Chlamydia in sheep, a bacterial infection known as enzootic abortion of ewes (EAE), is a significant concern for livestock health. It can lead to substantial reproductive losses within affected flocks. Understanding this infection, its transmission, and its impact on animal and human health is important for managing its spread.
The Chlamydia Affecting Sheep
The chlamydia primarily responsible for infections in sheep is Chlamydia abortus, previously known as Chlamydophila abortus. This organism is distinct from Chlamydia trachomatis, which causes sexually transmitted infections in humans. Chlamydia abortus is an obligate intracellular bacterium, meaning it can only replicate inside host cells. Its primary target in sheep is the placenta, leading to inflammation and damage. This bacterium can also affect other ruminants like goats and, less frequently, cattle.
How Infection Spreads Among Sheep
Infection with Chlamydia abortus typically spreads through the oral-nasal route when sheep ingest or inhale contaminated material. The main source of infection within a flock is the shedding of bacteria from infected sheep, particularly during lambing. Aborted fetuses, fetal membranes, and fluids released during birth are heavily contaminated. Susceptible sheep can become infected by consuming or contacting these materials, especially in communal lambing pens.
The organism can survive in the environment for days to months, increasing the risk of transmission. Non-pregnant sheep can become latently infected, harboring the bacteria without showing symptoms until pregnancy triggers its activation. Introducing latently infected new animals into a flock is a common way the disease enters and spreads, sometimes leading to an “abortion storm” in subsequent lambing seasons.
Impact on Sheep Health and Reproduction
The most noticeable consequence of Chlamydia abortus infection in sheep is reproductive failure, primarily abortion. This condition, known as enzootic abortion of ewes (EAE), usually occurs in the last two to three weeks of gestation. Affected ewes may show few signs of illness before aborting, though some behavioral changes or vulval discharge can be observed in the 48 hours prior. The bacteria damage the placenta, impairing nutrient transfer to the developing lamb and disrupting hormones essential for maintaining pregnancy.
Besides abortion, infection can result in stillbirths or the birth of weak lambs that often do not survive beyond 48 hours. An infected ewe might give birth to a mix of dead, weak, and healthy lambs in a multiple birth. The placenta of an aborted ewe often appears inflamed and thickened, with characteristic damage between the cotyledons. These reproductive losses have a significant economic impact for farmers due to reduced lamb crops and the associated costs of managing outbreaks.
Controlling and Preventing Outbreaks
Controlling Chlamydia abortus in sheep flocks involves vaccination and strict biosecurity measures. Live attenuated vaccines are available and are typically administered to ewes prior to breeding to boost their immunity. Vaccination can help prevent abortion and reduce the shedding of the organism, though it may not completely eradicate the infection from a flock.
Biosecurity practices are equally important to prevent the introduction and spread of the disease. This includes isolating aborting ewes immediately to prevent contamination of the environment. Proper disposal of aborted fetuses, placental material, and contaminated bedding is essential, as these materials contain high bacterial loads. Thorough cleaning and disinfection of lambing pens are also necessary. Testing new animals before introducing them into a flock can help prevent the entry of latently infected carriers. While antibiotics, such as oxytetracycline, can be used to manage outbreaks and reduce losses in pregnant ewes, they are not a cure. Their use should be guided by a veterinarian to avoid resistance.
Risks to Human Health
Chlamydia abortus is a zoonotic pathogen, meaning it can be transmitted from animals to humans. While human infection is rare, it can occur through close contact with infected sheep, especially during lambing or when handling aborted material. The most common transmission route to humans is inhalation of aerosols or dust contaminated with the bacteria.
Pregnant women are at particular risk, as exposure can lead to severe health complications. Symptoms in humans range from asymptomatic infection to a flu-like illness, including headache, chills, fever, and joint pains. In pregnant women, Chlamydia abortus infection can cause more severe illness, potentially leading to pneumonia, liver and kidney complications, miscarriage, or stillbirth, usually between 24 and 36 weeks of gestation.
For individuals at risk, such as those working with sheep, precautions include wearing protective clothing, gloves, and masks, particularly during lambing season or when handling potentially contaminated materials. Practicing good personal hygiene, including thorough handwashing, after contact with sheep or their environment is also advised. Anyone experiencing flu-like symptoms after potential exposure to sheep, especially pregnant women, should seek medical attention promptly and inform their healthcare provider about the animal contact.