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Biomedical subjects

M M Rweyemamu

Publications and source records attributed to M M Rweyemamu.

At least 19 recordsLinked to original sources
PubMed2005

Evaluation of the xerovac process for the preparation of heat tolerant contagious bovine pleuropneumonia (CBPP) vaccine.

The study was conducted with the aim of evaluating the xerovac process as a method for preparing contagious bovine pleuropneumonia (CBPP) vaccine with increased heat resistance. The thermo-protective effects of various concentrations of trehalose in mycoplasma growth medium, various concentrations of trehalose in the dehydration stabilizer and the importance of some divalent cations were assessed. The results obtained indicate that a rapid dehydration of CBPP vaccine following the xerovac method and in an excipient composed of a high concentration of trehalose, renders the product more heat tolerant than a similar vaccine prepared using a regular or an extended freeze drying regime. It was also demonstrated that the addition of chitosan as a mycoplasma precipitating agent conferred additional heat resistance to the vaccine. It is suggested that the application of the xerovac process in the dehydration of CBPP vaccine offers the advantages of a faster, cheaper and easier process over the conventional dehydration methods like freeze drying.

Animals↗
PubMed2002

The control of rinderpest in Tanzania between 1997 and 1998.

In January 1997, Tanzania requested international assistance against rinderpest on the grounds that the virus had probably entered the country from southern Kenya. Over the next few months, a variety of attempts were made to determine the extent of the incursion by searching for serological and clinical evidence of the whereabouts of the virus. At the clinical level, these attempts were hampered by the low virulence of the strain, and at the serological level by the lack of a baseline against which contemporary interpretations could be made. Once it became apparent that neither surveillance tool was likely to produce a rapid result, an infected area was declared on common-sense grounds and emergency vaccination was initiated. The vaccination programme had two objectives, firstly to prevent any further entry across the international border, and secondly to contain and if possible eliminate rinderpest from those districts into which it had already entered. On the few occasions that clinical rinderpest was subsequently found, it was always within this provisional infected area. Emergency vaccination campaigns within the infected area ran from January to the end of March 1997 but were halted by the onset of the long rains. At this time, seromonitoring in two districts showed that viral persistence was still theoretically possible and therefore a second round of emergency vaccination was immediately organized. Further seromonitoring then indicated a large number of villages with population antibody prevalences of over 85%. These populations were considered to have been 'immunosterilized'. Although no clinical disease had been observed in them, it was decided to undertake additional vaccination in a group of districts to the south of the infected area. Serosurveillance indicated that rinderpest could have been present in a number of these districts prior to vaccination. Serosurveillance in 1998 suggested that numerous vaccinated animals had probably moved into districts outside the infected and additional vaccination areas, but did not rule out the continued presence of field infection.

Animals↗
PubMed2002

Global perspective for foot and mouth disease control.

The world distribution of foot and mouth disease (FMD) is almost a mirror image of the global economic structure. In general, industrialised countries are free while the disease is endemic in developing countries. In recent years, several incursions of FMD have been recorded in countries belonging to the Organization for Economic Co-operation and Development (OECD), all of which have been financially and socially costly to eliminate. At the same time, this single disease bars many developing countries from participation in formal trade, both regionally and internationally. However, recent studies have predicted an unprecedented high demand for animal protein, which can only be met through enhanced participation of developing countries in trade in livestock products. Accordingly, globalisation trends will exacerbate the exclusion of poor communities and countries from markets unless a long-term strategy is implemented to progressively build market opportunities for these countries, without placing the livestock of industrialised countries at undue risk from FMD and other major transboundary animal diseases. The authors submit that there is sufficient knowledge of FMD to make an international initiative for the progressive control of FMD a viable objective. Consequently, a four-stage pathway is proposed for developing a global FMD programme. The proposed strategy involves a build-up of the epidemiology and global status of FMD, including establishing an international early warning system, a risk-reduction phase to lower the incidence of FMD in the primary endemic areas and a control phase leading to the creation of zones of assured FMD-freedom. The authors also propose that an international FMD programme be co-ordinated, based on the experience of the Global Rinderpest Eradication Programme, the Hemispheric Plan for the eradication of FMD for the Americas, the South-East Asia Foot and Mouth Disease control and eradication campaign and the European Commission for the Control of FMD.

Animals↗
PubMed1999

Disease prevention and preparedness: the Food and Agriculture Organization Emergency Prevention System.

In 1994, the Food and Agriculture Organization undertook to revitalise its activities in the control of transboundary animal disease by establishing a new special programme known as the Emergency Prevention System (EMPRES) against transboundary animal and plant pests and diseases. The emphasis of the EMPRES livestock component is placed on pre-empting outbreaks and losses experienced by agriculture through the enhancement of local capacity to detect and react rapidly to plague events. EMPRES concentrates on the co-ordination of the Global Rinderpest Eradication Programme--a time-bound eradication programme--whilst addressing the progressive control of the most serious epidemic diseases within a broad framework of emergency preparedness. Programme activities are discussed in relation to early warning, early reaction, facilitating research and co-ordination. In addition to rinderpest, particular attention has been paid to contagious bovine pleuropneumonia, a re-emerging disease in Africa targeted for strategic attention, and foot and mouth disease, for which co-ordinated regional control in Latin America and South-East Asia has been initiated. Tactical responses to other disease emergencies such as African swine fever, classical swine fever (hog cholera), Rift Valley fever, peste des petits ruminants and lumpy skin disease are described.

Animal Diseases↗
PubMed1995

Contagious bovine pleuropneumonia vaccines: the need for improvements.

Contagious bovine pleuropneumonia (CBPP) vaccines are routinely used only in Africa. The vaccines are usually produced from one of two strains (T1/44 and KH3J), each of which has a streptomycin-resistant variant. The necessity for a 'master seed strain' is evident. At least one manufacturer in Africa produces a broth culture vaccine, while others produce a freeze-dried product. A standardised manufacturing protocol needs to be developed, together with in-process and final product quality control procedures. Some CBPP vaccine manufacturing procedures do not allow sufficient leeway for the execution of typical quality control practices. For example, it is difficult to perform batch testing on broth culture vaccine, as the vaccine is produced in its final container. Quality control test results from the Pan African Veterinary Vaccine Centre (PANVAC) are analysed in terms of causes of batch failure and indicators for process development. Taking potency as an example, most vaccine batches tested by PANVAC pass only at the limit of the OIE minimum requirement of 10(7) colony-forming units per dose. To improve the titre of the vaccine, it will be necessary to modify the manufacturing process, either by increasing mycoplasma yield during the culture phase or by minimising losses during downstream processes, especially freeze-drying. Data on inactivated vaccines are scarce. Duration of the immunity achieved with live CBPP vaccines is relatively short, in comparison with other live vaccines. Data may be required on the molecular basis of virulence and immunogenicity, as well as on the molecular immunology of CBPP, to enable the development of improved vaccines.

Animals↗
PubMed1995

Regulatory framework and requirements for managing risks associated with veterinary biological products in Africa: present systems and future needs.

Veterinary vaccines are considered to be medicinal products. As such, they are subject to assessment for managing risks associated with their marketing and use. The current risk assessment procedures used in Africa are based on the quality testing methods standardised by the Pan-African Veterinary Vaccine Centre (PANVAC). The authors examine the risk assessment procedures related to the importation of products and to the release of live products into the environment. The lack of infrastructures, specialised personnel and financial resources prevents each individual country from establishing its own system for managing the risks associated with the importation of veterinary vaccines. Regional co-operation between African countries is therefore recommended, and must be based on the existing PANVAC network for the quality testing of priority vaccines. This is justified by the results obtained by PANVAC in the standardisation of production technologies for vaccines against rinderpest and contagious bovine pleuropneumonia, and in other areas. The authors recommend that PANVAC be used to aid regional co-operation in Africa in the management of risks associated with the marketing and use of veterinary vaccines.

Africa↗
PubMed1995

[Vaccination strategies for contagious bovine pleuropneumonia in Africa].

Contagious bovine pleuropneumonia (CBPP) is regarded as the second most important disease of cattle in Africa. The disease was eradicated from Europe through drastic slaughter campaigns with quarantine and restriction of cattle movements. CBPP was mastered in Australia using these methods combined with vaccination. However, the disease remains endemic in Asia and Africa, where it inhibits livestock farming. In these continents, vaccination is the preferred means of control; the aim is to reduce incidence until complementary disease control measures can be applied. The success of a vaccination campaign depends on four main factors: good planning and good organisation; staff who are well-trained, fully equipped and highly motivated; high quality vaccines; good international co-operation. Vaccine strains recommended for use in Africa are strain T1/44 and its variant T1-SR. To improve the immunogenicity of these strains, the Pan African Rinderpest Campaign (PARC) secured financial support for research into immunostimulating complexes (ISCOM). It is hoped that this technology can improve vaccines, leading to effective eradication of the disease. In the meanwhile, systematic and repeated vaccination is the method of choice against CBPP in Africa.

Africa↗
PubMed1993

Immune response in cattle induced by inactivated rabies vaccine adjuvanted with aluminium hydroxide either alone or in combination with avridine.

In a comparative study of two commercial baby hamster kidney rabies vaccines produced in Brazil, the authors were able to demonstrate the following: a) both vaccines provoked a high level of antibody response and protection against challenge in cattle b) in primary vaccination, at least, the addition of avridine (a synthetic lipoidal amine) enhances the immune response in terms of the level and persistence of antibody c) over 90% of cattle vaccinated with either vaccine were protected against experimental challenge one year after revaccination, and the antibody response profile indicated that these vaccines were capable of maintaining antibody titres above protective levels for more than two years after revaccination. On the basis of these results, the authors recommend optional revaccination of young animals (i.e. "primo-vaccinates") at six months of age. Thereafter, annual revaccination should be sufficient to ensure high levels of antibody between vaccination cycles.

Adjuvants, Immunologic↗
PubMed1990

Incidence, epidemiology and control of bovine virus diarrhoea virus in South America.

Outbreaks of diarrhoea associated with mucosal erosions of the mouth, tongue and digestive tract, clinically diagnosed as bovine virus diarrhoea-mucosal disease (BVD-MD), have been reported in Argentina and Brazil since the 1960's. However, primary isolation of the virus of BVD-MD is fairly recent, occurring in 1974 for Brazil, 1984 for Argentina, 1985 for Chile and 1981 for Colombia. In Argentina both cytopathogenic and non-cytopathogenic BVD virus strains have been identified. Elsewhere in South America this differentiation does not seem to have been carried out. Serological surveys have confirmed the existence of BVD virus infection in six countries (Argentina, Brazil, Chile, Colombia, Peru and Uruguay), with an incidence rate ranging between 37 and 77% of cattle in the areas surveyed. Diarrhoea in calves between 3 and 18 months of age, often associated with mucosal erosions, has been the most commonly observed syndrome. In some cases an upper respiratory tract involvement was described. In one epizootic, in the Sabana de Bogota plateau of Colombia, reproductive failure associated with abortions or birth of weak calves was the main clinical syndrome.

Animals↗
PubMed1986

Foot-and-mouth disease vaccination: a multifactorial study of the influence of antigen dose and potentially competitive immunogens on the response of cattle of different ages.

Groups of 68 and 66 cattle aged 12 and 24 months respectively were each subdivided into 16 groups and inoculated with foot-and-mouth disease vaccines containing O1 Campos, A24 Cruzeiro and C3 Pando virus strains. The 140S antigen mass of the O1 and A24 valencies was varied while that of C3 was held constant. Multifactorial comparisons between the 21 day serum neutralising antibody titres showed that over most of the range there was a linear log dose response relationship. Doubling the antigen dose increased the serum antibody titres against both A24 Cruzeiro and O1 Campos by approximately 0.15 log10. The A24 antigen was about 30 times more immunogenic than the O1 with C3 intermediate between the two. At high antigen doses the responses flattened but the level at which this occurred depended on the immunogen administered. No difference could be demonstrated between the responses of 12- and 24-month-old cattle and there was no evidence of competitive inhibition or enhancement between the virus strains included in the vaccines.

Aging↗
PubMed1986

Efficacy of avridine as an adjuvant for Newcastle disease virus antigen in chickens.

Avridine, a lipoidal amine with interferon-inducing and adjuvant properties, was an effective adjuvant for Newcastle disease antigen (NDA) in chickens. Eleven vaccine lots were evaluated: 2 commercial water-in-oil vaccines, 4 experimental oil emulsion vaccines, 4 avridine-containing vaccines, and a control lot of nonadjuvanted antigen. Avridine significantly enhanced the immunologic responses of chickens against NDA. Chickens vaccinated with the avridine-containing vaccines had significantly higher antibody titers (hemagglutination inhibition) than did chickens vaccinated with the commercial vaccines. Experimental oil emulsion vaccines prepared from the same antigens as avridine-adjuvanted vaccines induced higher hemagglutination inhibition antibody titers after primary but not after booster vaccination. Use of avridine as an adjuvant for NDA in vaccines for chickens induced immunologic protection rates similar to those induced by oil emulsion vaccines, without causing the reactogenic and tissue residue problems associated with the use of oil vaccines in chickens.

Adjuvants, Immunologic↗
PubMed1984

The effect of antiserum quality on strain specificity assessment of foot and mouth disease virus by the neutralization reaction.

The factors affecting the virus strain specificity of antibody to foot an mouth disease virus prepared by a variety of protocols in several species were evaluated by neutralization tests. The time at which the serum was taken, the antigen dose given, whether or not revaccination had occurred and the animal species in which the sera were prepared, did not appear to affect the strain specificity of serum prepared to inactivated antigens when measured in neutralization tests, probably because of the restricted nature of the antigenic site involved. However, variation was observed with convalescent animal sera or sera from animals which had received trypsin cleaved virus were used. For these reasons banks of reference antisera are prepared as pooled sera using one or two inoculations of inactivated antigen.

Animals↗
PubMed1984

Antigenic variation in foot-and-mouth disease: studies based on the virus neutralization reaction.

The neutralization reaction is the most appropriate in vitro reference test system for assessing intratypic antigenic variation as it involves the antigenic determinants responsible for virus strain specificity and evoking protective antibody. Antigenic relationships determined in different neutralization test systems were independent of the system used and were assumed to truly reflect antigenic variation. The two-dimensional microneutralization test was found to be appropriate for foot and mouth disease (FMD) virus strain differentiation. To minimize test to test variation, comparisons are performed as matched pairs. The pooled variance of the test system is used to assess the significance of the relationships obtained. Antisera from convalescent animals were less specific than those from vaccinates. Serum quality seemed less critical for the virus neutralization than the complement fixation reaction. A system for FMD virus strain differentiation based on the use of the virus neutralization reaction taking into account the statistical and biological significance of observed r values is recommended.

Animals↗
PubMed1984

The relationship between the 140S antigen dose in aqueous foot-and-mouth disease vaccines and the serum antibody response of cattle.

Groups of eight or 12 cattle were injected with dilutions of aqueous saponized vaccines containing 329 760 to 7 ng of 140S O1BFS 1860 strain foot-and-mouth disease antigen per dose. Four months later the animals were subdivided into groups of four and revaccinated with vaccines containing 329 760, 9160 and 42 ng of antigen per dose. Responses were established by taking serum samples from the animals periodically and examining these for neutralizing antibody activity. The results showed that after primary vaccination the dose of antigen in vaccines influenced the earliest time of protection, the peak antibody titres attained and probably, the duration of immunity. At 21 days after vaccination the log antigen-antibody response slope was linear between 7 and 9, 160 ng, with an inclination of 0.53, indicating that every doubling of the vaccine antigen dose produced an increase of 0.16 log10SN50 in the mean serum antibody titre. The secondary response was influenced by the antigen dose in the second vaccination and to a lesser extent by that in the first vaccination also.

Animals↗