Inter-Epidemic Transmission of Rift Valley Fever in\ud Livestock in the Kilombero River Valley, Tanzania:\ud A Cross-Sectional Survey

In recent years, evidence of Rift Valley fever (RVF) transmission during inter-epidemic periods in parts of Africa has increasingly been reported. The inter-epidemic transmissions generally pass undetected where there is no surveillance in the livestock or human populations. We studied the presence of and the determinants for inter-epidemic RVF transmission in an area experiencing annual flooding in southern Tanzania. A cross-sectional sero-survey was conducted in randomly selected cattle, sheep and goats in the Kilombero river valley from May to August 2011, approximately four years after the 2006/07 RVF outbreak in Tanzania. The exposure status to RVF virus (RVFV) was determined using two commercial ELISA kits, detecting IgM and IgG antibodies in serum. Information about determinants was obtained through structured interviews with herd owners. An overall seroprevalence of 11.3% (n = 1680) was recorded; 5.5% in animals born after the 2006/07 RVF outbreak and 22.7% in animals present during the outbreak. There was a linear increase in prevalence in the post-epidemic annual cohorts. Nine inhibition-ELISA positive samples were also positive for RVFV IgM antibodies indicating a recent infection. The spatial distribution of seroprevalence exhibited a few hotspots. The sex difference in seroprevalence in animals born after the previous epidemic was not significant (6.1% vs. 4.6% for females and males respectively, p = 0.158) whereas it was significant in animals present during the outbreak (26.0% vs. 7.8% for females and males respectively, p,0.001). Animals living .15 km from the flood plain were more likely to have antibodies than those living ,5 km (OR 1.92; 95% CI 1.04–3.56). Species, breed, herd composition, grazing practices and altitude were not associated with seropositivity. These findings indicate post-epidemic transmission of RVFV in the study area. The linear increase in seroprevalence in the post-epidemic annual cohorts implies a constant exposure and presence of active foci transmission preceding the survey

Foot-and-mouth disease in Tanzania from 2001 to 2006.

Foot-and-mouth disease (FMD) is endemic in Tanzania, with outbreaks occurring almost each year in different parts of the country. There is now a strong political desire to control animal diseases as part of national poverty alleviation strategies. However, FMD control requires improving the current knowledge on the disease dynamics and factors related to FMD occurrence so control measures can be implemented more efficiently. The objectives of this study were to describe the FMD dynamics in Tanzania from 2001 to 2006 and investigate the spatiotemporal patterns of transmission. Extraction maps, the space-time K-function and space-time permutation models based on scan statistics were calculated for each year to evaluate the spatial distribution, the spatiotemporal interaction and the spatiotemporal clustering of FMD-affected villages. From 2001 to 2006, 878 FMD outbreaks were reported in 605 different villages of 5815 populated places included in the database. The spatial distribution of FMD outbreaks was concentrated along the Tanzania-Kenya, Tanzania-Zambia borders, and the Kagera basin bordering Uganda, Rwanda and Tanzania. The spatiotemporal interaction among FMD-affected villages was statistically significant (P≤0.01) and 12 local spatiotemporal clusters were detected; however, the extent and intensity varied across the study period. Dividing the country in zones according to their epidemiological status will allow improving the control of FMD and delimiting potential FMD-free areas

A differential equations model of east coast fever transmission dynamics

In this study a differential equation model of the transmission dynamics of East Cost Fever caused by Theileria parva transmitted by Rhippicephalus appendiculatus was developed. In this model cattle were assigned to four categories: susceptible, T. parva incubating, infectious (clinically infected) and recovered cattle population having immunity and still infect ticks but at a lower rate. Ticks were also categorized into various stages: eggs, larvae, susceptible nymphs, infected nymphs, susceptible adult ticks and infected adult ticks. The parameters of the model were obtained from literature assumed or calculated. Simulations with R software were run with and without seasonal questing activity of adult ticks. The results of the simulation model explained the seasonal differences of R. appendiculatus activity and transmission of T. parva between tropical eastern and central Africa and sub – tropical southern Africa. Besides, it showed that nymphs are the stage of R. appendiculatus that play important role in transmission of T. parva in southern Africa while both nymphs and adults transmit in eastern and central Africa. Future developments and data required to further develop the model were proposed.Keywords: A model, Differential equations, Rhipicephalus appendiculatus, Theirelia parv

Risk Factors for Foot-and-Mouth Disease in Tanzania, 2001-2006

We developed a model to quantify the effect of factors influencing the spatio-temporal distribution of foot-and-mouth disease (FMD) in Tanzania. The land area of Tanzania was divided into a regular grid of 20 km x 20 km cells and separate grids constructed for each of the 12-month periods between 2001 and 2006. For each year, a cell was classified as either FMD positive or negative dependent on an outbreak being recorded in any settlement within the cell boundaries. A Bayesian mixed-effects spatial model was developed to assess the association between the risk of FMD occurrence and distance to main roads, railway lines, wildlife parks, international borders and cattle density. Increases in the distance to main roads decreased the risk of FMD every year from 2001 to 2006 (ORs ranged from 0.43 to 0.97). Increases in the distance to railway lines and international borders were, in general, associated with a decreased risk of FMD (ORs ranged from 0.85 to 0.99). Increases in the distance from a national park decreased the risk of FMD in 2001 (OR 0.80; 95% CI 0.68-0.93) but had the opposite effect in 2004 (OR 1.06; 95% CI 1.01-1.12). Cattle population density was, in general, positively associated with the risk of FMD (ORs ranged from 1.01 to 1.30). The spatial distribution of high-risk areas was variable and corresponded to endemic (2001, 2002 and 2005) and epidemic (2003, 2004 and 2006) phases. Roads played a dominant role in both epidemiological situations; we hypothesize that roads are the main driver of FMD expansion in Tanzania. Our results suggest that FMD occurrence in Tanzania is more related to animal movement and human activity via communication networks than transboundary movements or contact with wildlife

Bayesian evaluation of three serological tests for the diagnosis of bovine brucellosis in Bangladesh

We evaluated the performance of three serological tests – an immunoglobulin G indirect enzyme linked immunosorbent assay (iELISA), a Rose Bengal test and a slow agglutination test (SAT) – for the diagnosis of bovine brucellosis in Bangladesh. Cattle sera (n = 1360) sourced from Mymensingh district (MD) and a Government owned dairy farm (GF) were tested in parallel. We used a Bayesian latent class model that adjusted for the conditional dependence among the three tests and assumed constant diagnostic accuracy of the three tests in both populations. The sensitivity and specificity of the three tests varied from 84.6% to 93.7%, respectively. The true prevalences of bovine brucellosis in MD and the GF were 0.6% and 20.4%, respectively. Parallel interpretation of iELISA and SAT yielded the highest negative predictive values: 99.9% in MD and 99.6% in the GF; whereas serial interpretation of both iELISA and SAT produced the highest positive predictive value (PPV): 99.9% in the GF and also high PPV (98.9%) in MD. We recommend the use of both iELISA and SAT together and serial interpretation for culling and parallel interpretation for import decisions. Removal of brucellosis positive cattle will contribute to the control of brucellosis as a public health risk in Bangladesh

Matrix Gla protein deficiency impairs nasal septum growth, causing midface hypoplasia

Genetic and environmental factors may lead to abnormal growth of the orofacial skeleton, affecting the overall structure of the face. In this study, we investigated the craniofacial abnormalities in a mouse model for Keutel syndrome, a rare genetic disease caused by loss-of-function mutations in the matrix Gla protein (MGP) gene. Keutel syndrome patients show diffuse ectopic calcification of cartilaginous tissues and impaired midface development. Our comparative cephalometric analyses of micro-computed tomography images revealed a severe midface hypoplasia in Mgp-/- mice. In vivo reporter studies demonstrated that the Mgp promoter is highly active at the cranial sutures, cranial base synchondroses, and nasal septum. Interestingly, the cranial sutures of the mutant mice showed normal anatomical features. Although we observed a mild increase in mineralization of the spheno-occipital synchondrosis, it did not reduce the relative length of the cranial base in comparison with total skull length. Contrary to this, we found the nasal septum to be abnormally mineralized and shortened in Mgp-/- mice. Transgenic restoration of Mgp expression in chondrocytes fully corrected the craniofacial anomalies caused by MGP deficiency, suggesting a local role for MGP in the developing nasal septum. Although there was no up-regulation of markers for hypertrophic chondrocytes, a TUNEL assay showed a marked increase in apoptotic chondrocytes in the calcified nasal septum. Transmission electron microscopy confirmed unusual mineral deposits in the septal extracellular matrix of the mutant mice. Of note, the systemic reduction of the inorganic phosphate level was sufficient to prevent abnormal mineralization of the nasal septum in Mgp-/-;Hyp compound mutants. Our work provides evidence that modulation of local and systemic factors regulating extracellular matrix mineralization can be possible therapeutic strategies to prevent ectopic cartilage calcification and some forms of congenital craniofacial anomalies in humans