Factors affecting sow and gilt efficiency in commercial piggeries in Zambia

The research looked for simple answers to simple problems in the Zambian commercial pig industry. Due to logistical difficulties of working in a developing country it was designed to be a project that could be carried out in the third world and which did not involve reliance on sophisticated machinery or techniques.Thesis (M.Ag.Sci.) -- University of Adelaide, Dept. of Animal Science, 199

Designing programs for eliminating canine rabies from islands: Bali, Indonesia as a case study

<p>Background: Canine rabies is one of the most important and feared zoonotic diseases in the world. In some regions rabies elimination is being successfully coordinated, whereas in others rabies is endemic and continues to spread to uninfected areas. As epidemics emerge, both accepted and contentious control methods are used, as questions remain over the most effective strategy to eliminate rabies. The Indonesian island of Bali was rabies-free until 2008 when an epidemic in domestic dogs began, resulting in the deaths of over 100 people. Here we analyze data from the epidemic and compare the effectiveness of control methods at eliminating rabies.</p> <p>Methodology/Principal Findings: Using data from Bali, we estimated the basic reproductive number, R0, of rabies in dogs, to be ~1·2, almost identical to that obtained in ten–fold less dense dog populations and suggesting rabies will not be effectively controlled by reducing dog density. We then developed a model to compare options for mass dog vaccination. Comprehensive high coverage was the single most important factor for achieving elimination, with omission of even small areas (<0.5% of the dog population) jeopardizing success. Parameterizing the model with data from the 2010 and 2011 vaccination campaigns, we show that a comprehensive high coverage campaign in 2012 would likely result in elimination, saving ~550 human lives and ~$15 million in prophylaxis costs over the next ten years.</p> <p>Conclusions/Significance: The elimination of rabies from Bali will not be achieved through achievable reductions in dog density. To ensure elimination, concerted high coverage, repeated, mass dog vaccination campaigns are necessary and the cooperation of all regions of the island is critical. Momentum is building towards development of a strategy for the global elimination of canine rabies, and this study offers valuable new insights about the dynamics and control of this disease, with immediate practical relevance.</p&gt

Model description.

<p>(A) Secondary cases are drawn from the (i) offspring distribution, and become infectious at a date drawn from the (ii) generation interval distribution: here four secondary cases are generated by the index case (black dot) which become infectious on day 14, 21, 23, and 35. The occurrence of secondary cases depends on vaccination coverage in the grid cell at the time of transmission. (iii) With probability 1–<i>p</i> each offspring occurs at a location generated from the local dispersal kernel (solid black arrows). (iv) With probability <i>p</i>, each offspring occurs on any randomly chosen grid cell (broken black arrow). It took 2.2 years for rabies to be detected in all nine Regencies (grey band), consistent with <i>p</i> = 0.05–0.09 (black dots are medians with 95% PIs from 100 simulations). See <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002372#pntd-0002372-t001" target="_blank">Table 1</a> for parameterization of distributions. (v) Human rabies deaths versus confirmed dog rabies cases, showing the best-fit relationship (black line, see <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002372#s3" target="_blank">Results</a> for equation) and 95% confidence intervals (grey area). (B) 95% PI envelope of simulated cases (grey area) with annual campaigns of the ‘random’ mass vaccination strategy (green line, <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002372#pntd-0002372-t002" target="_blank">Table 2</a>), which is rolled out when cumulative cases reach 7,000 and from which point the time to eradication is measured.</p

Rabies incidence and spread in Bali prior to island-wide mass vaccination.

<p>(A) Cases in humans and dogs and corresponding control efforts. (B) The month that rabies was first confirmed in each village. The black dot marks the village where the index case occurred. Regencies are outlined in black.</p

Key epidemiological and operational variables determining the success of rabies vaccination programmes in terms of the predicted probability of eradication (grey y–axis and line) and time to eradication (black y–axis, medians and 95% PI), showing sensitivity to: (A) the basic reproductive number, <i>R</i>₀, (B) vaccination coverage (achieved at the time and location of the campaign (see Fig. 4)), (C) annual dog population turnover, with conversion into birth/death rate assuming constant population size (birth rates equal to death rates), and (D) duration of immunity provided by vaccine.

<p>Based on 1000 simulations generated using parameters in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002372#pntd-0002372-t001" target="_blank">Table 1</a> (unless specified) and annual campaigns of the ‘random’ mass vaccination strategy (<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002372#pntd-0002372-t002" target="_blank">Table 2</a>).</p

Modelled vaccination strategies.

<p> All campaigns were annual unless specified in the analyses.</p

Vaccination strategies.

<p>The probability of eradication following: (Ai) 1; (Aii) 2; (Aiii) 3 campaigns under a range of coverages (40, 60, 80%) and inter–campaign intervals (0, 6, 12 months); (Aiv) vaccination as implemented on Bali, and projected from January 2012 when rabies was still circulating. The time to eradication (medians with 95% PI) for a range of: (B) frequencies of human–mediated transport of dogs (<i>p</i> = 0, 0.02 or 0.05) and campaign strategies (<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002372#pntd-0002372-t002" target="_blank">Table 2</a>). 95% PI of the one-month ‘sync’ strategy is highlighted (grey band) for comparison with the six–month strategies; (C) coverages when campaigns last 1 month or 6 months. (D) The probability of eradication with % island area left unvaccinated, made up of either randomly chosen 1 km squares (solid lines) or randomly chosen blocks, and when human-mediated movement of dogs was either infrequent (<i>p</i> = 0.02, grey) or frequent (<i>p</i> = 0.05, black).</p

Parameters values and distributions used to model rabid dog movement and transmission processes.

<p>Parameters values and distributions used to model rabid dog movement and transmission processes.</p