Review/Oorsig Volume 23, Issue 02 - Page 5

Volume 23 • Issue 02 • 2019 Classification and importance of Chlamydia species of ruminants Based on the latest taxonomic classification Chlamydia species of ruminants are associated with two distinct syndromes namely: • • Enzootic abortion caused by Chlamydia abortus. Abortions or birth of weak lambs frequently occur in the absence of other so-called Chlamydia “syndromes” viz. conjunctivitis, polyarthritis, gastroenteritis, mastitis and meningoencephalitis. Sporadic abortion caused by Chlamydia pecorum. This syndrome in ruminants is characterised by outbreaks of conjunctivitis, polyarthritis, gastroenteritis, mastitis and meningoencephalitis and only sporadic abortions. Another separate Chlamydia specie, Chlamydia psittaci, is not associated with abortions in ruminants or with the other so-called Chlamydia “syndromes” and is not considered a primary lung pathogen of sheep or goats. Epidemiology Chlamydial abortion also known as enzootic abortion of ewes or ovine enzootic abortion, is a major cause of lamb mortality across the world and is currently one of the most common infectious causes of abortion in sheep and goats in South Africa. It is caused by the bacteria C. abortus which invades the placenta during pregnancy, and which can lead to abortion or the birth of weak lambs. Infection with C. abortus has both a direct and indirect effect on the developing lamb. Growth of the organism directly damages the placenta and negatively affects the development of the foetus resulting in late abortions or the birth of weak infected lambs The clinical consequences of infection are determined by, amongst other causes, the timing of infection, the immune status of the animal and the number of organisms (infection dose). When non- pregnant sheep, including young lambs, become infected, they develop latency in the uterus. Purchasing latently infected sheep is probably the most common source of initial infection in a flock. The stage at which an infection is picked up during pregnancy will determine the outcome as there is a lag period between infection and onset of clinical signs. At some point in mid pregnancy of infected ewes an unknown trigger causes the organism to become active resulting in a placentitis which often results in abortions or the birth of weak lambs. Organisms derived from infected birth fluids and placentas from recently or latently infected sheep are the main source of infection. A small number of abortions usually occur in the year after introduction of latently infected sheep with a storm (due to infection spread to other naive sheep within the flock) in the subsequent year. Once an ewe has been infected, she becomes immune, though will be a carrier of the disease in subsequent years. Understanding latent infection therefore is key to disease control as it is important to realize that infection in one year most often results in abortion in the following year. Clinical signs In an infected flock first and second lamb ewes are most susceptible to the disease. The ewe shows no signs of illness. Flocks infected for the first time may have an incidence of up to 70% of abortions but drops to 1-5% once the disease becomes endemic. Reproductive failure including abortion, mummification, stillbirth (occasionally one live lamb born along with a dead lamb) or the birth of weak lambs (rarely survive) are often experienced. It is common to have one or all these syndromes on a farm at the same time. Pathogenesis A high level of environmental contamination by infected ewes in lambing pens or fields is an important source of infection for other animals through ingestion and less commonly inhalation. Following infection, C. abortus colonize the intestine where they become established within the intestinal mucosa. In pregnant animals there is systemic spread from the intestinal mucosal to the uterus and placenta. Initially there is a localized placentitis at the level of the placentomes at roundabout 100 days of gestation Fig 2. Placental pathology is a hallmark of C. abortus infection. Note the numerous chlamydia bacteria intermingled with necrotic cells 5