Respiratory mycoplasmoses of cattle and goats with special reference to molecular epidemiology of contagious bovine pleuropneumonia in Tanzania.
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Date
2010
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Sokoine University of Agriculture
Abstract
The objective of this PhD study was to elucidate the mycoplasma flora in respiratory tract diseases of cattle and goats and to determine the genetic diversity among them. In a study of pneumonic lungs of Danish cattle, Mycoplasma dispar, M. bovis, M. bovirhinis, M. bovigenitalium and Ureaplasma spp. were the species encountered, predominantly occurring as mixed infections. There was a notable increase in prevalence ofM. bovis, thus calling for special attention upon this mycoplasma. Mycoplasmas belonging to the Mycoplasma mycoides cluster were not encountered in the examined lungs, suggesting that the Danish cattle population is still free from this group of mycoplasmas and that, it is not under special threat from contagious bovine pleuropneumonia (CBPP) if the Danish surveillance system for infectious diseases remains in place.
A study of the mycoplasma flora in the respiratory tract of indigenous cattle in selected regions of Tanzania revealed that Mycoplasma mycoides subsp. mycoides, Small Colony type (M. mycoides SC) was the predominant species affecting the animals, and thereby confirming that CBPP is the major respiratory mycoplasmosis of cattle in the study areas. A very low prevalence of M. arginini was recorded in cattle. Mycoplasma capricolum subsp. capripneumoniae (M. capripneumoniae), M. mycoides SC, M. ovipneumoniae and M. arginini were demonstrated in the respiratory tract specimens of goats originating from different regions of Tanzania. The isolation of M. capripneumoniae during outbreaks of caprine pleuropneumonia in the Coast and Morogoro regions confirmed the presence of contagious caprine pleuropneumonia (CCPP) in these regions. The demonstration of M. mycoides SC in goats with severe pleuropneumonia in the two regions suggests that this mycoplasma may be involved in the pathogenesis of the syndrome, and that goats may play a
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significant role in the epidemiology of CBPP if cross-transmission of the mycoplasma from cattle and goats and vice versa, does efficiently occur.
Amplified fragment length polymorphism (AFLP) fingerprinting of 42 M. bovis strains isolated from Danish cattle from 1981 to 1998 revealed a remarkable homogeneity among them. An epidemiological link between two separate outbreaks of M. Aov/'s-induced mastitis was demonstrated. The association between the first three strains ofAY. bovis isolated in 1981
and those isolated from various disease syndromes in different parts of the country in subsequent years was evidenced by the strong genomic similarity between them. AFLP and pulsed-field gel electrophoresis (PFGE) showed that genomic heterogeneity was more evident among M bovis strains isolated after 1991, probably indicating different origins from
those isolated before. The AFLP and PFGE profiles of M. bovis type strain (PG45T) were different from those of the field strains.
AFLP and PFGE analysis of 56 field strains of M mycoides SC isolated from cattle in six regions of Tanzania revealed a strong genomic homogeneity among them, which was highly suggestive of a common epidemiological source. This finding supports the idea that nearly all CBPP outbreaks in Tanzania since 1990 are due to spread of one particular epidemic clone of M mycoides SC, and it implies that it would have been possible and cheap to prevent the
spread of the disease if appropriate control measures were instituted to contain the initial outbreaks. Strains from Tanzania, Kenya, Botswana and Portugal displayed different genomic profiles, reflecting diversity in their epidemiological origins. In addition, the genomic difference between the Portuguese strain and those from Tanzania, Kenya and Botswana affirmed the separate clustering of the African and European strains of M
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mycoides SC. The type- (PG1T) and vaccine- (T1.SR49) strains showed indistinguishable AFLP profiles but exhibited different PFGE profiles, which were also different from those of the field strains. The genomic difference between the vaccine- and the field strains probably indicates that a genetic drift has occurred in the field strains, enabling them to avert the protective effects of the vaccine. Hence, the poor efficacy of the vaccine reported in eastern and southern Africa.
A strong genomic homogeneity was demonstrated among strains of M. capripneumoniae isolated from outbreaks of CCPP in Tanzania when analysed by AFLP and PFGE, suggesting a common epidemiological source. Genomic homogeneity was also evident among Tanzanian-, Kenyan- and Ugandan strains of M. capripneumoniae, supposing that cross- border transmission of CCPP between these countries was possible. However, subtle differences were also discernible among some Tanzanian and Kenyan strains of M capripneumoniae, probably indicating different evolutionary lineages or epidemiological origins of the strains. The AFLP profile of the type strain ofM capripneumoniae (F38T) was different from those of the field strains. PFGE analysis did not unveil genomic differences among the strains of M. capripneumoniae analysed. This may be due to the inherent strong homogeneity among the strains, but it may also be indicative of the limited discriminatory power of the protocol used for this mycoplasma, and therefore, suggesting further evaluation of the protocol using different restriction enzyme combinations and electrophoresis parameters in order to increase its discriminatory power.
Strains of M. mycoides SC isolated from goats with respiratory tract disease including cases of severe fibrinous pleuropneumonia in three regions of Tanzania exhibited indistinguishable
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AFLP and PFGE profiles, except for one strain which differed from the rest at only position. The AFLP and PFGE profiles ofM. mycoides SC from goats were indistinguishable from those isolated from CBPP-affected cattle in the same regions, suggesting a probable cross transmission of the mycoplasma between the two animal species especially because, in most
parts ofthe country, cattle and goats are reared together.
In conclusion, this work has demonstrated that mycoplasmas play a significant role in the aetiology of respiratory tract diseases of cattle and goats, thus emphasizing the need to control them. Furthermore, a strong intraspecies homogeneity has been demonstrated among strains of M. bovis, M. mycoides SC and M. capripneumoniae isolated from diseased cattle
and goats, which is strongly indicative of close epidemiological relatedness, and most likely common origins of the strains. This implies that it would have been possible to prevent the spread of these infections if effective surveillance and control programmes were in place. Thus, a review of the effectiveness of the existing disease surveillance systems is recommended. Moreover, the study has demonstrated that AFLP and PFGE can be used as additional tools in molecular epidemiological studies of mycoplasma infections in cattle and
goats. However, because the methods demonstrated variable levels of discrimination among strains of the mycoplasma species analysed, further studies are recommended to improve their discriminatory power.
Description
Dissertation
Keywords
Respiratory Myco Plasmoses, Cattle, Goats, Special Reference, Molecular Epidemiology, Contagious Bovine Pleuropneumonia, Tanzania