Review on epidemiological characterization of asymptomatic malaria infection and its risk factors

doi:10.12140/j.issn.1000-7423.2019.03.020

Abstract

Abstract:

Asymptomatic Plasmodium infection plays an important role in malaria transmission. The research on the epidemiological characterization of asymptomatic malaria infection poses high public health significance for malaria elimination. Prevalence of asymptomatic infections was documented to be highly diversified, depending on different host, Plasmodium, environment and vector breeding. This review updates definition, epidemiology and risk factors of asymptomatic malaria infections, in order to provide data for malaria elimination.

Key words: Malaria, Asymptomatic malaria infection, Epidemiology, Risk

CLC Number:

R531.3

Xiao-xiao WANG, Shui-sen ZHOU, Fang HUANG, Zhi-gui XIA, Shao-sen ZHANG. Review on epidemiological characterization of asymptomatic malaria infection and its risk factors[J]. CHINESE JOURNAL OF PARASITOLOGY AND PARASITIC DISEASES, 2019, 37(3): 352-359.

Figures/Tables 2

国家或地区	研究设计	调查对象	样本量/例	无症状感染率/%	恶性疟无症状感染率/%	间日疟无症状感染率/%
东南亚
柬埔寨^[43]	横断面	基于社区的 0~89岁全人群	6 931	2.00	0.91	1.06
泰国^[36]	横断面	基于社区的 10~45岁人群	475	1.89	0.8	0.42
泰国^[37]	横断面	成人	241	6.20	3.30	2.50
泰国^[27]	横断面	全人群	1 347	2.45
缅甸^[44]	横断面	全人群	1 638	2.32	1.10	0.37
缅甸^[45]	横断面	全人群	1 180	2.37	0.34	1.87
缅甸^[46]	横断面	0.5~80岁（Mong pawk） 0.8~81岁（Laiza）	346（Mong pawk） 385（Laiza）	7.80（Mong pawk） 14.55（Laiza）	7.80（Mong pawk） 2.34（Laiza）	0（Mong pawk） 12.21（Laiza）
印度尼西亚^[29]	横断面	5~15岁	1 197	7.77	6.10	1.50
湄公河次区域（泰缅边境、柬埔寨和越南）^[47]	横断面	6个月以上人群	4 975	19.86	3.30	7.18
亚洲其他国家
伊朗^[48]	横断面	基于社区的 0~60岁以上人群	500	0
伊朗^[49]	横断面	2~60岁以上人群	1 000	0
斯里兰卡^[31]	横断面	移动疟疾诊所的无症状就诊者	140	1.40	0	1.40
斯里兰卡^[31]	横断面	全人群	140	1.43	0	1.43
孟加拉国^[25]	横断面	全人群	1 418（雨季） 436（旱季）	23.62（雨季） 23.62（旱季）	13.61（雨季） 13.30（旱季）	3.17（雨季） 5.05（旱季）
孟加拉国^[6]	横断面	全人群	3 391	1.33	1.33	0.03
孟加拉国^[33]	队列	孕妇	716^a	4.61	4.61
印度^[50]	横断面	全人群	963	8.41	8.41
非洲
塞内加尔^[51]	横断面	2~10岁	372	13.71	13.71	0
塞内加尔^[38]	横断面	2~10岁儿童和 17~81岁妇女	2 231（儿童） 2 427（妇女）	2.15（儿童） 2.01（妇女）	2.03	0
乌干达^[52]	队列	1~10岁儿童	472	3.2	3.2	0
加纳^[53]	横断面	0~5岁	214	31.78
赞比亚^[54]	横断面	全人群	186（病例组^b） 141（对照组）	8.0 0.7	8.0 0.7	0
卢旺达^[30]	横断面	0~5岁	545	13.4	13.4	0
卢旺达^[32]	横断面	6~10岁	1 089	22.4	18.8	0
坦桑尼亚^[4]	横断面	6~14岁	200	57.50	57.50
坦桑尼亚^[55]	横断面	8~16岁	400	14.00	14.00
肯尼亚^[34]	队列	2.5~17岁	246	33.70	33.70	0
肯尼亚^[56]	横断面	全人群	10 430	34.04		0
刚果^[24]	横断面	1~9岁	313	16.29	16.29	0
刚果^[57]	横断面	5岁以下	700	23.1	23.1	0
埃塞俄比亚^[26]	横断面	6~15岁	385	6.75	5.19	1.56
埃塞俄比亚^[58]	横断面	2岁及以上全人群	1 094	8.23	6.12	2.74
尼日利亚^[59]	横断面	3~15岁	198	59.60
尼日利亚^[60]	横断面	4~15岁	117	25.6
美洲
巴西^[23]	横断面	5岁以上人群	324	13.9	1.2	12.7
巴西^[41]	横断面	全人群	3 799	3.71	3.40	0.32
海地^[61]	横断面	育龄妇女	653	16.54	16.54	0
大洋洲
所罗门群岛^[40]	横断面	全人群	1 725	18.5	9.1	11.7

References 78

[1]	World Health Organization.World Malaria Report 2018[R]. Geneva: WHO Press, 2018.
[2]	Kachur PS, Steinhardt LC, Lindblade KA, et al. The silent threat: asymptomatic parasitemia and malaria transmission[J]. Expert Rev Anti Infect Ther, 2013, 11(6): 623-639.
[3]	Bousema T, Drakeley C.Epidemiology and infectivity of Plasmodium falciparum and Plasmodium vivax gametocytes in relation to malaria control and elimination[J]. Clin Microbiol Rev, 2011, 24(2): 377-410.
[4]	Sumari D, Mwingira F, Selemani M, et al. Malaria prevalence in asymptomatic and symptomatic children in Kiwangwa, Bagamoyo district, Tanzania[J]. Malar J, 2017, 16(1): 222.
[5]	Laurens MB, Sissoko M, Doumbo OK, et al. Spatio-temporal dynamics of asymptomatic malaria: bridging the gap between annual malaria resurgences in a sahelian environment[J]. Am J Trop Med Hyg, 2017, 97(6): 1761-1769.
[6]	Shannon KL, Khan WA, Sack DA, et al. Subclinical P. falciparum infections act as year-round reservoir for malaria in the hypoendemic Chittagong Hill Districts of Bangladesh[J].Int J Infect Dis, 2016, 49: 161-169.
[7]	Sturrock HJW, Hsiang MS, Cohen JM, et al. Targeting asymptomatic malaria infections: active surveillance in control and elimination[J]. PLoS Medicine, 2013, 10(6): e1001467.
[8]	Hadi M, Azam S, Ahmad M, et al. Evaluation of malaria multiplex/nested PCR performance at low parasite densities and mixed infection in Iran: a country close to malaria elimination[J]. Infect Genet Evol, 2018, 65: 283-287.
[9]	Adams M, Joshi SN, Mbambo G, et al. An ultrasensitive reverse transcription polymerase chain reaction assay to detect asymptomatic low-density Plasmodium falciparum and Plasmodium vivax infections in small volume blood samples[J]. Malar J, 2015, 14(1): 520.
[10]	Harrison G.Mosquitoes, malaria and man: a history of the hostilities since 1880[J]. Med Hist, 1979, 23(3): 360.
[11]	Färnert A, Williams TN, Mwangi TW, et al. Transmission-dependent tolerance to multiclonal Plasmodium falciparum infection[J]. J Infect Dis, 2009, 200(7): 1166-1175.
[12]	Dunyo S, Milligan P, Edwards T, et al. Gametocytaemia after drug treatment of asymptomatic Plasmodium falciparum[J]. PLoS Clin Trials, 2006, 1(4): e20.
[13]	Coura JR, Suárez-Mutis M, Ladeia-Andrade S.A new challenge for malaria control in Brazil: asymptomatic Plasmodium infection-a review[J]. Mem Inst Oswaldo Cruz, 2006, 101(3): 229-237.
[14]	Bousema T, Okell L, Felger I, et al. Asymptomatic malaria infections: detectability, transmissibility and public health relevance[J]. Nat Rev Microbiol, 2014, 12(12): 833-840.
[15]	Boutlis CS, Tjitra E, Maniboey H, et al. Nitric oxide production and mononuclear cell nitric oxide synthase activity in malaria-tolerant papuan adults[J]. Infect Immun, 2003, 71(7): 3682-3689.
[16]	Bereczky S, Liljander A, Rooth I, et al. Multiclonal asymptomatic Plasmodium falciparum infections predict a reduced risk of malaria disease in a Tanzanian population[J]. Microbes Infect, 2007, 9(1): 103-110.
[17]	Ladeiaandrade S, Ferreira MU, Carvalho MED, et al. Age-dependent acquisition of protective immunity to malaria in riverine populations of the Amazon Basin of Brazil[J]. Am J Trop Med Hyg, 2009, 80(3): 452.
[18]	Kun JFJ, Missinou MA, Lell B, et al. New emerging Plasmodium falciparum genotypes in children during the transition phase from asymptomatic parasitemia to malaria[J]. Am J Trop Med Hyg, 2002, 66(6): 653.
[19]	Tada MS, Marques RP, Mesquita E, et al. Urban malaria in the Brazilian Western Amazon Region I. High prevalence of asymptomatic carriers in an urban riverside neighborhood is associated with a high level of clinical malaria. Memórias Do Instituto Oswaldo Cruz[J]. Mem Inst Oswaldo Cruz, 2007, 102(3): 263-269.
[20]	Rodulfo H, Donato D, Quijada I, et al. High prevalence of malaria infection in Amazonas State, Venezuela[J]. Rev Inst Med Trop Sao Paulo, 2007, 49(2): 79-85.
[21]	Cucunubá ZM, Guerra AP, Rahirant SJ, et al. Asymptomatic Plasmodium spp. infection in Tierralta, Colombia[J]. Mem Inst Oswaldo Cruz, 2008, 103(7): 668-673.
[22]	Males S, Gaye O, Garcia A.Long-Term Asymptomatic carriage of Plasmodium falciparum protects from malaria attacks: a prospective study among senegalese children[J]. Clin Infect Dis, 2008, 46(4): 516-522.
[23]	Katsuragawa TH, Gil LHS, Tada MS, et al. The dynamics of transmission and spatial distribution of malaria in riverside areas of Porto Velho, Rondбnia, in the Amazon Region of Brazil[J]. PLoS One, 2010, 5(2): e9245.
[24]	Koukouikilakoussounda F, Malonga V, Mayengue PI, et al. Genetic polymorphism of merozoite surface protein 2 and prevalence of K76T pfcrt mutation in Plasmodium falciparum field isolates from congolese children with asymptomatic infections[J]. Malar J, 2012, 11(1): 105.
[25]	Starzengruber P, Fuehrer HP, Ley B, et al. High prevalence of asymptomatic malaria in south-eastern Bangladesh[J]. Malar J, 2014, 13(1): 16.
[26]	Worku L, Damtie D, Endris M, et al. Asymptomatic malaria and associated risk factors among school children in Sanja Town, Northwest Ethiopia[J]. Inte Sch Res Not, 2014, 2014: 1-6.
[27]	Elisabeth B, Jetsumon S, Jeeraphat S, et al. Common asymptomatic and submicroscopic malaria infections in Western Thailand revealed in longitudinal molecular and serological studies: a challenge to malaria elimination[J]. Malar J, 2016, 15(1): 333.
[28]	Roper C, Richardson W, Elhassan IM, et al. Seasonal changes in the Plasmodium falciparum population in individuals and their relationship to clinical malaria: a longitudinal study in a Sudanese village[J]. Parasitology, 1998, 116(6): 501-510.
[29]	De MQ, Syafruddin D, Keijmel S, et al. Increased serum hepcidin and alterations in blood iron parameters associated with asymptomatic P. falciparum and P. vivax malaria[J]. Haematologica, 2010, 95(7): 1068.
[30]	Gahutu JB, Steininger C, Shyirambere C, et al. Prevalence and risk factors of malaria among children in southern highland Rwanda[J]. Malar J, 2011, 10(1): 134.
[31]	Gunasekera WMK, Abeyasinghe RR, Premawansa S, et al. Usefulness of polymerase chain reaction to supplement field microscopy in a pre-selected population with a high probability of malaria infections[J]. Am J Trop Med Hyg, 2011, 85(1): 6-11.
[32]	Sifft KC, Geus D, Mukampunga C, et al. Asymptomatic only at first sight: malaria infection among school children in highland Rwanda[J]. Malar J, 2016, 15(1): 553.
[33]	Khan WA, Galagan SR, Chai SP, et al. Asymptomatic Plasmodium falciparum malaria in pregnant women in the Chittagong Hill Districts of Bangladesh[J]. PLoS One, 2014, 9(5): e98442.
[34]	Baliraine FN, Afrane YA, Amenya DA, et al. High prevalence of asymptomatic Plasmodium falciparum infections in a highland area of Western Kenya: a cohort study[J]. J Infect Dis, 2009, 200(1): 66-74.
[35]	Gbalégba CGN, Ba H, Silué KD, et al. Distribution of Plasmodium spp. infection in asymptomatic carriers in perennial and low seasonal malaria transmission settings in West Africa[J]. Infect Dis Poverty, 2018, 7: 39.
[36]	Congpuong K, Saejeng A, Sug-Aram R, et al. Mass blood survey for malaria: pooling and real-time PCR combined with expert microscopy in north-west Thailand[J]. Malar J, 2012, 11(1): 288.
[37]	Kritsiriwuthinan K, Ngrenngarmlert W.Molecular screening of Plasmodium infections among migrant workers in Thailand[J]. J Vector Borne Dis, 2011, 48(4): 214.
[38]	Diallo A, Ndam NT, Moussiliou A, et al. Asymptomatic carriage of plasmodium in urban Dakar: the risk of malaria should not be underestimated[J]. PLoS One, 2012, 7(2): e31100.
[39]	Liljander A, Bejon P, Mwacharo J, et al. Clearance of asymptomatic P. falciparum infections interacts with the number of clones to predict the risk of subsequent malaria in Kenyan children[J]. PLoS One, 2011, 6(2): e16940.
[40]	Harris I, Sharrock WW, Bain LM, et al. A large proportion of asymptomatic Plasmodium infections with low and sub-microscopic parasite densities in the low transmission setting of Temotu Province, Solomon Islands: challenges for malaria diagnostics in an elimination setting[J]. Malar J, 2010, 9(1): 254.
[41]	Almeida A, Kuehn A, Castro A, et al. High proportions of asymptomatic and submicroscopic Plasmodium vivax infections in a peri-urban area of low transmission in the Brazilian Amazon[J]. Parasit Vectors, 2018, 11(1): 194.
[42]	Waltmann A, Darcy AW, Harris I, et al. High rates of asymptomatic, sub-microscopic Plasmodium vivax infection and disappearing Plasmodium falciparum malaria in an area of low transmission in Solomon Islands[J]. PLoS Negl Trop Dis, 2015, 9(5): e0003758.
[43]	Hoyer S, Nguon S, Kim S, et al. Focused screening and treatment (FSAT): a PCR-based strategy to detect malaria parasite carriers and contain drug resistant P. falciparum, Pailin, Cambodia[J]. PLoS One, 2012, 7(10): e45797.
[44]	Ghinai I, Cook J, Hla TT, et al. Malaria epidemiology in central Myanmar: identification of a multi-species asymptomatic reservoir of infection[J]. Malar J, 2017, 16(1): 16.
[45]	Nyunt MH, Shein T, Zaw NN, et al. Molecular evidence of drug resistance in asymptomatic malaria infections, myanmar, 2015[J]. Emerg Infect Dis, 2017, 23(3): 517-520.
[46]	Huang F, Takalaharrison S, Liu H, et al. Prevalence of clinical and subclinical Plasmodium falciparum and Plasmodium vivax malaria in two remote rural communities on the China-Myanmar Border[J]. Am J Trop Med Hyg, 2017, 97(5):1524-1531.
[47]	Imwong M, Nguyen TN, Tripura R, et al.The epidemiology of subclinical malaria infections in South-East Asia: findings from cross-sectional surveys in Thailand-Myanmar border areas, Cambodia, and Vietnam[J]. Malar J, 2015, 14(1): 381.
[48]	Turki H, Zoghi S, Mehrizi AA, et al. Absence of asymptomatic malaria infection in endemic area of bashagard district, Hormozgan Province, Iran[J]. Iran J Parasitol, 2012, 7(1): 36-44.
[49]	Zoghi S, Mehrizi AA, Raeisi A, et al. Survey for asymptomatic malaria cases in low transmission settings of Iran under elimination programme[J]. Malar J, 2012, 11(1): 126.
[50]	Ganguly S, Saha P, Guha SK, et al. High prevalence of asymptomatic malaria in a tribal population in eastern India[J]. J Clin Microbiol, 2013, 51(5): 1439-1444.
[51]	Vafa M, Troyeblomberg M, Anchang J, et al. Multiplicity of Plasmodium falciparum infection in asymptomatic children in Senegal: relation to transmission, age and erythrocyte variants[J]. Malar J, 2008, 7(1): 1-9.
[52]	Hsiang MS, Lin M, Dokomajilar C, et al. PCR-based pooling of dried blood spots for detection of malaria parasites: optimization and application to a cohort of Ugandan children[J]. J Clin Microbiol, 2010, 48(10): 3539-3543.
[53]	Crookston BT, Alder SC, Boakye I, et al. Exploring the relationship between chronic undernutrition and asymptomatic malaria in Ghanaian children[J]. Malar J, 2010, 9(1): 1-7.
[54]	Stresman GH, Kamanga A, Moono P, et al. A method of active case detection to target reservoirs of asymptomatic malaria and gametocyte carriers in a rural area in Southern Province, Zambia[J]. Malar J, 2010, 9(1): 265.
[55]	Mazigoi HD, Kidenya BR, Ambrose EE, et al. Association of intestinal helminths and P. falciparum infections in co-infected school children in northwest Tanzania[J]. Tanzan J Health Res, 2010, 12(4): 299-301.
[56]	Idris ZM, Chan CW, Kongere J, et al. High and heterogeneous prevalence of asymptomatic and sub-microscopic malaria infections on islands in Lake Victoria, Kenya[J]. Sci Rep, 2016, 6: 36958.
[57]	Maketa V, Mavoko HM, Luz RID, et al. The relationship between Plasmodium infection, anaemia and nutritional status in asymptomatic children aged under five years living in stable transmission zones in Kinshasa, Democratic Republic of Congo[J]. Malar J, 2015, 14(1): 1-9.
[58]	Golassa L, Baliraine FN, Enweji N, et al. Microscopic and molecular evidence of the presence of asymptomatic Plasmodium falciparum and Plasmodium vivax infections in an area with low, seasonal and unstable malaria transmission in Ethiopia[J]. BMC Infect Dis, 2015, 15(1): 310.
[59]	Singh R, Godson II, Singh S, et al. High prevalence of asymptomatic malaria in apparently healthy school children in Aliero, Kebbi state, Nigeria[J]. J Vector Borne Dis, 2014, 51(2): 128.
[60]	Olusola O, Adegbayi AM, Bolaji OS, et al. Asymptomatic falciparum malaria and intestinal helminths co-infection among school children in Osogbo, Nigeria[J]. J Res Med Sci, 2011, 16(5): 680-686.
[61]	Elbadry MA, Al-Khedery B, Tagliamonte MS, et al. High prevalence of asymptomatic malaria infections: a cross-sectional study in rural areas in six departments in Haiti[J]. Malar J, 2015, 14(1): 510.
[62]	Morris U, Xu W, Msellem MI, et al. Characterising temporal trends in asymptomatic Plasmodium infections and transporter polymorphisms during transition from high to low transmission in Zanzibar, 2005-2013[J]. Infect Genet Evol, 2015, 33: 110-117.
[63]	John CC, McHugh MM, Moormann AM, et al. Low prevalence of Plasmodium falciparum infection among asymptomatic individuals in a highland area of Kenya[J]. Trans R Soc Trop Med Hyg, 2005, 99(10): 780-786.
[64]	Bin Mohanna MA, Bin Ghouth AS, Rajaa YA.Malaria signs and infection rate among asymptomatic schoolchildren in Hajr Valley, Yemen[J]. East Mediterr Health J, 2007, 13(1): 35.
[65]	Wang N, Mueller I, Kumpitak C, et al. Very high carriage of gametocytes in asymptomatic low-density Plasmodium falciparum and P. vivax infections in western Thailand[J]. Parasit Vectors, 2017, 10(1): 512.
[66]	Eichner M, Diebner HH, Molineaux L, et al. Genesis, sequestration and survival of Plasmodium falciparum gametocytes: parameter estimates from fitting a model to malariatherapy data[J]. Trans R Soc Trop Med Hyg, 2001, 95(5): 497-501.
[67]	Bousema JT, Gouagna LC, Drakeley CJ, et al. Plasmodium falciparum gametocyte carriage in asymptomatic children in western Kenya[J]. Malar J, 2004, 3(1): 1-6.
[68]	Martins-Campos KM, Kuehn A, Almeida A, et al. Infection of Anopheles aquasalis from symptomatic and asymptomatic Plasmodium vivax infections in Manaus, western Brazilian Amazon[J]. Parasit Vectors, 2018, 11(1): 288.
[69]	Franks S, Koram KA, Wagner GE, et al. Frequent and persistent, asymptomatic Plasmodium falciparum infections in African infants, characterized by multilocus genotyping[J]. J Infect Dis, 2001, 183(5): 796.
[70]	Missinou MA, Lell B, Kremsner PG.Uncommon asymptomatic Plasmodium falciparum infections in gabonese children[J]. Clin Infect Dis, 2003, 36(9): 1198-1202.
[71]	Bruce MC, Donnelly CA, Packer M, et al. Age- and species-specific duration of infection in asymptomatic malaria infections in Papua New Guinea[J]. Parasitology, 2000, 121(3): 247-256.
[72]	Rojo-Marcos G, Cuadros-Gonzalez J, Gete-Garcia L, et al. Plasmodium ovale infection: description of 16 cases and a review[J]. Enferm Infec Microbiol Clin, 2011, 29(3): 204-208.
[73]	肖回回, 刘娟, 丰俊, 等. 中缅边境疟疾主动病例侦查范围与人群带虫者检测结果[J]. 中国寄生虫学与寄生虫病杂志, 2015, 33(2): 86-90.
[74]	Filipe JA, Riley EM, Drakeley CJ, et al. Determination of the processes driving the acquisition of immunity to malaria using a mathematical transmission model[J]. PLoS Comput Biol, 2007, 3(12): e255.
[75]	Obi RK, Okangba CC, Nwanebu FC, et al. Premunition in Plasmodium falciparum malaria[J]. Afr J Biotechnol\|, 2010, 9(10): 1397-1401.
[76]	Lyke KE, Wang A, Dabo A, et al. Antigen-specific B memory cell responses to Plasmodium falciparum malaria antigens and Schistosoma haematobium antigens in co-infected malian children[J]. PLoS One, 2012, 7(6): e37868.
[77]	Mayor A, Saute F, Aponte JJ, et al. Plasmodium falciparum multiple infections in Mozambique, its relation to other malariological indices and to prospective risk of malaria morbidity[M]. Med Int Health. 2003.
[78]	Orogade AA, Ogala WN, Aikhionbare HA.Asymptomatic malaria parasitaemia-A suitable index for evaluation of malaria vector control measures[J]. Niger J Paediatr, 2002, 29(2): 23-26.

国家或地区	研究设计	检测方法	判定标准
国家或地区	研究设计	检测方法	无症状持续时间	抗疟疾治疗
巴布亚岛^[15]	横断面	镜检	调查前1周内	调查前1周无治疗
坦桑尼亚^[16]	横断面	镜检/PCR	调查后1周内	调查前1个月内未开展治疗
肯尼亚^[11]	队列	镜检	调查后1周内	调查前4周未开展治疗
巴西^[17]	队列	镜检/PCR	调查前3 d和调查后15 d内	调查前30 d内未开展治疗
加蓬^[18]	队列	镜检	调查后5 d	无要求
巴西^[19]	横断面	镜检/PCR	调查后60 d内	无要求
赞比亚^[12]	横断面	镜检	两次筛查（间隔2 d）	无要求
委内瑞拉^[20]	横断面	PCR	调查后2周内	无要求
哥伦比亚^[21]	队列	镜检/PCR	镜检阳性后2周或PCR 阳性后28 d	无要求
塞内加尔^[22]	横断面	镜检	调查当月	无要求
巴西^[23]	横断面	PCR	基线调查后30 d内	无要求
刚果^[24]	横断面	镜检/PCR	调查前2周和调查后至少1周	无要求
孟加拉国^[25]	横断面	PCR	无要求	调查前7 d无治疗
埃塞俄比亚^[26]	横断面	镜检	近期	无要求
泰国^[27]	横断面	PCR	调查后5个月内	无要求
苏丹^[28],萨赫勒^[5]	队列	镜检	无要求	无要求
印度尼西亚^[29],卢旺达^[30]	横断面	镜检	无要求	无要求
斯里兰卡^[31],卢旺达^[32]	横断面	镜检/PCR	无要求	无要求