ABSTRACT

Objective.

To confirm the absence of Wuchereria bancrofti autochthonous cases in Manaus, a former focus of lymphatic filariasis in the Western Brazilian Amazon.

Methods.

A field survey was carried out in 2016 using immunochromatographic rapid tests (ICT card) for the detection of circulating filarial antigens in blood. The sample included a group of 3 000 schoolchildren aged 6 to 10 years enrolled in schools from different urban areas of Manaus (including the former lymphatic filariasis focus in the city) and a group of 709 adolescents and adults, between the ages of 11 and 85 years, born and raised in different areas of Manaus.

Results.

All of the individuals tested negative for W. bancrofti antigen.

Conclusions.

Although Manaus was once considered endemic, this focus no longer seems to be active for lymphatic filariasis transmission. The results of this study could support the certification by the World Health Organization of the lymphatic filariasis transmission elimination exercise in Brazil.

Keywords
Wuchereria bancrofti; elephantiasis; filarial; Brazil

RESUMEN

Objetivo.

Confirmar la ausencia de casos autóctonos de Wuchereria bancrofti en Manaos, anteriormente un foco de filariasis linfática en la Amazonia occidental de Brasil.

Métodos.

En el 2016 se llevó a cabo una encuesta en el terreno con pruebas rápidas inmunocromatográficas (tiras inmunocromatográficas) para detectar antígenos filáricos circulantes en sangre. La muestra constó de un grupo de 3 000 escolares de 6 a 10 años matriculados en escuelas de diferentes zonas urbanas de Manaos (incluida la zona que anteriormente era el foco de filariasis linfática en la ciudad) y de un grupo de 709 adolescentes y adultos, de edades comprendidas entre 11 y 85 años, nacidos y criados en diferentes áreas de Manaos.

Resultados.

Todas las personas dieron negativo en la prueba de antígeno de Wuchereria bancrofti.

Conclusiones.

Aunque hubo un tiempo en que Manaos se consideraba zona endémica, parece que este foco de transmisión de la filariasis linfática ya no está activo. Los resultados de este estudio podrían brindar apoyo a la certificación de la Organización Mundial de la Salud respecto de los esfuerzos realizados en Brasil para eliminar la transmisión de la filariasis linfática.

Palabras clave
Wuchereria bancrofti; filariasis linfática; Brasil

Palavras-chave
Wuchereria bancrofti; filariose linfática; Brasil

RESUMO

Objetivo.

Confirmar a ausência de casos autóctones de Wuchereria bancrofti em Manaus, anteriormente um foco da filariose linfática na parte leste da Amazônia brasileira.

Métodos.

Uma pesquisa de campo foi realizada em 2016 com o uso de teste rápido por imunocromatografia (cartão ICT) para detecção de antígenos de microfilárias circulantes no sangue. A amostra estudada consistiu de um grupo de 3 000 crianças escolares entre 6 e 10 anos de idade matriculados em escolas de diferentes áreas da zona urbana de Manaus (englobando a área anteriormente com o foco de filariose linfática) e um grupo de 709 adolescentes e adultos entre 11 e 85 anos de idade nascidos e crescidos em diferentes áreas de Manaus.

Resultados.

Todos os indivíduos pesquisados tiveram teste negativo para o antígeno da W. bancrofti.

Conclusões.

Apesar de Manaus ter sido anteriormente uma área endêmica, parece que não existe mais foco ativo de transmissão da filariose linfática na cidade. Os resultados deste estudo podem servir para embasar a certificação pela Organização Mundial da Saúde da eliminação da transmissão da filariose linfática no Brasil.

Keywords
Wuchereria bancrofti; elephantiasis; filarial; Brazil

Lymphatic filariasis (LF) is a vector-borne neglected tropical disease with serious social and economic impact. It is caused by three nematode species, Brugia malayi, B. timori, and Wuchereria bancrofti, the last of which is the main etiological agent, responsible for more than 90% of cases (¹1. World Health Organization [Internet]. Geneva: WHO; 2020 March 2 [cited 2020 May 21]. Lymphatic filariasis, Key facts. Available from: https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis
https://www.who.int/news-room/fact-sheet... , ²2. World Health Organization. Global programme to eliminate lymphatic filariasis: progress report, 2018. Wkly Epidemiol Rec. 2019;94(41):457–72. Available from: https://apps.who.int/iris/bitstream/handle/10665/329087/WER9441-eng-fre.pdf
https://apps.who.int/iris/bitstream/hand... ).

The disease impairs the lymphatic system, leading to chronic disability such as lymphedema, hydrocele, and elephantiasis, and is considered a global public health problem by the World Health Organization (WHO) (¹1. World Health Organization [Internet]. Geneva: WHO; 2020 March 2 [cited 2020 May 21]. Lymphatic filariasis, Key facts. Available from: https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis
https://www.who.int/news-room/fact-sheet... , ²2. World Health Organization. Global programme to eliminate lymphatic filariasis: progress report, 2018. Wkly Epidemiol Rec. 2019;94(41):457–72. Available from: https://apps.who.int/iris/bitstream/handle/10665/329087/WER9441-eng-fre.pdf
https://apps.who.int/iris/bitstream/hand... ). Currently, LF is found in 49 countries in Asia, Africa, and the Americas, affecting approximately 100 million people, and putting around 893 million people at risk of acquiring it (¹1. World Health Organization [Internet]. Geneva: WHO; 2020 March 2 [cited 2020 May 21]. Lymphatic filariasis, Key facts. Available from: https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis
https://www.who.int/news-room/fact-sheet... , ²2. World Health Organization. Global programme to eliminate lymphatic filariasis: progress report, 2018. Wkly Epidemiol Rec. 2019;94(41):457–72. Available from: https://apps.who.int/iris/bitstream/handle/10665/329087/WER9441-eng-fre.pdf
https://apps.who.int/iris/bitstream/hand... ). The two most recent countries to receive validation from WHO for the elimination of LF are Yemen and Kiribati, a Pacific island nation (³3. World Health Organization [Internet]. Geneva: WHO; 2019 August 15 [cited 2019 December 25]. Neglected tropical diseases. Despite challenges, Yemen eliminates lymphatic filariasis. Available from: https://www.who.int/neglected_diseases/news/yemen-eliminates-lymphatic-filariasis/en/.
https://www.who.int/neglected_diseases/n... ).

In the Americas, the disease is caused exclusively by W. bancrofti. It is believed to have been introduced as a result of the slave trade from Africa, the most unfortunate and tragic legacy of colonialism (⁴4. Orihel TC. Filariae. In: Beaver PC, Jung RC (editors). Animal agents and vectors of human disease. 5th ed. Philadelphia: Lea & Febiger, 1985;171–91.). Culex quinquefasciatus mosquitoes are considered to be the only competent vector species in this continent (⁵5. World Health Organization. Lymphatic filariasis: a handbook of practical entomology for national lymphatic filariasis elimination programmes. Geneva: WHO; 2013. Available from: https://www.who.int/lymphatic_filariasis/resources/9789241505642/en/.
https://www.who.int/lymphatic_filariasis... ). The parasite microfilariae found in patients circulate in the peripheral blood mainly at night (nocturnal periodicity) (⁶6. Fontes G, Rocha EMM, Brito AC, Fireman FA, Antunes CM. The microfilarial periodicity of Wuchereria bancrofti in northeastern Brazil. Ann Trop Med Parasitol. 2000;94:373–9. https://doi.org/10.1080/00034983.2000.11813552
https://doi.org/10.1080/00034983.2000.11... ), and can be detected in thick blood smear samples taken for diagnostic purposes.

In 1997, the World Health Assembly (Resolution WHA 50.29) set the year 2020 as the target for the elimination of LF as a global public health problem (⁷7. World Health Organization. Fiftieth World Health Assembly, Geneva 5–14 May 1997. Resolutions and decisions, annexes. Geneva: WHO; 1997 (Document WHA50/1997/REC/1).). In 2000, WHO launched the Global Programme to Eliminate Lymphatic Filariasis to achieve this goal (⁸8. World Health Organization. Preparing and implementing a national plan to eliminate lymphatic filariasis: a guideline for programme managers. Geneva: WHO; 2000. Available from: https://www.who.int/lymphatic_filariasis/resources/who_cds_cpe_cee_2000.15/en/.
https://www.who.int/lymphatic_filariasis... ). As per WHO recommendations, the main strategy to interrupt LF transmission is mass drug administration. This should be followed by a Transmission Assessment Survey and monitoring (⁹9. World Health Organization. Monitoring and epidemiological assessment of mass drug administration in the global programme to eliminate lymphatic filariasis: a manual for national elimination programmes. Geneva: WHO; 2011. Available from: https://apps.who.int/iris/handle/10665/44580
https://apps.who.int/iris/handle/10665/4... ).

LF foci persist in four countries of the Americas: Brazil, the Dominican Republic, Guyana, and Haiti (¹⁰10. World Health Organization. Global programme to eliminate lymphatic filariasis: progress report on mass drug administration, 2010. Wkly Epidemiol Rec. 2011;86(35):377–88. Available from: https://www.who.int/wer/2011/wer8635.pdf
https://www.who.int/wer/2011/wer8635.pdf... , ¹¹11. Fontes G, Leite AB, de Lima ARV, Freitas H, Ehrenberg JP, Rocha EMM. Lymphatic filariasis in Brazil: epidemiological situation and outlook for elimination. Parasit Vectors. 2012;5:272. https://doi.org/10.1186/1756-3305-5-272
https://doi.org/10.1186/1756-3305-5-272... ). Endemic areas of LF along the northeastern coast of Brazil are limited to Recife, in Pernambuco State, and three cities within the Recife metropolitan region (Olinda, Jaboatão dos Guararapes, and Paulista) (¹¹11. Fontes G, Leite AB, de Lima ARV, Freitas H, Ehrenberg JP, Rocha EMM. Lymphatic filariasis in Brazil: epidemiological situation and outlook for elimination. Parasit Vectors. 2012;5:272. https://doi.org/10.1186/1756-3305-5-272
https://doi.org/10.1186/1756-3305-5-272... , ¹²12. Xavier A, Oliveira H, Aguiar-Santos A, Barbosa Junior W, da Silva E, Braga C, et al. Assessment of transmission in areas of uncertain endemicity for lymphatic filariasis in Brazil. PLOS Negl Trop Dis. 2019;13(11):e0007836. https://doi.org/10.1371/journal.pntd.0007836
https://doi.org/10.1186/1756-3305-5-272... ). These foci are currently being reassessed through a Transmission Assessment Survey, in order for the Brazilian LF Elimination Program (PEFL) to certify the absence of active W. bancrofti transmission.

The cities of Belém (Pará State) and Manaus (Amazonas State), situated in the north of Brazil, were also known to be endemic, yet they are now considered nonendemic (¹¹11. Fontes G, Leite AB, de Lima ARV, Freitas H, Ehrenberg JP, Rocha EMM. Lymphatic filariasis in Brazil: epidemiological situation and outlook for elimination. Parasit Vectors. 2012;5:272. https://doi.org/10.1186/1756-3305-5-272
https://doi.org/10.1186/1756-3305-5-272... ). Interruption of transmission in Belém was confirmed in 2001. No microfilaremic subjects and no infected mosquitoes were found as a result of extremely thorough study (¹¹11. Fontes G, Leite AB, de Lima ARV, Freitas H, Ehrenberg JP, Rocha EMM. Lymphatic filariasis in Brazil: epidemiological situation and outlook for elimination. Parasit Vectors. 2012;5:272. https://doi.org/10.1186/1756-3305-5-272
https://doi.org/10.1186/1756-3305-5-272... , ¹³13. Fontes G, Braun RF, Neto HF, Vieira JBF, Padilha SS, Rocha RC, et al. Filariose linfatica em Belem, Estado do Para, Norte do Brasil e a perspectiva de eliminacao. Rev Soc Bras Med Trop. 2005;38(2):131–6.), attesting to the effectiveness of the measures adopted in that city. No study has been conducted to assess interruption of LF transmission in Manaus.

Results of a study conducted in Manaus in 1949 revealed LF positive findings in 2% (48/2 405) of the study population (autochthonous cases) (¹⁴14. Deane MP. Sobre a incidencia de filarias humanas em Manaus, Estado do Amazonas. Rev Serv Espec Saude Publica. 1949;2:849–58.). The last LF epidemiological study in the city was carried out in 1956, the findings of which revealed 0.2% positivity (microfilariae positive for W. bancrofti) among the 10 889 individuals examined (¹⁵15. Rachou RG, Lacerda NB. Transmissao da filariose brancroftiana em Manaus (Amazonas). Rev Bras Malariol Doencas Trop. 1956;8(2):369–71. PMID: 13494855. ). There is no further information relative to the distribution and prevalence of autochthonous cases of W. bancrofti in Manaus since these two earlier studies. Thus, the aim of this study was to reassess the occurrence of LF in Manaus to support the country’s dossier in the certification of interruption of LF transmission.

MATERIALS AND METHODS

Study area

The study was conducted in the urban area of Manaus (03º06'07" S, 60º01'30" W), capital of Amazonas State, located in the Western Amazon, Brazil (Figure 1). The city has a total area of 11 401 092 km², encompassing 63 neighborhoods with an estimated population of 2 182 763 inhabitants (population density of around 158.1/km²) (¹⁶16. Instituto Brasileiro de Geografia e Estatística [Internet]. Rio de Janeiro: IBGE; c2017 [cited 2019 December 9]. Brasil, Amazonas, Manaus [Data]. Available from: https://cidades.ibge.gov.br/brasil/am/manaus/panorama
https://cidades.ibge.gov.br/brasil/am/ma... ). Manaus is a city with areas of poverty, per capita income of 790.27 Brazilian reals, and a Municipal Human Development Index of 0.737 (¹⁶16. Instituto Brasileiro de Geografia e Estatística [Internet]. Rio de Janeiro: IBGE; c2017 [cited 2019 December 9]. Brasil, Amazonas, Manaus [Data]. Available from: https://cidades.ibge.gov.br/brasil/am/manaus/panorama
https://cidades.ibge.gov.br/brasil/am/ma... ), with high population density.

Sampling and collection

A cross-sectional randomized survey was conducted from September 2015 to July 2016. The study samples were composed of school-age children and general population.

School-age children.

Students aged 6 to 10 years from urban area municipal public elementary schools were investigated as per guidance of WHO (⁸8. World Health Organization. Preparing and implementing a national plan to eliminate lymphatic filariasis: a guideline for programme managers. Geneva: WHO; 2000. Available from: https://www.who.int/lymphatic_filariasis/resources/who_cds_cpe_cee_2000.15/en/.
https://www.who.int/lymphatic_filariasis... ) and the Transmission Assessment Survey of the Global Programme to Eliminate Lymphatic Filariasis (⁹9. World Health Organization. Monitoring and epidemiological assessment of mass drug administration in the global programme to eliminate lymphatic filariasis: a manual for national elimination programmes. Geneva: WHO; 2011. Available from: https://apps.who.int/iris/handle/10665/44580
https://apps.who.int/iris/handle/10665/4... ). WHO calls for a sample of 3 000 children to be tested following the rapid survey methodology based on rapid immunochromatographic test (ICT) cards to verify LF transmission in a suspected area.

The municipal education department provided an updated list with the names of the students enrolled in the elementary schools, to allow the survey to be carried out. In order to come up with the population to be surveyed among the city’s different neighborhoods, 20 (34.5%) out of 58 urban municipal public elementary schools (comprising a total of 18 990 school-age children) were randomly selected. The total population of the 20 selected schools was 7 562 children. Five of these schools were selected among those neighborhoods of Manaus where microfilariae carriers had been detected in the past (¹⁴14. Deane MP. Sobre a incidencia de filarias humanas em Manaus, Estado do Amazonas. Rev Serv Espec Saude Publica. 1949;2:849–58., ¹⁵15. Rachou RG, Lacerda NB. Transmissao da filariose brancroftiana em Manaus (Amazonas). Rev Bras Malariol Doencas Trop. 1956;8(2):369–71. PMID: 13494855. ). The other 15 schools were randomly chosen, representing the overall urban area of the city.

To reach the required total sample size of 3 000 children to be tested, the sample size withdrawal was proportional to the number of students enrolled in each school, in relation to the total students from the 20 chosen schools (7 562). Schoolchildren were randomly selected from the list of students provided by the schools. The children’s data (name, age, sex, and address) were obtained from the school’s administrative records.

Lectures about the disease and the survey were given to teachers, parents/legal guardians, and students at each school. The inclusion criterion was enrolled students aged 6 to 10 years. Consent forms were signed by the parents or legally authorized representatives of each child.

General population.

Adolescents (>10 years old) and adults were randomly selected from within the same areas as the sampled schoolchildren. The authors included this group in order to assess the status of people who were born, raised, and had lived for many years in one of the former LF-endemic neighborhoods. All participants were informed about the study and those ≥18 years old were asked to sign a consent form. Minors had the form signed by their parents or legal guardians.

Diagnostic tool and blood collection

Participants were tested using rapid ICT (BinaxNOW Filariasis, Alere Scarborough, Orlando, United States of America) for the detection of W. bancrofti circulating antigens. Briefly, capillary blood samples were obtained from finger pricks in a calibrated microhematocrit tube (100 μL) and transferred to the ICT card, according to the manufacturer’s instructions. The results of the tests were read by a trained technician after 10 minutes, and positives recorded.

Ethics approval

This study was approved by the Research Ethics Committee of the Fundação de Medicina Tropical Dr. Heitor Vieira Dourado, Manaus (CAAE No. 06959813.0.0000.0005). All data obtained and herein reported were treated anonymously by the investigators.

RESULTS

A total of 3 000 ICT-based tests were performed in schoolchildren attending a sample of public elementary schools. Table 1 shows the stratified school-age children sample by age and gender. The average age was 7.9 ± 1.1 years, and the gender distribution was 1 757 (58.6%) females and 1 243 (41.4%) males. No test was found positive for the presence of W. bancrofti circulating antigens. All 709 of the adolescents and adults (ages 11–85 years) tested had a negative result for circulating filarial antigen (Table 2).

DISCUSSION

Despite the efforts to control LF around the world, the disease remains endemic in 49 countries, including Brazil (¹1. World Health Organization [Internet]. Geneva: WHO; 2020 March 2 [cited 2020 May 21]. Lymphatic filariasis, Key facts. Available from: https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis
https://www.who.int/news-room/fact-sheet... ), where the microfilariae of W. bancrofti were described for the first time by Otto Wucherer in 1866 (¹⁷17. Gurgel CBFM, Carneiro F, Coutinho E. A contribuição brasileira para a descoberta do agente etiológico da filariose linfática. Rev Patol Trop. 2010;39(4):251–9.). However, the earliest systematic epidemiological studies on the distribution of Bancroftian filariasis in Brazil were conducted decades later (¹¹11. Fontes G, Leite AB, de Lima ARV, Freitas H, Ehrenberg JP, Rocha EMM. Lymphatic filariasis in Brazil: epidemiological situation and outlook for elimination. Parasit Vectors. 2012;5:272. https://doi.org/10.1186/1756-3305-5-272
https://doi.org/10.1186/1756-3305-5-272... , ¹⁸18. Rachou RG. Conceito e programa de profilaxia da filariose bancroftiana no Brasil. Rev Bras Malariol Doenças Trop. 1960;12: 11–40.). In a study conducted between 1951 and 1958, a total of 811 361 individuals were examined (using thick blood film), and 120 399 specimens of mosquito vectors were dissected (¹⁸18. Rachou RG. Conceito e programa de profilaxia da filariose bancroftiana no Brasil. Rev Bras Malariol Doenças Trop. 1960;12: 11–40.). The simultaneous discovery of microfilaremic individuals and infected mosquitoes provided evidence of local LF transmission in 11 cities of the country, including Manaus (Amazonas State) (¹⁸18. Rachou RG. Conceito e programa de profilaxia da filariose bancroftiana no Brasil. Rev Bras Malariol Doenças Trop. 1960;12: 11–40.). In fact, a previous study in Manaus in 1949 had already demonstrated a prevalence of 2.0% (48/2 405) of W. bancrofti microfilariae carriers in the neighborhoods of São Raimundo, Santo Antônio, Vila da Prata, Cachoeirinha, São Francisco, and Presidente Vargas (¹⁴14. Deane MP. Sobre a incidencia de filarias humanas em Manaus, Estado do Amazonas. Rev Serv Espec Saude Publica. 1949;2:849–58.). In 1956, Rachou and Lacerda (¹⁵15. Rachou RG, Lacerda NB. Transmissao da filariose brancroftiana em Manaus (Amazonas). Rev Bras Malariol Doencas Trop. 1956;8(2):369–71. PMID: 13494855. ) examined 10 889 persons in Manaus and identified that 0.2% were microfilariae-positive. Since then, beyond the selective treatment of infected patients, no specific measures focusing on the prevention of filarial infections were implemented, and no epidemiological surveys to investigate LF had been carried out. The Ministry of Health no longer considered Manaus to be LF endemic (¹⁹19. Ministério da Saúde. Controle das Endemias no Brasil (de 1979 a 1984). Superintendência de Campanhas de Saúde Pública. Brasília: SUCAM; 1985, 154 p.).

The present study revealed that LF had indeed been successfully eliminated in Manaus, despite the persistence of risk factors. The examined individuals live in areas where the environmental conditions and the lack of urban infrastructure and sanitation favor vector proliferation and W. bancrofti transmission. Furthermore, some of the surveyed schools are located in the very same neighborhoods where LF had been found to be endemic. These factors could very well facilitate LF reintroduction, should Manaus eventually receive infected people coming from LF-endemic areas.

Reintroduction of the infection through migration was described in Sri Lanka (²⁰20. Ramaiah KD, Das PK, Appavoo NC, Ramu K, Augustin DJ, Vijay Kumar KN, et al. A programme to eliminate lymphatic filariasis in Tamil Nadu State, India: compliance with annual single-dose DEC mass treatment and some related operational aspects. Trop Med Int Health. 2000;5(12):842–7.) and in the metropolitan areas of Recife in Brazil, where LF had already been eliminated (²¹21. Medeiros Z, Alves A, Brito JA, Borba L, Santos Z, Costa JP, et al. The present situation regarding lymphatic filariasis in Cabo de Santo Agostinho, Pernambuco, Northeast Brazil. Rev Inst Med Trop São Paulo. 2006;48(5):263–7.). Surveillance measures must therefore be sustained, focusing specially on immigrants from LF-endemic areas and countries. A study conducted by Silva et al. in 2014 (²²22. Silva EF, Lacerda MVG, Fontes G, Mourão MPG, Martins M. Wuchereria bancrofti infection in Haitian immigrants and the risk of re-emergence of lymphatic filariasis in the Brazilian Amazon. Rev Soc Bras Med Trop. 2017;50(2):256–9. https://dx.doi.org/10.1590/0037-8682-0407-2016
https://doi.org/10.1590/0037-8682-0407-2... ) on a population of Haitian refugees in Manaus showed very low prevalence rates of LF. Only one immigrant among the 244 evaluated (0.4%) was found to be positive. The possibility of reintroduction of LF should not be ruled out, as there is a large density of the main vector C. quinquefasciatus in the region, as well as adequate conditions for the transmission of the parasite (²³23. Barbosa MGV, Fé NF, Marcião AHR, Silva APT, Monteiro WM, Guerra MVF, et al. Record of epidemiologically important Culicidae in the rural area of Manaus, Amazonas. Rev Soc Bras Med Trop. 2008;41(6):658–63. https://doi.org/10.1590/S0037-86822008000600019
https://doi.org/10.1590/S0037-8682200800... ).

Three other cities (Humaitá, Guajará-Mirim, and Porto Velho) in the Western Brazilian Amazon region were studied by Korte et al. in 2013. There was a history of allochthonous cases of W. bancrofti infections dating back to the 1950s in all three cities (²⁴24. Korte RL, Fontes G, Camargo J de S, Rocha EMM, Araújo EA, Oliveira MZ, et al. Survey of Bancroftian filariasis infection in humans and Culex mosquitoes in the western Brazilian Amazon region: implications for transmission and control. Rev Soc Bras Med Trop. 2013;46(2):214–20.). No humans or mosquitoes were found to be infected with the parasite in the 2013 study, indicating that the area was no longer positive for LF transmission (²⁴24. Korte RL, Fontes G, Camargo J de S, Rocha EMM, Araújo EA, Oliveira MZ, et al. Survey of Bancroftian filariasis infection in humans and Culex mosquitoes in the western Brazilian Amazon region: implications for transmission and control. Rev Soc Bras Med Trop. 2013;46(2):214–20.). It appears that the small number of people infected and the mild nature of the microfilarial infection reported in the past were not sufficient to sustain transmission (²⁴24. Korte RL, Fontes G, Camargo J de S, Rocha EMM, Araújo EA, Oliveira MZ, et al. Survey of Bancroftian filariasis infection in humans and Culex mosquitoes in the western Brazilian Amazon region: implications for transmission and control. Rev Soc Bras Med Trop. 2013;46(2):214–20.).

ICT card tests are recommended by WHO as the diagnostic tool of choice to be used in LF elimination programs to define areas where mass drug administration is required and surveillance is to be maintained (⁸8. World Health Organization. Preparing and implementing a national plan to eliminate lymphatic filariasis: a guideline for programme managers. Geneva: WHO; 2000. Available from: https://www.who.int/lymphatic_filariasis/resources/who_cds_cpe_cee_2000.15/en/.
https://www.who.int/lymphatic_filariasis... ). The test is easy to perform in field settings and has a high level of sensitivity for the detection of filarial antigen (²⁵25. Njenga SM, Wamae CN. Evaluation of ICT filariasis card test using whole capillary blood: comparison with Knott's concentration and counting chamber methods. J Parasitol. 2001;87(5):1140–3. https://doi.org/10.1645/0022-3395(2001)087[1140:eoifct]2.0.co;2
https://doi.org/10.1645/0022-3395(2001)0... ).

According to WHO (⁸8. World Health Organization. Preparing and implementing a national plan to eliminate lymphatic filariasis: a guideline for programme managers. Geneva: WHO; 2000. Available from: https://www.who.int/lymphatic_filariasis/resources/who_cds_cpe_cee_2000.15/en/.
https://www.who.int/lymphatic_filariasis... , ⁹9. World Health Organization. Monitoring and epidemiological assessment of mass drug administration in the global programme to eliminate lymphatic filariasis: a manual for national elimination programmes. Geneva: WHO; 2011. Available from: https://apps.who.int/iris/handle/10665/44580
https://apps.who.int/iris/handle/10665/4... ), children between 6 and 10 years old should be the target of epidemiological surveys, because it is in this age group where a positive test will indicate a recent infection. The sample of 3 000 children as defined by WHO (⁸8. World Health Organization. Preparing and implementing a national plan to eliminate lymphatic filariasis: a guideline for programme managers. Geneva: WHO; 2000. Available from: https://www.who.int/lymphatic_filariasis/resources/who_cds_cpe_cee_2000.15/en/.
https://www.who.int/lymphatic_filariasis... ) is not useful to measure LF prevalence, but it is a fast way to determine whether transmission is still occurring in the area. The rationale for examining young children is therefore to assess recent infections. Negative findings provide a good indicator that transmission has ceased in the area (²⁶26. World Health Organization; Global Programme to Eliminate Lymphatic Filariasis. Monitoring and epidemiological assessment of the programme to eliminate lymphatic filariasis at implementation unit level. Geneva: WHO; 2005. Available from: https://apps.who.int/iris/handle/10665/69172
https://apps.who.int/iris/handle/10665/6... ). According to WHO, antigenemia levels of >0.1% indicate ongoing transmission. In this situation, a population survey to determine LF prevalence and morbidity would be required.

A sample of adolescents and adults was used in this study to assess the status of LF in people born, raised, and living for many years in a former LF-endemic area. This was important, as no LF survey had been carried out in the city since the 1950s. The Brazilian LF Program needs to look at all historical LF foci in order to prepare a dossier for submission to WHO to obtain the validation of elimination of LF as a public health problem in Brazil.

This is the first study that relied on the WHO criteria to evaluate the current LF situation in Manaus. The results presented here are quite promising, indicating that the historical LF focus in Manaus has indeed been eliminated. The Ministry of Health of Brazil considers that LF transmission has been interrupted in almost all the foci in the country, including Belém, Maceió (²⁷27. Fontes G. Consolidação dos inquéritos e estudos sobre a Filariose linfática realizados nos estados de Alagoas e Pará, visando à eliminação da enfermidade no Brasil. Documento Técnico. Brasília: MS/OPAS; 2015. 75p., ²⁸28. Ministério da Saúde do Brasil, Secretaria de Vigilância em Saúde. Departamento de Vigilância das Doenças Transmissíveis. Situação epidemiológica da filariose linfática no Brasil. Boletim Epidemiológico. 2016;47(9):1–5.), Salvador, Castro Alves, Florianópolis, Ponta Grossa, and Barra de Laguna (¹¹11. Fontes G, Leite AB, de Lima ARV, Freitas H, Ehrenberg JP, Rocha EMM. Lymphatic filariasis in Brazil: epidemiological situation and outlook for elimination. Parasit Vectors. 2012;5:272. https://doi.org/10.1186/1756-3305-5-272
https://doi.org/10.1186/1756-3305-5-272... ). It has since 2011 been working intensively to eliminate the remaining active foci in the Recife metropolitan region (²⁸28. Ministério da Saúde do Brasil, Secretaria de Vigilância em Saúde. Departamento de Vigilância das Doenças Transmissíveis. Situação epidemiológica da filariose linfática no Brasil. Boletim Epidemiológico. 2016;47(9):1–5.).

Certification of LF elimination as per the WHO standardized procedures and those of the Strategic and Technical Advisory Group for Neglected Tropical Diseases will require careful preparation of the dossier (²⁹29. World Health Organization. Report of the WHO Strategic and Technical Advisory Group for Neglected Tropical Diseases. Geneva: WHO; 2016. Available from: https://www.who.int/neglected_diseases/NTD_STAG_report_2016.pdf
https://www.who.int/neglected_diseases/N... , ³⁰30. World Health Organization. Validation of elimination of lymphatic filariasis as a public health problem. Geneva: WHO; 2017. Available from: https://apps.who.int/iris/bitstream/handle/10665/254377/9789241511957-eng.pdf
https://apps.who.int/iris/bitstream/hand... ). This study constitutes an important element of the dossier.

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Authors hold sole responsibility for the views expressed in the manuscript, which may not necessarily reflect the opinion or policy of the RPSP/PAJPH and/or PAHO.

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