Tjipura-Zaire, Georgina Ndjambi (2019) Experimental study on vaccines : 'Mycoplasma mycoides' subsp. 'mycoides' small colony type biofilm. Diagnostic techniques and humoral immune response in contagious bovine pleuropneumonia cattle in Namibia. (PhD thesis), Kingston University, .
Abstract
The control of contagious bovine pleuropneumonia (CBPP) has been identified as a priority by the Organisation of African Union/Inter-African Bureau of Animal Resources. This project aimed to address some of the issues associated with the diagnosis and control of CBPP infections in cattle. Experimental studies tested current and novel vaccines which were used to provide more information about the importance of humoral immune response to CBPP and assess current and new diagnostic tests. Differences between infections caused by planktonic and biofilm grown isolates were also studied to assess if biofilm grown cells remain infective or are more virulent. Two novel vaccine formulations, one consisting of five purified proteins and one using tween 20 washed cells, both formulations were combined with a commercial adjuvant designed to help stimulate the potentially prectective Th2 response. These novel vaccines efficacy was compared with the current T1/44 vaccine given subcutaneously as recommended, or intranasally to determine if that inoculation route stimulates a protective mucosal immune response. Six weeks after vaccination, the cattle were “in-contact” challenged using experimentally infected cattle. A total of 45 cattle of Sanga and Africaner breeds were randomly selected from a CBPP free area and ear tagged for identification. Five cattle per vaccine (T1/44 sub-cutaneously, T1/44 intranasally, Purified Protein and Tween 20) were vaccinated six weeks prior to placing them with 5 non-infected control cattle and 10 cattle endobronchially intubated with a local Mmm field strain 40F05. After 122 days the cattle were sacrificed and gross pathology compared at post mortem. The T1/44 vaccinated cattle had some small CBPP lesions but much less than the two novel vaccines. Both the Purified Protein and Tween 20 vaccines elicited low protection and in some cattle they appeared to have exacerbated the disease as their pathological lesions were comparable to the non-infected in-contact CBPP challenged control cattle. At the same time a study was carried out to determine if a biofilm prepared isolate would be more pathogenic than one grown conventionally. Five cattle were endobronchially intubated with Mmm biofilm and housed together with 5 non-treated control cattle for the same duration as mentioned above. The biofilm intubated group appeared less pathogenic than the comparative planktonic intubated group although some of the biofilm in-contact group succumbed to CBPP. Serological results obtained during the experiment were evaluated in four different tests, Lateral Flow Device (LFD), Competitive Enzyme Linked Immunosorbent Essay (cELISA), Lipoprotein Q Enzyme Linked Immunosorbent Essay (LPPQ ELISA) and Latex agglutination test (LAT). The results demonstrated that LFD is a promising field test at a cut-off point of 30%, but current serological tests are ineffective at detecting all stages of CBPP infection. Furthermore, serological results were used to establish the importance of humoral immune response in protection. A high response to IgA (Immunoglobulin subclass A) in an indirect ELISA was observed in sera from chronically infected animals. This suggests that a high IgA immune response is an indication of disease progression. Additionally, proteins with a molecular mass of 110, 95 and 48 kDa may be important part of the protevtive immune response since these proteins were present in T1/44 sub-cutaneously vaccinated cattle that had less CBPP lesions than the other groups. Further work is required to improve serological detection of CBPP and to develop more effective vaccines to help control the disease.
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