In Vitro And In Vivo Study Of Tylvalosin Prevention And Control Of Porcine Reproductive And Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus（PRRSV） is one of the most important virus in the swine industry worldwide, and impose a significant economic burden on pig producers. Sow reproductive disorder, boar semen carrier virus and respiratory syndrome of all age pigs are the typical clinical symptoms of PRRSV infection. Duration of PRRSV viremia is related to clinical signs of infected animals, and persistent infection animal excreted virus which infects the negative animals on every side. Vertical transmission could happen and fetus congenital infection when pregnant sow on viremia duration. Tylvalosin as a derivatives of Tylosin, has been reported by several studies could reduce the effect of in vitro and in vivo PRRSV infection. As a brand new antivirus veterinary drugs, this study is to assess the efficacy of Tylvalosin reduce PRRSV CPE in vitro, and viremia duration and challenge protection associated with PRRSV infection using an experimental pig infection model, as well as market application survey on this drug, which may provide a reference for swine producers apply Tylvalosin prevent and control PRRS.In vivo study use 0μg/ml、0.1μg/ml、1.0μg/ml、10μg/ml、50μg/ml tylvalosin incubated Marc145, each concentration has two groups, one group is control without virus invocation, another group of cell then infected 1% dose of CH-1r strain,the result show that Tylvalosin has no cytotoxicity to Marc145 cell and does not affect cell growth. Corresponding with the Tylvalosin concentration PRRSV yield reduction in TCID₅₀ is 10^7.22, 10^6.62, 10^6.26, 10^4.68 and 10^2.52 respectively, and which for blank control group is 0. CPE reduce could be observed at 1.0μg/ml tylvalosin concentration, and 50μg/ml concentration could obviously reduce virus replication. In vivo study indicate that tylvalosin can reduce PRRSV infection, and reduce virus infection ability and tylvalosin concentration is related. This in vivo study result is coincident with domestic and international experimental reports.In vitro study, fifteen weaned piglets, seronegative for PRRSV detected by ELISA and PCR were assigned for A, B and C group and 5 pigs each, Group A medicated 150 ppm tylvalosin premix, group B and C set up as positive control and negative control respectively. Group A and B piglets intramuscular injection and nasal drops 3ml 10^5.0 TCID₅₀/m L JXA-1 PRRSV respectively at trail day 7, blood was collected on 0, 3, 5, 7, 10, 14, 21 dpi and PRRSV levers determined by real-time RTPCR. Group A virus copies at 3 dpi was 0, and group B is 104 and reached a peak of 108.5 at 5 dpi. and decrease since then, 2 piglets died at 14 dpi. and another 1 piglets at 18 dpi., group C had no PRRSV viremia. This in vitro virus challenging study indicate that tylvalosin could reduce PRRSV infection and viremia or shorten viremia duration on experimental infected pigs.Another fifteen ELISA and PCR detect PRRSV seronegative weaned piglets randomly divided into A, B and C groups, group A medicated 150 ppm tylvalosin premix, and B is positive control and C is negative control, group A and B injection and nasal drops 3ml 10^5.0 TCID₅₀/m L JXA-1 PRRSV respectively at trail day 7, and continuously check rectal temperature, observe appetite, mental status and mortality for 21 days post inoculation, and pigs are weighed upon arrival and on trial day 7,14,21 and 28, contrast group weight gain as well as average daily gain. Pigs were euthanized and necropsied on trial day 28 or when pig dead in the course of the trial, and calculate lung lesion of each pig. The result show that group A animals fever last 1-2 days after PRRSV challenging and back normal on 3 dpi, group B animals start to fever on 3 dpi. and high fever last to 10 dpi, two pigs（B1 and B5） died on 11 and 12 dpi. Pulmonary lesion scores for A, B and C group is 16.4, 53.2 and 12.2 respectively.Field trial data proving tylvalosin currently mainly use on nursery pigs and fattening pigs treat respiratory syndrome to reduce piglets loss rate, as well as on gestation and lactation sows for reduce abortion and re-estrus rate. ECO animal health group with the invitation patent of tylvalosin globally annul sales growth is 11% and 18% in China.In brief, in vitro study on Marc-145 cell infect PRRSV CH1-r show that Tylvalosin could reduce CPE and TCID₅₀ value, oral medicated 150 ppm tylvalosin for 7 days then challenging JXA-1 PRRSV and blood collected on 3 dpi then real-time RT-PCR determine PRRSV levers were seronegative, and mild fever, mentally and feed intake depress only last 2 days after virus inoculation, and the group weight gain and average ADG is significantly higher than group B and C. This study indicates that tylvalosin could use in the field as one of the tools control PRRSV, decrease PRRSV virus load or shorten viremia duration, as well as reduce mortality and clinical symptoms of PRRSV infected pigs.