Location: Warmwater Aquaculture Research UnitTitle: Experimentally Induced Placentitis with Streptococcus equi zooepidemicus in Late Gestation Mares: Prevention of Preterm Birth Author
Submitted to: World Equine Veterinary Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/15/2007
Publication Date: 1/1/2008
Citation: Ryan, P.L., Christiansen, D., Smith, J., Hopper, R., Reed, R., Crouch, J., Moulton, K., Bennett, W., Leblanc, M. 2008. Experimentally Induced Placentitis With Streptococcus equi zooepidemicus in Late Gestation Mares: Prevention of Preterm Birth. World Equine Veterinary Association Proceedings, Moscow, Russia, January 28th-February 1, 2008. pp. 557-580. (perr reviewed) Interpretive Summary: Placentitis is the leading cause of pre-term labor in mares and women but current therapeutic strategies to prevent premature deliveries requires improvement. The objective of this study was to examine the efficacy of three strategies using antibiotics alone or in combination with immunomodulators to prevent preterm delivery and increase the survivability of foals in mares with experimentally induced ascending placentitis. The outcome of these studies show that timely intervention with therapies is essential, and that immunomodulators markedly improve maintenance of the pregnancy to near term. This is an important clinical observation when treating this condition in women. Stabilizing the pregnancy is imperative.
Technical Abstract: Placental infection due to opportunistic pathogens is the most common cause of abortion and premature delivery in horses. However, current therapies used to treat mares with placentitis are based on clinical experience, anecdotal information or on case reports. Thus, the objective of this study was to examine the efficacy of three strategies using antibiotics alone or in combination with immunomodulators to prevent preterm delivery and increase the survivability of foals in mares with experimentally induced ascending placentitis. Twenty four pregnant (Quarter Horse, Thoroughbred) mares matched by age were assigned to one of four treatments (Table 1). Seventeen mares were infected by intra-cervical inoculation with Streptococcus equi zooepidemicus (S. equi; 2x106 CFU) and assigned (Table 1) to receive trimethroprim sulfamethoxazole (TMS; 30 mg/kg, q 12 h, PO) alone; TMS with dexamethasone (D) given over 6 d with decreasing doses every two days (TMS+D; 40, 35, 25 mg, respectively, q 24 h, IV) or TMS with acetylsalicylic acid (TMS+A; aspirin 150 mg/kg, q 12 h, PO for 6 d). Six mares served as uninfected controls (CN). Blood samples were collected pre- and post-infection at 12, 24, 48, 72 h and 3x/week thereafter until delivery for progesterone (P4) analysis. Fetal and placental well-being was evaluated daily by ultrasonography. Treatment commenced upon initial signs of vaginal discharge and/or placental changes. Blood was collected from foals at 0 and 24 h post-partum for CBC, IgG and P4. Statistical analyses were performed using ANOVA and repeated measures procedures of StatView software (SAS Inst. Inc, Cary, NC), and significance was determined at P <0.05. Inoculation induced vaginal discharge within 48 h and increased (P<0.05) combined thickness of uterus and placenta (CTUP) in all mares (0.83 ± 0.03 to 1.5 ± 0.1 cm). Mean gestational age at parturition was shorter (307.6 ± 3.7 d; P < 0.05) in TMS+D mares than any of the other groups (CN, 338 ± 5.0; TMS, 318.8 ± 5.0; TMS+A, 322.6 ± 6.6 d). Foal birth weights were lower in TMS+D foals (36. 8 ± 1.7 kg; P <0.05) compared to foals of mares in the other treatment groups (CN, 45.5 ± 4.0; TMS, 44.6 ± 2.9; TMS+A, 45.2 ± 3.0 kg), but birth:placental weight ratio was higher (P <0.05) in all infected mares compared to controls. Mean serum P4 was not affected by inoculation or drug treatment, but P4 concentrations in foals from infected dams ranged from 4.6 to 24.5 and 0.9 to 15.3 ng/ml at 0 and 24 h, respectively. Serum IgG concentrations were undetectable at 0 hours in all foals but were lower in foals born to infected dams (range 4.00 to 12.8 mg/ml) compared to controls (range 12.8 to 27.5 mg/ml) at 24 h. Four mares delivered viable foals in each of the infected groups, two aborted in the TMS group, one live but euthanized at 12 h and one aborted in each of the TMS+D and one live but euthanized at 24 h in the TMS+A group, and six viable foals in the CN group. Placental pathology confirmed necrosuppurative placentitis in all inoculated mares and bronchopneumonia in aborted fetuses. Culture of stomach contents revealed heavy growth of S. equi. Data presented here indicate that timely onset of treatment once a mare is presented with clinical signs of placentitis is critical.