3 research outputs found
Towards an assessment of on-farm niches for improved forages in Sud-Kivu, DR Congo
Inadequate quantity and quality of livestock feed is a persistent constraint to productivity for mixed crop-livestock farming in eastern Democratic Republic of Congo. To assess on-farm niches of improved forages, demonstration trials and participatory on-farm research were conducted in four different sites. Forage legumes included Canavalia brasiliensis (CIAT 17009), Stylosanthes guianensis (CIAT 11995) and Desmodium uncinatum (cv. Silverleaf), while grasses were Guatemala grass (Tripsacum andersonii), Napier grass (Pennisetum purpureum) French Cameroon, and a local Napier line. Within the first six months, forage legumes adapted differently to the four sites with little differences among varieties, while forage grasses displayed higher variability in biomass production among varieties than among sites. Farmersâ ranking largely corresponded to herbage yield from the first cut, preferring Canavalia, Silverleaf desmodium and Napier French Cameroon. Choice of forages and integration into farming systems depended on land availability, soil erosion prevalence and livestock husbandry system. In erosion prone sites, 55-60% of farmers planted grasses on field edges and 16-30% as hedgerows for erosion control. 43% of farmers grew forages as intercrop with food crops such as maize and cassava, pointing to land scarcity. Only in the site with lower land pressure, 71% of farmers grew legumes as pure stand. When land tenure was not secured and livestock freely roaming, 75% of farmers preferred to grow annual forage legumes instead of perennial grasses. Future research should develop robust decision support for spatial and temporal integration of forage technologies into diverse smallholder cropping systems and agro-ecologies.</p
Genetic and antigenic variation of the bovine tick-borne pathogen Theileria parva in the Great Lakes region of Central Africa
BACKGROUND : Theileria parva causes East Coast fever (ECF), one of the most economically important tick-borne diseases
of cattle in sub-Saharan Africa. A live immunisation approach using the infection and treatment method (ITM)
provides a strong long-term strain-restricted immunity. However, it typically induces a tick-transmissible carrier state
in cattle and may lead to spread of antigenically distinct parasites. Thus, understanding the genetic composition of T.
parva is needed prior to the use of the ITM vaccine in new areas. This study examined the sequence diversity and the
evolutionary and biogeographical dynamics of T. parva within the African Great Lakes region to better understand the
epidemiology of ECF and to assure vaccine safety. Genetic analyses were performed using sequences of two antigencoding
genes, Tp1 and Tp2, generated among 119 T. parva samples collected from cattle in four agro-ecological zones
of DRC and Burundi.
RESULTS : The results provided evidence of nucleotide and amino acid polymorphisms in both antigens, resulting
in 11 and 10 distinct nucleotide alleles, that predicted 6 and 9 protein variants in Tp1 and Tp2, respectively. Theileria
parva samples showed high variation within populations and a moderate biogeographical sub-structuring due to the
widespread major genotypes. The diversity was greater in samples from lowlands and midlands areas compared to
those from highlands and other African countries. The evolutionary dynamics modelling revealed a signal of selective
evolution which was not preferentially detected within the epitope-coding regions, suggesting that the observed
polymorphism could be more related to gene flow rather than recent host immune-based selection. Most alleles
isolated in the Great Lakes region were closely related to the components of the trivalent Muguga vaccine.
CONCLUSIONS : Our findings suggest that the extensive sequence diversity of T. parva and its biogeographical distribution
mainly depend on host migration and agro-ecological conditions driving tick population dynamics. Such
patterns are likely to contribute to the epidemic and unstable endemic situations of ECF in the region. However, the fact that ubiquitous alleles are genetically similar to the components of the Muguga vaccine together with the limited
geographical clustering may justify testing the existing trivalent vaccine for cross-immunity in the region.Additional file 1: Table S1. Cattle blood sample distribution across agroecological
zones.Additional file 2: Table S2. Nucleotide and amino acid sequences of Tp1
and Tp2 antigen epitopes from T. parva Muguga reference sequence.Additional file 3: Table S3. Characteristics of 119 T. parva samples
obtained from cattle in different agro-ecological zones (AEZs) of The
Democratic Republic of Congo and Burundi.Additional file 4: Figure S1. Multiple sequence alignment of the 11 Tp1
gene alleles obtained in this study.Additional file 5: Table S4. Estimates of evolutionary divergence
between gene alleles for Tp1 and Tp2, using proportion nucleotide
distance.Additional file 6: Table S5. Tp1 and Tp2 genes alleles with their corresponding
antigen variants.Additional file 7: Table S6. Amino acid variants of Tp1 and Tp2 CD8+
T
cell target epitopes of T. parva from DRC and Burundi.Additional file 8: Figure S2. Multiple sequence alignment of the 10 Tp2
gene alleles obtained in this study.Additional file 9: Table S7. Distribution of Tp1 gene alleles of T. parva
from cattle and buffalo in the sub-Saharan region of Africa.Additional file 10: Table S8. Distribution of Tp2 gene alleles of T. parva
from cattle and buffalo in the sub-Saharan region of Africa.Additional file 11: Figure S3. Neighbor-joining tree showing phylogenetic
relationships among 48 Tp1 gene alleles described in Africa.Additional file 12: Figure S4. Phylogenetic tree showing the relationships
among concatenated Tp1 and Tp2 nucleotide sequences of 93 T.
parva samples from cattle in DRC and Burundi.This study is part of the PhD work supported by the University of Namur (UNamur,
Belgium) through the UNamur-CERUNA institutional PhD grant awarded
to GSA for bioinformatic analyses, interpretation of data and manuscript write
up in Belgium. The laboratory aspects (molecular biology analysis) of the
project were supported by the BecA-ILRI Hub through the Africa Biosciences
Challenge Fund (ABCF) programme. The ABCF Programme is funded by
the Australian Department for Foreign Affairs and Trade (DFAT) through the
BecA-CSIRO partnership; the Syngenta Foundation for Sustainable Agriculture
(SFSA); the Bill & Melinda Gates Foundation (BMGF); the UK Department for International Development (DFID); and the Swedish International Development
Cooperation Agency (Sida). The ABCF Fellowship awarded to GAS was
funded by BMGF grant (OPP1075938). Sample collection, field equipment and
preliminary sample processing were supported through the âTheileriaâ project
co-funded to the Université Evangélique en Afrique (UEA) by the Agence
Universitaire de la Francophonie (AUF) and the Communauté Economique
des Pays des Grands Lacs (CEPGL). The International Foundation for Science
(IFS, Stockholm, Sweden) supported the individual scholarship awarded to
GSA (grant no. IFS-92890CA3) for field work and part of field equipment to the
âTheileriaâ project.http://www.parasitesandvectors.comam2020Veterinary Tropical Disease
Mitochondrial phylogeography and population structure of the cattle tick Rhipicephalus appendiculatus in the African Great Lakes region
Abstract Background The ixodid tick Rhipicephalus appendiculatus is the main vector of Theileria parva, wich causes the highly fatal cattle disease East Coast fever (ECF) in sub-Saharan Africa. Rhipicephalus appendiculatus populations differ in their ecology, diapause behaviour and vector competence. Thus, their expansion in new areas may change the genetic structure and consequently affect the vector-pathogen system and disease outcomes. In this study we investigated the genetic distribution of R. appendiculatus across agro-ecological zones (AEZs) in the African Great Lakes region to better understand the epidemiology of ECF and elucidate R. appendiculatus evolutionary history and biogeographical colonization in Africa. Methods Sequencing was performed on two mitochondrial genes (cox1 and 12S rRNA) of 218 ticks collected from cattle across six AEZs along an altitudinal gradient in the Democratic Republic of Congo, Rwanda, Burundi and Tanzania. Phylogenetic relationships between tick populations were determined and evolutionary population dynamics models were assessed by mismach distribution. Results Population genetic analysis yielded 22 cox1 and 9 12S haplotypes in a total of 209 and 126 nucleotide sequences, respectively. Phylogenetic algorithms grouped these haplotypes for both genes into two major clades (lineages A and B). We observed significant genetic variation segregating the two lineages and low structure among populations with high degree of migration. The observed high gene flow indicates population admixture between AEZs. However, reduced number of migrants was observed between lowlands and highlands. Mismatch analysis detected a signature of rapid demographic and range expansion of lineage A. The star-like pattern of isolated and published haplotypes indicates that the two lineages evolve independently and have been subjected to expansion across Africa. Conclusions Two sympatric R. appendiculatus lineages occur in the Great Lakes region. Lineage A, the most diverse and ubiquitous, has experienced rapid population growth and range expansion in all AEZs probably through cattle movement, whereas lineage B, the less abundant, has probably established a founder population from recent colonization events and its occurrence decreases with altitude. These two lineages are sympatric in central and eastern Africa and allopatric in southern Africa. The observed colonization pattern may strongly affect the transmission system and may explain ECF endemic instability in the tick distribution fringes