Gametocytic Carriage of Plasmodium Falciparum in Asymptomatic Schoolchildren in Côte D’ivoire Volume 54- Issue 4

Akpa Paterne Gnagne^1*, Abibatou Konaté-Touré^1,2, Akoua Valérie Bédia-Tanoh^1,2 and William Yavo^1,2

• ¹Centre de Recherche et de Lutte contre le Paludisme, INSP, Abidjan, Côte d’Ivoire
• ²Département de Parasitologie-Mycologie, UFR Sciences Pharmaceutiques et Biologique, Abidjan, Côte d’Ivoire

Received: January 04, 2024; Published: January 23, 2024

*Corresponding author: Gnagne Akpa Paterne, Centre de Recherche et de Lutte contre le Paludisme, INSP, Abidjan, Côte d’Ivoire

DOI: 10.26717/BJSTR.2024.54.008581

Abstract PDF

Asymptomatic carriers of Plasmodium falciparum are considered to be the parasite’s reservoir in humans. They may therefore be at the origin of the expansion of chemoresistant plasmodial strains. The aim of this study was to determine the proportion of P. falciparum gametocyte carriage in asymptomatic children in Côte d'Ivoire. This cross-sectional study was carried out from May 2015 to April 2016 in 3 rural and urban schools in Grand-Bassam, Abengourou and San Pedro during the rainy and dry seasons. In each school, 11 pupils/class were drawn at random. Each pupil included was asked to complete a questionnaire. A venous blood sample was then taken in an EDTA tube for mixed smears. We obtained 29.5% asymptomatic carriers of P. falciparum. The average age was 9.4 ±2.5 years. Gametocyte density ranged from 8 to 48 gametocytes/μl blood. Gametocytes were detected in both the rainy season (23/52) and the dry season (29/52) in San-Pedro and Abengourou health districts. In Grand-Bassam health district, on other hand, they were found only during the rainy season. All age groups were affected by asymptomatic gametocyte carriage. However, the gametocytic rate of P. falciparum varied with the age of the asymptomatic carrier (p=0.010). The prevalence of asymptomatic P. falciparum gametocyte carriage was 8.70%. The high rate of asymptomatic P. falciparum gametocyte carriage suggests that asymptomatic carriers constitute a potential reservoir for malaria transmission. Malaria control strategies in rural and urban areas of Côte d'Ivoire are urgently needed to reduce the burden of disease in vulnerable populations.

Keywords: Plasmodium falciparum; Asymptomatic; Gametocyte

Abbreviations: NMCP: National Malaria Control Programme; CNER: National Committee for Research Ethics; SPSS: Statistical Package for Social Sciences; QT-NASBA: Quantitative-Nucleic acid Sequence-Based Amplification

By 2020, 95% of malaria cases (228 million) and 95% of deaths will have occurred in sub- Saharan Africa (World Health Organization and Global Malaria Programme, [1]). Substantial reductions in malaria transmission and morbidity have been reported in many parts of East Africa, due to intensified interventions in the region (Golassa et al. [2]). The percentage of malaria infections among the population at risk in sub-Saharan Africa, fell from 17% in 2010 to 13% in 2015. However, malaria remains a public health problem. Children aged 0-5 and pregnant women are the most vulnerable. In Côte d'Ivoire, malaria is a major public health problem, with around 33% of the population at risk. Malaria transmission remains stable year-round throughout the country, with recrudescences in the rainy season (National Malaria Control Programme (NMCP)). To combat this endemic, two strategies have been adopted: elimination of the vector agent using insecticides, and the use of antimalarial drugs for both curative treatment and prophylaxis. However, current control interventions are mainly aimed at symptomatic patients, yet cases of asymptomatic malaria are common in endemic areas and generally go untreated (Whittaker, et al. [3]). This situation may result in a significant source of gametocyte carriage, which could serve as a reservoir for malaria transmission (Mvumbi, et al. [4-7]) and may even be responsible for the spread of chemoresistant plasmodial strains within populations. The prevalence of symptomatic and asymptomatic infections in malaria-endemic areas has been well documented (Assoumou, et al [8-21). However, there are few data on gametocyte carriage in these asymptomatic individuals. The aim of this study was to determine the proportion of P. falciparum gametocyte carriage in asymptomatic children in Côte d'Ivoire.

Study Sites and Sample Collection

This was a cross-sectional study of malaria infestation carried out from May 2015 to April 2016 in schoolchildren aged 4 to 16 years in the rural and urban areas of Grand-Bassam, Abengourou and San Pedro in the rainy and dry seasons. In each zone, 3 elementary school and 11 pupils per class were randomly selected by drawing lots. A questionnaire was administered to each pupil and parent of a pupil after obtaining informed consent and assent for children over 9 years of age, in order to collect socio-demographic and clinical data. A blood sample was then taken from the elbow in an EDTA tube for thick drop and blood smear analysis. The slides were read by two independent laboratory technicians.

Ethical Aspects

This study was approved by the National Committee for Research Ethics (CNER) under Number 020/MSLS/CNER-dkn. It was conducted in accordance with the Helsinki declaration adopted by the 18^th World Medical Assembly in 1964 and its amendments, the ICH (International Conference on Harmonisation) recommendations for clinical studies and the national laws and regulations of Côte d'Ivoire.

Statistical Analysis

Data were entered using Epidata Version 3.1 and Microsoft Excel 2013, then transferred to Statistical Package for Social Sciences (SPSS) 18.0 for statistical analysis. Graphical representations were made using Microsoft Excel 2013. The significance level for statistical tests was set at 0.05. A subject was considered asymptomatic if he or she carried asexual forms of Plasmodium, was non febrile (temporal temperature below 37.8°C) and had no other clinical signs of malaria in the 48 hours before and after the medical visit.

Of a total of 2,361 samples, 1,190 or 50.4% were taken during the rainy season and 1,171 or 49.6% during the dry season. The male/female sex ratio in the study population was 0.9, and the mean age of participants was estimated at 9.4 years (SD 2.512 years). The plasmodic index was 39.9% (943/2361). It was 17.7%, 50.3% and 51.9% respectively in Grand-Bassam, Abengourou and San-Pedro. P. falciparum was the species most frequently found in monoinfestation, 95.7% (902/943). The prevalence of P.falciparum was 97.1%, 93.1% and 97.6% respectively in Grand-Bassam, Abengourou and San-Pedro (Table 1). Parasite density ranged from 15 to 79,520 trophozoites/μL blood, with a mean of 1,593 trophozoites/μL blood (standard deviation = 4,442 trophozoites/μL blood). Microscopic analysis of mixed smears coupled with clinical diagnosis of subjects revealed 409 (17.3%) symptomatic and 576 (24.4%) asymptomatic subjects out of 1952 (82.7%) subjects without clinical signs of malaria in the general population (2361). The percentage of subjects asymptomatic for P.falciparum malaria among those without clinical signs of malaria was therefore 29.5% (576/1952) Tables 2 & 3. In asymptomatic subjects, the mean parasite density was 1,243 trophozoites/μl blood (standard deviation 2,262 trophozoites/μl blood), with extremes of 15 trophozoites/μl and 17,120 trophozoites/μl blood. A total of 50 P. falciparum gametocytes were detected. The gametocyte- specific rate and gametocyte prevalence were 96.2% and 8.70% (50/576) respectively for P. falciparum in asymptomatic carriers. Gametocyte density ranged from 8 to 48 gametocytes/μl blood, with a mean of 13.6 gametocytes/μl blood and a standard deviation of 10.8 gametocytes/μl blood. Gametocytes were detected in both the rainy season (44.23% (23/52)) and the dry season (55.77% (29/52)) in the San-Pedro and Abengourou health districts. In the Grand-Bassam health district, on the other hand, they were only detected during the rainy season (Table 4). All age groups are concerned by asymptomatic gametocyte carriage (Table 5). However, the P. falciparum gametocytic rate varied with the age of the asymptomatic carrier (p=0.010).

Table 1: Prevalence of plasmodial species detected by light microscopy as a function of site and season.

Note: P.fal: Plasmodium falciparum; P.mal: Plasmodium malariae; P.ova : Plasmodium ovale

Table 2: Distribution of subjects by clinical status.

Table 3: Distribution of non-febrile subjects according to season.

Table 4: Prevalence of P. falciparum gametocytes as a function of season and locality in non-febrile subjects.

Table 5: Prevalence of P. falciparum gametocytes as a function of age in asymptomatic carriers.

The overall plasmodic rate was 39.9%. San-Pedro and Abengourou had roughly the same plasmodic rate. Grand-Bassam, on the other hand, had a lower plasmodic rate. Grand- Bassam is a coastal and lagoon area in the south of Côte d'Ivoire, very close to the economic capital Abidjan, while Abengourou is a forested area in the east of Côte d'Ivoire's cocoa belt. As for San-Pedro, in addition to being a forest area, it is also a coastal and lagoon area. Moreover, the practice of lowland rice-growing could explain the higher rate of Plasmodium found in San-Pedro and Abengourou than in Grand-Bassam. Rice paddies are an evolving environment where different types of biotopes, more or less favorable to Anopheles and particularly to Anopheles gambiae, succeed one another (Assi, et al. [22-25]). Our results indicate that malaria transmission in Côte d'Ivoire is also a function of phytogeographical area. Microscopic examinations showed that P. falciparum was the species responsible for most cases of Plasmodium infestation (97.1%) in Côte d'Ivoire in the present study. These data are similar to those of several studies carried out in Côte d'Ivoire (Assi, et al. [6,22,26-28]) (World Health Organization and Global Malaria Programme, 2017). The Plasmodium index of 29.5% in non-febrile subjects is high compared with that obtained by Assoumou et al. in 2001 in Abidjan (Assoumou, et al. [8]) Koukouikila-koussounda et al. in Congo (Koukouikila-Koussounda, et al. [29]) in 2010 (16.3%), Nzobo et al. in 2015 (Nzobo, et al. [30]) in Tanzania (5.4%), Balogun et al. (Balogun et al. [31]) Nigeria (12.7%) and Vafa et al. in 2008 (Vafa et al. [7]) in Senegal (13.7%).

In contrast, Baliraine et al. (Baliraine, et al. [32]) in Kenya and Pinto et al. in São Tomé et Principe (Pinto, et al. [33]) respectively obtained 25.8% and 35.7% of subjects asymptomatic for malaria. These results were very similar to our own. In contrast, Owusu-Agyei et al. and Sumari et al. obtained higher plasmodial indices (57.5%) and 82.5% respectively in asymptomatic subjects in Tanzania in 2014 and Ghana in 2002 (Owusu, et al. [6,34). The plasmodic rate obtained in the dry season (32.75) was significantly higher than that obtained in the rainy season (26.28). During periods of low transmission, most infections are asymptomatic, as population immunity is high during this period (Lindblade et al. [13]). Portugal et al. had obtained 26.3% at the dry-season thick drop in Mali in 2013 (Portugal et al. [15]). The prevalence of sexed forms of P. falciparum was determined in order to assess the impact of asymptomatic carriage of P. falciparum gametocytes on malaria transmission in Côte d'Ivoire. The gametocyte index was 96.2% for P. falciparum. This demonstrates that P. falciparum is the endemic species in Côte d'Ivoire.

The prevalence of P. falciparum gametocyte carriage was 8.95% and 9.09% in the rainy and dry seasons respectively. There was no significant difference between the gametocyte rate obtained in the dry and rainy seasons (p=0.555 and p=0.096). However, they reveal that gametocyte carriage is not related to the intensity of P. falciparum transmission. These results are in line with those found in 2010 by Balogun et al. in Nigeria (8.6%) in subjects aged 3-12 years (Balogun et al. [31]). The age of the asymptomatic subject was cross-referenced with the gametocytic index to determine its influence on asymptomatic gametocyte carriage. Gametocytes were found in all age groups. However, the proportion of gametocytes found in subjects over 5 years of age was highest (p=0.010). Our results concur with those obtained by some authors in Haiti between 2010 and 2013 respectively (Raccurt et al. [35]) in Mali in 2012 (Adomako-Ankomah, et al. [36]) and in Malawi between 2012 and 2013 (Coalson, et al. [37]). However, Ouedraogo et al, in a study carried out in Burkina Faso in 2003 using the QT-NASBA (Quantitative-Nucleic acid Sequence-Based Amplification) technique, found that the prevalence of gametocytes decreased with the age of the subject (Ouedraogo et al. [38]). Natama et al. found that median gametocyte density was significantly higher in asymptomatic infections than in clinical episodes in a study carried out in Nanoro, Burkina faso, between 2014 and 2015 (Natama et al. [39,40]). The difference observed would be due to the sensitivity of the QT-NASBA technique (more sensitive) for gametocyte detection.

Côte d'Ivoire is a hotbed of asymptomatic P. falciparum gametocyte carriage in children. High rates of asymptomatic infection and asymptomatic carriage of P. falciparum gametocytes suggest that asymptomatic carriers are a potential reservoir for malaria transmission. Preventive efforts in rural and urban areas of Côte d'Ivoire are needed to reduce morbidity in vulnerable populations.

We would like to thank the departmental health directors, primary education inspectors, teachers, parents and schoolchildren of Grand-Bassam, Abengourou and San-Pedro for their participation in this study.

Akpa Paterne Gnagne wrote the protocol, William Yavo coordinated the protocol ethics approval process, designed and supervised the field data collection. Akpa Paterne Gnagne carried out the statistical analysis and interpretation of the results. Akpa Paterne Gnagne drafted the initial version of the manuscript; Abibatou Konaté-Touré and Akoua Valérie Bédia-Tanoh revised the manuscript.

National Institute of Public Health of Côte d'Ivoire.

1. (2021) World Health Organization, Global Malaria Programme, World malaria report 2021.
2. Golassa L, Baliraine FN, Enweji N, Erko B, Swedberg G, et al. (2015) 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. BMC Infect Dis 15.
3. Whittaker C, Slater H, Nash R, Bousema T, Drakeley C, et al. (2021) Global patterns of submicroscopic Plasmodium falciparum malaria infection: insights from a systematic review and meta-analysis of population surveys. Lancet Microbe 2(8): e366-e374.
4. Mvumbi DM, Bobanga TL, Melin P, De Mol P, Kayembe JMN, et al. (2016) High Prevalence of Plasmodium falciparum Infection in Asymptomatic Individuals from the Democratic Republic of the Congo. Malar Res Treat 2016: 1-4.
5. Sumari D, Grimberg BT, Blankenship D, Mugasa J, Mugittu K, et al. (2016) Application of magnetic cytosmear for the estimation of Plasmodium falciparum gametocyte density and detection of asexual stages in asymptomatic children. Malar J 15: 113-121.
6. Sumari D, Mwingira F, Selemani M, Mugasa J, Mugittu K, et al. (2017) Malaria prevalence in asymptomatic and symptomatic children in Kiwangwa, Bagamoyo district, Tanzania. Malar J 16: 222-228.
7. Vafa M, Troye-Blomberg M, Anchang J, Garcia A, Migot-Nabias F (2008) Multiplicity of Plasmodium falciparum infection in asymptomatic children in Senegal: relation to transmission, age and erythrocyte variants. Malar J 7: 17.
8. Assoumou A, Adoubryn KD, Aboum KS, Kouadio-Yapo CG, Ouhon J (2008) Portage symptomatique et asymptomatique de Plasmodium falciparum chez les enfants de 6 mois à 6 ans à l’hôpital général d’Abobo (Abidjan, Côte d’Ivoire). Bull Soc Pathol Exot 101(1): 50-53.
9. Bassandja JO, Agasa SB, Likwela JL (2014) Prévalence du portage asymptomatique du plasmodium chez les donneurs bénévoles de sang à Kisangani, République Démocratique du Congo. Pan Afr Med J 17.
10. Chen I, Clarke SE, Gosling R, Hamainza B, Killeen G, et al. (2016) “Asymptomatic” Malaria: A Chronic and Debilitating Infection That Should Be Treated. PLOS Med 13(1): e1001942.
11. Diallo A, Ndam NT, Moussiliou A, Dos Santos S, Ndonky A, et al. (2012) Asymptomatic Carriage of Plasmodium in Urban Dakar: The Risk of Malaria Should Not Be Underestimated. PLoS ONE 7(2): e31100.
12. Laishram DD, Sutton PL, Nanda N, Sharma VL, Sobti RC, et al. (2012) The complexities of malaria disease manifestations with a focus on asymptomatic malaria. Malar J 11: 29.
13. Lindblade KA, Steinhardt L, Samuels A, Kachur SP, Slutsker L (2013) The silent threat: asymptomatic parasitemia and malaria transmission. Expert Rev Anti Infect Ther 11(6): 623-639.
14. Mukomena SE, Philipe CM, Désiré MK, Pascal LT, Ali MM, et al. (2016) Parasitémie asymptomatique chez les enfants de moins de 5 ans, enfants en âge scolaire et prise en charge des épisodes fébriles dans les ménages de Lubumbashi, République Démocratique du Congo. Pan Afr Med J 24.
15. Portugal S, Tran TM, Ongoiba A, Bathily A, Li S, et al. (2017) Treatment of Chronic Asymptomatic Plasmodium falciparum Infection Does Not Increase the Risk of Clinical Malaria Upon Reinfection. Clin Infect Dis 64(5): 645-653.
16. Rasamoel P, Jambou R, Ralamboranto L, Raharimalala L, Roux J (1998) Portage asymptomatique et accès palustre: un équilibre complexe. Arch Inst Pasteur Madag 64: 45-47.
17. Soulama I, Nébié I, Ouédraogo A, Gansane A, Diarra A, et al. (2009) Plasmodium falciparum genotypes diversity in symptomatic malaria of children living in an urban and a rural setting in Burkina Faso. Malar J 8: 135.
18. Stresman GH, Kamanga A, Moono P, Hamapumbu H, Mharakurwa S, et al. (2010) A method of active case detection to target reservoirs of asymptomatic malaria and gametocyte carriers in a rural area in Southern Province, Zambia. Malar J 9: 265.
19. Tukwasibwe S, Mugenyi L, Mbogo GW, Nankoberanyi S, Maiteki-Sebuguzi C, et al. (2014) Differential Prevalence of Transporter Polymorphisms in Symptomatic and Asymptomatic Falciparum Malaria Infections in Uganda. J Infect Dis 210(1): 154-157.
20. Zaw MT, Thant M, Hlaing TM, Aung NZ, Thu M, et al. (2017) Asymptomatic and sub-microscopic malaria infection in Kayah State, eastern Myanmar. Malar J 16.
21. Zhou G, Yewhalaw D, Lo E, Zhong D, Wang X, et al. (2016) Analysis of asymptomatic and clinical malaria in urban and suburban settings of southwestern Ethiopia in the context of sustaining malaria control and approaching elimination. Malar J 15.
22. Assi SB, Henry MC, Rogier C, Dossou-Yovo J, Audibert M, et al. (2013) Inland valley rice production systems and malaria infection and disease in the forest region of western Côte d’Ivoire. Malar J 12: 233.
23. Doannio JMC, Dossou-Yovo J, Diarrassouba S, Rakotondraibé ME, Chauvancy G, et al. (2002) La dynamique de la transmission du paludisme à Kafiné, un village rizicole en zone de savane humide de Côte d’Ivoire. Bull Soc Pathol Exot 95(1): 11-16.
24. Dossou-Yovo J, Ouattara A, Doannio JMC, Rivière E, Chauvancy G, et al. (1994) Aspects du paludisme dans un village de savane humide de Côte d’Ivoire. Med Trop 54: 331-336.
25. Henry MC, Rogier C, Nzeyimana I, Assi SB, Dossou-Yovo J, et al. (2003) Inland valley rice production systems and malaria infection and disease in the savannah of Cote d’Ivoire. Trop Med Int Health 8(5): 449-458.
26. Houngbedji CA, Chammartin F, Yapi RB, Hürlimann E, N’Dri PB, et al. (2016) Spatial mapping and prediction of Plasmodium falciparum infection risk among school-aged children in Côte d’Ivoire. Parasit Vectors 9.
27. Houngbedji CA, Prisca BN, Hürlimann E, Yapi RB, Silué KD, et al. (2015) Disparities of Plasmodium falciparum infection, malaria-related morbidity and access to malaria prevention and treatment among school-aged children: a national cross-sectional survey in Côte d’Ivoire. Malar J 14: 7.
28. Nzeyimana I, Henry MC, Dossou-Yovo J, Doannio JM, Diawara L, et al. (2002) The epidemiology of malaria in the southwestern forests of the Ivory Coast (Tai region). Bull Soc Pathol Exot 95(2): 89-94.
29. Koukouikila-Koussounda F, Malonga V, Mayengue PI, Ndounga M, Vouvoungui CJ, et al. (2012) Genetic polymorphism of merozoite surface protein 2 and prevalence of K76T pfcrt mutation in Plasmodium falciparum field isolates from Congolese children with asymptomatic infections. Malar J 11: 105.
30. Nzobo BJ, Ngasala BE, Kihamia CM (2015) Prevalence of asymptomatic malaria infection and use of different malaria control measures among primary school children in Morogoro Municipality, Tanzania. Malar J 14.
31. Balogun ST, Sandabe UK, Bdliya DN, Adedeji WA, Okon KO, et al. (2016) Asymptomatic falciparum malaria and genetic polymorphisms of Pfcrt K76T and Pfmdr1 N86Y among almajirai in northeast Nigeria. J Infect Dev Ctries 10(3): 290.
32. Baliraine FN, Afrane YA, Amenya DA, Bonizzoni M, Menge DM, et al. (2009) High prevalence of asymptomatic plasmodium falciparum infections in a highland area of western Kenya: a cohort study. J Infect Dis 200(1): 66-74.
33. Pinto J, Sousa CA, Gil V, Ferreira C, Gonçalves L, et al. (2000) Malaria in São Tomé and Príncipe: parasite prevalences and vector densities. Acta Trop 76(2): 185-193.
34. Owusu EDA, Buabeng V, Dadzie S, Brown CA, Grobusch MP, et al. (2016) Characteristics of asymptomatic Plasmodium spp. parasitaemia in Kwahu-Mpraeso, a malaria endemic mountainous district in Ghana, West Africa. Malar J 15.
35. Raccurt CP, Brasseur P, Cicéron M, Existe A, Lemoine F, et al. (2015) Portage de gamétocytes de Plasmodium falciparum en Haïti en 2010-2013. Bull Société Pathol Exot 108: 14-16.
36. Adomako-Ankomah Y, Chenoweth MS, Tocker AM, Doumbia S, Konate D, et al. (2017) Host age and Plasmodium falciparum multiclonality are associated with gametocyte prevalence: a 1-year prospective cohort study. Malar J 16: 473.
37. Coalson JE, Walldorf JA, Cohee LM, Ismail MD, Mathanga D, et al. (2016) High prevalence of Plasmodium falciparum gametocyte infections in school-age children using molecular detection: patterns and predictors of risk from a cross-sectional study in southern Malawi. Malar J 15.
38. Ouédraogo AL, Schneider P, de Kruijf M, Nébié I, Verhave JP, et al. (2007) Age-dependent distribution of Plasmodium falciparum gametocytes quantified by Pfs25 real-time QT-NASBA in a cross-sectional study in Burkina Faso. Am J Trop Med Hyg 76(4): 626-630.
39. Natama HM, Rovira-Vallbona E, Somé MA, Zango SH, Sorgho H, et al. (2018) Malaria incidence and prevalence during the first year of life in Nanoro, Burkina Faso: a birth-cohort study. Malar J 17.
40. Organisation Mondiale de la Santé (2013) 6ème journée mondiale de lutte contre le paludisme en Côte d’Ivoire. Bull D’information Bur Représentation L’OMS En Côte D’Ivoire Train de Vies 2.