The selection of this paper from 1979 in the Transactions of the Royal Society of Tropical Medicine and Hygiene highlights significant issues in relation to neglected tropical disease (NTD) programmes, specifically the Global Programme to Eliminate Lymphatic Filariasis (LF), and the wider concepts of eradication and elimination. Webber in other papers in the 1970s described the epidemiology of Wuchereria bancrofti filariasis in the Solomon Islands where W. bancrofti and P. falciparum malaria were co-endemic, both transmitted by Anopheles punctulatus complex mosquitoe

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FROMTHEARCHIVESTrans R Soc Trop Med Hyg 2018; 112: 476–478doi:10.1093/trstmh/try082Filariasis elimination, vector control and eradication challengesCommentary on Webber, R. Eradication of Wuchereria bancrofti infection through vector control.Trans Roy Soc Trop Med and Hyg 1979;73:722–4David H. Molyneux*Department of Parasitology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK*Corresponding author: E-mail: david.molyneux@lstmed.ac.ukReceived 19 June 2018; revised 5 July 2018; editorial decision 5 July 2018; accepted 6 July 2018Keywords: Anopheles, elimination, eradication, ﬁlariasis, malaria, neglected tropical diseases, Wuchereria bancroftiThe selection of this paper from 1979 in the Transactions of theRoyal Society of Tropical Medicine and Hygiene highlights signiﬁ-cant issues in relation to neglected tropical disease (NTD) pro-grammes, speciﬁcally the Global Programme to EliminateLymphatic Filariasis (LF), and the wider concepts of eradicationand elimination. Webber in other papers in the 1970s describedthe epidemiology of Wuchereria bancrofti ﬁlariasis in theSolomon Islands where W. bancrofti and P. falciparum malariawere co-endemic, both transmitted by Anopheles punctulatuscomplex mosquitoes. The Solomon Islands were amongst themost endemic countries for ﬁlariasis in the Paciﬁc region.1 Amalaria eradication programme had been initiated in 1968,based on 6-monthly indoor residual spraying (IRS) of DDT (seepapers quoted in Webber 1979).2 Webber’s paper points out thesigniﬁcant impact of vector control on the parasitological para-meters of W. bancrofti and, thus, the prospect of ‘eradication’where Anopheles were vectors, in contrast to other areas of thePaciﬁc where W. bancrofti was transmitted by Aedes.3 Webbercomments perceptively that the degree of reduction inAnopheles vectors that is required is much less than that to con-trol malaria, a fact particularly pertinent to African settingshighlighted by4 and conﬁrmed in Nigeria,5 where both impreg-nated bed nets, long-lasting impregnated nets and mass drugadministration were deployed together. This resulted in theFederal Ministry of Health of Nigeria recommending greatercoordination between the malaria and ﬁlariasis programmes inthat country.Furthermore, a recent study in the Gambia where ﬁlariasiswas historically endemic, with high prevalences6 showed adecline in prevalence over a 30-year period as a result ofAnopheles control, using bed nets to control malaria in a nation-wide programme,7 although no mass drug administration(MDA) was implemented to control ﬁlariasis. This study demon-strated that vector control alone could sustainably arrest W.bancrofti transmission and lead to national elimination in anAfrica setting,8 and also emphasized the importance of the useof long-lasting impregnated nets to complement MDA innational Filariasis programmes borne out by recent results fromZambia.9 Webber’s results in the Solomon islands clearly showthe rate of decline in the parasitological parameters from 22%prevalence in 1974 to 0% prevalence in 1977 when no drugswere used in LF control. Webber was also able to estimate fromhis studies the longevity of adult W. bancrofti of 7–12 years, animportant ﬁgure in the context of the current LF programmesdependent on MDA alone. At least 5 years of annual MDA isrecommended by WHO; given that the drugs are microﬁlaricidaland do not kill adult worms (macroﬁlaricidal) it could beexpected that after 7 years MDA viable adults will still be pre-sent and producing microﬁlaria, which could sustain transmis-sion. This could explain the persistent transmission in areas thathave received more than 10 years MDA–so-called hotspots. Inthis context the Onchocerciasis Control Programme (OCP) inWest Africa was initially scheduled to use a strategy of weeklylarvicidal treatment for a period of 20 years, which was basedon the estimated duration of adult Onchocerca volvulus wormlife. However, after several years of vector control had beendeployed it became clear from epidemiological studies that theestimated maximum longevity of adult Onchocerca was some14 years; the advent of ivermectin into the OCP further reducedthe estimated duration of combined MDA and vector control bysome 2 years.10The other feature of the paper2 is the use of the termeradication to describe the impact of indoor residual sprayingon ﬁlariasis in the Solomon Islands. The paper was publishedduring the ﬁnal stages of the global smallpox eradication pro-gramme, which was formally declared to be eradicated by theWorld Health Assembly in 1980—the only infection to be era-dicated to date—WHO having abandoned the global malariaeradication programme in 1970 for reasons related to thedevelopment of DDT and chloroquine resistance. Today, the© The Author(s) 2018. Published by Oxford University Press on behalf of Royal Society of Tropical Medicine and Hygiene. All rights reserved.For permissions, please e-mail: journals.permissions@oup.com.476Downloaded from https://academic.oup.com/trstmh/article-abstract/112/11/476/5156259 by Liverpool School of Tropical Medicine user on 05 November 2018term that should have been used is ‘elimination’, given thecurrent widely accepted deﬁnitions. In 1993, the InternationalTask Force for Disease Eradication had evaluated around 90candidate diseases and concluded that six were eradicable—mumps, rubella, lymphatic ﬁlariasis, cysticercosis, dracuncu-liasis and polio. Seminal books on eradication have since beenpublished11,12 and three diseases have been targeted by WHOfor eradication—poliomyelitis, dracunculiasis and yaws, theﬁrst two diseases with active and highly successful pro-grammes, which have yet to achieve the ultimate goaldeﬁned by WHO of the ‘Permanent reduction to zero of theworldwide incidence of infection caused by a speciﬁc agent asa result of deliberate efforts. Intervention measures are nolonger needed.’ The challenges to achieving the goals ofeither elimination or, indeed, eradication have been high-lighted.13,14 However, as has been pointed out,13 eliminationin island settings is more easily achieved than when infec-tions are on a continental or regional scale, where bordersrequire greater coordination between countries and15enhanced surveillance of vector migration (e.g. Simuliummovement in West Africa) and population movement carryinginfections. Islands provide a limited likelihood of vectorreinvasion; a recent example is the successful blackﬂy controlby larvicidal treatment, which eliminated transmission ofonchocerciasis in Bioko, Equitorial Guinea.16 Another exampleof successful island elimination is of Echinococcus granulosus(hydatid disease) in Iceland, Tasmania, Cyprus, the FalklandIslands and New Zealand.17 Isolated foci of O. volvulus inUganda have also been eliminated (where there was no riskof blackﬂy reinvasion) by vector control where S. neavei wasthe vector.18The use of the term eradication by Webber in the title isexcusable, but brings to attention the fact that, while elimin-ation in island settings is feasible, the global goals of permanentzero incidence of any speciﬁc pathogen certiﬁed for all countriesis an expensive journey that presents a huge challenge whenseeking to ‘prove a negative’ in some of the most inaccessible,resource poor and conﬂict affected parts of the world.13,19Consistency in the use of the deﬁnitions of eradication and elim-ination is also necessary, but it seems that even public healthpractitioners ﬁnd this difﬁcult to adhere to.20 These problemsare also compounded by World Health Assembly resolutionsthat use the term ‘as a public health problem’, which are fre-quently based on parameters that are difﬁcult to deﬁne andevaluate.Roger Webber’s work in the Solomon Islands deserves to berecalled given the success to-date of the Global FilariasisProgramme.21 This is because the value of vector control as aneffective way of stopping transmission in Anopheles driven set-tings has been downplayed, in particular in African settings,where parallel malaria vector control will have had a synergisticimpact where MDA has been deployed.8 Filariasis and other NTDMDA programmes should be linked to better resourced pro-grammes. However, there has been a relative neglect of theopportunities afforded by vector or intermediate host controlinterventions as MDA programmes for NTDs have expanded. Thefundamental fact is that transmission is generated by exposureto infected vectors or contact with cercariae-infected water orcopepod ingestion in the case of Guinea worm, where copepodcontrol has been an important intervention as part of a multi-faceted complement of the Guinea Worm Eradication pro-gramme.14 While elimination has been successful in some set-tings without vector control, as in the Onchocerciasis ControlProgramme in the Americas leading to veriﬁed cessation oftransmission in four countries (Colombia, Ecuador, Guatemala,Mexico), the duration of twice a year ivermectin MDA could havebeen foreshortened had vector control been feasible.The use of ‘eradication’ in Webber’s title (more correctly elim-ination) raises the challenges of what eradication really means.Eradication deﬁned as ‘zero global incidence of a speciﬁc infec-tious agent’ needs a ‘buyer beware’ notice and reality-checkwarning. The current experience of polio and dracunculiasis pro-grammes demonstrate that the last mile is proving remarkablydifﬁcult. Both polio and Guinea worm are recording a handful ofhuman cases each year, in some of the countries where it ismost difﬁcult to implement programmes and access popula-tions. In addition, a recently conﬁrmed human case of Guineaworm infection in Angola, close to the Namibian border, is causefor serious concern, given that this case is so distant from thenearest remaining endemic areas in Chad, Ethiopia and Mali.22This unexpected event needs urgent investigation, while theemergence of previously unsuspected animal hosts (dogs andbaboons) of Dracunculus medinensis should temper expecta-tions that zero global incidence of the pathogen can be proven—‘expect the unexpected’ as remarked by the Dahlem eradica-tion meeting.12 Webber’s work on ﬁlariasis beneﬁtted from themalaria control programme. Malaria eradication is now on theagenda. However, malaria ‘eradication’ itself does not complywith the accepted deﬁnition as malaria is a disease; the causa-tive agents are the six human species of Plasmodium—two ofwhich are proven zoonoses in primates. For ‘malaria eradication’to be achieved each species of human Plasmodium must beconﬁrmed as having zero global incidence. Perhaps it is time toconsider a serious reality check?Authors’ contributions: DHM is the sole author; he selected the paperfor comment, developed the ideas and wrote the paper.Acknowledgements: None.Funding: None.Competing interests: None declared.Ethical approval: Not required.References1 Ichimori K, Graves P. Overview of PacELF—the Paciﬁc Programme forthe Elimination of Lymphatic Filariasis. Trop Med Health 2017;45:34.2 Webber R. Eradication of Wuchereria bancrofti infection through vec-tor control. Trans R Soc Trop Med Hyg 1979;73:722–4.Transactions of the Royal Society of Tropical Medicine and Hygiene477Downloaded from https://academic.oup.com/trstmh/article-abstract/112/11/476/5156259 by Liverpool School of Tropical Medicine user on 05 November 20183 Pichon G. Limitation and facilitation in the vectors and other aspectsof the dynamics of ﬁlarial transmission: the need for vector controlagainst Anopheles transmitted ﬁlariasis. Ann Trop Med Parasitol2002;96(Suppl 2):S143–52.4 Molyneux DH, Nantulya V. Linking disease control programmes inrural Africa: a pro-poor strategy to reach Abuja targets and millen-nium development goals. Br Med J 2004;328:1129–32.5 Eigege A, Kal E, Miri E et al. Long lasting nets are synergistic withmass drug administration for interruption of lymphatic ﬁlariasistransmission in Nigeria. PLoS Negl Trop Dis 2013;7:e2508.6 McGregor IA, Gilles HM. Diethylcarbamazine control of bancroftian ﬁl-ariasis; follow-up of a ﬁeld trial in West Africa. Br Med J 1956;1(4962):331–2.7 Rebollo MP, Sambou SM, Brent T et al. Elimination of lymphatic ﬁlar-iasis in the Gambia. PLoS Negl Trop Dis 2015;9:e0003642.8 Kelly-Hope LA, Molyneux DH, Bockarie MJ. Can malaria vector controlaccelerate the interruption of lymphatic ﬁlariasis transmission inAfrica; capturing a window of opportunity? Parasit Vectors 2013;6:39.9 Nsakashalo-Senkwe M, Mwase E, Chizema-Kawesha E et al.Signiﬁcant decline in lymphatic ﬁlariasis associated with nationwidescale-up of insecticide-treated nets in Zambia. Parasite EpidemiolControl 2017;2:7–14.10 Boatin B, Richards FR. Control of onchocerciasis. Adv Parasitol 2006;61:349–94.11 Cochi S, Dowdle WR, eds. Disease Eradication in the 21st Century;implications for Global Health. Strungman Forum Reports.Cambridge, MA: MIT Press, 2011; p. 319.12 Dowdle WR, Hopkins DR, eds. The eradication of infectious diseases.Chichester: John Wiley & Sons, 1998; p. 218.13 Molyneux D. Eradication and elimination: facing the challenges, tem-pering expectations. Int Health 2015;7:299–301.14 Molyneux D, Sankara DP. Guinea worm eradication: progress andchallenges—should we beware of the dog? PLoS Negl Trop Dis 2017;11:e0005495.15 Gustavsen K, Sodahlon Y, Bush S. Cross-border collaboration forneglected tropical disease efforts—lessons learned from onchocer-ciasis control and elimination in the Mano River Union (West Africa).Global Health 2016;12(1):44.16 Traoré S, Wilson MD, Sima A et al. The elimination of the onchocer-ciasis vector from the island of Bioko as a result of larviciding by theWHO African Programme for Onchocerciasis Control. Acta Trop 2009;111:211–18.17 Craig PS, Larrieu E. Control of cystic echinococcosis/hydatidosis:1863–2002. Adv Parasitol 2006;61:443–508.18 Katabarwa MN, Katamanywa J, Lakwo T et al. The Imaramagamboonchocerciasis focus in southwestern Uganda: interruption of trans-mission after disappearance of the vector Simulium neavei and itsassociated freshwater crabs. Am J Trop Med Hyg 2016;95:417–25.19 Jacobson J, Bush S. Neglected tropical diseases, neglected commu-nities, and conﬂict: how do we leave no one behind? Trends Parasitol2018;34:175–7.20 Molyneux DH, Hopkins DR, Zagaria N. Disease eradication, eliminationand control: the need for accurate and consistent usage. TrendsParasitol 2004;20:347–51.21 World Health Organization. Global programme to eliminate lymphaticﬁlariasis: progress report 2016. Wkly Epidemiol Rec 2017;91:589–608.22 World Health Organization. 2018. http://www.who.int/neglected_diseases/news/Surveillance-presence-of-dracunculiasis-in-Angola/en/(accessed 3 July 2018).D. H. Molyneux478Downloaded from https://academic.oup.com/trstmh/article-abstract/112/11/476/5156259 by Liverpool School of Tropical Medicine user on 05 November 2018

Filariasis elimination, vector control and eradication challenges: Commentary on Webber, R. Eradication of Wuchereria bancrofti infection through vector control. Trans Roy Soc Trop Med and Hyg 1979;73:722-4.

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Filariasis elimination, vector control and eradication challenges: Commentary on Webber, R. Eradication of Wuchereria bancrofti infection through vector control. Trans Roy Soc Trop Med and Hyg 1979;73:722-4.

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