Experience in control of avian influenza in Africa.

The first outbreak of H5N1 highly pathogenic avian influenza (HPAI) in Africa was confirmed at Kaduna, Nigeria, on 8 February 2006. Within three months, seven other countries on the continent, Burkina Faso, Cameroon, Côte d'Ivoire, Djibouti, Egypt, Niger and Sudan, were infected. More recently Ghana and Togo became infected. The origin of the introduction of the disease to Nigeria and the other infected countries is still unknown, owing to lack of adequate tracing of the movements of poultry and poultry products and lack of reliable epidemiological data from the affected countries. The preventive measures adopted in countries free from H5N1 HPAI include selective or total bans on the importation of poultry and poultry products from infected countries. All the infected countries have implemented more or less the same internationally recommended disease control measures including quarantine, stamping-out and active surveillance, while poultry vaccination was carried out in Côte d'Ivoire and Egypt. These control measures, adopted and implemented by weak veterinary services, cannot explain the apparent 'epidemiological silence' of H5N1 HPAI in Africa, and further studies are needed to explain the different behaviour of the H5N1 HPAI virus in Africa and Asia.

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.

Xerovac: an ultra rapid method for the dehydration and preservation of live attenuated Rinderpest and Peste des Petits ruminants vaccines.

The accepted procedure for the long-term preservation of live viruses and bacteria in vaccines has been lyophilisation. We show that thermolabile viruses can be dehydrated in vitro, within 18 h, in an excipient containing trehalose. We further demonstrate that in the resulting dehydrated state, where the viruses are captive in a metastable glass composed of trehalose, they are capable of resisting 45 degrees C for a period of 14 days with minimal loss of potency. The degree of thermotolerance achieved matches that of current 'thermostable' lyophilised vaccines, but with the distinct advantage of a shorter, cheaper and simpler process. The development and utilisation of this process can make significant improvements in current live virus vaccine production. It presents a further step away from dependence on mandatory low temperature refrigerated storage and could lead to greater confidence in vaccine stability, potency and efficacy.

Late lesions of experimental contagious caprine pleuropneumonia caused by Mycoplasma capricolum ssp. capripneumoniae.

A clinical, bacteriological, serological and patho-anatomical study was carried out on 12 goats surviving the acute stage of contagious caprine pleuropneumonia (CCPP), experimentally produced with Mycoplasma capricolum ssp. capripneumoniae (M. capripneumoniae), with the major aims of investigating the chronic stage of the disease and elucidating the possibility of a carrier state beyond the acute fulminant phase. The goats were killed 9, 16, 82 or 126 days after the onset of acute clinical signs. On day 9, clinical signs included low grade fever and persistent coughing. Thereafter, only intermittent coughing was recorded. Serum titres of complement-fixing antibodies to M. capripneumoniae were high at the period of fever but dropped thereafter. Post-mortem examination showed acute fibrinous pleuropneumonia on days 9 and 16, and chronic pleuropneumonia on days 82 and 126, including sequester formations in goats killed on day 126. Mycoplasma capripneumoniae was isolated on days 9 and 16 but not on later occasions. The study showed that goats recovered from acute CCPP may have lesions for a long time thereafter but provide no evidence of a carrier state among long-term survivors.

Contagious bovine pleuropneumonia vaccines: the current situation and the need for improvement.

The control of contagious bovine pleuropneumonia (CBPP) has been clearly identified by the Organisation of African Unity/Inter-African Bureau of Animal Resources as a priority. In the first part of this article, the authors introduce the past and present vaccines, based on the two classic strains, T1, and KH3J. They describe the guidelines for vaccine production technology, and the quality control requirements for CBPP vaccines of the Office International des Epizooties. The failure of the currently used T1-SR vaccine to provoke satisfactory immunity in cattle, particularly in the newly infected areas of Africa, is pointed out. Other shortcomings of the current CBPP vaccines are also highlighted. Thus, there is a need to improve CBPP vaccines and the authors propose detailed emergency measures to address this problem. In the second part of the article, a subunit approach using immunostimulating complex technology is outlined. The authors emphasise the importance of current research in cell-mediated immunity and immunopathology, which is aimed at improving the efficacy of CBPP vaccines.

[Vaccination strategies for contagious bovine pleuropneumonia in Africa]. / Stratégies de vaccination contre la péripneumonie contagieuse bovine en Afrique.

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.

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.

Contagious caprine pleuropneumonia: some observations in a field vaccination trial using inactivated Mycoplasma strain F38.

The efficacy of an inactivated Mycoplasma strain F38-saponin vaccine in natural infection with contagious caprine pleuropneumonia was investigated. A total of 10,000 goats were vaccinated, out of which 400 were regularly monitored for a period of six months post-vaccination. Immunised animals remained free from infection throughout the period of observation. The antibody response was followed using complement fixation and slide agglutination tests. Both tests could detect F38 antibody in the majority of vaccinated goats but the slide agglutination test was found to be more sensitive than complement fixation. The significance of the results is discussed.

Detection of antibody to mycoplasma F38 in goat sera by an enzyme-linked immunosorbent assay.

An indirect enzyme-linked immunosorbent assay (ELISA) was developed to screen goat sera at a single dilution for antibody to mycoplasma F38. Antibody was detected in sera of six convalescent goats following experimental infection. Antibody was also detected in 34 sera three to four weeks after vaccination. No antibody was detected in 164 sera from goats without a history of vaccination or infection with contagious caprine pleuropneumonia. The ELISA was more sensitive than the complement fixation test in detecting antibody in vaccinated goats.