Achievements and challenges of lymphatic filariasis elimination in Sierra Leone

Background

Lymphatic filariasis (LF) is targeted for elimination in Sierra Leone. Epidemiological coverage of mass drug administration (MDA) with ivermectin and albendazole had been reported >65% in all 12 districts annually. Eight districts qualified to implement transmission assessment survey (TAS) in 2013 but were deferred until 2017 due to the Ebola outbreak (2014–2016). In 2017, four districts qualified for conducting a repeat pre-TAS after completing three more rounds of MDA and the final two districts were also eligible to implement a pre-TAS.

Methodology/Principal findings

For TAS, eight districts were surveyed as four evaluation units (EU). A school-based survey was conducted in children aged 6–7 years from 30 clusters per EU. For pre-TAS, one sentinel and one spot check site per district (with 2 spot check sites in Bombali) were selected and 300–350 persons aged 5 years and above were selected. For both surveys, finger prick blood samples were tested using the Filariasis Test Strips (FTS).

For TAS, 7,143 children aged 6–7 years were surveyed across four EUs, and positives were found in three EUs, all below the critical cut-off value for each EU. For the repeat pre-TAS/pre-TAS, 3,994 persons over five years of age were surveyed. The Western Area Urban had FTS prevalence of 0.7% in two sites and qualified for TAS, while other five districts had sites with antigenemia prevalence >2%: 9.1–25.9% in Bombali, 7.5–19.4% in Koinadugu, 6.1–2.9% in Kailahun, 1.3–2.3% in Kenema and 1.7% - 3.7% in Western Area Rural.

Conclusions/Significance

Eight districts in Sierra Leone have successfully passed TAS1 and stopped MDA, with one more district qualified for conducting TAS1, a significant progress towards LF elimination. However, great challenges exist in eliminating LF from the whole country with repeated failure of pre-TAS in border districts. Effort needs to be intensified to achieve LF elimination.

Lymphatic filariasis or elephantiasis is targeted for elimination in Sierra Leone, with annual mass treatment with ivermectin and albendazole, and required coverage was achieved in all 12 districts annually. In 2017, transmission assessment survey (TAS) was conducted in eight districts to assess whether treatment can be stopped and pre-TAS was conducted in six other districts to assess whether TAS can be conducted. Eight TAS districts were surveyed as four evaluation units (EU), and a school-based survey was conducted in 1703–1926 children aged 6–7 years from 30 clusters per EU. Six pre-TAS districts were surveyed with one sentinel and one/two spot check sites per district and 300–350 persons aged ≥5 years were tested. All tests were using the Filariasis Test Strips with finger prick blood samples. There were 0–7 positive cases in each TAS EU respectively, all below the critical cut-off value, confirming that mass treatment was no longer needed in these eight districts, a significant progress towards LF elimination. One district had prevalence of <1% in two sites and qualified for TAS, while other five districts had sites with prevalence >2%, suggesting that mass treatment needs to continue. Repeated failure of pre-TAS poses great challenge to eliminate LF in Sierra Leone.YMB is the former NTDP manager and coordinated the MDAs with AC and MS. JBK designed and oversaw the early NTDP and baseline surveys. JP, MB designed and led the TAS, pre-TAS field work data collection. MB and VRS conducted the data analysis. VRS and MH reanalysed the coverage data. YZ produced the point prevalence map. MH drafted the manuscript. MH and YZ revised the manuscript. All authors reviewed and approved the final manuscript.

Canine vector-borne pathogens from dogs and ticks from Tamil Nadu, India

Canine vector-borne diseases (CVBDs) pose a major health problem in dogs globally, with the potential to cause zoonoses, in particular in developing countries where scientific knowledge on the topic is minimal. Blood samples and ticks were collected from stray dogs in Tamil Nadu, South India to assess the prevalence of CVBD-causing pathogens (Anaplasma spp., Babesia spp., Ehrlichia spp., Hepatozoon spp., filarioids and Leishmania spp.). Of the 230 dogs examined, 229 (99.6%) were infested by ticks (mean intensity, 5.65) with Rhipicephalus sanguineus sensu lato and Rhipicephalus haemaphysaloides being morphologically identified in the 98.3% and 1.7% of the infested dogs, respectively. Overall, the 67.8% (n = 156) of dogs was positive for at least one pathogen with Hepatozoon canis being the most prevalent (37.8%) followed by Anaplasma platys (22.6%), Ehrlichia canis (16.1%) Babesia vogeli (10%), Anaplasma phagocytophilum (0.4%) and Babesia gibsoni (0.4%). Two filarioids (Dirofilaria sp. "hongkongensis" and Brugia malayi, 0.4%) were diagnosed in sampled animals. Co-infection with H. canis and A. platys was the most prevalent (8.3%, P = 0.00001), whilst all animals scored negative for Leishmania spp.. Out of 295 ticks analysed, 215 R. sanguineus s.l. (75.4%) and 8 R. haemaphysaloides (88.9%) were positive for at least one pathogen with H. canis as the predominant species (42.5%), followed by A. platys (33.8%), E. canis (16.9%), B. vogeli (3.8%) and A. phagocytophilum (0.3%). Fifty-six dogs (35.9%) harboured the same pathogen as the respective tick specimens, while 29 dogs (18.6%) had a different pathogen. Thirteen sequence types (STs) were identified for H. canis, with ST2 (49.4%) as the most representative in dogs and ST1 (73.5%) in ticks. Similarly, seven STs were found for Anaplasma spp. (i.e., five for A. platys, one for A. phagocytophilum and one for Anaplasma sp.), with ST2 as the most representative in dogs (70.6%) and ST3 (52.5%) in ticks for A. platys. Only one ST was identified for B. vogeli, B. gibsoni, E. canis, D. sp. "hongkongensis" and B. malayi. Regular surveillance and adoption of adequate treatment and control measures are needed to reduce the risk of disease-causing pathogens in stray dogs and of pathogens with zoonotic potential.

Assessment of MALDI-TOF mass spectrometry for filariae detection in Aedes aegypti mosquitoes

Matrix Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) is an emerging tool for routine identification of bacteria, archaea and fungi. It has also been recently applied as an accurate approach for arthropod identification. Preliminary studies have shown that the MALDI-TOF MS was able to differentiate whether ticks and mosquitoes were infected or not with some bacteria and Plasmodium parasites, respectively. The aim of the present study was to test the efficiency of MALDI-TOF MS tool in distinguishing protein profiles between uninfected mosquitoes from specimens infected by filarioid helminths. Aedes aegypti mosquitoes were engorged on microfilaremic blood infected with Dirofilaria immitis, Brugia malayi or Brugia pahangi. Fifteen days post-infective blood feeding, a total of 534 mosquitoes were killed by freezing. To assess mass spectra (MS) profile changes following filariae infections, one compartment (legs, thorax, head or thorax and head) per mosquito was submitted for MALDI-TOF MS analysis; the remaining body parts were used to establish filariae infectious status by real-time qPCR. A database of reference MS, based on the mass profiles of at least two individual mosquitoes per compartment, was created. Subsequently, the remaining compartment spectra (N = 350) from Ae. aegypti infected or not infected by filariae were blind tested against the spectral database. In total, 37 discriminating peak masses ranging from 2062 to 14869 daltons were identified, of which 17, 11, 12 and 7 peak masses were for legs, thorax, thorax-head and head respectively. Two peak masses (4073 and 8847 Da) were specific to spectra from Ae. aegypti infected with filariae, regardless of nematode species or mosquito compartment. The thorax-head part provided better classification with a specificity of 94.1% and sensitivity of 86.6, 71.4 and 68.7% of D. immitis, B. malayi and B. pahangi respectively. This study presents the potential of MALDI-TOF MS as a reliable tool for differentiating non-infected and filariae-infected Ae. aegypti mosquitoes. Considering that the results might vary in other mosquito species, further studies are needed to consolidate the obtained preliminary results before applying this tool in entomological surveillance as a fast mass screening method of filariosis vectors in endemic areas.

Filariosis is a disease group affecting humans and animals, caused by nematode parasites of the family Onchocercidae, superfamily Filarioidea. These parasites can be transmitted, essentially, by mosquitoes during blood meals of infected female specimens. Screening vectors for these filariae currently relies on time- and resource-consuming methods such as dissection and polymerase chain reaction-based methods. Here, we applied matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to assess whether this tool can detect changes in the protein profiles of Aedes aegypti infected with filarioid helminths compared to those uninfected by testing different parts of mosquitoes. First a reference mass spectra database from Ae. aegypti infected or not infected by filariae was created using MS from 47 specimen compartments. Then we tested the remaining mass spectra (350 x 4) in a blind validation test. Regardless of filariae species, the best correct classification rate was obtained from the thorax-head part with a specificity of 94.1% and sensitivity of 86.6, 71.4 and 68.7% for non-infected and D. immitis, B. malayi and B. pahangi infected mosquitoes respectively. The results indicated that MALDI-TOF MS is potentially able to screen Aedes aegypti mosquitoes as being non-infected or filariae-infected. Furthermore, complementary works using other mosquito species infected with different filarioids are needed to reinforce these preliminary results prior to apply this tool on field samples.

Identification of Ecdysone Hormone Receptor Agonists as a Therapeutic Approach for Treating Filarial Infections

Background

A homologue of the ecdysone receptor has previously been identified in human filarial parasites. As the ecdysone receptor is not found in vertebrates, it and the regulatory pathways it controls represent attractive potential chemotherapeutic targets.

Methodology/ Principal Findings

Administration of 20-hydroxyecdysone to gerbils infected with B. malayi infective larvae disrupted their development to adult stage parasites. A stable mammalian cell line was created incorporating the B. malayi ecdysone receptor ligand-binding domain, its heterodimer partner and a secreted luciferase reporter in HEK293 cells. This was employed to screen a series of ecdysone agonist, identifying seven agonists active at sub-micromolar concentrations. A B. malayi ecdysone receptor ligand-binding domain was developed and used to study the ligand-receptor interactions of these agonists. An excellent correlation between the virtual screening results and the screening assay was observed. Based on both of these approaches, steroidal ecdysone agonists and the diacylhydrazine family of compounds were identified as a fruitful source of potential receptor agonists. In further confirmation of the modeling and screening results, Ponasterone A and Muristerone A, two compounds predicted to be strong ecdysone agonists stimulated expulsion of microfilaria and immature stages from adult parasites.

Conclusions

The studies validate the potential of the B. malayi ecdysone receptor as a drug target and provide a means to rapidly evaluate compounds for development of a new class of drugs against the human filarial parasites.

The human filarial parasites are the causative agents of two neglected tropical diseases targeted for elimination by the international community. The current elimination programs rely upon the mass distribution of a limited number of drugs, leaving the programs open to failure in the event that resistance develops. Thus, there is a critical need for novel chemotherapeutic agents to supplement the current arsenal. The filarial parasites are ecdysozoans, whose developmental processes are controlled by a master regulator, the ecdysone receptor. Here we validate the potential of the filarial ecdysone receptor as a chemotherapeutic target and report the development of high throughput and virtual screening assays that may be used to compounds that target it.

A TaqMan-based multiplex real-time PCR assay for the simultaneous detection of Wuchereria bancrofti and Brugia malayi

With the Global Program for the Elimination of Lymphatic Filariasis continuing to make strides towards disease eradication, many locations endemic for the causative parasites of lymphatic filariasis are realizing a substantial decrease in levels of infection and rates of disease transmission. However, with measures of disease continuing to decline, the need for time-saving and economical molecular diagnostic assays capable of detecting low levels of parasite presence is increasing. This need is greatest in locations co-endemic for both Wuchereria bancrofti and Brugia parasites because testing for both causative agents individually results in significant increases in labor and reagent costs. Here we describe a multiplex, TaqMan-based, real-time PCR assay capable of simultaneously detecting W. bancrofti and Brugia malayi DNA extracted from human bloodspots or vector mosquito pools. With comparable sensitivity to established singleplex assays, this assay provides significant cost and labor savings for disease monitoring efforts in co-endemic locations.

Relevance of the eosinophil blood count in bancroftian filariasis as a screening tool for the treatment

BACKGROUND

Lymphatic filariasis constitutes a major public health issue in French Polynesia. Diagnosis has been revolutionized with the availability of circulating filarial antigen (CFA) tests which are easy to perform but are costly. Filariasis is responsible for acquired eosinophilia and eosinophil blood count (EBC) is commonly used as a screening tool.

METHODS

We retrospectively analysed all the results of EBCs and CFA tests performed in our laboratory over a 2-year period. We calculated the prevalence of antigenemia for nine different eosinophil cutoffs. We calculated the number of patients detected by CFA testing and the number of estimated CFA-positive patients according to their EBC.

RESULTS

Over a 2-year period, we detected 7503 eosinophilic patients. For an EBC above 500/mm(3), the prevalence of positive CFA was 25·78% and the estimated number of positive CFA patients was 1934. During the same period, as CFA determination is not routinely performed, only 141 patients were detected and treated.

CONCLUSION

Our current strategy against lymphatic filariasis which combines annual mass drug administration, systematic treatment of antigenemic and microfilaraemic patients, and vector control; failed to reach the target of 1% prevalence. Unfortunately, mainly for economical reasons, the antigenemia cannot be determined for all patients. In complement to existing strategy, we propose an additional action based on the treatment of eosinophilic patients in order to reduce the filariasis prevalence in our country.

[Process for lymphatic filariasis elimination in Jiangsu Province, China]

OBJECTIVE

To review the process of lymphatic filariasis elimination in Jiangsu Province, and summarize the control experience.

METHODS

The data of epidemic status, control and surveillance of lymphatic filariasis were collected and analyzed in Jiangsu Province from 1950s to 1990s.

RESULTS

Lymphatic filariasis was endemic in 71 counties (cities) among all 75 counties (cities) in Jiangsu Province. Filariasis bancrofti distributed widely in the province, and in some areas of the south of Jiangsu, there were filariasis bancrofti and Brug' s filariasis co-existing. Before 1971, the microfilaria rate (mfr) in some areas had ever reached 20. 15% , from 1979, large scale control programme was carried out and the mfr in all endemic villages decreased to below 1% , and in 1989, the rate dropped to 0.016%. By 2001, the whole regions of the province reached the criteria of filariasis elimination.

CONCLUSION

The elimination of lymphatic filariasis in Jiangsu Province provides valuable experience for lymphatic filariasis control in other areas.

Comparison of conventional versus real-time PCR detection of Brugia malayi DNA from dried blood spots from school children in a low endemic area

Microscopic detection of active phase of lymphatic filariasis is indicated by the presence of microfilaria in whole blood. This method is not sensitive and requires relatively large amount of blood sample. PCR allows very sensitive detection of the parasite DNA using a smaller amount of blood; and the use of dried blood spots facilitates sample transportation. Nevertheless, limited studies have been reported on PCR using dried blood spot for detection of Brugia malayi. In this study, we investigated the effects of concentrating whole blood genomic DNA sample and the amplification methods [conventional PCR (C-PCR) and real-time PCR] on the detection of B. malayi DNA from dried blood spots from a very low endemic area in Malaysia. Both C-PCR and real-time PCR detected 2 out of 18 (11%) samples as positive from non-concentrated genomic DNA preparations. After the DNA samples were pooled and concentrated, both C-PCR and realtime PCR detected B. malayi DNA amplifications in 7 out of 18 (39%) samples. However one sample which showed faint band in C-PCR was detected as highly positive in real-time PCR. In conclusion, both C-PCR and real-time PCR using dried blood spots from a low endemic area demonstrated equal sensitivity for detection of B. malayi DNA.

Successful control of lymphatic filariasis in the Republic of Korea

A successful experience of lymphatic filariasis control in the Republic of Korea is briefly reviewed. Filariasis in the Republic of Korea was exclusively caused by infection with Brugia malayi. Over the past several decades from the 1950s to 2006, many investigators exerted their efforts to detection, treatment, and follow-up of filariasis patients in endemic areas, and to control filariasis. Mass, combined with selective, treatments with diethylcarbamazine to microfilaria positive persons had been made them free from microfilaremia and contributed to significant decrease of the microfilarial density in previously endemic areas. Significant decrease of microfilaria positive cases in an area influenced eventually to the endemicity of filariasis in the relevant locality. Together with remarkable economic growth followed by improvement of environmental and personal hygiene and living standards, the factors stated above have contributed to blocking the transmission cycle of B. malayi and led to disappearance of this mosquito-borne ancient disease in the Republic of Korea.

DNA-based diagnosis of lymphatic filariasis

Lymphatic filariasis (LF) is still a major public health problem. The disease is ranked by the World Health Organization (WHO) as the second leading cause of permanent and long-term disability, and has been targeted for elimination by 2020. Effective diagnosis LF is required for treatment of infected individuals, for epidemiological assessment and for monitoring of the control program. Conventional diagnosis of LF depends on detection of microfilariae (Mf) in blood specimens, which has low sensitivity and specificity. Detection of specific circulating filarial antigens is regarded by WHO as the 'gold standard' for diagnosis of LF. However, the limitations of the antigen tests are cost and inconsistent availability. Although anti-filarial IgG4 antibody levels are associated with active LF infections, however, cross-reactivity with other filarial parasites is common. Not as sensitive as antigen tests, DNA-based techniques have been developed to diagnose and differentiate filarial parasites in humans, animal reservoir hosts, and mosquito vectors. These include DNA hybridization, polymerase chain reaction (PCR) amplification using specific primers (eg Ssp I repeat, pWb12 repeat, pWb-35 repeat, and LDR repeat for Wuchereria bancrofti and Hha I repeat, glutathione peroxidase gene, mitochondrial DNA for Brugia malayi), and universal primers, multiplex-PCR, PCR-restriction fragment length polymorphism (PCR-RFLP), PCR-enzyme linked immunosorbent assay (PCR-ELISA), as well as quantitative PCR. Furthermore, because bancroftian filariasis is endemic on the Thai-Myanmar border, the potential now exists for a re-emergence of bancroftian filariasis in Thailand, and random amplified polymorphic DNA (RAPD) analysis has proved effective to differentiate Thai and Myanmar strains of W. bancrofti.

Relevance of anti-BmR1 IgG4 antibodies in children from an area endemic for Brugia malayi infection in Kerala, India

Brugian filariasis prevalent mostly in South-East Asian countries including India contributes to a small but significant proportion of the socioeconomic burden due to lymphatic filariasis. Along with bancroftian filariasis, brugian filariasis has been targeted for elimination globally. The lack of a reliable daytime diagnostic test has been seen as an important barrier to the successful implementation and monitoring of elimination programmes in brugia endemic areas. We evaluated an anti-BmRI-IgG4 antibody test namely, 'Brugia Rapid' in a large study meant to understand the clinical and pathological manifestations of brugian filariasis in children. We found the test superior to traditional night blood screening for microfilaraemia. Although an antibody detection test, we found it to be a reliable indicator of brugian infection. Among the 100 children studied extensively, 94% of the microfilaraemics, 86% of those showing filarial dance sign indicating presence of, live adult worms and 78% having abnormal lymphatics on lymphoscintigraphy were IgG4 positive. Coupled with its advantages like ease of use any time of the day, high sensitivity and specificity, this test may be the ideal tool to assist programme managers in their efforts to eliminate lymphatic filariasis where brugian infections are found.

High resolution melting real-time PCR for rapid discrimination between Brugia malayi and Brugia pahangi

OBJECTIVE

To identify two closely related Brugia malayi and B. pahangi in cat reservoirs by using high resolution melting real-time PCR (HRM real-time PCR).

MATERIAL AND METHOD

HRM analysis on the Corbett Rotor-Gene 6000 instrument was used to test 5 Brugia specimens by using five sets of specific primers for HhaI repetitive region (HR), small heat shock protein (SHP), small subunit ribosomal DNA (18S rDNA), internal transcribed spacer region (ITS), and trans-spliced leading Exon I gene (SLX1).

RESULTS

HRM analysis of ITS and SLX clearly generated 2 profiles of B. malayi and B. pahangi while those of HR, 18S rDNA, and SHP could classify B. pahangi.

CONCLUSION

HRM is a simple and rapid method for identification of two closely related B. malayi and B. pahangi in which it can detect both parasites within 30 min after real-time PCR detection. This assay is probe-free HRM and reduces a risk of PCR carryover. It does not require multiplex methods and DNA sequencing; therefore, HRM provides a new approach for genetic screening and rapid detection of closely related species in a clinical laboratory.

Intraspecies variation of Brugia spp. in cat reservoirs using complete ITS sequences

The internal transcribed spacer (ITS) region was used to study the intraspecies variation of Brugia spp. in cat reservoirs. Blood specimens from seven naturally infected cats were collected from two different geographical brugian-endemic areas in Thailand. The DNAPAR tree of these Brugia spp. was constructed using a maximum likelihood approach based on ITS nucleotide sequences and was compared to those of Brugia malayi, Brugia pahangi, and Dirofilaria immitis that were previously reported in GenBank. The phylogenetic trees inferred from ITS1, ITS2, and complete ITS sequences indicated that B. malayi and B. pahangi were separated into two clades, and subgroups were generated within each clade. The data revealed that ITS2 sequences were less informative than ITS1 for studying intraspecies variation of Brugia spp. Our results are primary data for intraspecies variation of B. malayi and B. pahangi in cat reservoirs. The information could be applicable for studying the molecular epidemiology and the dynamic nature of the parasites.

Rapid detection of Wuchereria bancrofti and Brugia malayi in mosquito vectors (Diptera: Culicidae) using a real-time fluorescence resonance energy transfer multiplex PCR and melting curve analysis

We developed a single-step real-time fluorescence resonance energy transfer (FRET) multiplex polymerase chain reaction (PCR) merged with melting curve analysis for the detection of Wuchereria bancrofti and Brugia malayi DNA in blood-fed mosquitoes. Real-time FRET multiplex PCR is based on fluorescence melting curve analysis of a hybrid of amplicons generated from two families of repeated DNA elements: the 188 bp SspI repeated sequence, specific to W. bancrofti, and the 153-bp HhaI repeated sequence, specific to the genus Brugia and two pairs of specific fluorophore-labeled probes. Both W. bancrofti and B. malayi can be differentially detected in infected vectors by this process through their different fluorescence channel and melting temperatures. The assay could distinguish both human filarial DNAs in infected vectors from the DNAs of Dirofilaria immitis- and Plasmodium falciparum-infected human red blood cells and noninfected mosquitoes and human leukocytes. The technique showed 100% sensitivity and specificity and offers a rapid and reliable procedure for differentially identifying lymphatic filariasis. The introduced real-time FRET multiplex PCR can reduce labor time and reagent costs and is not prone to carry over contamination. The test can be used to screen mosquito vectors in endemic areas and therefore should be a useful diagnostic tool for the evaluation of infection rate of the mosquito populations and for xenomonitoring in the community after eradication programs such as the Global Program to Eliminate Lymphatic Filariasis.

Molecular genetics analysis for co-infection of Brugia malayi and Brugia pahangi in cat reservoirs based on internal transcribed spacer region 1

This study described the diagnosis of a mixed infection of Brugia malayi and Brugia pahangi in a single domestic cat using the internal transcribed spacer 1 (ITS1) region. Following polymerase chain reaction amplification of the ITS1 region, the 580 bp amplicon was cloned, and 29 white colonies were randomly selected for DNA sequencing and phylogenetic tree construction. A DNA parsimony tree generated two groups of Brugia spp with one group containing 6 clones corresponding to B. pahangi and the other 23 clones corresponding to B. malayi. This indicated that mixed infection of the two Brugia spp, B. pahangi and B. malayi, had occurred in a single host.

Lymphoscintigraphic evidence of lymph vessel dilation in the limbs of children with Brugia malayi infection

Lymphatic filariasis (LF) is targeted for global elimination by the year 2020. It was earlier believed that LF is mostly a disease of adults. Recent studies indicate that in endemic countries filarial infection starts mostly in childhood even though the disease manifestations occur much later in life. The initial damage to the lymph vessels where the adult worms are lodged is dilation, thought to be irreversible even with treatment. Most of these studies relate to bancroftian filariasis. Studies that address this early pathology in brugian filariasis in humans are scarce. We report here for the first time, the lymphatic abnormalities seen on lymphoscintigraphy (LSG) in children with Brugia malayi filariasis. LSG was performed in 100 children aged between 3-15 years, who were enrolled in the study either because they were microfilaremic; had present or past filarial disease or were positive for antifilarial IgG4 antibodies. Inguinal and axillary lymph nodes were imaged in most children. Dilated lymph vessels were visualized in 80 children and this pathology was evenly distributed in all the three study groups. Lymph vessels dilation was seen even in three year old children. The implications of these findings for management of LF and control programmes are discussed.

Rapid detection of Brugia malayi in mosquito vectors using a real-time fluorescence resonance energy transfer PCR and melting curve analysis

We developed real-time fluorescence resonance energy transfer (FRET) polymerase chain reaction (PCR) combined with melting curve analysis for detection of Brugia malayi DNA in blood-fed mosquitoes. Real-time FRET PCR is based on a fluorescence melting curve analysis of hybrid formed between amplicons generated from a family of repeated DNA element, 153-bp HhaI repeated sequence, specific to genus Brugia and specific fluorophore-labeled probes. The B. malayi-infected mosquitoes were differentiated from Wuchereria bancrofti-infected and uninfected mosquitoes and from genomic DNA of Dirofilaria immitis--and Plasmodium falciparum--infected human red blood cells and human leukocytes by their melting temperature. Sensitivity and specificity were both 100%. Melting curve analysis produces a rapid, accurate, and sensitive alternative for specific detection of B. malayi in mosquitoes, allows high throughput, and can be performed on small samples. This method has the potential for endemic area mapping or monitoring effect of brugian filariasis mass treatment programs.

The development and evaluation of a single step multiplex PCR method for simultaneous detection of Brugia malayi and Wuchereria bancrofti

A single step novel multiplex polymerase chain reaction (PCR) has been developed for simultaneous detection of human filarial parasites, Brugia malayi and Wuchereria bancrofti, from blood samples and mosquitoes. The primers used were novel and have been tested with the parasite DNA amplifying 188bp (BM) and 129bp (WB) DNA fragments, specific to B. malayi and W. bancrofti, respectively, in a single reaction. The specificity of the PCR product was confirmed by DNA sequencing and slot blot hybridization assay. The test was found highly sensitive for both B. malayi and W. bancrofti by detecting the parasitaemia up to the level of one microfilaria per reaction. The assay was further evaluated on 98 blood samples and 144 mosquito samples collected from filarial endemic areas. The PCR was found to be more efficient in comparison to microscopy by detecting 8% and 5% more filarial parasites in field-collected blood and mosquito samples, respectively. This novel PCR that offers scope for simultaneous detection of both the parasites may be used as a diagnostic tool for the detection of filariasis in population and can be adopted for rapid surveillance and monitoring of mosquitoes for use in the effective control of filariasis.

Preliminary findings from a cross-sectional study on lymphatic filariasis in children, in an area of India endemic for Brugia malayi infection

As the more obvious clinical manifestations of the disease are very uncommon in children, lymphatic filariasis has been considered to be primarily a disease of adults. In many recent reports, however, there is evidence indicating not only that filarial infection is commonly acquired in childhood but also that many infected children already have irreversible damage to their lymphatics. The preliminary results of a cross-sectional study on the patterns of Brugia-attributable pathology in 7934 children (aged 3-15 years) who live in an area of India with endemic B. malayi infection confirm these trends. The children were screened for microfilaraemia, evidence of filarial disease, and the presence of antifilarial IgG(4) antibodies. One hundred children who were microfilaraemic but asymptomatic (32), with filarial disease or an history of such disease or microfilaraemia (29) or amicrofilaraemic and asymptomatic but seropositive for antifilarial IgG(4) (39) were investigated further. They were given detailed clinical examinations, their levels of microfilaraemia were evaluated (by counting microfilariae filtered out of blood samples), their lymphatics were explored by Doppler sonography, and their limbs were checked by lymphoscintigraphy. The 'filarial dance sign', which indicates the presence of live adult worms, was detected by sonography in 14 children (apparently the first time this sign has been observed in brugian filariasis). Lymphoscintigraphy revealed dilated lymphatic channels in the limbs of 80 of the children. At the end of the study, each of the 100 hospitalized children was treated with a single combined dose of diethylcarbamazine and albendazole; the aim is to follow-up the treated children every 6 months for 3 years. Even these preliminary results have important implications for filariasis-control programmes and emphasise the need for disability-alleviation efforts among children as well as adults.

Persistence of Brugia malayi DNA in vector and non-vector mosquitoes: implications for xenomonitoring and transmission monitoring of lymphatic filariasis

Xenomonitoring (detection of filarial larvae or their DNA in mosquitoes) is a sensitive marker for assessing the endemicity of filariasis and a useful tool for evaluating elimination programs. To examine the fate of microfilariae (mf) and filarial DNA in vector competent and non-competent mosquito strains, we compared the detection of Brugia malayi parasites by dissection and by quantitative real-time polymerase chain reaction (PCR) in three different mosquito strains. We conclude that PCR is much more sensitive than dissection for detecting filarial larvae, especially their remnants in mosquitoes. However, parasite DNA can be detected in both vector and non-vector mosquitoes for two weeks or longer after they ingest mf-positive blood. Thus, although xenomonitoring with vector and non-vector mosquito species may be a sensitive method for indirectly detecting filarial parasites in human populations, positive test results for parasite DNA in mosquitoes do not necessarily prove that transmission is ongoing in the study area.

Detection of adult Brugia malayi filariae by ultrasonography in humans in India and Indonesia

In bancroftian filariasis, ultrasonography (USG) is a suitable tool to monitor infection by the detection of adult filariae in addition to antigen detection tests (ICT, Og4C3). However, in brugian filariasis, ultrasound examinations in humans have so far failed to detect adult worms and no antigen test is available to verify infections in patients who are carriers of adult worms but amicrofilaraemic. In this study, we describe the feasibility of detection of adult Brugia malayi filariae by USG. Worm nests were detected in 4 of 32 patients in India and Indonesia, located in the breast, the thigh, the calf and an inguinal lymph node. The study shows that adult filariae of B. malayi in humans can be detected by USG, but the technique is limited by the fact that worm nests seem not to be stable over time in humans, as is the case in bancroftian filariasis.

Detection of filarial parasites in domestic cats by PCR-RFLP of ITS1

Lymphatic filariasis has been targeted by the World Health Organization (WHO) to be eliminated by the year 2020. In addition to chemotherapy and vector control, the control of reservoir hosts is necessary for the control program to succeed. Malayan filariasis, caused by Brugia malayi, is endemic in the South of Thailand where domestic cats serve as the major reservoir host. However, in nature, domestic cats also carry B. pahangi, Dirofilaria immitis and D. repens infections and it is difficult to distinguish the different filarial species from each other just by morphology. To assess the burden of filarial parasites, we performed a study on domestic cats in an endemic area of malayan filariasis in the Prasang district, of Surat Thani, a province in Southern Thailand. Together with Giemsa staining and acid phosphatase activity studies, we performed PCR-RFLP analysis on the first internal transcribed spacer (ITS1) region of ribosomal DNA (rDNA). PCR-RFLP with Ase I could clearly differentiate between B. malayi, B. pahangi, D. immitis and D. repens. Out of the 52 cats studied, filarial parasites were identified in 5 (9.5%) cats, of which 4 (7.6%) were B. pahangi and 1 (1.9%) D. immitis. This PCR-RFLP technique detected two additional cats that were not detected by microscopy. The domestic cats are not an important host of B. malayi in this region. We could develop the PCR-RFLP assay test for differentiating filarial nematodes which can be applied to survey human, animal reservoir hosts and mosquito vectors in endemic areas.

Localization of Brugia malayi (sub-periodic) adults in different organs of Mastomys coucha and its influence on microfilaraemia and host antibody response

Lymphatic filariasis caused by nematode parasites Wuchereria bancrofti or Brugia malayi is a spectral disease and produces wide range of immune responses and varying levels of microfilaraemia in infected individuals. The relationship between the immune response of host and the developmental stage of the parasite as well as the microfilariae (mf) density and specific location of the adult worms is yet to be understood. As an experimental model, B. malayi adapted in the experimental animal Mastomys coucha has been used widely for various studies in filariasis. The present study was to assess microfilaraemia as well as the humoral immune response of M. coucha during various stages of B. malayi development and their localization in different organs. The result showed that the density of mf in the circulating blood of the experimental animal depended upon the number of female worms as well as the location and co-existence of male and female worms. The mf density in the blood increased with the increase in the number of females. The clearance of inoculated infective stage (L3) or single sex infection or segregation of male and female to different organs of infected host resulted in a microfilaraemic condition. With respect to antibody response, those animals cleared L3 after inoculation and those with adult worm as well as mf showed low antibody levels. But those with developmental fourth stage and/or adult worms without mf showed significantly higher antibody levels.

Protection against L3 induced Brugia malayi infection in Mastomys coucha pre-immunized with BmAFII fraction of the filarial adult worm

The present study was aimed at investigating protective efficacy of BmAFII (Sephadex G-200 eluted fraction of Brugia malayi adult worm extract) against establishment of infective larvae (L3)-induced B. malayi infection in Mastomys coucha and to delineate immunological responses induced in the host. Healthy male M. coucha were immunized with BmAFII and subsequently inoculated with B. malayi L3. Specific IgG and cell mediated immune responses (cellular proliferation) including release of tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), transforming growth factor-beta (TGF-beta) and nitric oxide (NO) from host's cells stimulated with BmAFII or lipopolysaccharide (LPS)/concanavalin A (Con A) in vitro were determined. Immunization with BmAFII reduced the adult worm recovery by 85.7% (P<0.001) and microfilaraemia by 77-95% of unimmunized controls (P<0.05-0.01). Immunization alone resulted in downregulation of responses of cellular proliferation, IFN-gamma, TNF-alpha and NO production (P<0.01) but increased TGF-beta release (P<0.001) whereas the converse was seen after L3 inoculation in these animals. In unimmunized+L3 inoculated animals all the above parameters were found downregulated (P<0.01-0.001). The cell proliferative response of BmAFII immunized+L3 challenged animals was larger for Con A (P<0.001) but not for BmAFII. Specific IgG levels were higher in immunized, immunized+L3 inoculated and unimmunized+L3 inoculated groups (P<0.001) compared to unimmunized animals, the highest level being shown by immunized+L3 inoculated group. In conclusion, immunization with BmAFII suppresses establishment of L3-induced infection in M. coucha by stimulating proinflammatory responses to L3.

Detection and differentiation of filarial parasites by universal primers and polymerase chain reaction-restriction fragment length polymorphism analysis

Filarial nematode parasites are a serious cause of morbidity in humans and animals. Identification of filarial infection using traditional morphologic criteria can be difficult and lead to misdiagnosis. We report on a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-based method to detect and differentiate a broad range of filarial species in a single PCR. The first internal transcribed spacer 1 (ITS1) along with the flanking 18S and 5.8S ribosomal DNA (rDNA) were isolated and cloned from Wuchereria bancrofti, Brugia malayi, and Brugia pahangi. Sequence analysis identified conserved sites in the 18S and 5.8S rDNA sequence that could be used as universal priming sites to generate ITS1-distinctive PCR products that were useful for distinguishing filariae at the genus level. The addition of a digestion of the ITS1 PCR product with the restriction endonuclease Ase I generated a fragment profile that allowed differentiation down to the species level for W. bancrofti, B. malayi, B. pahangi, Dirofilaria immitis, and D. repens. The PCR-RFLP of ITS1 rDNA will be useful in diagnosing and differentiating filarial parasites in human, animal reservoir hosts, and mosquito vectors in disease-endemic areas.

Combined detection of Brugia malayi and Wuchereria bancrofti using single PCR

A single step PCR method has been developed for the combined detection of the human filarial parasites, Brugia malayi and Wuchereria bancrofti. Parasites' DNA were isolated from filaria positive blood samples that were collected from endemic areas. The primers used were Hha1 and Ssp I, which amplified the DNA fragments of 322 bp and 188 bp specific to B. malayi and W. bancrofti, respectively. The sensitivity of the assay was tested with blood and mosquito samples having one W. bancrofti in a pool of 10 B. malayi. The assay was further evaluated on field collected blood and mosquito samples. Use of this assay as a diagnostic tool for the detection of filariasis being the most promising aspect of this study, offers scope for detection of both the parasites even at low levels of infection.

Field validation of sensitivity and specificity of rapid test for detection of Brugia malayi infection

We conducted a field study of a rapid test (Brugia Rapid) for detection of Brugia malayi infection to validate its sensitivity and specificity under operational conditions. Seven districts in the state of Sarawak, Malaysia, which are endemic for brugian filariasis, were used to determine the test sensitivity. Determination of specificity was performed in another state in Malaysia (Bachok, Kelantan) which is non-endemic for filariasis but endemic for soil-transmitted helminths. In Sarawak both the rapid test and thick blood smear preparation were performed in the field. The rapid test was interpreted on site, whereas blood smears were taken to the district health centres for staining and microscopic examination. Sensitivity of Brugia Rapid dipstick as compared with microscopy of thick blood smears was 87% (20/23; 95% CI: 66.4-97.2) whereas the specificity was 100% (512/512). The lower sensitivity of the test in the field than in laboratory evaluations (> or =95%), was probably due to the small number of microfilaraemic individuals, in addition to difficulties in performing the test in remote villages by field personnel. The overall prevalence of brugian filariasis as determined by the dipstick is 9.4% (95% CI: 8.2-0.5) while that determined by microscopy is 0.90% (95% CI: 0.5-1.3) thus the dipstick detected about 10 times more cases than microscopy. Equal percentages of adults and children were found to be positive by the dipstick whereas microscopy showed that the number of infected children was seven times less than infected adults. The rapid dipstick test was useful as a diagnostic tool for mapping and certification phases of the lymphatic filariasis elimination programme in B. malayi-endemic areas.

Tropical pulmonary eosinophilia: a case series in a setting of nonendemicity

BACKGROUND

Tropical pulmonary eosinophilia (TPE) is a rare but serious manifestation of infection with the lymphatic filarial parasites Wuchereria bancrofti and Brugia malayi. Although endemicity is limited to the tropical and subtropical regions of Africa, South America, and Asia, immigration and travel practices have led to the diagnosis of TPE in areas of nonendemicity.

METHODS

We herein present a case series of all patients with TPE who presented to the Toronto General Hospital during 1990-2003.

RESULTS

Seventeen individuals presented with TPE during the study period, and all were of South Asian ancestry. All 17 received an incorrect diagnosis at presentation (median number of consultations before diagnosis, 2), the most frequent of which was asthma (76%). Eosinophil count, serum immunoglobulin E levels, and anti-filarial antibody titers were elevated in all patients. Ten of 14 patients had an abnormal chest radiograph finding, and 11 of 12 patients had abnormal results of pulmonary function tests.

CONCLUSIONS

TPE is an important diagnostic consideration in patients with eosinophilia, respiratory symptoms, and history of exposure to this disease. In the untreated individual, TPE can lead to chronic and progressive respiratory compromise and death. Prompt recognition and treatment with diethylcarbamazine is therefore key to minimizing morbidity and mortality.

Brugia malayi infection in Meriones unguiculatus: antibody response to recombinant BmR1

BmR1 recombinant antigen has previously been shown to demonstrate high sensitivity and specificity in the serological diagnosis of brugian filariasis in humans. In this study, the pattern of recognition of antibody to BmR1 during Brugia malayi infection was investigated by employing Meriones unguiculatus as the experimental model. Thirty two gerbils were infected subcutaneously with 120 L(3); and two control groups each comprising 25 animals were employed. ELISA using BmR1 was used to detect filaria-specific IgG antibodies elicited by the gerbils; using sera collected from the day 1 until day 150 post-inoculation (p.i.). The results showed that BmR1 detected B. malayi infection in gerbils harboring adult worms irrespective of the presence of circulating microfilaria, and was exemplified by positive ELISA results in nine a microfilaraemic animals that harbored live adult worms. The initial time of the antibody recognition was at day 8 p.i. and the antibody titre showed some correlation with adult worm burden.

Clustering of filarial infection in an age-graded study: genetic, household and environmental influences

A statistical method that analyses correlation structures in families to delineate the contribution of genetic, household and environmental factors on clustering of infection, has been applied to data collected in an area endemic for brugian filariasis in South Sulawesi, Indonesia. Infection was assessed both by microfilaraemia and by anti-filarial IgG4. The results confirmed earlier findings that genetic factors play an important role in clustering of infection. When clustering of infection was analysed in children (< 10 years of age) and adults (> 20 years of age) separately, it was found that the genetic factors influence clustering of infection in children more profoundly than environmental or household effects. In contrast, genetic factors could not fully explain the clustering of infection seen in adults, which seemed to be mainly determined by household and environmental effects. The data have implications for genotyping studies in brugian filariasis; they indicate that it may be important to concentrate on the younger age groups where individual environmental effects have not yet overruled the genetic influences on gain/loss of infection.

Population dynamics of Wolbachia bacterial endosymbionts in Brugia malayi

The human filarial nematode Brugia malayi contains an endosymbiotic bacterium, Wolbachia. We used real-time quantitative polymerase chain reaction (QPCR) and microscopy to investigate the population dynamics of the bacterium-nematode association. Two Wolbachia (wsp and ftsZ) and one nematode (gst) genes were amplified from all life-cycle stages of B. malayi and results expressed as gene copies per worm and as Wolbachia/nematode ratios. Since the genes were single copy and there was one genome per Wolbachia, the gene copy numbers were equivalent to the numbers of bacteria. These were similar in microfilariae and the mosquito-borne larval stages (L2 and L3), with the lowest ratios of Wolbachia/nematode DNA. However, within 7 days of infection of the mammalian host, bacteria had increased 600-fold and the bacteria/worm ratio was the highest of all life-cycle stages. The rapid multiplication continued throughout L4 development, so that the major period of bacterial population growth occurred within 4 weeks of infection of the definitive host. Microscopy confirmed that there were few bacteria in mosquito-derived L3 but many, in large groups, in L4 collected 9 and 21 days after infection. In adult male worms up to 15 months of age, the bacterial populations were maintained, whilst in females, bacteria numbers increased as the worms matured and as the ovary and embryonic larval stages became infected. These results support the hypothesis that the bacteria are essential for larval development in the mammalian host and for the long-term survival of adult worms.

Impact of a filariasis control program on intestinal helminthic infections; a pilot study in Narathiwat Province, Thailand

This study was conducted in 9 villages located in endemic areas for brugian filariasis in Narathiwat Province, Thailand. Parasitological and anthropometric examinations were cross-sectionally performed to assess the prevalence of intestinal parasitic infections of 539 villagers. Paired stool samples were collected before and after mass treatment for the filariasis control program in 150 participants in order to study the impact of the filariasis control program on intestinal helminthiasis. The results found that 50.3% of the villagers were infected with one or more types of intestinal parasites. Double and triple infections were found in 10.9% and 1.6% of infected individuals respectively. The prevalence of intestinal parasitic infections peaked in the 1-10 year old age-group, which are pre-school and young school-age children. A significant reduction of intestinal helminthic infections in the post-treatment stool sample was observed in the 150 participants who were examined six months after mass treatment. Integrating an intestinal helminthic control program alongside the existing filariasis control program would be an appropriate and cost-effective strategy in the control of intestinal helminths. However, reinfection of parasites was observed.

An antigen detection assay for diagnosing filariasis

In this study we examined the diagnostic potential of monoclonal antibodies (MAb) reactive to antigens of adult Brugia malayi, their microfilariae and antigen of Dirofilaria immitis. The MAb of clone 17E10, which were of IgM isotype, reacted to the inner cuticles and internal content of both male and female worms and also to the sheath and internal content of microfilariae in utero. However, these MAb did not react to the sheath of blood circulating microfilariae. The MAb 17E10 produced a smear pattern between 37 to > 200 kDa in the Western blot analysis against a SDS-PAGE separated extract of B. malayi. The epitopes were non-protein in nature as indicated by their resistance to proteinase-K treatment. The MAb 17E10 were applied in a sandwich ELISA to detect filarial antigen in the buffy coat and plasma of patients. We tested patients with different clinical manifestations of brugian filariasis, i.e. microfilaremia (M), lymphangitis (L) and elephantiasis (E), as well as non-symptomatic inhabitants of a filariasis endemic area (NE), and compared them to samples from non-symptomatic inhabitants of disease non-endemic areas (NNE). It was found that 22 of 31 (70.9%) of M, 7 of 13 (53.8%) of L, 2 of 14 (14.2%) of E, 10 of 100 (10.0%) of NE and none (0%) of the NNE were positive for antigenaemia. The assay was also positive in 14 of 15 (93.3%) blood samples from B. malayi microfilaremic cats and in 7 of 7 (100%) blood samples of Dirofilaria immitis microfilaremic dogs. The so-developed test has a high potential for routine diagnosis of active filariasis, for epidemiological studies in both humans and reservoir animals and for monitoring treatment efficacy.

[Studies on detecting Brugia malayi larva in mosquitoes by polymerase chain reaction]

OBJECTIVE

To establish a specific, sensitive and simple assay for the detection of Brugia malayi larva in Anopheles sinensis.

METHODS

Using a new DNA purification technique (Microcon 100) and two pairs of oligonucleotide primers (p1, p2 and p3, p4) suitable for detecting B. malayi in seven areas in our country, the mosquito vectors infected by B. malayi were detected by polymerase chain reaction(PCR).

RESULTS

This PCR method could amplify separately a 322-basepair(bp) and a 155 bp DNA fragment and detect as few as 1/64 of one L1 in 1 mosquito, the detectable limit was nearly 4 pg DNA of filarial larvae, and it could also detect 1 infected mosquito with one L3 of B. malayi in pools of up to 200 mosquitoes. In contrast, no such specific 322 bp or 155 bp DNA band was detected in Dilofilaria immitis and normal mosquito.

CONCLUSION

This PCR technique established for supervision of mosquito vector in B. malayi endemic areas is specific, sensitive, and simple.

Multicentre laboratory evaluation of Brugia Rapid dipstick test for detection of brugian filariasis

A multicentre evaluation of the Brugia Rapid dipstick test was performed using 1263 serum samples in four international laboratories, i.e. T.D. Medical College (TDMC, India), National Institutes of Health (NIH, USA), Swiss Tropical Institute (STI, Switzerland) and Leiden University Medical Centre (LUMC, Netherlands). In comparison with microscopy, the dipstick demonstrated sensitivities of 97.2% (70 of 72) at TDMC, 91.6% (175 of 191) at LUMC and 100% (six of six) at STI. Sera of chronic patients showed a positivity rate of 11.3% (19 of 168) and 61.2% (71of 116) at TDMC and LUMC, respectively. All 266 sera of non-endemic normals from STI, NIH and LUMC tested negative with the dipstick. At LUMC, sera of 'endemic normals' (amicrofilaraemics with no clinical disease) from an area with approximately 35% microfilaria positivity showed 60.8% positive results (31 of 51), thus demonstrating the likelihood of many cryptic infections occurring in this population. Specificities of the test with Onchocerca volvulus sera were 98.8% (80 of 81) and 100% (10 of 10) at the NIH and STI, respectively; while specificity with Loa loa sera at the NIH was 84.6% (44 of 52). At the STI, the dipstick test also demonstrated 100% specificity when tested with 75 sera from various protozoan and helminthic infections.

Analysis of the Brugia malayi HSP70 promoter using a homologous transient transfection system

Biolistic transient transfection of Brugia malayi embryos with constructs driving the expression of a luciferase reporter gene was used to identify regions of the upstream sequence of the heat shock protein 70 (HSP70) gene of B. malayi necessary for transgene expression. Analysis of 1160 nucleotides upstream of the start codon of the HSP70 gene identified several potentially important elements, including putative CAAT and TATA boxes, a core promoter domain, a polypurine stretch, and a spliced leader addition site. Nested deletion analysis of the HSP70 upstream domain mapped the promoter of the HSP70 gene to the region 396 to 31 nucleotides upstream of the start codon. This encompassed the putative CAAT and TATA boxes, and putative core promoter. Deletion of the putative CAAT box did not result in any diminution of reporter activity, while constructs in which the TATA box or core promoter were deleted retained roughly half of the activity of the undeleted construct. Unlike the native gene, transcripts derived from constructs containing the HSP70 upstream sequences were not trans-spliced. However, incorporation of the 495 nucleotides downstream of the start codon (encompassing exon 1, intron 1 and part of exon 2) resulted in the production of transcripts that were correctly cis- and trans-spliced. Similarly, a construct containing the 495 downstream nucleotides in which most of exon 1 was deleted, was correctly cis- and trans-spliced. This finding suggests that downstream intron sequences in addition to the splice leader addition site are necessary for trans-splicing in B. malayi.

A survey of Brugia malayi infection on the Heugsan Islands, Korea

Lymphatic filariasis due to Brugia malayi infection was endemic in several areas of South Korea. The infection was controlled, or disappeared, in most areas, with the exception of the remote southwestern islands of Jeonranam-do, including the Heugsan Islands. To discover its current situation, a small-scale survey was performed on the Heugsan Islands in September 2000. A total of 378 people, 151 male and 227 female, living in 8 villages (6 on Daeheugsan-do, 1 on Daejang-do, and 1 on Yeongsan-do) were subjected to a night blood survey for microfilaremia, and physical examination for elephantiasis on the extremities. There were 6 (1.6%) microfilaria positive cases, all in females aged 57-72 years, and from only two villages of the Daeheugsan-do area. There were 4 patients with lower leg elephantiasis, but they showed no microfilaremia. The results show that a low-grade endemicity of filariasis remains on the Daeheugsan-do.

Polymerase chain reaction-based detection of lymphatic filariasis

PCR-based diagnostic assays are promising tools for the monitoring and evaluation of the Global Programme for Elimination of Lymphatic Filariasis. Sensitive and specific assays have been described for the detection of Wuchereria bancrofti, Brugia malayi, or Brugia timori infection in blood, sputum, and vectors. These techniques can be most cost-effective when employed for pool screening, which is important in the later stages of control programs when infection rates of humans and vectors are low, and large numbers of samples must be examined.

Short communication: use of a recombinant antigen-based ELISA to determine prevalence of brugian filariasis among Malaysian schoolchildren near Pasir Mas, Kelantan-Thailand border

Brugian filariasis infects 13 million people in Asia. The routine prevalence survey method using night thick blood smear is not sensitive enough to reflect the actual infection prevalence. In 1997-2001, only three microfilaraemic cases (of 5601 individuals screened; 0.05%) were reported in Pasir Mas, a district in Kelantan (Malaysia), which shares a border with Thailand. We therefore investigated the infection prevalence in this district by employing a sensitive and specific serological assay (Brugia-Elisa). This test is based on detection of specific IgG4 antibody against a Brugia malayi recombinant antigen. A total of 5138 children, aged 7-12 years, from 16 primary schools, were tested. Eighteen pupils in eight schools, located in five subdistricts, tested positive, giving an overall prevalence rate of 0.35%. Infection in these children is significant as they represent more recent cases. These subdistricts should be included in the national filariasis elimination programme.

Brugia malayi: establishment in inbred and outbred strains of mice

Immunocompetent mouse model for human filarial parasite Brugia malayi is urgently required in view of the paucity of commercial reagents for other susceptible rodent viz. mastomys and gerbil. Genes within the major histocompatibility complex have been reported to influence the susceptibility of mouse to helminth parasites. Attempts have therefore been made in the present investigation to experimentally infect various inbred strains of mice viz. NZB/BINJ, BALB/c, AKR, C(3)H, and SJL/J with H-2 haplotype (H-2: d, d, k, k, s, respectively) and outbred strains of mice viz. Parks and Swiss. Findings indicate that susceptibility of mice to B. malayi is strain associated. This is the first report on the successful completion of full developmental cycle of subperiodic B. malayi in NZB/BINJ, an immunocompetent mouse strain. In some of the other strains, partial development or low degree of establishment of worms was observed.

PCR-based detection and identification of the filarial parasite Brugia timori from Alor Island, Indonesia

Brugia timori is widely distributed on Alor Island, Indonesia, where it causes a high degree of morbidity. The HhaI tandem repeat of B. timori was found to be identical to that of B. malayi, for which sensitive PCR-based assays have already been developed. Using one of these assays, a single microfilaria (mf) of B. timori, present in a spot of dry blood on filter paper, could be detected. The assay was equally sensitive in the detection of B. timori and B. malayi. When the collected mosquitoes were pooled according to species and tested with the assay, 39 (64%) of the 61 Anopheles barbirostris pools (containing a total of 642 mosquitoes) were positive. As none of the 33 Culex pools tested (which contained 624 mosquitoes) gave a positive result, and An. barbirostris is the only Anopheles species commonly caught on human bait in Alor, An. barbirostris is assumed to be the main and perhaps only local vector. Brugia timori could be differentiated from B. malayi by restriction-endonuclease digestion of the PCR-amplified mitochondrial cytochrome oxidase subunit 2. A few distinct nucleotide exchanges were also found in the second internal transcribed ribosomal spacer of the filariae, and in the 16S rDNA and FTSZ gene of their Wolbachia endobacteria. The results show that B. timori can be effectively detected using the PCR-based assay developed for B. malayi and can then be differentiated from B. malayi by other molecular markers. PCR-based techniques targeting the HhaI repeat can therefore be employed for monitoring B. timori in the framework of the Global Programme to Eliminate Lymphatic Filariasis.

[SurveilLance on filariasis after its basic elimination in Hunan Province]

AIM

To explore the fluctuation pattern of prevalence and to detect the residual infection in Hunan Province where filariasis had been basically eliminated since 1986.

METHODS

Longitudinal surveillance and cross-sectional surveillance were extensively carried out by using parasitological, entomological and serological methods in areas previously endemic for filariasis.

RESULTS

In 55 counties, cross-sectional surveillance on filariasis had been executed for 11-19 years. The results showed that microfilaria cases had not been found for 4 years, and filaria larvae had failed to be detected from mosquito vectors for 12 years. Serological surveillance in the population revealed that the mean positive rate of IFAT had dropped from 13.15% in 1987 to 1.06% in 1996, the latter rate being similar to that of the nonendemic area. 6 longitudinal surveillance spots in 5 counties (cities) had been observed for 10-17 years. Annual quantitative blood examination of 11 microfilariemia cases showed that 10 cases became negative in 1-10 years, and the remaining 1 case remained positive at the 14th year. A. sinensis were dissected with no filaria larvae found in 2 surveillance spots of malayan filariasis. Culex quinquefasciatus were dissected with filaria larvae found only in the first to third year, the natural infection rates were 0.38%-1.98% in 4 surveillance spots of bancroftian filariasis.

CONCLUSION

Since the basic elimination of filariasis in Hunan Province in 1986, the number of residual microfilariemia cases decreased year after year, suggesting that the transmission of filariasis has been interrupted.

Interferon-gamma and nitric oxide production are not required for the immune-mediated clearance of Brugia malayi microfilariae in mice

Previous research has shown that Brugia malayi microfilariae (Mf) primarily induce type 1 cytokine production, and that in-vitro nitric oxide (NO) can mediate Mf killing. This study addresses the role of interferon (IFN)-gamma-mediated immune responses in the clearance of Mf from fast-clearing (CBA/Ca) and slow-clearing (C57Bl/6) mouse strains. Analysis of spleen cell cytokine production at early timepoints p.i. showed that Mf-induced IFN-gamma and nitrite (NO-) levels were significantly greater in CBA/Ca mice than C57Bl/6 mice. However, in-vivo neutralization of IFN-gamma or inhibition of NO- production in CBA/Ca mice did not alter Mf survival kinetics. Similarly, the rate of Mf clearance in both C57Bl/6 mice lacking the IFN-gamma gene and (C57Bl/6 x 129) mice deficient in the receptor for IFN-gamma was similar to that of wild-type animals. Furthermore, the dramatic abrogation of NO- production in IFN-gammaR-/- mice suggests that Mf clearance in slow-clearing mouse strains is also independent of NO- production. Thus, in both rapid-clearing and slow-clearing mouse strains, IFN-gamma-mediated mechanisms are not a requirement for Mf clearance from the bloodstream.

PCR based method for identification of zoonostic Brugia malayi microfilariae in domestic cats

The survey of 326 human blood samples in the endemic area of Surat Thani and Narathiwat, the provinces in the south of Thailand, revealed that 5 of them were infected with Brugia malayi. Similarly, 53 feline blood samples were also investigated and found that 15 of the domestic cats were also infected with B. malayi. Upon the examination of human and feline blood specimens, a pair of human and domestic cat stayed in the same house and region. The periodicities of human B. malayi and feline B. malayi were similar as well as the results of Giemsa and acid phosphatase stained blood films of microfilaria positive cases. Likewise, the PCR-RFLP profile of Hha I repeat genes and PCR amplification of Trans-Spliced Leader Exon I (SLX) demonstrated that 15 samples the feline B. malayi were the same as those of human B. malayi. The data indicated that domestic cat plays an important role as the animal reservoir for B. malayi in the endemic areas of Thailand.

Comparison of Brugia-Elisa and thick blood smear examination in a prevalence study of brugian filariasis in Setiu, Terengganu, Malaysia

A total of 1,134 finger-pricked blood samples were collected from residents of Setiu, Terengganu. A drop of blood was used to make thick blood smear and about four drops were used for obtaining serum. The smears were stained and examined by the State Vector Control Unit in Kuala Terengganu, while the serum samples were tested for specific IgG4 antibodies to a novel recombinant antigen using Brugia-Elisa. Prevalence of filariasis in these areas were found to be 0.26% (3/1,134) using thick blood smear examination and 2.47% (28/1,134) using Brugia-Elisa, thus demonstrating the greater sensitivity of the latter test. In addtion, Brugia-Elisa showed a high level of specificity (97.8%, 1,106/1,131) when compared to thick blood smear examination.

Specificity and sensitivity of a rapid dipstick test (Brugia Rapid) in the detection of Brugia malayi infection

A total of 753 serum samples from 6 institutions in 3 countries (Malaysia, Indonesia and India) were used to evaluate an immunochromatographic rapid dipstick test, Brugia Rapid, for diagnosis of Brugia malayi infection. The samples comprised sera from 207 microfilaria-positive individuals and 546 individuals from filaria non-endemic areas. The latter consisted of 70 individuals with soil-transmitted helminth infections, 68 with other helminth infections, 238 with protozoan infections, 12 with bacterial and viral infections and 158 healthy individuals. The dipstick is prepared with a goat anti-mouse antibody control line and a B. malayi recombinant-antigen test line. First, the dipstick is dipped into a well containing diluted patient serum, thus allowing specific anti-filarial antibody in the serum to react with the recombinant antigen. Then the dipstick is placed into an adjacent well containing reconstituted anti-human IgG4-gold. After 10 min, development of 2 red-purplish lines denotes a positive result and one line indicates a negative reaction. The overall results of the evaluation showed 97% sensitivity, 99% specificity, 97% positive predictive value and 99% negative predictive value. Brugia Rapid is thus a promising diagnostic tool for detection of B. malayi infection, and would be especially useful for the brugian filariasis elimination programme.

Brugia malayi in a naturally infected cat from Narathiwat Province, southern Thailand

Brugia malayi-like from an infected cat from Narathiwat Province, southern Thailand was identified intensively by microfilarial morphometry, acid phosphatase activity, and adult morphology. The results indicated that both microfilarial and adult characteristics conformed to the topotypic B. malayi.

A rapid and simplified method of DNA extraction for the detection of Brugia malayi infection in mosquitoes by PCR assay

Currently used protocols for the extraction of filarial parasite DNA from mosquito samples are tedious and involve extensive use of expensive and hazardous chemicals. Therefore, in order to arrive at a simple procedure, four different methods (A, B, C and D) were tried for the extraction of DNA from mosquitoes infected with filarial parasite, Brugia malayi. Method D was found to be as efficient as the current procedure for the extraction of DNA from a single microfilaria in pools of 25 mosquitoes and the DNA was suitable for polymerase chain reaction (PCR) amplification, yielding a band of 322 base pairs with primers specific for B. malayi. Method D involved drying and crushing the mosquitoes to a powder, which was homogenized in 100 microl TE buffer, vortexed, boiled for 10 min, centrifuged at 14000 r.p.m. for 10 min, and the supernatant used for the PCR assay. Dot-blot hybridization confirmed the specificity of the PCR amplified fragment. The DNA extracted by this method was stable for about 1 year. When comparing with the standard method, the cost of a single PCR reaction, inclusive of DNA extraction, was reduced by 50% and the hands on time was minimized fivefold. Hence, this simple TE-based method is rapid, safe and also cost-effective in assessing the B. malayi infection in pools of vector mosquitoes.

Lymphatic filariasis caused by Brugia malayi in an endemic area of Narathiwat Province, southern of Thailand

Lymphatic filariasis caused by Brugia malayi is highly prevalent in Narathiwat province of Thailand. The World Health Organization has aimed to eliminate the disease globally by the year 2020. To achieve the goal, assessment of the real disease situation should be integrated as part of the control program. The preliminary data for long-term study of the disease situation in this endemic area is necessary for the elimination program of lymphatic filariasis. By using the conventional microscopic method, the microfilarial rate of B. malayi in an endemic area of Narathiwat province was 1.38 per cent. The microfilarial densities ranged from 17 microfilariae/ml to 1,250 microfilariae/ml median = 50. The highest prevalence was found in the age group > 45-60 (4.69%). The lowest microfilarial rate was in the age group < or = 15 (0.37%). The infection in males was about three fold the number in females. A PCR-based method was employed to detect a B. malayi-specific Hha I repetitive DNA sequence with high specificity and sensitivity. The PCR assay will be useful in assisting the elimination program of lymphatic filariasis in control and monitoring the disease in Thailand.