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Enzootic Abortion of Ewes (EAE)


Introduction

Enzootic Abortion of Ewes (EAE), also known as ovine chlamydiosis, is a significant infectious reproductive disease of sheep characterized by late-term abortion, stillbirths, and the birth of weak lambs. It is one of the most important causes of abortion in small ruminants and has both economic and zoonotic significance.

Etiology
Causative Agent

EAE is caused by Chlamydia abortus, an obligate intracellular bacterium.

Organism Characteristics
  • Gram-negative-like bacterium
  • Obligate intracellular pathogen
  • Exists in two forms: elementary body (infectious) and reticulate body (replicative)
  • Survives in the environment for limited periods under favorable conditions
Epidemiology
Species Affected
  • Sheep (primary host)
  • Goats (also susceptible)
Transmission
  • Ingestion or inhalation of contaminated materials
  • Exposure to aborted fetuses, placentas, and uterine discharges
  • Contaminated feed, water, and bedding
Risk Factors
  • Introduction of infected animals into naïve flocks
  • Poor hygiene in lambing areas
  • High stocking density
  • Mixing of pregnant animals
Pathogenesis
Initial Infection

The organism enters via oral or respiratory routes and establishes a latent infection in non-pregnant animals.

Reactivation in Pregnancy
  • Infection localizes in the placenta during pregnancy
  • Rapid bacterial multiplication occurs in placental tissues
Placental Damage
  • Necrosis and inflammation of placentomes
  • Reduced nutrient and oxygen supply to fetus
Outcome
  • Late-term abortion
  • Stillbirths or weak lambs
Clinical Signs
In Ewes
  • Late-term abortion (last 2–3 weeks of gestation)
  • Minimal premonitory signs
  • Occasionally vaginal discharge before abortion
In Lambs
  • Stillbirths
  • Weak lambs with poor survival
Flock Pattern
  • Abortion storms in naïve flocks
  • Lower abortion rates in subsequent pregnancies due to immunity
Summary for Practitioners

EAE should be suspected when late-term abortions occur in multiple ewes with minimal clinical signs, especially following introduction of new animals.

Postmortem Findings
Placental Lesions
  • Thickened, leathery placenta
  • Necrotic cotyledons with exudate
  • Intercotyledonary areas appear opaque and edematous
Fetal Lesions
  • Usually minimal gross lesions
  • Occasional fluid accumulation in body cavities
Microscopic Lesions
  • Necrosis and inflammation of placental tissues
  • Intracellular organisms in trophoblasts
Diagnosis
Clinical Diagnosis

Based on abortion pattern, gestational stage, and flock history.

Laboratory Diagnosis
  • PCR for detection of Chlamydia abortus
  • Isolation of organism (specialized laboratories)
  • Serology (ELISA)
  • Histopathology of placenta
Differential Diagnosis
  • Toxoplasmosis
  • Campylobacteriosis
  • Brucellosis
  • Salmonellosis
Summary for Practitioners

Diagnosis relies on laboratory testing of placenta and fetal tissues, as multiple infectious agents can cause abortion in ewes.

Treatment
General Approach

Treatment is limited and mainly preventive rather than curative.

Antibiotic Therapy
  • Tetracyclines may reduce abortion rates if administered during pregnancy
  • Does not eliminate infection completely
Summary for Practitioners

Treatment may reduce losses during outbreaks but does not eradicate infection from the flock.

Control and Prevention
Vaccination
  • Live and inactivated vaccines available
  • Vaccination prior to breeding is recommended
Biosecurity
  • Quarantine and test new animals
  • Avoid introducing infected stock
Management Practices
  • Isolate aborting ewes
  • Proper disposal of aborted materials
  • Thorough cleaning and disinfection of lambing areas
Summary for Practitioners

Effective control requires vaccination, strict hygiene during lambing, and careful management of flock introductions.

Zoonotic Importance

Chlamydia abortus is zoonotic and can cause severe disease, including abortion, in pregnant women. Strict precautions should be taken when handling aborted materials.

Economic Importance

EAE causes significant economic losses due to abortion storms, reduced lamb crop, veterinary costs, and decreased flock productivity.

Summary

Enzootic Abortion of Ewes is a major infectious cause of late-term abortion in sheep caused by Chlamydia abortus. Control depends on vaccination, biosecurity, and proper management of lambing environments.