample the large solution space of candidate regression models for estimating population density. Results We accurately estimated the population densities and counts of 20 neighborhoods in the city of Bo, Sierra Leone, using statistical measures derived from Landsat multi-band satellite imagery. The best regression model proposed estimated the latter with an absolute median proportional error of 8.0%, while the total population of the 20 neighborhoods was estimated with an error of less than 1.0%. We also compare our results with those obtained using an empirical Bayes approach. Conclusions Our approach provides a rapid and effective method for constructing predictive models for population densities and counts utilizing remote sensing imagery. Our results, including cross-validation analysis, suggest that masking non-urban areas in the Landsat section images prior to computing the candidate covariate regressors should further improve model generality

Methods for determining the uncertainty of population estimates derived from satellite imagery and limited survey data: a case study of Bo city, Sierra Leone.

This study demonstrates the use of bootstrap methods to estimate the total population of urban and periurban areas using satellite imagery and limited survey data. We conducted complete household surveys in 20 neighborhoods in the city of Bo, Sierra Leone, which collectively were home to 25,954 persons living in 1,979 residential structures. For five of those twenty sections, we quantized the rooftop areas of structures extracted from satellite images. We used bootstrap statistical methods to estimate the total population of the pooled sections, including the associated uncertainty intervals, as a function of sample size. Evaluations based either on rooftop area per person or on the mean number of occupants per residence both converged on the true population size. We demonstrate with this simulation that demographic surveys of a relatively small proportion of residences can provide a foundation for accurately estimating the total population in conjunction with aerial photographs

Seroprevalence of hepatitis B surface antigen (HBsAg) in Bo, Sierra Leone, 2012–2013

Abstract Objective The aim of this study was to determine the prevalence of hepatitis B surface antigen (HBsAg) among febrile individuals tested at Mercy Hospital Research Laboratory (MHRL) in Bo, Sierra Leone. Results A total of 860 febrile individuals ages 5 years and older were tested by MHRL between July 2012 and June 2013 with a Standard Diagnostics Bioline HBsAg rapid diagnostic test. The overall HBsAg prevalence rate was 13.7%, including a rate of 15.5% among males and 12.6% among females. The HBsAg rate did not differ by child or adult age group (p > 0.5). The prevalence rate in Bo was similar to the 11–15% HBsAg prevalence rates reported in the past decade from other studies across West Africa. Scaling up the infant hepatitis B vaccination program in Sierra Leone will be important for reducing the future burden of disease and premature death attributable to chronic viral hepatitis B disease

Use of real-time multiplex PCR, malaria rapid diagnostic test and microscopy to investigate the prevalence of Plasmodium species among febrile hospital patients in Sierra Leone

Background Malaria continues to affect over 200 million individuals every year, especially children in Africa. Rapid and sensitive detection and identification of Plasmodium parasites is crucial for treating patients and monitoring of control efforts. Compared to traditional diagnostic methods such as microscopy and rapid diagnostic tests (RDTs), DNA based methods, such as polymerase chain reaction (PCR) offer significantly higher sensitivity, definitive discrimination of Plasmodium species, and detection of mixed infections. While PCR is not currently optimized for routine diagnostics, its role in epidemiological studies is increasing as the world moves closer toward regional and eventually global malaria elimination. This study demonstrates the field use of a novel, ambient temperature-stabilized, multiplexed PCR assay in a small hospital setting in Sierra Leone. Methods Blood samples from 534 febrile individuals reporting to a hospital in Bo, Sierra Leone, were tested using three methods: a commercial RDT, microscopy, and a Multiplex Malaria Sample Ready (MMSR) PCR designed to detect a universal malaria marker and species-specific markers for Plasmodium falciparum and Plasmodium vivax. A separate PCR assay was used to identify species of Plasmodium in samples in which MMSR detected malaria, but was unable to identify the species. Results MMSR detected the presence of any malaria marker in 50.2% of all tested samples with P. falciparum identified in 48.7% of the samples. Plasmodium vivax was not detected. Testing of MMSR P. falciparum-negative/universal malaria-positive specimens with a panel of species-specific PCRs revealed the presence of Plasmodium malariae (n = 2) and Plasmodium ovale(n = 2). The commercial RDT detected P. falciparum in 24.6% of all samples while microscopy was able to detect malaria in 12.8% of tested specimens. Conclusions Wider application of PCR for detection of malaria parasites may help to fill gaps existing as a result of use of microscopy and RDTs. Due to its high sensitivity and specificity, species coverage, room temperature stability and relative low complexity, the MMSR assay may be useful for detection of malaria and epidemiological studies especially in low-resource settings