Longitudinal monitoring of Ehrlichia ruminantium infection in Gambian lambs and kids by pCS20 PCR and MAP1-B ELISA

<p>Abstract</p> <p>Background</p> <p>The epidemiology of <it>E. ruminantium </it>infection in extensively managed young animals is not adequately understood. Thus in this study, we monitored the onset (age at first infection) and kinetics of <it>E. ruminantium </it>infection and antibody response in extensively managed newborn lambs and kids at three sites in The Gambia.</p> <p>Methods</p> <p>We used a nested pCS20 PCR and MAP1-B ELISA in a longitudinal study to monitor the onset (age at first infection) and kinetics of <it>E. ruminantium </it>infection and antibody response respectively, in 77 newborn lambs and kids under a traditional husbandry system at three sites (Kerr Seringe, Keneba, Bansang) in The Gambia where heartwater is known to occur. The animals were monitored for field tick infestation and the comparative performance of the two assays in detecting <it>E. ruminantium </it>infection was also assessed.</p> <p>Results</p> <p>The infection rate detected by pCS20 PCR varied between 8.6% and 54.8% over the 162-day study period. Nineteen per cent of the animals in week 1 post-partum tested positive by pCS20 PCR with half of these infections (7/14) detected in the first 3 days after birth, suggesting that transmission other than by tick feeding had played a role. The earliest detectable <it>A. variegatum </it>infestation in the animals occurred in week 16 after birth. Antibodies detected by MAP1-B ELISA also varied, between 11.5% and 90%. Although there is considerable evidence that this assay can detect false positives and due to this and other reasons serology is not a reliable predictor of infection at least for heartwater. In contrast to the pCS20 PCR, the serological assay detected the highest proportion of positive animals in week 1 with a gradual decline in seropositivity with increasing age. The pCS20 PCR detected higher <it>E. ruminantium </it>prevalence in the animals with increasing age and both the Spearman's rank test (<it>r</it>_{<it>s </it>}= -0.1512; P = 0.003) and <it>kappa </it>statistic (-0.091 to 0.223) showed a low degree of agreement between the two assays.</p> <p>Conclusion</p> <p>The use of pCS20 PCR supported by transmission studies and clinical data could provide more accurate information on heartwater epidemiology in endemic areas and single-occasion testing of an animal may not reveal its true infection status. The view is supported because both the vector and vertical transmission may play a vital role in the epidemiology of heartwater in young small ruminants; the age range of 4 and 12 weeks corresponds to the period of increased susceptibility to heartwater in traditionally managed small ruminants.</p

Trypanotolerance in Djallonke sheep and West African Dwarf goats : Importance of trypanosomosis, nutrition, helminth infections and management factors

The main breeds of sheep and goats in The Gambia, the Djallonke sheep and West African Dwarf goats are trypanotolerant. The Djallonke sheep, however, have a higher degree of trypanotolerance than the WAD goats. This trait is genetically linked although the mechanism of trypanotolerance is different from the one in cattle. It is defined as a resilience to infection rather than resistance. Both breeds are well adapted to the locally prevailing diseases and environmental conditions under which they live. Moreover, they feature the capacity of making good use of low quality feed resources. For the rural farmer, small ruminant production is an attractive enterprise and seems to be profitable even under a low input management system. Small ruminant production also has a large potential under more intensified peri-urban conditions. Trypanosomosis remains an important constraint to optimal productivity. In particular when combined with other diseases, poor nutritional status and poor husbandry practises there is a clear effect on productivity and thus profitability. All these factors should be regarded as equally important. Based on the results of research and surveys presented in this thesis, some recommendations are formulated for interventions in order to reduce the disease constraint, improve the nutritional status and adapt the management of small ruminant production systems. Further research will be carried out to study the impact of the proposed interventions and their adaptation to the local conditions

Trypanotolerance in Djallonke sheep and West African Dwarf goats : Importance of trypanosomosis, nutrition, helminth infections and management factors

The main breeds of sheep and goats in The Gambia, the Djallonke sheep and West African Dwarf goats are trypanotolerant. The Djallonke sheep, however, have a higher degree of trypanotolerance than the WAD goats. This trait is genetically linked although the mechanism of trypanotolerance is different from the one in cattle. It is defined as a resilience to infection rather than resistance. Both breeds are well adapted to the locally prevailing diseases and environmental conditions under which they live. Moreover, they feature the capacity of making good use of low quality feed resources. For the rural farmer, small ruminant production is an attractive enterprise and seems to be profitable even under a low input management system. Small ruminant production also has a large potential under more intensified peri-urban conditions. Trypanosomosis remains an important constraint to optimal productivity. In particular when combined with other diseases, poor nutritional status and poor husbandry practises there is a clear effect on productivity and thus profitability. All these factors should be regarded as equally important. Based on the results of research and surveys presented in this thesis, some recommendations are formulated for interventions in order to reduce the disease constraint, improve the nutritional status and adapt the management of small ruminant production systems. Further research will be carried out to study the impact of the proposed interventions and their adaptation to the local conditions

Trypanotolerance in small ruminants of sub-Saharan Africa

Although a lot of information is currently available on trypanotolerance in cattle, until recently the trypanotolerant nature of small ruminants was not well known. Trypanotolerance in small ruminants is less pronounced than in cattle and should be considered as resilience rather than resistance. West African Dwarf (WAD) goats seem to be less trypanotolerant than Djallonke sheep. However, recent studies have shown that there is an important introgression of genes of trypanosusceptible breeds into WAD goat populations, which possibly explains the loss of trypanotolerance in these animals. Measures need to be taken to safeguard and upgrade the genetic purity of trypanotolerant goat and sheep breeds in Africa

A Genetic Exploration in a Last Refuge: The Common Angelshark (Squatina squatina) in the Canary Islands

The common angelshark (Squatina squatina) has been extirpated from nearly the entirety of its historical eastern North Atlantic and Mediterranean range and is listed as ‘Critically Endangered’ by the IUCN Red List of Threatened Species. Currently, only a single known remnant population of any abundance exists, occurring within the waters surrounding the Canary Islands. Nothing is known about the genetic population dynamics of this species. To assess the common angelshark’s genetic connectivity and diversity, tissue samples (n = 509) were collected between 2009-2016 from three separate islands within the archipelago: Gran Canaria and Tenerife – which are separated by a deep ocean channel (~3000 m) which potentially serves as a barrier to dispersal for this benthic species, and Lanzarote. To date, DNA sequences have been obtained from four mitochondrial loci [control region (CR) (n = 233), Cytochrome c oxidase subunit 1 (COI) (n = 16), NADH dehydrogenase subunit 4 (ND4) (n =28), and NADH dehydrogenase subunit 2 (ND2) (n =4)] revealing exceptionally low genetic diversity across all regions, as identical haplotypes were found in nearly all analyzed individuals. Additionally, next-generation sequencing has been used to develop a species-specific library for novel microsatellites and preliminary screening of each of 18 markers has shown these loci to be monomorphic across 16 individuals. Further screening of additional loci (mitochondrial and microsatellite) and individuals is ongoing. Such potentially low levels of genetic diversity may have far reaching implications for the persistence of this species and ultimately underscore the common angelsharks’ highly vulnerable state