A hierarchical network approach for modeling Rift Valley fever epidemics with applications in North America

Rift Valley fever is a vector-borne zoonotic disease which causes high morbidity and mortality in livestock. In the event Rift Valley fever virus is introduced to the United States or other non-endemic areas, understanding the potential patterns of spread and the areas at risk based on disease vectors and hosts will be vital for developing mitigation strategies. Presented here is a general network-based mathematical model of Rift Valley fever. Given a lack of empirical data on disease vector species and their vector competence, this discrete time epidemic model uses stochastic parameters following several PERT distributions to model the dynamic interactions between hosts and likely North American mosquito vectors in dispersed geographic areas. Spatial effects and climate factors are also addressed in the model. The model is applied to a large directed asymmetric network of 3,621 nodes based on actual farms to examine a hypothetical introduction to some counties of Texas, an important ranching area in the United States of America (U.S.A.). The nodes of the networks represent livestock farms, livestock markets, and feedlots, and the links represent cattle movements and mosquito diffusion between different nodes. Cattle and mosquito (Aedes and Culex) populations are treated with different contact networks to assess virus propagation. Rift Valley fever virus spread is assessed under various initial infection conditions (infected mosquito eggs, adults or cattle). A surprising trend is fewer initial infectious organisms result in a longer delay before a larger and more prolonged outbreak. The delay is likely caused by a lack of herd immunity while the infections expands geographically before becoming an epidemic involving many dispersed farms and animals almost simultaneously

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

The abundance and host-seeking behavior of culicine species (Diptera: Culicidae) and Anopheles sinensis in Yongcheng city, people's Republic of China

<p>Abstract</p> <p>Background</p> <p>The knowledge of mosquito species diversity and the level of anthropophily exhibited by each species in a region are of great importance to the integrated vector control. Culicine species are the primary vectors of Japanese encephalitis (JE) virus and filariasis in China. <it>Anopheles sinensis </it>plays a major role in the maintenance of <it>Plasmodium vivax </it>malaria transmission in China. The goal of this study was to compare the abundance and host-seeking behavior of culicine species and <it>An. sinensis </it>in Yongcheng city, a representative region of <it>P. vivax </it>malaria. Specifically, we wished to determine the relative attractiveness of different animal baits versus human bait to culicine species and <it>An. sinensis</it>.</p> <p>Results</p> <p><it>Culex tritaeniorhynchus </it>was the most prevalent mosquito species and <it>An. sinensis </it>was the sole potential vector of <it>P. vivax </it>malaria in Yongcheng city. There were significant differences (P < 0.01) in the abundance of both <it>An. sinensis </it>and <it>Cx. tritaeniorhynchus </it>collected in distinct baited traps. The relative attractiveness of animal versus human bait was similar towards both <it>An. sinensis </it>and <it>Cx. tritaeniorhynchus</it>. The ranking derived from the mean number of mosquitoes per bait indicated that pigs, goats and calves frequently attracted more mosquitoes than the other hosts tested (dogs, humans, and chickens). These trends were similar across all capture nights at three distinct villages. The human blood index (HBI) of female <it>An. sinensis </it>was 2.94% when computed with mixed meals while 3.70% computed with only the single meal. 19:00~21:00 was the primary peak of host-seeking female <it>An. sinensis </it>while 4:00~5:00 was the smaller peak at night. There was significant correlation between the density of female <it>An. sinensis </it>and the average relative humidity (P < 0.05) in Wangshanzhuang village.</p> <p>Conclusions</p> <p>Pigs, goats and calves were more attractive to <it>An. sinensis </it>and <it>Cx. tritaeniorhynchus </it>than dogs, humans, and chickens. Female <it>An. sinensis </it>host-seeking activity mainly occurred from 19:00 to 21:00. Thus, we propose that future vector control against <it>An. sinensis </it>and <it>Cx. tritaeniorhynchus </it>in the areas along the Huang-Huai River of central China should target the interface of human activity with domestic animals and adopt before human hosts go to bed at night.</p

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

Causes and Risk Factors of Non-traumatic Sub-arachnoid Haemorrhage among Patients at Kenyatta National Referral Hospital, Kenya

Background: Subarachnoid Haemorrhage (SAH) has been shown to have a global incidence of 2-49 cases per 100 000 population, and it is associated with a high morbidity and mortality. There is a scarcity of data regarding this condition in Kenya. This paper presents the causes and risk factors for this condition in patients presenting to our hospital. Methods: This descriptive cross sectional study was conducted in Kenyatta National Hospital in Kenya. All patients admitted between December 2010 and March 2011 with a diagnosis of SAH, were included in the study. A total of 55 patients with SAH were recruited in the study. Results: Slightly more females suffered from SAH than men, with a male: female ratio of 1: 1.1. The mean age was 47.6 years with a modal age group being 41-50 years. Intracranial aneurysms were seen in 29% of patients, the commonest location being in the anterior communicating artery (31%). Arterio-venous malformations were seen in 4% of patients. 51% of the patients had poorly controlled hypertension. Other risk factors included alcohol intake (31%), cigarette smoking (15%), and use of hormonal contraceptives was reported in 22% female study subjects. Conclusion: In our population, the commonest cause of spontaneous SAH is aneurysmal bleeds mainly in the anterior circulation. Further, most of the risks involved in causation of SAH are modifiable therefore interventions such as proper blood pressure control should be put in place so as to reduce the burden of this disease

Causes and Risk Factors of Non-traumatic Sub-arachnoid Haemorrhage among Patients at Kenyatta National Referral Hospital, Kenya

Background: Subarachnoid Haemorrhage (SAH) has been shown to have a global incidence of 2-49 cases per 100 000 population, and it is associated with a high morbidity and mortality. There is a scarcity of data regarding this condition in Kenya. This paper presents the causes and risk factors for this condition in patients presenting to our hospital. Methods: This descriptive cross sectional study was conducted in Kenyatta National Hospital in Kenya. All patients admitted between December 2010 and March 2011 with a diagnosis of SAH, were included in the study. A total of 55 patients with SAH were recruited in the study. Results: Slightly more females suffered from SAH than men, with a male: female ratio of 1: 1.1. The mean age was 47.6 years with a modal age group being 41-50 years. Intracranial aneurysms were seen in 29% of patients, the commonest location being in the anterior communicating artery (31%). Arteriovenous malformations were seen in 4% of patients. 51% of the patients had poorly controlled hypertension. Other risk factors included alcohol intake (31%), cigarette smoking (15%), and use of hormonal contraceptives was reported in 22% female study subjects. Conclusion: In our population, the commonest cause of spontaneous SAH is aneurysmal bleeds mainly in the anterior circulation. Further, most of the risks involved in causation of SAH are modifiable therefore interventions such as proper blood pressure control should be put in place so as to reduce the burden of this disease.East and Central African Journal of Surgery. 2011 Nov/ December;16 (3

Prevalence and Phylogenetic Diversity of Pathogenic Fusarium Species in Genotypes of Wheat Seeds in Three Rift Valley Regions, Kenya

Wheat is a source of nutrients for around 40% world’s population and the second most important cereal crop in Kenya. However, Fusarium head blight (FHB) hinders sustainable sufficient production of the crop, causing both economic and health losses. With the emerging unfavorable climatic changes, effective disease management strategies and adequate seed system are necessary to meet the deficiency. Current information on prevalence of the causative pathogens in varieties of wheat genotypes is a critical prerequisite to such strategies. This study aimed at determining the prevalence of pathogenic Fusarium species in seeds of developed varieties of wheat genotypes in three major wheat-producing regions in Kenya. A total of 260 samples of 18 wheat genotypes from 123 farms were collected. Peptone pentachloronitrobenze agar was used for fungal isolation, while identification of Fusarium spp. was based on the gene encoding translation elongation factor 1-α (tef1-alpha) sequence analysis. Fusarium spp. isolated include Fusarium poae, F. tricinctum, F. heterosporum, F. culmorum, F. equiseti, Fusarium sp., F. verticillioides, and F. oxysporum. There was no significant difference in prevalence of Fusarium spp. pathogens among the three regions studied. Fusarium spp. diversity index for Nakuru was 2.008, Narok was 1.4603, and Uasin Gishu was 1.2337. Wheat produce from farm-saved seeds yielded 66.25% of the isolates, while the produce from certified commercial wheat seeds yielded 33.75% of the isolates. The significant finding of the study is that Fusarium spp. associated with mycotoxins that contaminate the wheat food chain seem to be flourishing in all the sampled wheat seed genotypes from the regions studied. Information on the prevalence and diversity of the pathogens on persistence of the disease in the crop is critical in advancing integrative FHB control measures

The effect of host plants on Tetranychus evansi, Tetranychus urticae (Acari: Tetranychidae) and on their fungal pathogen Neozygites floridana (Entomophthorales: Neozygitaceae)

In a series of tritrophic-level interaction experiments, the effect of selected host plants of the spider mites, Tetranychus evansi and Tetranychus urticae, on Neozygites floridana was studied by evaluating the attachment of capilliconidia, presence of hyphal bodies in the infected mites, mortality from fungal infection, mummification and sporulation from fungus-killed mite cadavers. Host plants tested for T. evansi were tomato, cherry tomato, eggplant, nightshade, and pepper while host plants tested for T. urticae were strawberry, jack bean, cotton and Gerbera. Oviposition rate of the mites on each plant was determined to infer host plant suitability while host-switching determined antibiosis effect on fungal activity. T. evansi had a high oviposition on eggplant, tomato and nightshade but not on cherry tomato and pepper. T. urticae on jack bean resulted in a higher oviposition than on strawberry, cotton and Gerbera. Attachment of capilliconidia to the T. evansi body, presence of hyphal bodies in infected T. evansi and mortality from fungal infection were significantly higher on pepper, nightshade and tomato. The highest level of T. evansi mummification was observed on tomato. T. evansi cadavers from tomato and eggplant produced more primary conidia than those from cherry tomato, nightshade and pepper. Switching N. floridana infected T. evansi from one of five Solanaceous host plants to tomato had no prominent effect on N. floridana performance. For T. urticae, strawberry and jack bean provided the best N. floridana performance when considering all measured parameters. Strawberry also had the highest primary conidia production. This study shows that performance of N. floridana can vary with host plants and may be an important factor for the development of N. floridana epizootics. (C) 2011 Elsevier Inc. All rights reserved.Academy of Sciences for the Developing World (TWAS)Brazilian National Council for Scientific and Technological Development (CNPq)Norwegian Foundation for Research Levy on Agricultural Products (FFL)Agricultural Agreement Research Funds (JA)[190407/110

Social Support Mitigates Negative Impact of Food Insecurity on Antiretroviral Adherence Among Postpartum Women in Western Kenya

Food insecurity (FI), low social support, and low health-related quality of life (HRQoL) are associated with self-reported nonadherence to antiretroviral therapy (ART) among postpartum women, but these relationships have not been evaluated using objective adherence indicators. Hair samples were therefore analyzed among 83 postpartum Kenyan women living with HIV on efavirenz and nevirapine ART drug regimens in an observational cohort (NCT02974972). FI (0-27), social support (0-40), and HRQoL (8-40) in the prior month were also assessed. In multivariable models, each point increase in FI and decrease in HRQoL were associated with a 45.1% (95% CI:&nbsp;-64.3%,&nbsp;-15.6%) and 10.5% decrease (95% CI: 1.0%, 22.1%) in hair ART drug concentrations respectively, when social support was held constant. A significant interaction between social support and FI (β = 0.02, p = 0.017) indicated that greater social support was predicted to mitigate the negative impacts of FI on ART adherence. Addressing these modifiable barriers could improve ART adherence during this critical period