A cohort study on the duration of Plasmodium falciparum infections during the dry season in The Gambia

Background: In areas where Plasmodium falciparum malaria is highly seasonal, a dry season reservoir of blood-stage infection is essential for initiating transmission during the following wet season, bridging transmission seasons several months apart. Understanding infections during the dry season could thus inform approaches for malaria control. Methods: In The Gambia, a cohort of 42 individuals with qPCR positive P. falciparum infections at the end of the transmission season (December) were followed monthly until the end of the dry season (May) to evaluate the duration of detectable infections. The influence of human host (age, sex, haemoglobin concentration and genotype, and P. falciparum-specific antibodies), and parasitological (parasite density, gametocyte density and genotypic multiplicity of infection) factors was investigated. Results: A large proportion of individuals infected at the end of the wet season had detectable infections until the end of the dry season (40.0%; 16/40), with the majority of these infections also harbouring gametocytes (81.3%; 13/16). 22 infections were classified as persistent (detectable for at least 3 months), 17 were classified as short-lived (undetectable within 2 months), and 3 were treated (due to symptoms). At the start of the dry season, the majority of persistent infections (82%; 18/22) had parasite densities >10 p/uL compared to only 5.9% (1/17) of short-lived infections. Persistent infections (59%; 13/22) were also more likely to be multi-clonal than short-lived infections (5.9%; 1/17), they were most common in 5 to 15 year old children (63%; 12/19), and were associated with individuals having higher levels of P. falciparum-specific antibodies (p = 0.058). Conclusions: Asymptomatic persistent dry season infections in The Gambia were multiclonal with higher parasite densities at the beginning of the dry season, mostly occurring in school age children and adults with higher P. falciparum-specific antibodies. Screening and treating asymptomatic, malaria-infected individuals during the dry season may reduce the human reservoir of malaria responsible initiating transmission in the wet-season.

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High cases of submicroscopic Plasmodium falciparum infections in a suburban population of Lagos, Nigeria

Malaria Journal ◽

10.1186/s12936-019-3073-7 ◽

2019 ◽

Vol 18 (1) ◽

Cited By ~ 1

Author(s):

Florence A. Umunnakwe ◽

Emmanuel T. Idowu ◽

Olusola Ajibaye ◽

Blessed Etoketim ◽

Samuel Akindele ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Large Scale ◽

Quantitative Polymerase Chain Reaction ◽

Age Groups ◽

Malaria Diagnosis ◽

School Age Children ◽

Asymptomatic Malaria ◽

High Prevalence ◽

Study Population ◽

Low Sensitivity

Abstract Background Asymptomatic malaria parasites are significant sources of infections for onward malaria transmission. Conventional tools for malaria diagnosis such as microscopy and rapid diagnostic test kits (RDT) have relatively low sensitivity, hence the need for alternative tools for active screening of such low-density infections. Methods This study tested var acidic terminal sequence-based (varATS) quantitative polymerase chain reaction (qPCR) for screening asymptomatic Plasmodium falciparum infections among dwellers of a sub-urban community in Lagos, Nigeria. Clinically healthy participants were screened for malaria using microscopy, RDT and varATS qPCR techniques. Participants were stratified into three age groups: 1–5, 6–14 and > 14 years old. Results Of the 316 participants screened for asymptomatic malaria infection, 78 (24.68%) were positive by microscopy, 99 (31.33%) were positive by RDT and 112 (35.44%) by varATS qPCR. Participants aged 6–14 years had the highest prevalence of asymptomatic malaria, with geometric means of ~ 116 parasites/µL and ~ 6689 parasites/µL as detected by microscopy and varATS, respectively. Conclusion This study has revealed high prevalence of asymptomatic malaria in the study population, with varATS detecting additional sub-microscopic infections. The highest concentration of asymptomatic malaria was observed among school-age children between 6 and 14 years old. A large-scale screening to identify other potential hotspots of asymptomatic parasites in the country is recommended.

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Impact of an Irrigation Dam on the Transmission and Diversity of Plasmodium falciparum in a Seasonal Malaria Transmission Area of Northern Ghana

Journal of Tropical Medicine ◽

10.1155/2020/1386587 ◽

2020 ◽

Vol 2020 ◽

pp. 1-8 ◽

Cited By ~ 1

Author(s):

Eric Kyei-Baafour ◽

Bernard Tornyigah ◽

Benjamin Buade ◽

Langbong Bimi ◽

Abraham R. Oduro ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Malaria Transmission ◽

Parasite Density ◽

Parasite Prevalence ◽

Dry Season ◽

Water Bodies ◽

Northern Ghana ◽

Wet Season ◽

Transmission Area ◽

Dam Site

Water bodies such as dams are known to alter the local transmission patterns of a number of infectious diseases, especially those transmitted by insects and other arthropod vectors. The impact of an irrigation dam on submicroscopic asexual parasite carriage in individuals living in a seasonal malaria transmission area of northern Ghana was investigated. A total of 288 archived DNA samples from two cross-sectional surveys in two communities in the Bongo District of Northern Ghana were analysed. Parasite density was determined by light microscopy and PCR, and parasite diversity was assessed by genotyping of the polymorphic Plasmodium falciparum msp2 block-3 region. Submicroscopic parasitaemia was estimated as the proportional difference between positive samples identified by PCR and microscopy. Dry season submicroscopic parasite prevalence was significantly higher (71.0%, p=0.013) at the dam site compared with the nondam site (49.2%). Similarly, wet season submicroscopic parasite prevalence was significantly higher at the dam site (54.5%, p=0.008) compared with the nondam site (33.0%). There was no difference in parasite density between sites in the dry season (p=0.90) and in the wet season (p=0.85). Multiplicity of infection (MOI) based on PCR data was significantly higher at the dam site compared with the nondam site during the dry season (p<0.0001) but similar between sites during the wet season. MOI at the nondam site was significantly higher in the wet season than in the dry season (2.49, 1.26, p<0.0001) but similar between seasons at the dam site. Multivariate analysis showed higher odds of carrying submicroscopic parasites at the dam site in both dry season (OR = 7.46, 95% CI = 3.07–18.15) and in wet season (OR = 1.73, 95% CI = 1.04–2.86). The study findings suggest that large water bodies impact year-round carriage of submicroscopic parasites and sustain Plasmodium transmission.

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Risk factors for Plasmodium falciparum infection in pregnant women in Burkina Faso: a community-based cross-sectional survey

Malaria Journal ◽

10.1186/s12936-021-03896-8 ◽

2021 ◽

Vol 20 (1) ◽

Author(s):

Jean Baptiste Yaro ◽

Alphonse Ouedraogo ◽

Amidou Diarra ◽

Salif Sombié ◽

Z. Amidou Ouedraogo ◽

...

Keyword(s):

Risk Factors ◽

Plasmodium Falciparum ◽

Burkina Faso ◽

Pregnant Women ◽

Malaria Control ◽

Dry Season ◽

Malaria In Pregnancy ◽

Wet Season ◽

Cross Sectional ◽

In Pregnancy

Abstract Background Malaria in pregnancy remains a public health problem in sub-Saharan Africa. Identifying risk factors for malaria in pregnancy could assist in developing interventions to reduce the risk of malaria in Burkina Faso and other countries in the region. Methods Two cross-sectional surveys were carried out to measure Plasmodium falciparum infection using microscopy in pregnant women in Saponé Health District, central Burkina Faso. Data were collected on individual, household and environmental variables and their association with P. falciparum infection assessed using multivariable analysis. Results A total of 356 pregnant women were enrolled in the surveys, 174 during the dry season and 182 during the wet season. The mean number of doses of sulfadoxine–pyrimethamine for Intermittent Preventive Treatment in pregnancy (IPTp-SP) was 0.4 doses during the first trimester, 1.1 doses at the second and 2.3 doses at the third. Overall prevalence of P. falciparum infection by microscopy was 15.7%; 17.8% in the dry season and 13.7% in the wet season. 88.2% of pregnant women reported sleeping under an insecticide-treated net (ITN) on the previous night. The odds of P. falciparum infection was 65% lower in women who reported using an ITN compared to those that did not use an ITN (Odds ratio, OR = 0.35, 95% CI 0.14–0.86, p = 0.02). IPTp-SP was also associated with reduced P. falciparum infection, with each additional dose of IPTp-SP reducing the odds of infection by 44% (OR = 0.56, 95% CI 0.39–0.79, p = 0.001). Literate women had a 2.54 times higher odds of P. falciparum infection compared to illiterate women (95% CI 1.31–4.91, p = 0.006). Conclusions The prevalence of P. falciparum infection among pregnant women remains high in Burkina Faso, although use of IPTp-SP and ITNs were found to reduce the odds of infection. Despite this, compliance with IPTp-SP remains far from that recommended by the National Malaria Control Programme and World Health Organization. Behaviour change communication should be strengthened to encourage compliance with protective malaria control tools during pregnancy.

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Increased investment in gametocytes in asymptomatic Plasmodium falciparum infections in the wet season

BMC Infectious Diseases ◽

10.1186/s12879-020-05761-6 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Colins O. Oduma ◽

Sidney Ogolla ◽

Harrysone Atieli ◽

Bartholomew N. Ondigo ◽

Ming-Chieh Lee ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Limit Of Detection ◽

Parasite Prevalence ◽

Dry Season ◽

Control Measures ◽

Wet Season ◽

Western Kenya ◽

Vector Abundance ◽

Asymptomatic Infections ◽

Asymptomatic Individuals

Abstract Background Transmission stemming from asymptomatic infections is increasingly being recognized as a threat to malaria elimination. In many regions, malaria transmission is seasonal. It is not well understood whether Plasmodium falciparum modulates its investment in transmission to coincide with seasonal vector abundance. Methods We sampled 1116 asymptomatic individuals in the wet season, when vectors are abundant, and 1743 in the dry season, in two sites in western Kenya, representing different transmission intensities (Chulaimbo, moderate transmission, and Homa Bay, low transmission). Blood samples were screened for P. falciparum by qPCR, and gametocytes by pfs25 RT-qPCR. Results Parasite prevalence by qPCR was 27.1% (Chulaimbo, dry), 48.2% (Chulaimbo, wet), 9.4% (Homabay, dry), and 7.8% (Homabay, wet). Mean parasite densities did not differ between seasons (P = 0.562). pfs25 transcripts were detected in 119/456 (26.1%) of infections. In the wet season, fewer infections harbored detectable gametocytes (22.3% vs. 33.8%, P = 0.009), but densities were 3-fold higher (wet: 3.46 transcripts/uL, dry: 1.05 transcripts/uL, P < 0.001). In the dry season, 4.0% of infections carried gametocytes at moderate-to-high densities likely infective (> 1 gametocyte per 2 uL blood), compared to 7.9% in the wet season. Children aged 5–15 years harbored 76.7% of infections with gametocytes at moderate-to-high densities. Conclusions Parasites increase their investment in transmission in the wet season, reflected by higher gametocyte densities. Despite increased gametocyte densities, parasite density remained similar across seasons and were often below the limit of detection of microscopy or rapid diagnostic test, thus a large proportion of infective infections would escape population screening in the wet season. Seasonal changes of gametocytemia in asymptomatic infections need to be considered when designing malaria control measures.

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Constant rate of Plasmodium falciparum sexual commitment promotes variable gametocyte proportions as infection progresses over time

10.1101/2021.11.05.467456 ◽

2021 ◽

Author(s):

Silvia Portugal ◽

Hannah van Dijk ◽

Nathalia Ferreira Lima ◽

Martin Kampmann ◽

Michael Gabel ◽

...

Keyword(s):

Dry Season ◽

Phospholipid Content ◽

Wet Season ◽

Gametocyte Density ◽

Blood Concentrations ◽

Constant Rate ◽

Chronic Carriage ◽

Asymptomatic Subjects ◽

Over Time

In areas of seasonal malaria, resuming transmission every wet season relies on persistent asexual parasites during dry season that maintain the ability to produce gametocytes until the mosquito population resurges, following the start of annual rains. Although human asymptomatic P. falciparum reservoirs in the dry season are widely recognized, the longitudinal dynamics of parasite sexual commitment and gametocytogenesis are unclear. Here, we compared the density and proportion of P. falciparum gametocytes in blood of asymptomatic subjects during the dry season versus subjects with symptomatic malaria in the wet season. Blood concentrations of phospholipids potentially involved in gametocytogenesis and parasite transcriptomes were also compared. While blood densities of gametocytes and asexual parasites were lower during the dry season, we found that gametocytes were proportionally higher during the dry versus wet season. Levels of parasite transcripts involved in sexual commitment were similar throughout the year, and phospholipid content in the plasma throughout the year did not affect sexual commitment in vitro. We demonstrate experimentally and through mathematical modelling that gametocyte density and proportion diverge as infections progress from recently transmitted to chronic carriage, without significant alterations in the rate of sexual commitment over time.

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Plasmodium falciparum increases its investment in gametocytes in the wet season in asymptomatic individuals

10.1101/2020.08.04.236950 ◽

2020 ◽

Author(s):

Colins O. Oduma ◽

Sidney Ogolla ◽

Harrysone Atieli ◽

Bartholomew N. Ondigo ◽

Ming-Chieh Lee ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Malaria Transmission ◽

Parasite Prevalence ◽

Dry Season ◽

Wet Season ◽

Western Kenya ◽

Gametocyte Carriage ◽

Vector Abundance ◽

Asymptomatic Individuals

AbstractIn many regions, malaria transmission is seasonal, but it is not well understood whether P. falciparum modulates its investment in transmission in response to seasonal vector abundance. In two sites in western Kenya (Chulaimbo and Homa Bay), we sampled 1116 asymptomatic individuals in the wet season, when vectors are abundant, and 1743 in the dry season. We screened for P. falciparum by qPCR, and gametocytes by pfs25 RT-qPCR. Parasite prevalence in Chulaimbo and Homa Bay was 27.1% and 9.4% in the dry season, and 48.2% and 7.8% in the wet season respectively. Mean parasite densities did not differ between seasons (P=0.562). A contrasting pattern of gametocyte carriage was observed. In the wet season, fewer infections harbored gametocytes (22.3% vs. 33.8%, P=0.009), but densities were 3-fold higher (P<0.001). Thus, in the wet season, among gametocyte positive individuals, higher proportion of all parasites were gametocytes, reflecting an increased investment in transmission.

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Risk Factors for Plasmodium Falciparum Infection in Pregnant Women in Burkina Faso: A Community-Based Malaria Cross-Sectional Survey

10.21203/rs.3.rs-337686/v1 ◽

2021 ◽

Author(s):

Jean Baptiste Yaro ◽

Alphonse Ouedraogo ◽

Amidou Diarra ◽

Salif Sombié ◽

Z Amidou Ouedraogo ◽

...

Keyword(s):

Risk Factors ◽

Plasmodium Falciparum ◽

Burkina Faso ◽

Pregnant Women ◽

Malaria Control ◽

Dry Season ◽

Malaria In Pregnancy ◽

Wet Season ◽

Cross Sectional ◽

In Pregnancy

Abstract Background: Malaria in pregnancy remains a public health problem in sub-Saharan Africa. Identifying risk factors for malaria in pregnancy could assist in developing interventions to reduce the risk of malaria in Burkina Faso and other countries in the region.Methodology: Two cross-sectional surveys were carried out to measure Plasmodium falciparum infection using microscopy in pregnant women in Saponé Health District, central Burkina Faso. Data were collected on individual, household and environmental variables and their association with P. falciparum infection assessed using multivariate analysis. Results: A total of 356 pregnant women were enrolled in the surveys, 174 during the dry season and 182 during the wet season. The mean number of doses of sulphadoxine pyrimethamine for Intermittent Preventive Treatment in pregnancy (IPTp-SP) was 0.4 doses during the first trimester, 1.1 doses at the second and 2.3 doses at the third. Overall prevalence of P. falciparum infection by microscopy was 15.7%; 17.8% in the dry season and 13.7% in the wet season. 88.2% of pregnant women reported sleeping under an insecticide-treated net on the previous night. P. falciparum infection risk in pregnancy was reduced in those women who reported using an ITN (Odds ratio, OR=0.31, 95% CI 0.12-0.79, p=0.02) and an increasing number of IPTp-SP doses during pregnancy, with each additional dose reducing the odds by 40% (OR=0.59, 95% CI 0.43–0.81, p<0.001). ConclusionThe prevalence of P. falciparum infection among pregnant women remains high in Burkina Faso although use of IPTp-SP and ITNs were found to reduce the odds of infection. Despite this, compliance with IPTp remains far from that recommended by the National Malaria Control Programme and World Health Organization. Behaviour change communication should be improved to encourage compliance with protective malaria control tools during pregnancy.

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Population dynamics of Plasmodium falciparum in an unstable malaria area of eastern Sudan

Parasitology ◽

10.1017/s0031182099005387 ◽

2000 ◽

Vol 120 (2) ◽

pp. 105-111 ◽

Cited By ~ 26

Author(s):

H. A. BABIKER ◽

A. A. ABDEL-MUHSIN ◽

A. HAMAD ◽

M. J. MACKINNON ◽

W. G. HILL ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Population Dynamics ◽

Malaria Transmission ◽

Dry Season ◽

Allele Frequencies ◽

Wet Season ◽

Transmission Season ◽

Large Repertoire ◽

Eastern Sudan

The Plasmodium falciparum population in Asar village, eastern Sudan, where malaria transmission is markedly seasonal, was monitored monthly over a period of 15 months. A cohort of infected patients was treated and then followed monthly throughout the dry season until the next transmission season. Parasitaemia detected by microscopy among the cohort reduced dramatically following treatment, but remained sporadic during the dry season, and reappeared following the onset of the next wet season. However between 40 and 50% of the cohort retained a persisting parasitaemia detectable by PCR throughout the dry season. These parasites were genetically complex, consisting of multiple clones with a large repertoire of alleles of the studied genes. While the number of clones per host dropped significantly following treatment of acute cases during the transmission season, drug treated people nevertheless maintained an average of one clone throughout the dry season. Allele frequencies of MSP-1, MSP-2 and GLURP showed slight, statistically insignificant, fluctuations between the dry and wet seasons. A higher frequency of inbreeding was estimated among the parasites that survived the dry season compared to the wet season.

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The seasonal changes of the gut microbiome of the population living in traditional lifestyles are represented by characteristic species-level and functional-level SNP enrichment patterns

BMC Genomics ◽

10.1186/s12864-021-07372-0 ◽

2021 ◽

Vol 22 (1) ◽

Author(s):

Xue Zhu ◽

Jiyue Qin ◽

Chongyang Tan ◽

Kang Ning

Keyword(s):

Gut Microbiome ◽

Seasonal Changes ◽

Dry Season ◽

Urban Setting ◽

Snp Analysis ◽

Wet Season ◽

Human Gut ◽

Human Gut Microbiome ◽

Genome Level ◽

Prevalent Species

Abstract Background Most studies investigating human gut microbiome dynamics are conducted on humans living in an urban setting. However, few studies have researched the gut microbiome of the populations living traditional lifestyles. These understudied populations are arguably better subjects in answering human-gut microbiome evolution because of their lower exposure to antibiotics and higher dependence on natural resources. Hadza hunter-gatherers in Tanzania have exhibited high biodiversity and seasonal patterns in their gut microbiome composition at the family level, where some taxa disappear in one season and reappear later. Such seasonal changes have been profiled, but the nucleotide changes remain unexplored at the genome level. Thus, it is still elusive how microbial communities change with seasonal changes at the genome level. Results In this study, we performed a strain-level single nucleotide polymorphism (SNP) analysis on 40 Hadza fecal metagenome samples spanning three seasons. With more SNP presented in the wet season, eight prevalent species have significant SNP enrichment with the increasing number of SNP calling by VarScan2, among which only three species have relatively high abundances. Eighty-three genes have the most SNP distributions between the wet season and dry season. Many of these genes are derived from Ruminococcus obeum, and mainly participated in metabolic pathways including carbon metabolism, pyruvate metabolism, and glycolysis. Conclusions Eight prevalent species have significant SNP enrichments with the increasing number of SNP, among which only Eubacterium biforme, Eubacterium hallii and Ruminococcus obeum have relatively high species abundances. Many genes in the microbiomes also presented characteristic SNP distributions between the wet season and the dry season. This implies that the seasonal changes might indirectly impact the mutation patterns for specific species and functions for the gut microbiome of the population that lives in traditional lifestyles through changing the diet in wet and dry seasons, indicating the role of these variants in these species’ adaptation to the changing environment and diets.

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Seasonal Climate Impacts on Vocal Activity in Two Neotropical Nonpasserines

Diversity ◽

10.3390/d13070319 ◽

2021 ◽

Vol 13 (7) ◽

pp. 319

Author(s):

Cristian Pérez-Granados ◽

Karl-L. Schuchmann

Keyword(s):

Air Temperature ◽

Daily Rainfall ◽

Climatic Conditions ◽

Dry Season ◽

Climate Impacts ◽

Calling Behavior ◽

Wet Season ◽

Focal Species ◽

Calling Activity ◽

Vocal Activity

Climatic conditions represent one of the main constraints that influence avian calling behavior. Here, we monitored the daily calling activity of the Undulated Tinamou (Crypturellus undulatus) and the Chaco Chachalaca (Ortalis canicollis) during the dry and wet seasons in the Brazilian Pantanal. We aimed to assess the effects of climate predictors on the vocal activity of these focal species and evaluate whether these effects may vary among seasons. Air temperature was positively associated with the daily calling activity of both species during the dry season. However, the vocal activity of both species was unrelated to air temperature during the wet season, when higher temperatures occur. Daily rainfall was positively related to the daily calling activity of both species during the dry season, when rainfall events are scarce and seem to act as a trigger for breeding phenology of the focal species. Nonetheless, air temperature was negatively associated with the daily calling activity of the Undulated Tinamou during the wet season, when rainfall was abundant. This study improves our understanding of the vocal behavior of tropical birds and their relationships with climate, but further research is needed to elucidate the mechanisms behind the associations found in our study.

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