Objective To study the cross-immune responses and epidemiological significance of three pathogenic Yersinia species to host rats. Methods The host animals of plague in Guangdong province, Rattus losea, R. tanezumi, and R. norvegicus, were immunized four times (2×10⁹, 3×10⁹, 6×10⁹, and 7×10⁹ cells/rat, respectively) with two strains of live Y. pseudotuberculosis and three strains of live Y. enterocolitica, respectively, and the control group of rats were set at the same time. Then the appropriate amount of Y. pestis EV₇₆ strain solution mixed with 0.3 ml of 0.30% ferric ammonium citrate solution was used for a challenge test to evaluate the presence or absence of cross-immune protection. The rates were compared by using χ² test or Fisher's exact test. Results Rattus losea:Y. pestis EV₇₆ strain was cultured at 28℃ and given at 2.5×10⁹ cells/rat in the challenge test; the mortality rate was 9.09% (2/22) for the Y. pseudotuberculosis immunization group, 31.25% (10/32) for the Y. enterocolitica immunization group, and 68.75% (22/32) for the control group, with significant differences among the Y. pseudotuberculosis immunization group, Y. enterocolitica immunization group, and the control group (χ²=18.793, P<0.001; χ²=9.000, P=0.003), but there was no significant difference between the Y. pseudotuberculosis immunization group and the Y. enterocolitica immunization group (χ²=2.533, P=0.112). Rattus tanezumi:Y. pestis EV₇₆ strain was cultured at 37℃ and given at 3.8×10⁹ cells/rat in the challenge test; the mortality rate was significantly lower in the Y. pseudotuberculosis immunization group than in the control group[18.18% (4/22) vs 91.30% (21/23), χ²=24.350, P<0.001]; there was no significant difference in mortality rate between the Y. enterocolitica immunization group and the control group[90.91% (30/33) vs 91.30% (21/23), χ²=0.000, P=1.000]; there was a significant difference in mortality rate between the Y. pseudotuberculosis immunization group and the Y. enterocolitica immunization group (χ²=29.580, P<0.001). Another group of R. tanezumi:Y. pestis EV₇₆ strain was cultured at 37℃ and given at 3×10⁹ cells/rat in the challenge test; the mortality rate was significantly different between the Y. enterocolitica immunization group and the control group[3.45% (1/29) vs 45.45% (5/11), P=0.004]. Rattus norvegicus:Y. pestis EV₇₆ strain was cultured at 37℃ and given at 3.5×10⁹ cells/rat in the challenge test; the mortality rate was significantly different between the Y. enterocolitica immunization group and the control group[3.70% (1/27) vs 61.11% (11/18), χ²=15.384,P<0.001]. Conclusion With effective immunity, Y. pseudotuberculosis can provide strong cross-immune protection against Y. pestis in host rats, and Y. enterocolitica can also provide a certain cross-immune protection.

　　【Abstract】　Objective 　To study the control effect of cashew nut shell liquid（CNSL） and anacardic acid from CNSL to Oncomelania  hupensis,  and provide  the basis  for  the  application of CNSL.  Methods　 The  mixture of anacardic acid was obtained by separating extracts by silica gel column. The  molluscicidal  activities  of  CNSL  and  the  mixture  of  anacardic acid against O.hupensis were tested according to laboratory molluscicidal test method recommended by WHO. Results　The purity  of anacardic acid extracted by silica gel column was 89.32%. The LC₅₀ values of CNSL and anacardic acid mixture to snails were 0.831 mg/L and 0.523 mg/L after treatment for 48 hours, and the LC₉₀ values were 2.180 mg/L and 1.439 mg/L respectively. The inhibition rates of CNSL and anacardic acid to up?climbing of snails were 16.7% and 13.3% at the concentration of 2 mg/L, respectively. When the concentration was all 2 mg/L. However, when the concentration exceeded 4 mg/L，the up?climb rate was zero. Conclusion　It is very effective for CNSL to control snails, and anacardic acids is the main active ingredient. CNSL, as plant molluscicide, will be widely used in the control of snails.

　　【Abstract】　Objective　To understand the population composition and seasonal fluctuation of fleas parasitized on Rattus tanezumi in Leizhou city. Methods　R.tanezumi were captured in selected districts of Leizhou city from 1985 to 2004. Fleas were collected from their body surface and identified to count the flea index and its  composition  proportion.  Results　A total of  1721 R.tanezumi were caught, and about 2345 fleas belonged to 4 species were collected. Among them, Xenopsylla cheopis and Leplopsylla segnis were the dominant species, the average index of them were 1.24 and 0.12, and the proportion of them were 91.13% and 8.66%, respectively. The index and composition proportion of  Pulex irritans and Ctenocephalides felis felis were very low. Conclusion　R.tanezumi was the dominant host of X.cheopis and L.segnis. The number of X.cheopis increased year by year, but that of L.segnis decreased year after year.

Objective To determine the susceptibility of Rattus tanezumi to Brodifacoum in the laboratory.Methods No-choice feed was performed according to the method of rodent resistance monitoring group of China.Firstly,the males and females were separated,then divided into groups at random.The rodent was feed with 0.000 16% brodifacoum bait at 5 different feeding days.The data was analyzed with Bliss software.Results There was no significant difference between the susceptibility of different sex R.tanezumi to Brodifacoum(P_b>0.05,P_LFP50>0.05).The virulence regression equation was y=2.49+5.70x,and the LFP₅₀,LFP₉₉ and its 95% confidence limits were 2.75(2.39-3.17)d and 7.04(4.89-10.13)d days respectively.Conclusion According to the revised standard of WHO that the integer of LFP99 value was the resistance distinguish standard,the survivor that were fed with 0.000 16% bait for 8 d was the resistance species in Zhanjiang.