A mathematical model of the dynamics of scrapie in a sheep flock

A mathematical model is developed for the dynamics of an outbreak of scrapie in a single sheep flock with the aim of assisting the interpretation of field data. The model incorporates age structure of the sheep population, both horizontal and vertical transmission, genetic predisposition to infection, variable initial load of the infectious agent, and increasing infection load during an incubation period of the same order as sheep life expectancy. This leads to system of partial differential equations with respect to time, age and infection load. Numerical analyses using this model demonstrate that a scrapie outbreak is likely to be of long duration (several decades), will lead to reduction of scrapie susceptible allele frequency (but not to zero), and has different dynamics in homozygous and heterozygous susceptible sheep, even if these genotypes are equally susceptible, due to the different contributions of vertical infection to transmission to genotypes.     

Community analysis for health planning: strategies for primary care practitioners

Primary care practitioners have an important role in planning for the health of individuals and selected target populations. Community analysis and needs assessment are the first steps in health planning. Community analysis involves identifying health issues within a community; gathering data about the community, the target group, and the health concern; analyzing data; and assessing community needs. Community needs assessment involves identifying both existing and potential health problems as well as health promotion needs. By using appropriate skills in carrying out needs assessments, primary care practitioners become active contributors in planning for the health of individuals, groups, and the nation as a whole. This article provides strategies for identifying, analyzing, and evaluating the health needs of a community.     

Caesarean section in a pygmy hippopotamus (Choeropsis liberiensis) and the management of the wound

A laparohysterotomy was performed on a 17-year-old pygmy hippopotamus (Choeropsis liberiensis) to remove a dead over-sized fetus. The operation was successful and the animal recovered, but the surgical wound broke down and healed slowly by second intention.     

Realtime high resolution data acquisition unit for an MC68000 system

The general procedure for data acquisition in digital signal processing systems is to acquire a block of data and then analyse it. In a single-processor system, a considerable amount of data can be lost because, while data is being analysed by the processor, it is not sampled from the A/D converter. A dual-tasking machine has therefore been developed for continuous data analysis. The design requirements of the system are discussed. A block diagram of the system is presented, and the analogue-to-digital converter board is described in detail. The memory interchange board is also considered in depth.     

Kinetics and thermodynamics of emulsion delivery of lipophilic antioxidants to cells in culture

Oil-in-water emulsions are being used increasingly for the delivery of lipophilic drugs, but the fundamental physicochemical principles governing such delivery have not been explored. We determined the kinetics and thermodynamics of delivery from emulsions to cells in culture for two lipophilic compounds, U74006 and U74500. Two fundamental properties dominate the delivery, (a) the concentration of the compound in the lipid phase of the emulsion is directly proportional to the concentration of the compound in cells at equilibrium, and (b) the rate of transfer is directly proportional to the concentration of particles in contact with the cells. Thus, the transfer is consistent with direct partitioning from the lipid phase of the emulsion to cells and occurs by the direct collision of emulsion particles with cells. The details of the mechanism of delivery differ between the two compounds. Specifically, delivery of U74006 is first-order with respect to the drug accumulating in the cells. The transfer of U74500 is best described as a sum of two simultaneous pseudo first-order processes consistent with delivery from a single donor compartment to two receiver compartments. Furthermore, two molecules of U74500 appear to be involved in each transfer event. Our results show that relatively simple principles govern the delivery of compounds from oil-in-water emulsions to cells.