Genomic Epidemiology in Filarial Nematodes: Transforming the Basis for Elimination Program Decisions

Onchocerciasis and lymphatic filariasis are targeted for elimination, primarily using mass drug administration at the country and community levels. Elimination of transmission is the onchocerciasis target and global elimination as a public health problem is the end point for lymphatic filariasis. Where program duration, treatment coverage, and compliance are sufficiently high, elimination is achievable for both parasites within defined geographic areas. However, transmission has re-emerged after apparent elimination in some areas, and in others has continued despite years of mass drug treatment. A critical question is whether this re-emergence and/or persistence of transmission is due to persistence of local parasites-i.e., the result of insufficient duration or drug coverage, poor parasite response to the drugs, or inadequate methods of assessment and/or criteria for determining when to stop treatment-or due to re-introduction of parasites via human or vector movement from another endemic area. We review recent genetics-based research exploring these questions in Onchocerca volvulus, the filarial nematode that causes onchocerciasis, and Wuchereria bancrofti, the major pathogen for lymphatic filariasis. We focus in particular on the combination of genomic epidemiology and genome-wide associations to delineate transmission zones and distinguish between local and introduced parasites as the source of resurgence or continuing transmission, and to identify genetic markers associated with parasite response to chemotherapy. Our ultimate goal is to assist elimination efforts by developing easy-to-use tools that incorporate genetic information about transmission and drug response for more effective mass drug distribution, surveillance strategies, and decisions on when to stop interventions to improve sustainability of elimination.

Therapeutic efficacy of doxycycline in domestic cats naturally infected with Brugia malayi in field condition

OBJECTIVE

The aim of this study was to evaluate the efficacy of oral doxycycline treatment for Brugia malayi as measured by microfilarial and filarial DNA clearance in naturally infected domestic cats.

METHODS

This study included 8 domestic cats that lived with families that resided in Tak Bai District of Narathiwat Province, which is located in Southern Thailand. The study area is a known B. malayi endemic area. All study cats received doxycycline treatment doses by their respective owners according to a previously described protocol. Briefly, doxycycline (VibraVet^@) was given orally once a day during weeks 1-4, 10-11, and 16-17. Blood collections were performed at baseline before treatment, and then every month for 12 months after the initial dose of doxycycline to assess microfilaraemia by Giemsa stain, and filarial DNA detection by high-resolution melt (HRM) real-time polymerase chain reaction (PCR).

RESULTS

One month after the start of doxycycline treatment, five of eight cats were negative for microfilaraemia, and 4 of those were negative for filarial DNA. All cats receiving doxycycline treatment were negative for microfilaria by Giemsa stain, and for filarial DNA by HRM real-time PCR within 8 months after receiving the initial dose of doxycycline treatment.

CONCLUSION

Administration of oral doxycycline to domestic cats naturally infected with B. malayi in disease endemic areas can significantly reduce microfilaraemia at 1 month and filarial DNA was undetectable by 8 months after the initial dose of doxycycline treatment. No recurrence of microfilaraemia or filarial DNA was observed in study cats at 1 year after the start of doxycycline. Included cats appeared to tolerate doxycycline (VibraVet^@) well, with no adverse drug reactions reported by any study cat owner.

Preventive chemotherapy reverses covert, lymphatic-associated tissue change in young people with lymphatic filariasis in Myanmar

OBJECTIVES

This longitudinal comparative study investigated the effect of preventive chemotherapy (PC) on covert tissue changes associated with lymphatic filariasis (LF) among young people living in an LF-endemic area in Myanmar.

METHODS

Tissue compressibility and extracellular free fluid in the lower limbs of people aged 10-21 years were measured using indurometry and bioimpedance spectroscopy (BIS). Baseline measures were taken in October 2014, annual mass drug administration (MDA) of PC was delivered in December, and in March 2015 further PC was offered to LF-positive cases who had missed MDA. Follow-up measures were taken in February and June 2015.

RESULTS

A total of 50 antigen-positive cases and 46 antigen-negative controls were included. Self-reported PC consumption was 60.1% during 2014 MDA and 66.2% overall. At second follow-up, 24 of 34 cases and 27 of 43 controls had consumed PC. Significant and clinically relevant between-group differences at baseline were not found post-PC. Bayesian linear mixed models showed a significant change in indurometer scores at both calves for antigen-positive cases who consumed any PC (dominant calf: -0.30 [95% CI -0.52, -0.07], P < 0.05 and non-dominant calf: -0.35 [95% CI -0.58, -0.12], P < 0.01). Changes in antigen-negative participants or those not consuming PC were not significant.

CONCLUSION

This study is the first attempt to use simple field-friendly tools to track fluid and tissue changes after treatment of asymptomatic people infected with LF. Results suggested that PC alone is sufficient to reverse covert lymphatic disturbance. Longer follow-up of larger cohorts is required to confirm these improvements and whether they persist over time. These findings should prompt increased efforts to overcome low PC coverage, which misses many infected young people, particularly males, who are unaware of their infection status, unmotivated to take PC and at risk of developing lymphoedema. Indurometry and BIS should be considered in assessment of lymphatic filariasis-related lymphedema.

Progress on elimination of lymphatic filariasis in Sierra Leone

Background

A baseline survey in 2007–2008 found lymphatic filariasis (LF) to be endemic in Sierra Leone in all 14 districts and co-endemic with onchocerciasis in 12 districts. Mass drug administration (MDA) with ivermectin started in 2006 for onchocerciasis and was modified to add albendazole in 2008 to include LF treatment. In 2011, after three effective MDAs, a significant reduction in microfilaraemia (mf) prevalence and density was reported at the midterm assessment. After five MDAs, in 2013, mf prevalence and density were again measured as part of a pre-transmission assessment survey (pre-TAS) conducted per WHO guidelines.

Methods

For the pre-TAS survey, districts were paired to represent populations of one million for impact assessment. One sentinel site selected from baseline and one spot check site purposefully selected based upon local knowledge of patients with LF were surveyed per pair (two districts). At each site, 300 people over five years of age provided mid-night blood samples and mf prevalence and density were determined using thick blood film microscopy. Results are compared with baseline and midterm data.

Results

At pre-TAS the overall mf prevalence was 0.54% (95% CI: 0.36–0.81%), compared to 0.30% (95% CI: 0.19–0.47) at midterm and 2.6% (95% CI: 2.3–3.0%) at baseline. There was a higher, but non-significant, mf prevalence among males vs females. Eight districts (four pairs) had a prevalence of mf < 1% at all sites. Two pairs (four districts) had a prevalence of mf > 1% at one of the two sites: Koinadugu 0.98% (95% CI: 0.34–2.85%) and Bombali 2.67% (95% CI: 1.41–5.00%), and Kailahun 1.56% (95% CI: 0.72–3.36%) and Kenema 0% (95% CI: 0.00–1.21%).

Conclusions

Compared to baseline, there was a significant reduction of LF mf prevalence and density in the 12 districts co-endemic for LF and onchocerciasis after five annual LF MDAs. No statistically significant difference was seen in either measure compared to midterm. Eight of the 12 districts qualified for TAS. The other four districts that failed to qualify for TAS had historically high LF baseline prevalence and density and had regular cross-border movement of populations. These four districts needed to conduct two additional rounds of LF MDA before repeating the pre-TAS. The results showed that Sierra Leone continued to make progress towards the elimination of LF as a public health problem.

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.

Evaluation of mass drug administration in the program to control imported lymphatic filariasis in Thailand

Background

Migration plays a major role in the emergence and resurgence of lymphatic filariasis (LF) in many countries. Because of the high prevalence of Imported Bancroftian Filariasis (IBF) caused by nocturnally periodic Wuchereria bancrofti and the intensive movement of immigrant workers from endemic areas, Thailand has implemented two doses of 6 mg/kg diethylcarbamazine (DEC) with interval of 6 months to prevent IBF. In areas where immigrants are very mobile, the administration of DEC may be compromised. This study aimed to evaluate DEC administration and its barriers in such areas.

Methods

A cross-sectional study with two-stage stratified cluster sampling was conducted. We selected Myanmar immigrants aged >18 years from factory and fishery areas of Samut Sakhon Province for interview with a structured questionnaire. We also interviewed health personnel regarding the functions of the LF program and practice of DEC delivery among immigrants. Associations were measured by multiple logistic regression, at P <0.05.

Results

DEC coverage among the immigrants was 75 %, below the national target. All had received DEC only once during health examinations at general hospitals for work permit renewals. None of the health centers in each community provided DEC. Significant barriers to DEC access included being undocumented (adjusted OR = 74.23; 95 % CI = 26.32–209.34), unemployed (adjusted OR = 5.09; 95 % CI = 3.39–7.64), daily employed (adjusted OR = 4.33; 95 % CI = 2.91–6.46), short-term immigrant (adjusted OR = 1.62; 95 % CI = 1.04–2.52) and living in a fishery area (adjusted OR = 1.57; 95 % CI = 1.04–2.52). Incorrect perceptions about the side-effects of DEC also obstructed DEC access for Myanmar immigrants. All positive LF antigenic immigrants reported visiting and emigrating from LF-endemic areas.

Conclusion

Hospital-based DEC administration was an inappropriate approach to DEC delivery in areas with highly mobile Myanmar immigrants. Incorporating health-center personnel in DEC delivery twice yearly and improving the perceptions of DEC side effects would likely increase DEC coverage among Myanmar immigrants.

Border malaria associated with multidrug resistance on Thailand-Myanmar and Thailand-Cambodia borders: transmission dynamic, vulnerability, and surveillance

This systematic review elaborates the concepts and impacts of border malaria, particularly on the emergence and spread of Plasmodium falciparum and Plasmodium vivax multidrug resistance (MDR) malaria on Thailand-Myanmar and Thailand-Cambodia borders. Border malaria encompasses any complex epidemiological settings of forest-related and forest fringe-related malaria, both regularly occurring in certain transmission areas and manifesting a trend of increased incidence in transmission prone areas along these borders, as the result of interconnections of human settlements and movement activities, cross-border population migrations, ecological changes, vector population dynamics, and multidrug resistance. For regional and global perspectives, this review analyzes and synthesizes the rationales pertaining to transmission dynamics and the vulnerabilities of border malaria that constrain surveillance and control of the world's most MDR falciparum and vivax malaria on these chaotic borders.