The 2006-2007 Rift Valley fever outbreak in Kenya: sources of early warning messages and response measures implemented by the Department of Veterinary Services

The authors characterised sources of early warning messages about occurrences of Rift Valley fever (RVF) and examined the response measures that were used by the Department of Veterinary Services (DVS) to manage the 2006-2007 RVF outbreaks in Kenya. The study was conducted between November 2009 and March 2010 and it included national, provincial and district veterinary officers who were involved in the management of the outbreak. Structured questionnaires were used to collect the data. Although the majority of the respondents reported having limited capacity to implement response measures, they perceived that the measures implemented were effective. Vaccination, movement control and market closures were the main response measures implemented, particularly in districts that had cases in both livestock and humans. Vaccination, however, was implemented too late and the coverage achieved was too low to be effective. The authors suggest ways to improve the capacity of the DVS to respond to similar outbreaks in the future.

More appropriate disease control policies for the developing world

Investment in disease control should be targeted to critical points that provide the greatest benefit to the livelihoods of livestock-dependent stakeholders. Risk-based targeting should balance the impacts of diseases against the feasibility of their control. This requires sensitive and specific surveillance systems that provide representative overviews of the animal health situation for accurate assessment of disease impact and transmission patterns. Assessment of impact should include household and market effects. The key in surveillance is involving livestock owners using active methods that ensure their disease priorities are addressed. Epidemiological targeting of interventions to critical points in disease transmission cycles should be done to obtain maximal disease reduction. Interventions should be delivered in full partnership with both private and community-based stakeholders to assure high uptake and sustainability. In developing countries, approaches such as participatory disease surveillance and community-based animal health programs have been effective and comply with international animal health standards.

Participatory epidemiology in disease surveillance and research

Participatory epidemiology is the application of participatory methods to epidemiological research and disease surveillance. It is a proven technique which overcomes many of the limitations of conventional epidemiological methods, and has been used to solve a number of animal health surveillance and research problems. The approach was developed in small-scale, community animal health programmes, and then applied to major international disease control efforts. The Global Rinderpest Eradication Program adopted participatory epidemiology as a surveillance tool for controlling rinderpest. This approach was subsequently used in both rural and urban settings in Africa and Asia, for foot and mouth disease, peste des petits ruminants and highly pathogenic avian influenza. Participatory disease surveillance has made an important contribution towards controlling both rare and common diseases. This paper reviews the principal applications of participatory epidemiology and highlights the lessons learned from field applications. In addition, the authors examine future challenges and consider new areas for research.

A heterogeneous population model for contagious bovine pleuropneumonia transmission and control in pastoral communities of East Africa

Pastoral cattle live in highly structured communities characterized by complex contact patterns. The present paper describes a spatially heterogeneous model for the transmission of contagious bovine pleuropneumonia (CBPP) developed specifically for pastoral communities of East Africa. The model is validated against serological data on the prevalence of CBPP infection in several communities of southern Sudan and against livestock owner information on community structure, livestock contact and cattle exchange. The model is used to assess the impact of alternative control strategies including mass and elective vaccination programmes, potential treatment regimes and the combination of vaccination and treatment in a single unified strategy. The results indicate that the eradication of CBPP using mass vaccination with currently available vaccines is unlikely to succeed. On the other hand, elective control programmes based on herd level vaccination, treatment of clinical cases or a combination of both vaccination and treatment enabled individual livestock owners to capture a large benefit in terms of reduced animal-level prevalence and mortality experience. The most promising intervention scenario was a programme which combined the vaccination of healthy animals with treatment of clinical cases.

A model of contagious bovine pleuropneumonia transmission dynamics in East Africa

The dynamics of contagious bovine pleuropneumonia (CBPP) transmission vary widely between livestock production systems. This paper describes the development of a homogeneous, stochastic, compartmental model for CBPP transmission in pastoral herds of East Africa. The model was built using parameter estimates based on data published in the literature and on observations of livestock owners obtained through participatory research. The basic reproduction number for CBPP in southern Sudan was estimated to range from 3.2 to 4.6. The homogeneous model indicates that the critical community size for the persistence of CBPP falls within the typical herd sizes for pastoral communities in East Africa suggesting that individual isolated herds are capable of maintaining infection indefinitely. Vaccination alone with currently available vaccines was unlikely to eradicate the disease.

Ex-ante economic analysis of animal disease surveillance

This paper provides an ex-ante economic analysis comparing four alternative intervention strategies for the control and eradication of rinderpest against a scenario of no intervention in a cattle population similar in size to that of Ethiopia. The interventions were three different coverage levels of mass vaccination and one surveillance-based programme where vaccination targeted infected sub-populations. For each scenario, the disease impact was estimated using an open-population, state-transition SEIR ('susceptible', 'exposed', 'infectious', 'recovered') disease transmission model with parameter estimates developed for lineage 1 rinderpest virus. Projected economic surplus gains and costs estimated from the rinderpest eradication programme in Ethiopia were analysed using benefit-cost methods. Social net present values (NPVs) and benefit-cost ratios (BCRs) were calculated. Although the economic model found that BCRs were greater than one for all interventions examined, the scenarios of intensive mass vaccination (75% vaccination coverage) and surveillance with targeted vaccination were economically preferable. The BCRs for these strategies were 5.08 and 3.68, respectively. Sensitivity analysis revealed that an increase in market prices for beef and milk increased the value of economic loss, the economic surplus and returns to investments in terms of NPVs and BCRs. An increase in demand and supply elasticities for beef and milk decreased the value of economic losses. This also had a negative effect on economic surplus and NPVs. The effect of an increase in the discount rate reduced returns to investments, with lower NPVs and BCRs. The authors note that 75% mass vaccination coverage was attempted in Ethiopia in the early 1990s, but failed to eradicate rinderpest because the approach was logistically too difficult to implement in practice. Subsequently, an effective surveillance and epidemiologically targeted vaccination programme was developed and has apparently resulted in the eradication of rinderpest from Ethiopia (the last case was recorded in 1996). The authors conclude that epidemio-surveillance with targeted vaccination is both an economically viable and realistic strategy and offers benefits that extend beyond rinderpest eradication.

Rinderpest surveillance performance monitoring using quantifiable indicators

This paper describes an objective system of monitoring the performance of disease surveillance. The system was developed through dialogue with a number of countries in Africa and adopted as part of the Global Rinderpest Eradication Programme of the Food and Agriculture Organization of the United Nations. The performance monitoring system uses a clinical stomatitis-enteritis case definition, an outbreak investigation classification scheme, and a series of eight performance indicators to measure the sensitivity, specificity and timeliness of the surveillance system. Field-testing indicates that the approach is successful when good record-keeping is practiced and highlights the importance of dialogue in helping to ensure that the system is simple and acceptable. The system provides a quantitative measure of the efficacy of national disease surveillance programmes and of the quality of data derived from such programmes for use in international disease control, animal health information exchange and trade risk analysis.

A model of lineage-1 and lineage-2 rinderpest virus transmission in pastoral areas of East Africa

The development of a stochastic, state-transition model of rinderpest transmission dynamics is described using parameter estimates obtained from both laboratory and participatory research. Using serological data, the basic reproduction numbers for lineage-1 rinderpest virus in southern Sudan and for lineage-2 rinderpest virus in Somali livestock were estimated as 4.4 and between 1.2 and 1.9, respectively. The model predictions for the inter-epidemic period in Sudan and Somalia (1.2 and 4.2 years, respectively) were in agreement with analysis of livestock-owner reports (1-2 years and 5 years, respectively).

Para-veterinary professionals and the development of quality, self-sustaining community-based services

Livestock are a major asset for rural households throughout the developing world and are increasingly regarded as a means of reducing poverty. However, many rural areas are characterised by limited or no accessibility to veterinary services. Economic theory indicates that primary level services can be provided by para-veterinary professionals working as private operators and as an outreach component of veterinary clinics and pharmacies in small urban centres. Experience from the development of community-based animal health worker (CAHW) systems indicates that these workers can have a substantial impact on livestock morbidity and mortality through the treatment or prevention of a limited range of animal health problems. Factors for success include community involvement in the design and implementation of these systems, and involvement of the private sector to supply and supervise CAHWs. Examples of privatised and veterinary supervised CAHW networks are cited to show the considerable potential of this simple model to improve primary animal health services in marginalised areas. An analysis of constraints indicates that inappropriate policies and legislation are a major concern. By referring to the section on the evaluation of Veterinary Services in the OIE (World organisation for animal health) Terrestrial Animal Health Code, the paper proposes guidelines to assist governments in improving the regulation, quality, and co-ordination of privatised, veterinary supervised CAHW systems.

Use of participatory epidemiology in studies of the persistence of lineage 2 rinderpest virus in East Africa

In 1994, rinderpest virus of African lineage 2 was detected in East Africa after an apparent absence of more than 30 years. In 1996, a disease search, based on participatory epidemiological techniques supplemented by serological and virological analyses, was undertaken in southern Somalia and north-eastern Kenya to collate past and current epidemiological information about rinderpest-compatible disease events, and to test the hypothesis that African lineage 2 rinderpest virus persists in populations of transhumant cattle in the Somali ethnic areas. The findings in Afmadu in Lower Juba led the search for rinderpest to the communities in the Bardera area and then on to the Kenya/Somalia border areas between Mandera and El Wak. The herders had a specific knowledge of the clinical signs of rinderpest and provided detailed and accurate descriptions of cases. They differentiated between classical acute rinderpest and a milder syndrome characterised by an ocular discharge and diarrhoea, few oral lesions, corneal opacity and occasional mortality. The studies provided evidence for the endemic occurrence of rinderpest back to at least 1981, with a periodicity of five years in the incidence of the disease. After a period of high mortality in 1992 to 1993, around Afmadu, herders reported a mild disease, with occasional increases in mortality, from other areas of Lower Juba and the Gedo Region. Reports by herders of a rinderpest-compatible disease in the El Wak area were pursued until active cases were located and rinderpest was confirmed.

Immunohistochemical detection of rinderpest virus: effects of autolysis and period of fixation

Samples of eyelid, tongue, soft palate and palatine tonsil were collected from calves infected experimentally with rinderpest virus. The tissues were fixed in 10 per cent neutral buffered formalin immediately, 24 or 48 hours post mortem. Then, after three days, 10 days, 28 days or three months in formalin, they were processed into paraffin blocks and examined immunohistochemically for rinderpest viral antigen. The tonsil was the best of the four tissues in providing a consistently positive immunohistochemical signal for the presence of virus, despite autolytic changes and/or prolonged fixation.

Antibodies to hemorrhagic fever viruses in domestic livestock in Niger: Rift Valley fever and Crimean-Congo hemorrhagic fever

A repository of domestic animal sera collected in Niger between 1984 and 1988 was assayed for antibody against two zoonotic hemorrhagic fever viruses known to be present in the West African Sahel. A total of 2,540 serum samples from 2,324 cattle, sheep, goats, and camels were tested by an IgG-specific enzyme-linked immunosorbent assay (ELISA) and the 80% plaque reduction neutralization test (PRNT80) for Rift Valley fever (RVF) virus antibody. Of the 2,540 sera tested for RVF-specific IgG antibody, 1,676 sera from cattle, sheep, and goats were examined for RVF-specific IgM antibody by ELISA. A subset of 2,263 sera were examined for evidence of Crimean-Congo hemorrhagic fever (CCHF) virus antibody by an IgG-specific ELISA. Antibody against CCHF virus was found to be most prevalent in adult cattle (422 of 732 or 57.7% positive) sampled at nine locations in the Niamey area. The highest prevalence for RVF neutralizing antibodies was found in camels from the Agadez Department with 67 (47.5%) of 141 positive. The results indicate that both CCHF and RVF viruses are circulating in Niger and are potential zoonotic health risks.

The use of thermostable Vero cell-adapted rinderpest vaccine as a heterologous vaccine against peste des petits ruminants

The thermostable Vero cell-adapted rinderpest vaccine was evaluated in terms of immunogenicity as a heterologous vaccine against peste des petits ruminants. A titration to establish the minimum immunising dose was performed in American mixed breed goats by vaccinating test subjects with dilutions of Vero cell-adapted rinderpest vaccine and then challenging 26 days later with virulent peste des petits ruminants virus. All animals were followed for virus neutralising antibodies against both rinderpest and peste des petits ruminants virus after vaccination and challenge. The antibody response to vaccination was primarily against rinderpest virus with very low levels of cross-reactivity to peste des petits ruminants virus. Following challenge, animals which possessed anti-rinderpest neutralising antibodies remained clinically normal but mounted strong anti-peste des petits ruminants virus neutralising antibody responses indicating that replication of challenge virus took place without the induction of illness. The 50 per cent minimum goat immunising dose was 3 tissue culture infectious doses 50 per cent (TCID50) as established by serological response and protection against challenge. The thermostable Vero cell-adapted rinderpest vaccine is a suitable immunogen for the protection of goats against peste des petits ruminants.

An immunohistochemical study of the pneumonia caused by peste des petits ruminants virus

Ten goats were inoculated with peste des petits ruminants virus, a paramyxovirus closely related to rinderpest virus. All goats developed severe clinical disease, 8/10 having coughing or dyspnea as prominent clinical signs. In addition, all of the goats had stomatitis and diarrhea. Histopathologic and immunohistochemical studies were done only on the respiratory tracts. Pathologic changes ranged from mild multifocal bronchiolitis and bronchitis to severe bronchointerstitial pneumonia. Lesions were more severe in anteroventral than caudal lobes. The histologic nature of the viral process in the goat lungs had many features in common with the processes of pneumonia in dogs, due to canine distemper, or pneumonia in human beings, due to measles virus. Immunohistochemical staining of formalin-fixed, paraffin-embedded respiratory tract tissue was performed using an indirect system with rabbit anti-rinderpest virus serum, biotinylated anti-rabbit antibody, streptavidin-alkaline phosphatase, and nitroblue tetrazolium chromogen. Staining was sensitive, highlighting the presence of viral antigen in both lung and trachea of all goats. Viral antigen was found in both cytoplasm and nucleus of tracheal, bronchial, and bronchiolar epithelial cells, type II pneumocytes, syncytial cells, and alveolar macrophages. In general, the amount of staining correlated directly with the severity of the inflammatory process.

The serological response to a thermostable Vero cell-adapted rinderpest vaccine under field conditions in Niger

A lyophilized thermostable Vero cell-adapted ringerpest vaccine, stabilized with lactalbumin hydrolysate and sucrose, was tested for safety, serological response and suitability for use with an abbreviated cold chain under field conditions in Niger. A total of 480 cattle, 90 goats and 55 sheep of unknown serological status were vaccinated on government ranches and observed for at least 22 days. No untoward effects of the vaccine were detected. The serological response to the vaccine stored at environmental temperatures for 30 to 34 days was determined in 144 previously unvaccinated yearling calves. Seroconversion was demonstrated in 98% of the yearling calves using seroneutralization. The un-refrigerated vaccine retained a titer of 3.69 log10 TCID50 per dose through day 34.

Comparison of the effect of various chemical stabilizers and lyophilization cycles on the thermostability of a Vero cell-adapted rinderpest vaccine

The thermostability of a rinderpest vaccine produced on Vero cells was evaluated using a variety of chemical stabilizers and lyophilization protocols. Three stabilizer preparations and three lyophilization schedules were examined using accelerated stability testing at 37 degrees C. The vaccine preparation exhibiting the greatest stability at 37 degrees C was tested at three additional temperatures, 42, 45 and 56 degrees C, and an Arrhenius plot was constructed from the data. The stability of the reconstituted vaccine produced with the two most efficacious stabilizers was examined using three different diluent preparations. The stabilization method and high Vero cell virus batch titers resulted in a lyophilized vaccine which maintained the minimum required dose of log10 2.5 TCID50 tissue culture infectious dose for more than 20 weeks at 37 degrees C.

Enhanced biliary bilirubin excretion after heparin-induced erythrocyte mass depletion

The effect of large-dose heparin therapy on erythrocyte mass depletion in ponies was investigated to determine whether stimulation of reticuloendothelial cell activity and catabolic function would be evidenced by enhanced catabolism of heme to bilirubin. Ponies with chronic external biliary fistula were used to examine biliary excretion of bilirubin both before and after heparin loading (107 U/kg, IV, plus 320 U/kg, subcutaneously) and at maintenance dosages of 320 U/kg given (subcutaneously) at 12 and 24 hours after initial loading with heparin. Results indicated that by 48 hours after ponies were first treated with heparin, catabolism of heme increased, resulting in a 35% increase in plasma bilirubin concentration and a 65% enhancement in biliary bilirubin excretion. During this period, both hematocrit and blood hemoglobin concentrations decreased by 35%. After the last heparin treatment at 24 hours after initial heparin loading, all measured variables returned toward base line within 48 hours. These studies indicated that heparin augments phagocytosis of erythrocytes, resulting in enhanced plasma bilirubin concentration and biliary bilirubin excretion.