BPA
Maître de Conférences
Scientific activity
Researcher profile
Faculty researcher at the University of Yaoundé I. Grade: Maître de Conférences.
Scientific publications
Michel Thierry ONANA NGONO, Jeannette Tombi, Ivan Ndongo
Systematic Parasitology
Michel Thierry ONANA NGONO, Jeannette Tombi, Ivan NDONGO
Research Square
Brice Natchema Soh Fonkou, Magellan Tchouakui, Benjamin D. Menze, Jeannette Tombi, Charles S. Wondji
Research Square
Paulette Ndjeunia-Mbiakop, Idriss Nasser Ngangue-Siewe, Abdou Talipouo, Arnold Princewil Chi Nji, Roland Bamou, Joël Djoufounna and 2 more
Current Research in Parasitology and Vector-Borne Diseases
ABSTRACT The East Region of Cameroon has over 150 malaria cases per 1000 inhabitants per year. Factors contributing to this high malaria prevalence are not well understood. This study assessed the bionomics of vectors involved in malaria transmission, their susceptibility to insecticides, and the efficacy of insecticide-treated nets. Entomological studies were conducted twice yearly in Belabo and Ouami from 2021 to 2023 using both human landing catches and CDC light traps to collect adult mosquitoes. Anopheline species were separated using morphological identification keys and Anopheles gambiae ( s.l .) were molecularly identified to species. Plasmodium falciparum presence was detected by ELISA. Susceptibility of 3–5-day old An. gambiae ( s.l. ) to deltamethrin, permethrin, malathion and bendiocarb was assessed. A WHO cone test was performed to assess bed-net efficacy against mosquitoes. Out of 7634 mosquitoes collected, 47.44% were anophelines. Anopheles gambiae ( s.l. ) was the most abundant species, followed by An. ziemanni , An. funestus and An. paludis in both localities. The mosquito biting rate was similar in Belabo and Ouami. Both Anopheles gambiae ( s.l. ) and An. funestus were infected with P. falciparum at Ouami but only An. gambiae ( s.l. ) was infected at Belabo. Anopheles gambiae ( s.l. ) was less susceptible to both deltamethrin and permethrin. None of the 48 bednets tested were effective against field populations of Anopheles gambiae ( s.l. ) in both sites. High malaria transmission associated with high pyrethroid resistance rate was recorded in vectors from the East region of Cameroon supporting the high endemicity of malaria in the area.
Idriss Nasser Ngangue-Siewe, Paulette Ndjeunia-Mbiakop, André Barembaye Sagna, Abdoul-Aziz Maiga, Roland Bamou, Antoine Sanon and 5 more
PLoS ONE
Malaria and Aedes-borne diseases remain major causes of mortality, morbidity, and disability in most developing countries. Surveillance of transmission patterns associated with vector control remains strategic for combating these diseases. Due to the limitions of current surveillance tools used to assess human exposure to mosquito bites, human antibody (Ab) responses to salivary peptides from Anopheles (gSG6-P1) and Aedes (Nterm-34kDa) are increasingly being used to measure direct human-Anopheles or Aedes contact. This study reports on the assessment of Human IgG Ab responses to gSG6-P1 and Nterm-34-kDa salivary peptides as biomarkers to track exposure to Anopheles and Aedes bites, in rural localities of Cameroon. Blood samples were collected between October and November 2022 from 173 individuals residing in four villages: Njombe, Kekem, Belabo, and Ouami. Sociodemographic characteristics and information regarding Long Lasting Insecticide Net (LLIN) ownership, use, and net characteristics were recorded using a questionnaire. The measurement of human IgG levels to gSG6-P1 and Nterm-34kDa peptides was conducted in blood samples using ELISA. The levels of IgG responses to Anopheles gSG6-P1 and Aedes Nterm-34kDa salivary peptides varied significantly across villages (all p<0.05). IgG responses to Anopheles gSG6-P1 were higher in Njombe compared to Belabo and Ouami (all p<0.01), while IgG responses to Aedes Nterm-34kDa were higher in Kekem compared to the other villages (all p<0.0001). Aweak correlation was observed between IgG responses to Anopheles and Aedes salivary peptides (Spearman r = 0.2689, p = 0.0003). However, the median level of IgG to Anopheles gSG6-P1 was higher than IgG to Aedes Nterm-34kDa in Njombé, Belabo, and Ouami. Individuals not using their LLIN, those using damaged bed nets, and those who reported vegetation around their houses developed higher IgG responses to gSG6-P1 and Nterm-34 kDa compared to those who did not (all p<0.05). The immune-epidemiological biomarkers have shown promising potential as indicators for monitoring human exposure to various mosquito bites and their heterogeneity in the same site. However, additional research is needed to validate the efficacy of this technique for surveillance purposes and to assess the effectiveness of vector control interventions.
brice Natchema S. F., Magellan Tchouakui, Benjamin D. Menze, Leon M. J. Mugenzi, Derrick Fofie, Daniel Nguifo-Nguete and 3 more
Research Square
Abstract Background The impact of metabolic resistance to insecticide on malaria transmission remains poorly characterised notably through application of entomological parameters. The lack of resistance markers has been one of the limiting factors preventing robust assessment of such impact. To this end, the present study sought to investigate how L119F- Gste2 metabolic gene influences entomological parameters underpinning mosquitos’ propensity to transmit Plasmodium species. Methods Longitudinal studies were carried out in Mibellon and Elende, two different eco-climatic settings in Cameroon and mosquitoes were collected using Human Landing Catch (HLC), Centre for Disease Control Light Trap (CDC-LT) and Pyrethrum Spray Catch (PSC) technics. Plasmodium sporozoite parasites were detected by TaqMan and Nested PCR, and blood meal origin with ELISA. The allele-specific PCR (AS-PCR) method was used to genotype the L119F-GSTe2 marker and association with malaria transmission was established by comparing key transmission parameters such as the Entomologic Inoculation Rate (EIR) between individuals with different L119F- GSTe2 genotypes. Results An. funestus s.l was the predominant malaria vector collected during the entomological survey in both sites (86.6% and 96.4% in Elende and Mibellon respectively) followed by An. gambiae s.l (7.5% and 2.4%). Sporozoite infection rates were very high in both collection sites (8.7% and 11% respectively in Elende and Mibellon). An. funestus s.s exhibited a very high entomological inoculation rate (EIR) (66 ib/h/month and 792 ib/h/year) and was responsible for 98.6% of all malaria transmission events occurring in both sites. Human Blood Index was also high in both locations (HBI = 94%). An. funestus s.s. mosquitoes with both 119F/F (RR) and L119F (RS) genotypes had a significantly higher transmission intensity than their susceptible L/L119 (SS) counterparts (IRR = 2.2, 95%CI (1.1–5.2), p = 0.03; IRR = 2.5, 95% CI (1.2–5.8), p = 0.01 respectively). Conclusion This study highlights the major role that An. funestus s.s plays in malaria transmission in Cameroon with an aggravation from GSTe2-based metabolic resistance.
Idriss Nasser Ngangue-Siewe, Paulette Ndjeunia-Mbiakop, Nelly Armanda Kala-Chouakeu, Roland Bamou, Abdou Talipouo, Landre Djamouko-Djonkam and 6 more
Pathogens
The spread of pyrethroid resistance in malaria vectors is a major threat affecting the performance of current control measures. However, there is still not enough information on the resistance profile of mosquitoes to carbamates and organophosphates which could be used as alternatives. The present study assessed the resistance profile of Anopheles gambiae s.l. to bendiocarb and malathion, at the phenotypic and molecular levels, in different eco-epidemiological settings in Cameroon. Anopheles gambiae s.l. mosquitoes were collected from four eco-epidemiological settings across the country and their susceptibility level to bendiocarb and malathion was determined using WHO tubes bioassays. The ace-1 target site G119S mutation was screened by PCR. Reverse Transcription quantitative PCR 3-plex TaqMan assays were used to quantify the level of expression of eight genes associated with metabolic resistance. Resistance to malathion and/or bendiocarb was recorded in all study sites except in mosquitoes collected in Kaélé and Njombé. The Ace-1 (G119S) mutation was detected in high frequencies (>40%) in Kékem and Santchou. Both An. gambiae and An. coluzzii were detected carrying this mutation. The cytochrome P450s gene Cyp6p3 associated with carbamate resistance and the glutathione S-transferase gene Gste2 associated with organophosphate resistance were found to be overexpressed. Genes associated with pyrethroid (Cyp6m2, Cyp9k1, Cyp6p3) and organochlorine (Gste2, Cyp6z1, Cyp6m2) and cuticle resistance (Cyp4g16) were also overexpressed. The rapid spread of resistance to organophosphates and carbamates could seriously compromise future control strategies based on IRS. It is therefore becoming important to assess the magnitude of bendiocarb and malathion resistance countrywide.
Dominique Mieguim Ngninpogni, Cyrille Ndo, Patrick Ntonga Akono, Anicet Nguemo, Amine Nguepi, Danale Rosine Metitsi and 3 more
Parasites & Vectors
BACKGROUND: In Mvoua, a village situated in a forested area of Cameroon, recent studies have reported high prevalence of Plasmodium falciparum infection among the population. In order to understand factors that can sustain such a high malaria transmission, we investigated the biology of Anopheles vectors and its susceptibility to insecticides, as well as long-lasting insecticidal net (LLIN) coverage, use and bio-efficacy. METHODS: A longitudinal entomological survey was conducted from July 2018 to April 2019. Adult mosquitoes were collected using the human landing catch (HLC) method and identified using morphological and molecular techniques. Anopheles gambiae (s.l.) larvae were sampled from several stagnant water pools throughout the village and reared to generate F1 adults. The presence of P. falciparum circumsporozoite antigen was detected in the heads and thoraces of mosquitoes collected as adults using an enzyme-linked immunosorbent assay. The insecticide susceptibility status of the local An. gambiae (s.l.) F1 population to the pyrethroid insecticides deltamethrin 0.5% and permethrin 0.75% was determined using World Health Organization-tube bioassays, while the frequency of the knockdown resistance (kdr) mutation was determined by PCR. Coverage, use and physical integrity of LLINs were assessed in households, then cone assays were used to test for their bio-efficacy on both the reference insecticide-susceptible Kisumu strain and on field F1 An. gambiae (s.l.) RESULTS: In total, 110 Anopheles mosquitoes were collected, of which 59.1% were identified as Anopheles funestus (s.l.), 38.18% as An. gambiae (s.l.) and 2.72% as An. ziemanii. Anopheles funestus was the most abundant species except in the long rainy season, when An. gambiae (s.l.) predominated (65.8%). In the dry seasons, vectors were principally endophagous (76% of those collected indoors) while they tended to be exophagous (66% of those collected outdoors) in rainy seasons. High Plasmodium infection was observed in An. gambiae (s.l.) and An. funestus, with a circumsporozoitic rate of 14.29 and 10.77%, respectively. Anopheles gambiae (s.l.) was highly resistant to pyrethroid insecticides (mortality rates: 32% for permethrin and 5% for deltamethrin) and harbored the kdr-L1014F mutation at a high frequency (89.74%). Of the 80 households surveyed, only 47.69% had achieved universal coverage with LLNs. Around 70% of the LLINs sampled were in poor physical condition, with a proportionate hole index > 300. Of the ten LLNs tested, eight were effective against the An. gambiae reference insecticide-susceptible Kisumu strain, showing mortality rate of > 80%, while none of these LLINs were efficient against local An. gamabie (s.l.) populations (mortality rates < 11.5%). CONCLUSION: A combination of elevated P. falciparum infection in Anopheles vector populations, insufficient coverage and loss of effectiveness of LLINs due to physical degradation, as well as high resistance to pyrethroid insecticides is responsible for the persistence of high malaria transmission in forested rural area of Mvoua, Cameroon.
Jeannette Tombi, Bwame Agnès Solange Sandje, John Francis Akoumba, Charles Félix Bilong Bilong
Journal of Applied Biosciences
Objective: In September 2014, 56 specimens of Barbus camptacanthus were captured in the Koukoum River at Makak (Cameroon) in order to study some ecological aspects of their monogenean gill parasites. Methodology and Results: After host sampling and parasites mounting, determination of various monogenean species was carried out in the laboratory by classical methods. Gill helminthofauna of this fish consisted of Dactylogyrus amieti , D. valeti and Dogielius njinei . The parasite load of core species increased progressively with the size of the fish. The impact of host sex was observed for D. amieti and Dogielius njinei parasite load. The infestation rate and the parasite load did not statistically vary with the side of the host. The colonization profile of different gradients varied depending on the parasite species. Conclusion and Application: The study of the distribution of these organisms has identified the most vulnerable hosts. Such information allows envisaging some protocols for monitoring parasitic infection in intensive fish farming. In hatcheries, much care should be given to fry and young fish since they have not yet developed robust immunological processes that enable them to effectively fight against polyparasitism. Keywords: Barbus camptacanthus , gills, monogeneans, distribution, Koukoum River
Jeannette Tombi, Akoumba John Francis, Bilong Bilong, Charles Félix
Jeannette Tombi, Bilong Bilong Charles Félix
International Journal of Fisheries and Aquaculture
Changes in Barbus martorelli gill arch occupation models by its parasite component community were investigated for nine months. The work revealed three different categories of models. The first category follows the combined action of the respiratory water current and the colonized surface of each gill arch. The second category based on the mode of infestation of Monopisthocotylean larvae while the third category is established as a result of perturbations. Thus, the occupation models of B. martorelli gill arches by its microfauna are constantly changing. Key words: Barbus martorelli, gill parasites, arch occupation models, perturbations month.
Jeannette Tombi, Charles Félix Bilong Bilong, Sergé Morand
Parasite
The structure and stability of parasite communities have been mainly explained by high diversity and strong interactions among parasite species. During 16 months, 558 Barbus martorelli gill infracommunities were studied in a tropical zone to determine whether parasite infrapopulations interact. Three levels were retained: the infracommunity level, the gill filament level, and the filament fraction level. Single species infections in Barbus martorelli were very rare and only concerned the core species: Dactylogyrus bopeleti, D. insolitus, D. simplex and Myxobolus barbi. Mixed infections appeared as a general rule in this fish species. Interspecific interactions at all three levels were statistically non significant. Our results suggest that Barbus martorelli gill parasites are non interactive (isolationist).
Jacques Nack, Jeannette Tombi, N. A. Bitja, Charles Félix Bilong Bilong
Journal of Applied Biosciences
Jeannette Tombi, Jacques Nack, Bilong Bilong Charles Félix
African Journal of Agricultural Research
The gill parasite fauna of Barbus martorelli is much diversified and this raises up the problem of biotope partitioning by these pathogens. The gill colonization analysis of these organisms as well as four distribution gradients: transversal, lateral, longitudinal and vertical was undertaken as a function of the host’s side.The distribution of B. martorelli gill parasites did not reveal any asymmetry in function of the host’s side. The transversal partitioning applied solely toDactylogyrus insolitus and Myxobolus barbi. The lateral partitioning was inexistent except for D. insolitus which was mostly concentrated on the posterior hemibranch of arch II and Myxobolus njinei which colonized mostly the anterior face of the same arch. The longitudinal partitioning was observed only for M. barbiwhich mostly encysted into sectors which are more opened to respiratory water current. The vertical partitioning of Monogeneans was subject to the size of their sclerified haptorial pieces; therefore, Dactylogyrus bopeleti and D. insolitus, which are robust, accumulate mostly in the filamentary distal zone whereasDactylogyrus simplex and Dactylogyrus maillardi, which are weaker, prefer the basal zone. The volume of ventilated water currents and certain intrinsic factors of these fish parasites may determine their spatial gill distribution. Key words: Barbus martorelli, gill parasites, Myxosporidia, Monogenea, spatial distribution, intrinsic factors.
CF Bilong Bilong, Jeannette Tombi
Journal of the Cameroon academy of sciences
No Abstract Available Journal of the Cameroon Academy of Sciences Vol.4(3) 2004: 211-218
Jeannette Tombi, Charles Félix Bilong Bilong
Revue d’élevage et de médecine vétérinaire des pays tropicaux
L’étude de la parasitofaune branchiale de 558 Barbus martorelli a été menée dans un cours d’eau douce aux alentours de Yaoundé (Cameroun) en milieu tropical, afin d’obtenir des informations sur la répartition des agents pathogènes dans une population d’hôtes sauvages ; ces données sont indispensables dans la recherche de moyens pour éviter les pertes énormes souvent observées en pisciculture intensive. Cette analyse a révélé la présence de deux espèces de myxosporidies (Myxobolus barbi et M. njinei) et de huit espèces de monogènes (Dactylogyrus bopeleti, D. insolitus, D. simplex, D. maillardi, Dogielius martorellii, Dogielius sp., une espèce de Gyrodactylidae et une larve de Polystomatidae). Quatre poissons n’ont pas présenté de parasites, 24 ont présenté une infection monospécifique et 530 une infection plurispécifique. Chaque individu infesté a hébergé en moyenne quatre espèces de parasites. Alors que la prévalence et l’intensité moyenne parasitaire diminuaient avec la taille de l’hôte pour les protozoaires, le phénomène inverse a été observé pour les helminthes. L’effet sexe a été noté dans l’infestation de B. martorelli par la myxosporidie M. njinei et par la plupart des espèces de monogènes. Les femelles ont ainsi été plus infestées que les mâles en raison de leur biologie en période de frai. Enfin, la richesse des espèces parasitaires a semblé affecter négativement le poids des hôtes.
Noura Efietngab Atembeh, Jean Patrick Molu, Jeanne Valerie Emvoutou Maboulou, Boris Fominyam, Rodrigue Nanfack Dongmo, Gabriel Bertrand Zambo and 5 more
Parasite Epidemiology and Control
Background: Urbanization coupled with poverty has promoted the exploitation of risk zones like flood-prone areas in the city of Yaoundé. The overcrowding and poor hygiene observed in these areas are responsible for the unsmiling variations in environmental cleanliness, exploitation of river water for domestic purposes thus putting them at risk for parasitic disease transmissions. This study was conducted in order to assess the risks of human helminthiases outbreaks in relation to water physico-chemical factors in the city of Yaoundé. Method: Water samples were collected monthly from January to June 2022 in 12 stations from 4 rivers (Biyeme, Ebogo, Olezoa and Tongolo) situated in flood plains in the town of Yaoundé. Intestinal parasite resistant forms were identified using the basic sedimentation technique, while water parameters were assessed using standard procedures. Results: = 0.238) respectively. Conclusion: Flood areas constitute a potential risk zone for the maintenance and spread of human helminthiases. Maintaining proper personal cleanliness, environmental sanitation through the building of functional and accessible faecal disposal facilities and drainages and abstaining from using the rivers as waste dumps are essential in this area to prevent parasitic helminth disease outbreaks.
Michel-Thierry Onana-Ngono, Ivan Ndongo, Jeannette Tombi
Parasitology Research
Brice Natchema Soh Fonkou, Magellan Tchouakui, Benjamin D. Menze, Leon M. J. Mugenzi, Derrick Fofie, Daniel Nguiffo-Nguete and 3 more
BMC Infectious Diseases
BACKGROUND: The impact of metabolic resistance to insecticides on malaria transmission remains poorly characterised notably through application of entomological parameters. The lack of resistance markers has been one of the limiting factors preventing a robust assessment of such impact. To this end, the present study sought to investigate how the L119F-Gste2 metabolic gene influences entomological parameters underpinning mosquitos' propensity to transmit Plasmodium spp. METHODS: Longitudinal studies were carried out in Mibellon and Elende, two different eco-climatic settings in Cameroon and mosquitoes were collected using Human Landing Catch (HLC), Centre for Disease Control Light Trap (CDC-LT) and Pyrethrum Spray Catch (PSC) technics. Plasmodium sporozoite parasites were detected by TaqMan and Nested PCR, and blood meal origin by ELISA. The allele-specific PCR (AS-PCR) method was used to genotype the L119F-GSTe2 marker and association with malaria transmission was established by comparing key transmission parameters such as the Entomological Inoculation Rate (EIR) between individuals with different L119F-GSTe2 genotypes. RESULTS: An. funestus s.l was the predominant malaria vector collected during the entomological survey in both sites (86.6% and 96.4% in Elende and Mibellon, respectively) followed by An. gambiae s.l (7.5% and 2.4%, respectively). Sporozoite infection rates were very high in both collection sites (8.7% and 11% in Elende and Mibellon, respectively). An. funestus s.s exhibited a very high entomological inoculation rate (EIR) (66 ib/h/month and 792 ib/h/year) and was responsible for 98.6% of all malaria transmission events occurring in both sites. The Human Blood Index was also high in both locations (HBI = 94%). An. funestus s.s. mosquitoes with both 119 F/F (RR) and L119F (RS) genotypes had a significantly higher transmission intensity than their susceptible L/L119 (SS) counterparts (IRR = 2.2, 95%CI (1.1-5.2), p = 0.03; IRR = 2.5, 95% CI (1.2-5.8), p = 0.01 respectively). CONCLUSION: This study highlights the major role that An. funestus s.s plays in malaria transmission in Cameroon with an aggravation from GSTe2-based metabolic resistance.
Ivan Ndongo, John Francis Akoumba, Jeannette Tombi, Sergé Morand, Abraham Fomena
Acta Parasitologica
Gery Wamba, Clarisse Njua-Yafi, Jeannette Tombi
The International Journal of Tropical Veterinary and Biomedical Research
Primates are known to harbour different gastrointestinal parasite species that affect their survival and reproductive activity. Entamoeba histolytica infects humans predominantly as well as non-human (NH) primates causing amoebiasis. Amoebic dysentery is common amongst non-human primates in captive sites. The purpose of the study was to evaluate the risk factors associated with the prevalence of amoebic dysentery in captive NH primates of the Mefou Primate Sanctuary (MPS) in Cameroon. The faecal samples of 277 NH primates were analysed by qualitative (direct smear and evergreen kit sedimentation technique) coprology from January to July 2019. Factors such as habitat type, keeper’s age and level of education were assessed to evaluate their effect on the prevalence of amoebic dysentery. The prevalence of Entamoeba histolytica was 46.2% (P=0,079 and χ2=18.13). E histolytica was the most predominant parasite species detected and it was present in all instances of mixed parasite infections. Amongst the NH primates positive for E. histolytica, 28 suffered from amoebic dysentery giving a prevalence of 21.9% and one of the infected primates (Cercopithecus pogonias) actually died from amoebic dysentery. The prevalence of mixed infections was significantly lower amongst NH primates living in outdoor enclosures compared to those living in other habitat types (P=0.015, χ2=10.46). The rate of re-infection was significantly higher amongst NH primates under the care of keepers with the lowest (primary school) level of education (P=0.001, χ2=13.09) on one hand and of older keepers (≥50s) (P = 0.008, χ2=13.708) on the other hand. This study shows that amoebic dysentery is a cause for a major concern in the MPS. The housing conditions of the NH primates at the sanctuary, the keeper’s age and level of education were important factors that influenced the prevalence of amoebic dysentery. Adequate measures should be put in place to address the situation.
IVAN NDONGO, Michel Thierry ONANA NGONO, Jeannette Tombi
Asian Fisheries Science
Monogenea is a taxon containing flatworms that are primarily parasites of the skin and gills of fish. The African tetra, Brycinus kingsleyae (Günther, 1896), is a commercial fish species in artisanal fisheries in Southern Cameroon. Although the gill monogeneans of this fish species have been described, no ecological research has been carried out on this component community. The present study was conducted in the Nyong River to provide the first data about some factors that influence the structure of its infracommunities. In dry seasons, 70 fish specimens consisting of 27 males and 43 females of fork length between 9.5 and 14.1 cm were sampled.The analysis of their gill filament number indicated that the gill system of B. kingsleyae is heterogeneous because this factor varies with the length of the fish and depends on the gill arch. The studied guild consisted only of core species: Annulotrema combesi Birgi, 1988, Annulotrema maillardi Birgi, 1988, Annulotrema nyongensis Birgi, 1988, Annulotrema bouixi Birgi, 1988, and Characidotrema regia Birgi, 1988. The number of gill filaments and the parasitic load increased with the fish length, indicating that larger hosts provide a greater diversity of niches for parasites. Monogenean species exhibit various occupation patterns of gill arches, sectors, zones and gender differences in parasitological indices. This study reveals that the host length and sex, filament number, gill arch, sector and zone are largely responsible for structuring the studied component community.
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