| Procine epidemic diarrhea(PED)is an acute and highly contacting enteric infectious disease caused by porcine epidemic diarrhea virus(PEDV).Pigs of different strains and ages are all susceptible.Vaccination can prevent classical strains efficiently.However,PEDV mutant strain has caused intractable diarrhea which was characterized by seriously vomiting,watery diarrhea,enteric tympanites,enterorrhagid and high mortality in piglets since December,2010.The morbidity and mortality have significantly raised.It indicates that PEDV has mutated during evolution,and classical vaccine strains fail to provide effective cross-immune protection.Thus,it is necessary to reduce the economic loss caused by the mutant strain,by means of epidemiological investigation,immune program optimization and effective therapy.In this study,we took epidemiological surveillance and optimized immunization procedures and treatment scheme according to the needs of PEDV infection prevention and control in an intensive pig farm in Jiangsu province.We conducted the integration,promotion and application of the new shceme in the whole field,which achieved active effects.1.Epidemiological analysis of PED and immune procedure optimization1.1 Epidemiological survey of PED in a farmAccording to the survey and statistics of outbreaks and seasons of PED in 7 farms in the farm area from 2012 to 2019,it stated that the seasonal characteristics of PED tend to be less obvious.The outbreak was analyzed on the basis of the incidence times,and the main reasons for the control of this epidemic in the later period were summarized as follows:1.In the years with severe epidemic,feed-back was used as an important means to control the epidemic;2.The vaccine strain highly homologous to epidemic strains was used;3.Focus of prevention and control was shift from winter to four seasons;4.Probiotics could effectively control the spread of viral diarrhea in a long period of treatment exploration.At present,considering the decreasing positive rate of PED samples tested,PED is generally controllable under high-level biological safety.1.2 Analysis of PEDV epidemic strains16 PEDV epidemic strains were identified through PCR amplification and cloning and sequencing from suspected PED pig samples from 2015 to 2017.Based on genetic evolution analysis,all 16 sequences were in the same evolutionary branch with the S gene sequence of the G2b subtype reference strain,which indicated that strains in the monitored pig farms belong to the G2b subtype.1.3 Immune procedure optimizationDifferent vaccine combinations were selected to evaluate the protective effect of different immune procedures;sows were immunized at different time points before delivery,and the colostrum of the sows was collected after delivery for IgA antibody testing.The results showed that there was no significant difference in the immune effect of the same weak strain at different immune time;there was significant difference in the immune effect of different attenuated strains at the same immune time(P<0.05),but there was no significant difference in different times of prenatal immunization(P>0.05),and IgA antibody in the colostrum of sows which were immunized 24+10 days before delivery is higher.Considering the infection rate of piglets within 10 days after delivery,the monitoring results showed that the vaccine with variant strains had the highest the protection rate,and the immune procedure with 2 times of the attenuated vaccine 24+10 days before delivery was better.2.Supportive therapeutic efficacy of probiotics on pigs infected with PED A total of 204 piglets aged 7-10 days with PEDV positive detected by PED rapid test kit were selected from the pig farm,and divided into two groups.The first group contains 101 piglets and the second 103.During the experiment,the piglets freely consumed rehydration salts and artificial milk.Group 1 was treated by intramuscular injection of enoxacin antibiotics for 4 days.Group 2 was treated with Bacillus subtilis 6.7*107CFU orally for 4 days continuously.Each group was observed for 3 days.The results showed that the mortality of group 1 was 59.4%,and that of group 2 was 30.1%.The livability of group 2 was significantly higher than that of group 1;the cure rate of diarrhea after treatment in group 2(62.5%)was significantly higher than that in group 1(9.7%).The average final weight of group 2 treated with Bacillus subtilis was significantly increased(P<0.05)compared with group 1.It proved that the Bacillus subtilis preparation has a good therapeutic effect on PEDV-infected piglets,and the symptoms of weight loss in piglets due to diarrhea have been significantly relieved.The feasibility of oral medication of Bacillus subtilis to treat piglet diarrhea was proved by experiments.In addition,the sow-piglet joint treatment was compared to the piglet single treatment,and the results showed that the cure time of the sow-piglet joint treatment is 3.2 days,significantly lower than that of the single piglet treatment(3.95 days),which indicated the sow-piglet joint treatment could shorten the course of disease and accelerate the recovery of piglets with diarrhea. |
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