Mapping H5N1 highly pathogenic avian influenza risk in Southeast Asia.

The highly pathogenic avian influenza (HPAI) H5N1 virus that emerged in southern China in the mid-1990s has in recent years evolved into the first HPAI panzootic. In many countries where the virus was detected, the virus was successfully controlled, whereas other countries face periodic reoccurrence despite significant control efforts. A central question is to understand the factors favoring the continuing reoccurrence of the virus. The abundance of domestic ducks, in particular free-grazing ducks feeding in intensive rice cropping areas, has been identified as one such risk factor based on separate studies carried out in Thailand and Vietnam. In addition, recent extensive progress was made in the spatial prediction of rice cropping intensity obtained through satellite imagery processing. This article analyses the statistical association between the recorded HPAI H5N1 virus presence and a set of five key environmental variables comprising elevation, human population, chicken numbers, duck numbers, and rice cropping intensity for three synchronous epidemic waves in Thailand and Vietnam. A consistent pattern emerges suggesting risk to be associated with duck abundance, human population, and rice cropping intensity in contrast to a relatively low association with chicken numbers. A statistical risk model based on the second epidemic wave data in Thailand is found to maintain its predictive power when extrapolated to Vietnam, which supports its application to other countries with similar agro-ecological conditions such as Laos or Cambodia. The model's potential application to mapping HPAI H5N1 disease risk in Indonesia is discussed.

Epidemiology and Economics Support Decisions about Freedom from Aquatic Animal Disease.

In this study, we review the application of epidemiology and economics to decision-making about freedom from aquatic animal disease, at national and regional level, and recent examples from Europe. Epidemiological data (e.g. pathogen prevalence and distribution) determine the technical feasibility and cost of eradication. The eradication of pathogens which exist in wild populations, or in a latent state, is technically difficult, uncertain and expensive. Notably, the eradication of diseases of molluscs is rarely attempted because host populations (farmed and wild) cannot be completely removed from open water systems. Doubt about the success of eradication translates into uncertain ex-ante cost estimates. Additionally, the benefits of an official disease-free status cannot be estimated with any accuracy. For example, in Europe, official freedom from epizootic ulcerative syndrome and white spot syndrome virus has not been pursued, arguably because the evidence does not exist for the benefits (reduced risk of disease in wild populations) to be estimated and thus weighed against the costs of maintaining disease freedom (e.g. restriction on imports). Economic analysis must assess not only whether the benefits of disease freedom outweigh costs, but whether it is the economically optimal disease control option. Government may also want to compare investment in aquatic animal health with other opportunities. As resources become scarce, governments have sought to share costs of disease control with industry, and thus to ensure equity, the distribution benefits must be known so costs can be borne by those who benefit. The economic principles to support decisions about disease freedom are well established, but their application is constrained by lack of epidemiological data, which may explain the lack of economic analysis in support of aquatic animal management in Europe. The integration of epidemiology and economics in disease control planning will identify research aimed at improving the underpinning evidence base.

Epidemiology and control of east coast fever in Zambia. A field trial with traditionally managed Sanga cattle.

The main objective of the reported field trial was to compare different East Coast Fever (ECF) control strategies for their efficacy, effect on cattle productivity and cost-effectiveness. Five strategies were tested in groups of traditionally managed Sanga cattle over a period of 2.5 years. Two groups were under intensive tick control, one group immunized by the infection and treatment method and the other non-immunized. Two groups were under no tick control, one group immunized and the other non-immunized (the control group). The fifth group was under strategic tick control and was immunized against ECF. All ECF control methods tested significantly reduced mortality, but no marked differences to the control group were seen in other production parameters. No difference in mortality was observed between animals protected from ECF by immunization or by tick control. The most cost-effective method of controlling the disease was by immunization. A financial analysis showed that under the prevailing conditions the break-even price for immunization ranged from US$21.5 to US$25.7 depending of the proportion of reactors. The carrier state induced by immunization did not lead to a persistent high incidence of ECF in non-immunized animals using the same grazing area.

A global livestock production and health atlas (GLiPHA) for interactive presentation, integration and analysis of livestock data.

An interactive electronic atlas has been developed with the purpose of providing a scaleable overview of spatial and temporal variation in animal production and health-related information for decision and policy makers in national and international institutions. The information contained in the atlas is currently managed and presented using the Key Indicators Mapping System (KIMS), and will also be integrated using the Key Indicators Database System (KIDS). Both systems were developed by the World Agricultural Information Centre of the FAO (FAO-WAICENT), the former as a stand-alone application and the latter for access via the Internet. Components of the atlas include vector maps, livestock disease and production databases, rules for country-level disease risk classification and 'disease cards' containing basic background information on diseases included in the atlas. The disease data is currently based primarily on Office International des Epizooties (OIE) disease reports, and the livestock production data on the FAO-WAICENT database. The atlas is highly interactive and allows visual presentation of information using maps, tables and charts. It also contains links to relevant resource information on the Internet. Diseases covered in the animal health layer include most OIE List A diseases and a subset of OIE List B diseases. Extensive analyses have been conducted to develop a set of qualitative and semi-quantitative criteria that allow improved disease status classifications based on 5-years cumulative OIE disease reports, and official disease control declarations. Classification rules were determined depending on the epidemiological features of each disease and considering spatial heterogeneity of disease presence in local regions.

Effect of different East Coast fever control strategies on disease incidence in traditionally managed Sanga cattle in Central Province of Zambia.

A clinical trial, including five East Coast fever (ECF) control strategies (involving tick control and/or immunisation by infection-and-treatment) in five different groups of traditionally managed Sanga cattle, was conducted in Central Province of Zambia over 2.5 years between 1992 and 1995. Two groups were kept under intensive tick control by weekly acaricide treatment by hand spray; (one immunised and one non-immunised), two groups were under no tick control (one immunised and one non-immunised), and a fifth, immunised group was maintained under strategic tick control (18 sprays yr-1). ECF-specific mortality was highest in the non-immunised and non-treated group, while no difference in ECF-specific mortality could be observed between animals treated for ECF by immunisation or by tick control. Acaricide treatment and/or immunisation reduced the risk of clinical ECF by 92%. The results of an artificial challenge experiment at the end of the field trial indicated that about 60% of the animals in the control group had become infected with Theileria parva without showing clinical signs. ECF incidence in non-vaccinated cattle markedly declined six months after immunisation--suggesting that the carrier state induced by immunisation did not lead to a persistent high incidence, and might accelerate the progress to endemicity.

An outbreak of East Coast fever in a herd of Sanga cattle in Lutale, Central Province of Zambia.

An outbreak of East Coast fever (ECF) occurred in an experimental herd of Sanga cattle maintained under a traditional rangeland grazing system at Lutale, Central Province of Zambia. Two groups of cattle had been kept under different tick-control regimens for several years prior to the introduction of the disease and epidemiological information on the outbreak were recorded. Weekly tick control was no sufficient to achieve full protection against Theileria parva infection. Systematic body temperature monitoring seems to be a good method for early detection of infection resulting in an important reduction of the case fatality rate after treatment with anti-theilerial drugs.

Methods of economic impact assessment.

A broad framework for the assessment of the economic impact of animal diseases and control of these diseases is described. Various levels of analysis are discussed, from the herd, to the household, the sector, the nation and the region. For each of these levels, methods of economic impact assessment are outlined and discussed with respect to the objectives, data requirements and outputs of each type of assessment. In addition, the authors attempt to describe the conditions under which the various methods might be used. To conclude, a discussion of the state of the art is presented, and areas of further research are identified.

Inter-relationships of periparturient diseases in dairy cows.

The associations between periparturient diseases in 3603 lactations over three calving seasons were assessed on 10 dairy farms in the south west of England by using logistic regression. Calf mortality and dystocia were strongly associated. Twinning and dystocia were important predictors of calf mortality. Twinning was also a significant predictor for retained fetal membranes. Retained fetal membranes, twins, calf mortality and dystocia, in that order of importance, were risk factors for vulval discharge. Twinning, dystocia, retained fetal membranes and lameness before service increased the risk of mastitis before service. Similarly, mastitis and dystocia before service increased the risk of lameness before service. Oestrus was less likely to be observed in cows that had twinned or suffered lameness before service, the latter having a significantly greater influence in first calvers than older cows.

Blame apportioning and the emergence of zoonoses over the last 25 years.

Over the last 25 years zoonoses have emerged and re-emerged worldwide without a specific pattern or trend. The most recent ones (1998-2008) are geographically limited to Southeast Asia, making this salient region the most immediate culprit. The media, experts and politicians have helped shape public perceptions regarding the origin of emerging zoonoses. Assigning blame to certain countries or regions can results in social, political, cultural and economic consequences that turn out to be unjustified, unfair and ultimately detrimental.

The epidemiology of Newcastle disease in rural poultry: a review.

Rural poultry are the dominant form of poultry kept in the developing world. They are a natural resource whose potential is not fully exploited for the welfare of rural populations. The most devastating disease of rural poultry is Newcastle disease (ND). ND is an epidemic disease in intensive poultry and is responsible for high economic losses. Its epidemiology in intensive poultry is well understood, but little has been published on its behaviour in village poultry populations. Some research has been carried out during the past few years and it now appears that rural poultry are receiving increasing support for research and development from many government and international funding agencies throughout the world. All strains of Newcastle disease virus (NDV) occur in rural poultry, but velogenic strains are reported to be more common. Serological surveys in conjunction with isolation studies have shown that velogenic NDV strains are endemic in rural poultry populations even in isolated villages and possibly in isolated flocks. Although NDV is endemic in village poultry, the clinical disease usually follows an epidemic pattern. ND outbreaks often occur once or twice a year at regular intervals affirming the endemicity of the virus, however, 'mini' outbreaks in individual flocks and sporadic cases in individual birds may occur. Epidemics usually occur at times of climatic stress, leading to seasonal occurrence. The spread of NDV within and between village poultry populations is relatively slow due to a low contact rate. The major mode of transmission appears to be by the faecal-oral route. The respiratory route may also play a role in flocks where close bird-to-bird associations exist. Other poultry species, wild and feral birds, wild animals, communal water reservoirs and domestic animals may play a role in transmission; however, their role has not been properly investigated. In non-immune, intensively reared poultry, introduction of a sufficient quantity of virulent NDV is sufficient to cause severe outbreaks, but in rural poultry epidemic disease depends upon a number of factors. These include NDV pathotype, age structure and immunity of the host population, breed susceptibility, concurrent disease and seasonal influences. Although ND is endemic in rural poultry, many aspects of the epidemiology and economics of ND have not been fully understood. Well-designed, longitudinal studies made within a socio-economic framework are required to improve our understanding of the main problems of rural poultry systems.

Trypanosoma vivax in Colombia: epidemiology and production losses.

The present paper reports information obtained between 1982 and 1989 in the tropical lowlands of the Atlantic coast of Colombia. The studies confirmed that Trypanosoma vivax was widely but unevenly distributed within the study area and that incidence ranged from sporadic transmission to localised epidemics in which virtually all susceptible animals become infected within a period of 3 months. Quantitative epidemiological methods substantiated impressions of previous workers that T. vivax infections were associated with low-lying swampy areas and tabanid activity. Overt clinical trypanosomosis was rare in herds in which T. vivax was endemic. However, in these herds primary T. vivax infections were shown to cause subclinical alterations in calves. The infection consistently caused a temporary depression of packed cell volume (PCV) as well as a reduction in growth rate. There was no evidence of compensatory growth at a later stage.

Liveweight estimation of cattle by scale and by tape, a method comparison study.

The repeatability of weight estimation of cattle by scale and by tape and the agreement of weight estimates obtained by the 2 methods were evaluated. The within-subject standard deviation of replicates was used as a measure of repeatability while the agreement of the 2 methods was evaluated by analysis of the differences in weight estimates. In young cattle, the measurement error of the tape was about twice that of the scale while in adult cattle it was more than 4 times as great. Although weight estimates by the 2 methods were highly correlated, considerable differences occurred in individual cattle. The same was true for estimates of weight gain. It does not appear advisable to use the tape in trials where weight is an independent variable whereas the use of the tape can be justified in experiments where weight is the dependent variable.

Recurrence odds ratios for periparturient diseases and reproductive traits of dairy cows.

The recurrence odds ratios were calculated for a number of periparturient diseases and reproductive traits from 1490 pairs of successive lactations in dairy cattle. Vulval discharge, oestrus not observed and mastitis diagnosed before service had summary recurrence ratios of 1.39, 1.37 and 1.49 respectively, all statistically significant at the 5% level. Retained foetal membranes and calf mortality had higher summary risk ratios of 1.84 and 1.76 respectively, but were not significant at the 5% level. Whilst the number of services per conception did have a recurrence ratio above 1, the result was not significant at the 5% level.

Prevalence of piroplasmosis in equines in the Colombian province of Cordoba.

Eighty-two equine sera from 13 farms in northern Colombia were examined for antibodies to Babesia caballi and B. equi using the complement fixation (CF) and the indirect fluorescent antibody (IFA) test. Seroreactors to both piroplasms were present on all farms. The IFA test indicated a prevalence of 90% for B. caballi and 94% for B. equi. The CF test detected antibodies to B. caballi in 41% and to B. equi in 65% of the animals. The prevalence of seroreactors in different age groups revealed a significant decline in CF antibodies to B. caballi in animals older than three years. IFA titres for both Babesia spp. gradually declined with increasing age of the animals but were still present in most animals of the oldest age group (over nine years old). Anocentor nitens was found on all farms whereas Amblyomma cajennese was found only on two farms located on the coast.

Comparative studies of Trypanosoma (Duttonella) vivax isolates from Colombia.

The characterization of four Trypanosoma vivax isolates from Colombia in South America showed that although minor phenotypic differences existed between them, these parasites are antigenically related and belong to a single serodeme. Characterization by isoenzyme assay, karyotyping and DNA probe analysis, showed the Colombian isolates to be more similar to the West African than to Kenyan T. vivax. There was, however, little serological cross-reactivity between South American and African groups of T. vivax. Although the T. vivax isolates from Colombia were pathogenic for dairy calves which showed the typical sign of progressive emaciation, these parasites failed to infect mice or tsetse and could not be cultivated as bloodstream forms in vitro. This study represents initial attempts to establish the phenotypic and serological diversity amongst T. vivax isolates from South America.