Absence of Lymphatic Filariasis in Oman-EMHJ-10

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    1059  Absence o lymphatic flariasis inection amongsecondary-school children in Oman  S.T. Al Awaidy, 1 S. Bawikar, 1 P.K. Patel,  2 P. Kurup,  3 G.S. Sonal, 4 S. Al Mahrooqi  1 and R. Ramzy  1 ABSTRACT The endemicity status o lymphatic lariasis in Oman is uncertain, with only sporadic cases reported,mostly imported. Immunochromatographic card test surveys were carried out to assess the presence o circulating Wuchereria bancroti  antigenaemia as a marker or active inection in children rom suspected high-risk areas o Oman (South Batinah and Dhoar). Lot quality assurance sampling surveys were carried out on a minimum o 250secondary-school children aged 17–18 years in each o 8 districts rom February 2004 to March 2004. All testedstudents were negative or circulating W. bancroti  antigen. Based on these ndings as well as previous data,Oman may possibly be classied as a nonendemic country, with no evidence o indigenous lymphatic lariasistransmission. 1 Department o Communicable Disease Surveillance and Control, Ministry o Health, Muscat, Oman (Correspondence to S.T. Al Awaidy: salah.awaidy@gmail.com).  2 Department o Health Aairs, Dhahira Region, Oman.  3 Department o Health Aairs, South Batinah Region, Oman. 4 Department o Health Aairs, Dhoar Region, Oman. Received: 07/01/09; accepted: 19/02/09   : ..) ( 18   17   250   2004 / /..  Absence de flariose lymphatique chez les élèves de l’enseignement secondaire à Oman RÉSUMÉ Le statut de l’endémicité de la lariose lymphatique à Oman est fou : seuls des cas sporadiques, pour la plupart importés ont été notiés. Des études ondées sur des tests immunochromatographiques sur carte ontété eectuées pour déterminer la présence d’antigènes circulants spéciques de Wuchereria bancroti  , en tantque marqueur d’une inection active chez les enants dans les régions suspectées de présenter un haut risque àOman (Batinah-sud et Dhoar). Un sondage pour le contrôle de la qualité des lots a été réalisé sur un minimumde 250 élèves de l’enseignement secondaire âgés de 17 à 18 ans, dans chacun des huit districts entre évrier etmars 2004. Tous les élèves testés présentaient des résultats négatis pour l’antigène circulant spécique de W.bancroti  . En onction de ces résultats et de données précédentes, Oman peut être classé comme un pays nonendémique ne présentant aucun signe de transmission indigène de la lariose lymphatique.  EMHJ ã Vol. 16 No.10 ã 2010Eastern Mediterranean Health JournalLa Revue de Santé de la Méditerranée orientale 1060 Introduction Lymphatic lariasis (LF) is one of themost debilitating, disguring and stig  - matizing diseases of the tropical andsubtropical regions of the world. LF isendemic in more than 80 countries. Itis estimated that 120 million peopleare infected and one-third of them suf  - fer from chronic manifestations of thedisease. Worldwide, an additional 1 bil - lion individuals are at risk of acquiring the infection [1–4]. e World HealthOrganization (WHO) estimates that5.1 million disability-adjusted life years(DALYs) are lost due to LF [5].Estimates suggest that approximate - ly 12.6 million LF-infected individu - als, 1% of the LF global burden, live incountries of the Eastern MediterraneanRegion, where LF is entirely caused by  Wuchereria bancrofi and is ransmited primarily by  Culex spp. mosquitoes inmostly rural and semi-urban areas [6].LF is endemic in Egypt, Sudan and Yemen and is targeted for eliminationunder the Global Programme for theElimination of Lymphatic Filariasis(GPELF) [7]. e LF situation in Dji -  bouti, Oman, Pakistan, Saudi Arabiaand Somalia is currently described asuncertain. However, clinical cases have been reported from Oman, Pakistan,Saudi Arabia and Somalia [4,7].Oman has a population of approxi - mately 2.34 million, of whom 23.9%are expatriates (2003 census data).Many of these expatriates are from LF-endemic countries such as Egypt, Indiaand Sri Lanka. LF is a notiable diseasein Oman, and between 1991 and 200115 cases were reported, mostly classiedas imported based on the history of thepatient’s stay in LF-endemic countries.Of these, 7 were Omanis who lived forsome time in LF endemic areas [6,8]. With such sporadic cases it is necessary to verify the LF status of Oman. A study conducted by Scrimgeour et al. foundan LF antigenaemia prevalence of 4.2% based on the immunochromatographictest (ICT) among Indian expatriatesliving in Oman [9]. However, in theglobal perspective, Oman is includedamong countries with an uncertain LFsituation, i.e. there is no clear evidenceeither of the presence or absence of localtransmission [6].e ICT lariasis card test is arapid format test that detects circulating larial antigens released by adult worms[10] and can thus detect active infec - tion independent of microlaraemia.Several eld studies have evaluated therapid test and showed that the ICTtest can use blood collected during theday or night; the sensitivity of the testreached 98%–100% among microlariacarriers with 100% specicity [11–14].erefore, WHO has recommendedthe use of the ICT card test for mapping LF endemic areas [15].e present study aimed to evaluatethe LF status in Oman by carrying outICT-card surveys to detect W. bancrofi   antigenaemia among secondary-schoolchildren aged 17–18 years in these 2regions. Methods Study design is was a lot quality assurance sam - pling (LQAS) school-based survey conducted during the academic year2004–05 among secondary-schoolchildren from areas identied as having the potential for LF transmission. Study area e process of verication includedinitial use of qualitative methods (ques - tionnaire surveys of key informants) toidentify possible LF endemic areas. is was followed by LQAS antigenaemiasurveys in these possible endemic areas.e key informant surveys identied2 possible LF endemic areas: SouthBatinah and Dhofar region (adminis - tratively described as the governorateof Dhofar).Initial rapid assessment question - naire surveys had revealed that theprobability of local transmission washighest in the 6 districts of South Bati - nah region and 2 districts representing 81% of the population in the Dhofargovernorate. Hence, the current antigensurveys were conducted in these 8 dis - tricts of 2 regions of Oman. Study population e target population was childrenaged 17–18 years aending secondary schools. e rationale for selecting thisage group for the surveys was that LF isa chronic disease with a long incubationperiod that requires repeated exposureover an extended period of time be - fore the infection is acquired. It takeseven longer for the clinical signs andsymptoms of lymphatic obstructionto appear. erefore, the secondary-school students of this age group wouldoer epidemiological evidence of thepresence or absence of indigenous LFinfection in Oman because they wouldrepresent an exposure history of 17–18 years. Sampling e WHO guidelines for preparing and implementing a national plan toeliminate LF require that LQAS surveysare conducted to assess the prevalenceof antigenaemia in a district to decide oninitiation of mass treatment. us it wasdecided that a sample of 250 childrenfrom the target age group from eachdistrict would be examined using ICT. A cut-o point of 1% was set to classify the district as endemic for LF [16].Out of 6 districts from South Bati - nah region 3 districts have a signicantly lower population compared with theother 3. Hence, it was decided to testthe whole secondary-school populationin these 3 districts (295, 235 and 257students). In the other 3 districts , Barka,Musanah and Rustaq, the selection of the students was done according to theproportional target population. us358, 347 and 506 students were select - ed from these districts respectively, by considering each class in the secondary     1061 schools as 1 cluster and randomly se - lecting the classes. Similarly, 499 and248 students were selected from Salalahand Taqah districts of Dhofar regionrespectively. Survey e eld part of the study was conductedfrom February to March 2004. A eld protocol was developed toensure uniformity and smooth conductof the surveys and also to ensure quality. A national team was formed to overseethe survey activities including the train - ing of sta. e eld investigators werethe school health sta, including doc - tors and nurses of the respective district. A standardization training workshop was organized before the eld part of thestudy to detail the survey methodology. All aspects of the ICT kit procedure were explained and demonstrated to theeld sta. e sta were given hands-ontraining followed by a eld evaluationof the acquired skills to ensure quality.Each survey team consisted of 1 doctorand 2 sta nurses. One nurse lled thedata collection forms while the othercollected blood samples and performedthe ICT test. e doctor was responsi -  ble for reading the card results and over - all quality control. Data were collectedonto pre-tested school forms. ICT test kit e NOW ICT lariasis kit (catalog no. 620-000, Binax Inc.) was used forthe qualitative detection of  W. bancrofi   antigen. e tests were developed andread according to the manufacturer’sinstructions. e test is useful for thedemonstration of the W. bancrofi ani- gen at any time of the day and with any accessible population. A 100 µL bloodsample collected by ngerprick during the day was added without pre-treat - ment to a pink and white sample padcoupled to colloidal gold that containeddried polyclonal antibody (PAb) andmonoclonal antilarial antibody (MAb)respectively. e teams were asked toconduct the tests in lots of 10 studentsto ensure a smooth ow of the test pro - cedures. e results were read aer 10minutes. e test was recorded positiveif 2 lines (test and control) were seenin the viewing window, even when thetest line appeared lighter or darker thanthe control line. e test was consideredinvalid if the control line did not appear;the test was then repeated according tothe manufacturer’s instructions. Ethics e study was approved by the OmaniMinistry of Health and regional healthadministrators as well as the RegionalCommiee of the World Health Or - ganization Regional Oce for the East - ern Mediterranean. e students as wellas the parents and community at large were briefed about the purpose of thesurvey. Informed consent was obtained before conducting the survey. Statistics e data were computed and analysedusing the statistical program  Epi-Ino   2000. Frequencies, proportions andprevalence rates were calculated. Results  A total of 2745 students aged 17–18 years were subjected to antigenaemiatesting with a minimum of 250 studentsin each of the 8 districts. A total of 1998(72.8%) were from South Batinah re - gion and the remaining 747 (27.2%) were from Dhofar region. e study subjects were from classes belonging to 34 randomly selected secondary schools in the study areas. e male tofemale ratio was 0.9:1.Of the 2745 tested, none of thestudents tested positive for circulating  W. bancrofi antigen (Table 1). During the surveys 2 card tests were doubtfully positive in South Batinah region and14 cards were read as invalid in Dhofarregion. ese tests were repeated laterand also found to be negative. Discussion LF is uncommon in Oman. e en - demicity status is uncertain [6]; how  - ever some areas have been suggestedas endemic areas [4]. Only 15 cases of LF were reported in Oman during thesurveillance period 1991–2001. Mostcases were classied as imported [6].In our LQAS surveys of 2745 sec - ondary-school students in South Batinahregion and Salalah and Taqah districts of the Dhofar region, all were uniformly antigen-negative and therefore noneof the study districts were LF endemic.Other countries have used detection of  Table 1 Antigenaemia survey or the presence o lymphatic flariasis amongschoolchildren aged 17–18 years in Oman according to district and sex Region/districtNo. o schoolsNo. o children testedNo. antigen-positiveBoysGirlsTotal  South Bathinah Rustaq52432635060Musannah41731743470Barka42101483580Wadi Maawil2991362350Nakhl31281672950Al Awabi41081492570 Dhofar  Salalah72332664990Taqah51381102480Total341332141327450  EMHJ ã Vol. 16 No.10 ã 2010Eastern Mediterranean Health JournalLa Revue de Santé de la Méditerranée orientale 1062 antigenaemia by the ICT card test insurveys to estimate the prevalence of LFinfection (Table 2). Similar to our study,the prevalence of LF was zero in somestudies in Trinidad [16,17].It is generally believed that the vectorsof LF are abundant in Oman, althoughthe specic mosquito species have not been formally identied. Nevertheless,LF is most likely not endemic in Oman.e existence of isolated infected casesin areas where transmission is extremely unlikely (e.g. immigrants from a LF en - demic country to a nonendemic coun - try) does not require development of a national LF elimination programme.Such a situation requires implementa - tion of a passive surveillance system by testing blood routinely collected frommilitary recruits, university students, blood donors and hospitalized patients.Similarly, examination of blood samplesfrom expatriates and treatment of in - fected subjects would also be necessary. Conclusions e prevalence of larial antigenaemiaamong students aged 17–18 years in thesuspected transmissible areas was zero.From this evidence it can reasonably  be concluded that LF is not endemicin Oman and there is no evidence of itstransmission.e data suggest that Oman couldseek to be awarded a certicate of LFelimination.  Acknowledgements  We are grateful to the WHO RegionalOce for the Eastern Mediterraneanfor providing the Binax ICT kits free of charge for the survey as well as provid - ing technical expertise. We are thankfulto Dr Ali Jaer Mohammed, AdvisorHealth Aairs and the survey sta andthe Directorate sta from South Bati - nah and Dhofar region for completionof the survey. We also thank the Regional Direc - torate General of Education, schoolsprincipals and teachers for their excep - tional cooperation and the students forthe participation. We acknowledge theexcellent support of the regional teamsof doctors and health inspectors for thisstudy. Table 2Prevalence o lymphatic flariasis by antigenaemia in selected countries Study reerenceCountryPrevalence (%)Study subjects Present studyOman0.0Schoolchildren[16]Trinidad0.0Schoolchildren[17]Kuwait18.3 Adults[18]Cambodia0.7Adults[19]Suriname0.22Adults[20]Nigeria22.5Adult males[21]Uganda, Alebtong29.0Schoolchildren[21]Uganda, Lwala18.0 Schoolchildren[21]Uganda, Obalanga30.0 Schoolchildren[13]Egypt17.2Schoolchildren Reerences Ottesen EA. Major progress toward eliminating lymphatic1.lariasis. New England Journal o Medicine , 2002, 347(23):1885–1886.Zagaria N and Savioli L. Elimination o lymphatic lariasis: a2.public–health challenge  Annals o Tropical Medicine and Para- sitology  , 2002, 96(Suppl. 2):3–13. Out flariasis now. Report o the second meeting o the Global Alli- 3. ance to Eliminate Lymphatic Filariasis. New Delhi, World HealthOrganization Regional Oce or South-East Asia, 2002.Ottesen EA et al. Strategies and tools or the control/elimina-4.tion o lymphatic lariasis. Bulletin o the World Health Organi- zation , 1997, 75:491–503. Regional strategic plan or elimination o lymphatic flariasis 5. (2004–2007). New Delhi, World Health Organization Region-al Oce or South-East Asia, 2004 (SEA-FIL-29).El Setouhy M, Ramzy RM. Lymphatic lariasis in the East-6.ern Mediterranean Region: current status and prospectsor elimination. Eastern Mediterranean Health Journal  , 2003,9(4):534–541. DCD Division o Communicable Disease Control annual report  7.  2002 . Cairo, World Health Organization Regional Oce or the Eastern Mediterranean, 2002:7.Chapter 9: morbidity and mortality8. . Tables 9–15. In:  Annual health report  . Muscat, Oman Ministry o Health, 2001.Scrimgeour EM et al. Bancrotian lariasis in residents o 9.Oman.  Acta Tropica , 2001, 79(3):241–244.Weil GJ, Lammie PJ, Weiss N. The ICT lariasis test: a rapid10.ormat antigen test or diagnosis o bancrotian lariasis. Para- sitology Today  , 1997, 13:401–404.Ramzy RM et al. Field evaluation o a rapid-ormat kit or diag-11.nosis o bancrotian lariasis in Egypt. Eastern MediterraneanHealth Journal  , 1999, 5:880–887.Njenga SM, Wamae, CN. Evaluation o ICT lariasis card test12.using whole capillary blood: comparison with Knott’s concen-tration and counting chamber methods.  Journal o Parasitol-ogy  , 2001, 87:1140–1143.Ramzy RM et al. Ecient assessment o lariasis endemicity13.by screening or larial antigenaemia in a sentinel population. Transactions o the Royal Society o Tropical Medicine and Hy- giene , 1994, 88(1):41–44.
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