Simple blood-spot sampling with nested polymerase chain reaction detection for epidemiology studies on Brugia malayi

Lymphatic Filariasis in Mainland Southeast Asia: A Systematic Review and Meta-Analysis of Prevalence and Disease Burden

Accurate prevalence data are essential for the elimination of lymphatic filariasis (LF) as a public health problem. Despite it bearing one of the highest burdens of disease globally, there remains limited reliable information on the current epidemiology of filariasis in mainland Southeast Asia. We conducted a systematic review and meta-analysis of available literature to assess the recent and current prevalence of infection and morbidity in the region. Fifty-seven journal articles and reports containing original prevalence data were identified, including over 512,010 participants. Data were summarised using percentage prevalence estimates and a subset combined using a random effects meta-analysis by country and year. Pooled estimates for microfilaraemia, immunochromatographic card positivity and combined morbidity were 2.64%, 4.48% and 1.34% respectively. Taking into account pooled country estimates, grey literature and the quality of available data, we conclude that Lao People's Democratic Republic (PDR), Myanmar and Northeast India demonstrate ongoing evidence of LF transmission that will require multiple further rounds of mass drug administration. Bangladesh, Malaysia, Thailand and Vietnam appear close to having eliminated LF, whilst Cambodia has already achieved elimination status. We estimate that the burden of morbidity is likely high in Thailand; moderate in Cambodia, Myanmar, and Northeast India; and low in Bangladesh. There was insufficient evidence to accurately estimate the disease burden in Lao PDR, Malaysia or Vietnam. The results of this study indicate that whilst considerable progress toward LF elimination has been made, there remains a significant filariasis burden in the region. The results of this study will assist policy makers to advocate and budget for future control programs.

Detection of lymphatic Wuchereria bancrofti in carriers and long-term storage blood samples using semi-nested PCR

The semi-nested PCR was conducted for detection of Wuchereria bancrofti in patients' blood. The primers were designed based on the repetitive DNA sequences of the parasite. The results demonstrated that the semi-nested PCR could detect as little as 0.001 fg of parasite DNA. In addition, the primers showed no PCR amplification from human and other hemoparasites such as Brugia malayi, Plasmodium falciparum and P. vivax DNAs. This technique was used for detection of 18 W. bancrofti infected blood samples with a long-term storage, the data revealed that all samples were positive. The results obtained from this study clearly indicated that the semi-nested PCR is specific, sensitive, and suitable for detection of the disease carriers.

Sensitivity of the nested-polymerase chain reaction (PCR) assay for Brugia malayi and significance of 'free' DNA in PCR-based assays

The blood filtration method was used as the gold standard to determine the detection level of simple blood-spot sampling and nested-polymerase chain reaction (PCR) for Brugia malayi. Of 100 samples, 48 were filtration-positive. Of these, 26 had microfilaria counts that were low enough (<1-29 microfilariae/ml) to accurately assess the limit of detection by nested-PCR. Nested-PCR consistently detected B. malayi DNA in samples with > or = 10 microfilariae/ml. Post-filtration, microfilaria-depleted, blood-spots from microfilaria-positive samples were screened by nested-PCR and B. malayi specific 'free' DNA was detected in 51.7% of these samples. There was no evidence for 'free' DNA in microfilaria-negative individuals from this endemic community.

The control of the human filariases

There is a growing momentum for the global control and elimination of the major human filariases as public health problems worldwide. The renewed optimism for undertaking this objective reflects the development of simple and potentially cost-effective strategies for mass drug delivery in onchocerciasis and the availability of new extremely effective drug combinations to treat infection, and new methods of morbidity control in lymphatic filariasis. It also reflects the development and current availability of very effective diagnostic, surveillance and control modeling tools for both parasites. Control programming will also be aided by our greater understanding of the biology of transmission, host immunity and disease pathogenesis.