| Coccidiosis is a disease of major economic importance to the poultry industry. Control of the disease is presently accomplished by prophylactic chemotherapy, but the rapid emergence of drug-resistance parasites, coupled with the difficulty and expense of developing new drugs and specially the increasing public awareness of the drug residues, has led to a search for new approaches to coccidiosis control, such as development of effective vaccines. But the efficiency of vaccines was varied, which may be caused by the antigenic diversities between the strains of field and vaccine. Eimeria maxima is one of the most common species of coccidian occurring in flocks all over the world, and it is the most immunogenic of the seven species of Eimeria that infected the domestic chicken, and has also been demonstrated to be partial immunity to other species. As a result, E. maxima is almost included in all type of vaccines. Paradoxically, immunological differences within the strains of E. maxima are common, which led to a failed immunization. So the design and application of vaccine depend on the studies of strains isolated from the different regions, especially the analysis of antigenic patterns and its molecular background.E. maxima has been diagnosised from poultry farms in twenty-five provinces in China, but there were litter reports on molecular biology of E. maxima, and the strains that could be used to study also were not enough. The comparative studies between strains have not been reported in China. The eleven strains were therefore isolated from fields in Jiangsu, Anhui, Shandong, Guangdong, Fujian and Shanghai and a coccidiosis vaccine made in USA, and a scientific research was commenced here on purpose to clarify the biological characteristics of E.maxima, and to explore the antigenic patterns of E. maxima which were prevalent in major regions of poultry industry as to provide the theoretical directions for the application of vaccines, specially those introduced from outside, and to analyse the genetic relations among these strains and try to find out the molecular basis, and provide the suitable strains for the design of vaccines and other researches such as anti-drugs, immunology, genetics and molecular biology. The results could also enrich the contents of avian coccidiosis.1 Isolation and biological characterization of eleven geographical strains of Eimeria maximaUsing single oocyst infected techniques, eleven pure species were isolated from ten geographical regions in Jiangsu, Anhui, Shandong, Guangdong, Fujian and Shanghai in China and a coccidiosis vaccine made in USA, and all found to be Eimeria maxima (Tyzzer,1929) according to the seven criterion. Data including thickness of wall, length and width of oocyst and sporocyst, and shape index were subjected to analysis with Duncan's multiple range test. Results demonstrated that there were significant differences between the strains from USA and from China. Under the light and scanning electron microscopy, the oocyst structures of eleven strains were similar, and there was a micropyle on the wall.2 The pathogenicities of eleven geographical strains of Eimeria maximaSuqiu Yellow chickens were used to study the pathogenicities of eleven geographical strains of E. maxima, assessed by weight gain, lesion score and mortality. The results were as follows: The body weights in all infected groups were affected, and except the groups at 0.1 104 bird-1, the weight gains were significantly different from that of the control groups (P < 0.5). When the dose was 10 104 bird"1, the weight gains were lowest in groups infected with SH strain and largest in groups infected with SZ and LY strain. And the lesion scores were lowest in groups infected with SZ and LY strain, and largest in groups infected with YZ strain, but except SZ strain, there were no significant differences (P > 0.5) . The infections with YZ, LYG, FZ, GZ and USA strain at dose of 10 104 bird-1 caused a mortality of 20 %, 10 %, 10 %, 10 % and 10 %, respectively. It suggested that YZ and SH strain were highest... |
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