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Abbreviations:
AST

aspartate aminotransferase

CK

creatine kinase

CTUP

combined thickness of the uterus and placenta

Hydropic conditions of the equine placenta are rare, with hydrallantois1–4 reported more frequently than hydramnios.2,5 Much remains unknown about the etiology and pathophysiology of the condition. Suggested etiologies for hydramnios include abnormal fetal deglutination because of fetal head anomaly and renal agenesis or dysgenesis.6 Placentitis,7 increased production of transudate or decreased transplacental fluid absorption6 are potential etiologies suggested for hydrallantois. Heritability has also been reported.7

Placentitis is caused by a variety of bacterial, fungal, viral, and protozoal organisms.8 Leptospirosis has been implicated as a bacterial cause of equine placentitis.8–10 Equine Leptospira abortion, first reported in the 1950s, has been documented worldwide.11,12 Approximately 250 serovars of Leptospira spp. have been identified; however, equine Leptospira abortion in North America is primarily attributed to Leptospira interrogans serogroup Pomona serovar Kennewicki.13

This case report describes 2 cases of equine hydrallantois associated with L. interrogans. The 2 pluriparous mares described presented for transabdominal ultrasound evaluation of the fetus and uteroplacental unit because of an abnormal increase in abdominal size and clinical signs consistent with placentitis. This article describes the clinical, ultrasonographic, and pathologic findings in mares with hydrallantois associated with L. interrogans.

Case 1

  1. Top of page
  2. Case 1
  3. Case 2
  4. Discussion
  5. Footnotes
  6. References

A 7-year-old, pluriparous, Thoroughbred mare presented to the McGee Medicine Center for fetal ultrasound examination at approximately 269 days of gestation. Premature udder development and lactation were noted 1 day before presentation. Transrectal ultrasound examination performed by the referring veterinarian yielded a presumptive diagnosis of hydrallantois. The combined thickness of the uterus and placenta (CTUP) at the cervical star was normal.

On arrival the mare was bright, comfortable, and in good body condition score (6/9). Abdominal size was increased for gestational age and the mare's udder was enlarged. Physical examination revealed normal vital parameters. On rectal examination, an enlarged, fluid-filled uterus was palpated, precluding fetal ballottement. Transabdominal ultrasound examination revealed a pregnancy in the right uterine horn. The fetal biophysical parameters indicated that the fetus had a heart rate of 60–66 beats/min (bpm) and no acceleration in heart rate was noted with fetal activity. CTUP measured at the ventral uterine body wall was normal (≤5 mm at <270 days of gestation14). The allantoic cavity, within the right uterine horn, was enlarged with a maximal vertical depth of 25 cm (normal: 13.4 ± 4.4 cm, range: 4.7–22.1 cm15,16). The volume of fluid present was not quantitated. The nonpregnant left uterine horn was also distended with fetal fluids, the depth of which was not ascertained. The amniotic cavity, within the right uterine horn, was of normal depth (normal: 7.9 ± 3.5 cm, range: 0.8–14.9 cm15,16) and echogenicity. Based on ultrasonographic findings the presumptive diagnosis of hydrallantois was confirmed. Repeat transabdominal ultrasound examination was performed 1 week later to monitor the progression of the hydrallantois. This revealed that the allantoic cavity, within the right uterine horn, had increased in size to a maximum vertical depth of 25.94 cm. Resting fetal heart rate was 77 bpm, which accelerated to 97 bpm with fetal activity, and there was no evidence of fetal stress at this time. As both mare and fetus were stable at the time of examination, it was decided to perform a repeat examination and transabdominal ultrasound evaluation 1 week later to determine any decline in clinical status.

The mare, however, aborted the pregnancy 24 hours after examination. No complications were noted during or after the abortion. The fetus and fetal membranes were submitted for necropsy.

At necropsy, the external appearance of the male fetus was normal. Internal abnormalities included an enlarged liver, mottled tan-mahogany in color on both the parietal and cut surfaces. The kidneys were enlarged (right kidney 12 × 11 × 4 cm; left kidney 10 × 10 × 4 cm) and the surfaces irregular with pale renal cortices on cross-section. The spleen was 2.5 times normal size. The fetal musculature had an icteric tinge.

The placenta weighted 8 lb (3.64 kg). The allantochorion was thin near the cervical star and the body and pregnant horn were thin, autolyzed, and sparsely villous. Focal amniotic hemorrhages were noted near the attachment to the umbilical cord.

Histopathology of the kidneys revealed that both the renal cortices and medullary cavities were infiltrated with neutrophils. The renal tubules were dilated and contained polymorphonuclear cells. The interstitial regions were expanded containing dense multifocal aggregates of inflammatory cells. Multinucleated giant cells were also present.

Histopathology of the placenta revealed a focal infiltration of neutrophils and eosinophilic necrotic material at the chorionic surface of the pregnant, right uterine horn. Fibrin and leukocytes were lightly distributed along the amniotic surface of the umbilical cord.

Fluorescent antibody tests performed on placental tissue and fetal renal tissue were positive for Leptospira spp. Streptococcus equisimilis was also isolated from the placenta.

Microscopic agglutination test performed on fetal serum was positive for Leptospira Pomona (1 : 102, 400).

Case 2

  1. Top of page
  2. Case 1
  3. Case 2
  4. Discussion
  5. Footnotes
  6. References

A 19-year-old, pluriparous, Thoroughbred mare presented at day 229 of gestation for transabdominal ultrasound evaluation of the fetus and uteroplacental unit. Mucoid vaginal discharge developed 3 days before presentation. Transrectal ultrasound examination revealed a normal CTUP at the region of the cervical star. A cervical swab was submitted for culture/antibiogram and treatment for suspected placentitis in the form of broad spectrum antibiotics (sulfamethoxazole and trimethoprim tabletsa 30 mg/kg PO q12h and gentamicin sulfateb 6.6 mg/kg IV q24h), anti-inflammatories (flunixin megluminec 1.1 mL/kg IV q12h and pentoxyfyllined 10 mL/kg PO q12h: inhibition of proinflammatory cytokine production) and progesterone (altrenogeste 0.088 mg/kg PO q24h) was initiated. Cervical culture yielded a scant growth of Escherichia coli and Enterobacter cloacae susceptible to ciprofloxacin, imipenem, and nitrofuratoin. Antibiotics were subsequently changed by the referring veterinarian to ciprofloxacinf (4 mg/kg PO q24h).

At presentation the mare was quiet and comfortable; however, abdominal size was enlarged for gestational age. Physical examination revealed normal vital parameters. The udder development was not increased and no vaginal discharge was noted. Transabdominal ultrasound examination revealed a viable fetus in the right uterine horn with a normal heart rate (100 bpm), which accelerated to 125 bpm with activity. CTUP measured at the ventral uterine body was normal. A small area (3.5 × 3.5 cm) consistent with either a cystic lesion or an area of placental detachment was visualized in the caudoventral region of the right uterine horn. The depth and echogenicity of the amniotic and allantoic fluid within the right uterine horn were normal. It was elected to perform a recheck transabdominal ultrasound examination 2 weeks later to reassess the suspect area of placental detachment. At recheck evaluation, a viable fetus with a heart rate of 104 bpm was visualized. CTUP at the ventral uterine body measured 0.88–1.03 cm. The area of suspect placental detachment was not visualized. The allantoic fluid, within the right uterine horn, was of normal echogenicity, but the depth had increased to 24.0 cm, indicating hydrallantois. Rectal palpation revealed an enlarged, fluid filled uterus preventing fetal ballottement. Reevaluation of the hydrallantois was performed 2 weeks later, which revealed that the allantoic cavity, within the right uterine horn, had increased to a maximum vertical depth of 27.46 cm. The nonpregnant left uterine horn also contained an increased amount of fetal fluids, the depth of which was not determined. The fetal heart rate was not accurately ascertained because of fetal movement in the excessive allantoic fluid, the volume of which was not quantitated. A blood sample was submitted for creatine kinase-2 (CK-2) and aspartate aminotransferase (AST) analysis to determine if subclinical ventral abdominal muscle or prepubic tendon injury was present. Both these values were normal (CK-2: 205 U/L, range: 67–377 U/L; AST: 209 U/L, range: 127–399 U/L). Treatment options included admitting the mare to the clinic for controlled termination of the pregnancy or allowing the mare to continue with the pregnancy. Because of value of the unborn foal, the farm elected to continue with the pregnancy. One week later the mare's abdomen was more pendulous than previously and abdominal size was further increased. Repeat transabdominal ultrasound examination revealed the allantoic fluid depth, within the right uterine horn, had increased to 29.52 cm. CK-2 (276 U/L) remained within reference range. Because of increased volume of allantoic fluid it was elected to admit the mare to the hospital for controlled drainage of the excessive fluid in an attempt to salvage the pregnancy and maintain the health of the mare.

On admission, the mare was at day 264 of gestation. Fourteen gallons (52.64 L) of allantoic fluid was slowly drained from the allantoic cavity. During the procedure, the mare developed signs consistent with hypotensive shock (increased heart rate >80 bpm and full body muscle fasciculations). Allantoic fluid drainage was discontinued and treatment for shock was administered (hypertonic saline solution 7.2%g [2–4 mL/kg IV]), colloids [hetastarchh 10 mL/kg IV], and additional crystalloid fluids [Plasma-lyte Ai 30 mL/kg/h IV]). Because of the complications associated with controlled drainage of allantoic fluid it was decided to abort the pregnancy the following day after stabilization of the mare overnight. A further 15 gallons of allantoic fluid was subsequently drained and a live fetus was delivered by assisted vaginal delivery. The fetus was humanely euthanized (pentobarbitalj 10– mL/100 lb body weight). Postpartum, the mare retained the fetal membranes for 48 hours. The fetus and fetal membranes were subsequently submitted for necropsy.

At necropsy, the small, male, moderately autolyzed fetus had fractures with associated hemorrhage present at ribs 5 through to 8 on the right side of the thoracic cavity. The lungs were partially inflated and mildly firm to palpate. No further gross abnormalities of the fetus were visualized. The placenta was dark, shredded, and autolyzed after retention.

Histopathology revealed that the fetal hepatic portal areas were infiltrated with low numbers of neutrophils and mononuclear cells and contained homogeneous eosinophilic material indicative of edema. Pulmonary lesions included an accumulation of a low number of neutrophils and macrophages in the alveolar spaces and lumina of the bronchioles and bronchi. Mineral accumulation was noted in the lumina of the small arterioles. Bacteria were present. No significant lesions were noted on examination of the other internal organs. Histopathology of the placenta revealed moderate, subacute, multifocal accumulations of lymphocytes and plasma cells in the region of the umbilical attachment to the amnion indicating lymphoplasmacytic funisitis.

Fluorescent antibody tests performed on placental and fetal renal and hepatic tissues were positive for Leptospira species. Aerobic culture of placental, fetal pulmonary and hepatic tissues yielded growth of E. cloacae. Aerobic culture of fetal stomach contents yielded growth of Enterobacter faecalis.

Microscopic agglutination test performed on fetal serum was positive for Leptospira Pomona (1 : 3, 200).

Discussion

  1. Top of page
  2. Case 1
  3. Case 2
  4. Discussion
  5. Footnotes
  6. References

Both of the mares described in this case report presented for transabdominal ultrasound evaluation of the fetus and uteroplacental unit after the development of an abnormal increase in abdominal size and clinical signs consistent with placentitis during the final trimester of pregnancy. Serial transabdominal ultrasound examinations were subsequently performed which revealed an increased depth of fluid within the allantoic cavity (>22.1 cm) leading to a diagnosis of hydrallantois in both cases. Hydrallantois is infrequently diagnosed in the late gestation mare. The precise etiology of hydrops requires elucidation; however, placentitis remains one of the most frequently suggested etiologies.7

The 2 mares presented reside in Central Kentucky, an endemic region for leptospirosis, with L. interrogans serogroup Pomona serovar Kennewicki the most frequently isolated serovar.13 The skunk is the believed maintenance host for this serovar17 with infected urine acting as the primary source of leptospires for susceptible animals. Leptospira spp. have been implicated as a cause of placentitis since the 1950s.11,12 Placentitis is believed to occur secondary to Leptospira-induced vasculitis.18,19 Fluorescent antibody tests performed on placental tissue (cases 1 and 2) and fetal renal (cases 1 and 2) and hepatic tissue (case 2) yielded a diagnosis of Leptospira infection. Microscopic agglutination tests performed on fetal serum were positive for Leptospira Pomona in both cases.

Gross pathological placental lesions are observed in the allantochorion, amnion, and umbilical cord after Leptospira infection.11 In 1 study, 56.3% of allantochorionic membranes examined had green discoloration and nodular cystic allantoic masses.11 The cystic lesion visualized during the initial transabdominal ultrasound examination of case 2 may have been a nodular cyst secondary to Leptospira infection.

Gross fetal Leptospira lesions are most frequently diagnosed in the liver (71% of cases) and kidney (18.4% of cases).11 Hepatic lesions observed include swelling, icterus, and mottling, while renal lesions include swelling or white radiating streaks or both.11 Gross fetal examination findings in case 1 were consistent with these lesions.

Histopathology reveals lesions in 96% of Leptospira-positive fetuses or placentas or both.11 Frequently observed allantochorionic lesions, which are seen in up to 95.1% of cases, include cystic dilatation and focal, multifocal to diffuse infiltration of the stroma, and chorionic villi with leukocytes. Amniotic lesions include multifocal infiltration of neutrophils, necrotic calcified foci, vascular thrombosis, and edema while umbilical lesions include edema, leukocytic infiltration, and multifocal hemorrhage.11 Histopathology performed on placental tissue confirmed that both mares in this case report had placentitis. Examination of the case 1 allantochorion revealed a focal infiltration of neutrophils at the level of the pregnant, right uterine horn. A light distribution of fibrin and leukocytes was noted on the amniotic surface of the umbilical cord indicating a leukocytic funisitis. Histopathology of the case 2 placenta revealed lymphoplasmacytic funisitis.

Up to 82.6% of Leptospira-positive fetuses have hepatic lesions, which consist of mild to moderate, multifocal portal, and perivascular mixed leukocytic infiltration. Variable numbers of giant hepatocytes are observed.11 Such lesions are consistent with hepatic histopathology findings on the case 2 fetus. Renal histopathologic lesions have been noted in 44.8% of cases. Lesions include microabscesses with variable numbers of giant cells, dilated tubules, and focal to multifocal nonsuppurative interstitial nephritis.11 These lesions are consistent with renal histopathology findings on the case 1 fetus.

S. equisimilis was also isolated from the case 1 allantochorion. While the majority of the gross and histopathological lesions observed are consistent with Leptospira infection, there is still a possibility that a coinfection with S. equisimilis resulted in hydrallantois. Similarly lesions observed at necropsy of the case 2 fetus and fetal membranes are primarily consistent with Leptospira infection. E. cloacae was, however, isolated from the case 2 fetus and placenta and E. faecalis from the gastric contents of the fetus. Coinfection with E. cloacae and E. faecalis may have also contributed to the development of hydrallantois noted in case 2.

The animals presented in this case report demonstrate the possibility of L. interrogans as a cause for hydrallantois. Leptospira infection has been described in human neonates in association with hydrops fetalis and polyhydramnios20; however, to the authors' knowledge, no cases of hydrallantois associated with Leptospira spp. have been described previously in the literature for equids. In endemic areas such as Kentucky, leptospirosis should be considered as a potential etiology in horses that present for a hydropic condition. Diagnostic tests should include serum titers for leptospires. Because of widespread exposure of horses to leptospires, results of serological tests should be interpreted with caution with single increased titers >1,600 in association with clinical signs being indicative of acute Leptospira infection. A 4-fold change in antibody titer in samples taken 2 weeks apart is considered as being stronger evidence for a diagnosis of leptospirosis.21

Footnotes

  1. Top of page
  2. Case 1
  3. Case 2
  4. Discussion
  5. Footnotes
  6. References

a Amneal Pharmaceuticals of New York, Hauppauge, NY

b Sparhawk Laboratories Inc, Lenexa, KS

c Banamine, Schering-Plough Animal Health, Union, NJ

d Pentoxifylline Oral Gel, HDM Pharmacy LLC, Lexington, KY

e Regumate 0.22%, Intervet, Millsboro, DE

f Cipro, Bayer Healthcare Pharmaceuticals Inc, Wayne, NJ

g Hypertonic Saline Solution 7.2%, Bimeda Inc, Le Sueur, MN

h Hespan, B. Braun Medical Inc, Irvine, CA

i Plasma-lyte A, Baxter Healthcare Corporation, Deerfield, IL

j Beuthanasia, Schering-Plough Animal Health

References

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  2. Case 1
  3. Case 2
  4. Discussion
  5. Footnotes
  6. References
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    Vinh T, Adler B, Faine S. Glycolipoprotein cytotoxin from Leptospira interrogans serovar Copenhageni. J Gen Microbiol 1986;132:111123.
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