Chlamydia pecorum (previously Chlamydia psittaci and Chlamydophila pecorum) is a well know cause of polyarthritis in lambs especially rapidly growing weaned prime and British breed lambs. However, C. pecorum is implicated in keratoconjuctivitis (sometimes concurrently with polyarthritis) and has been reported as a cause of abortions, pneumonia and mastitis. Chlamydia abortus, a separate species (Polkinghorne, 2011) that causes enzootic abortion in ewes and orchitis in rams appears to be absent from Australia.
Chlamydial polyarthritis typically affects large rapidly growing lambs up to about six months of age. While I have invariably seen the problem in weaned lambs, Barry Kemp in the 1986 proceedings of the Association of Veterinary Inspectors, reported that lambs as young as two weeks of age were affected. I have not seen the problem in lambs older than about six months of age but Tammemagi and Simmons in an early report (1968) diagnosed 'viral' polyarthritis in a group of thirteen month old dorset rams.
The disease often develops rapidly in affected flocks and is characterised a morbidity of up to 50% but insignificant mortality. However occasionally it causes lameness in a few lambs only. Affected lambs are usually febrile and walk with a stiff, 'proppy gait.' Lambs usually 'warm out' of the lameness making them more difficult to detect when mustered into yards. However, in the paddock affected lambs are reluctant to walk and may lie down. Chronic cases appear stiff and lose weight.
Multiple joints may be involved and these joints may not necessarily be obviously warm and swollen. Conjunctivitis is reported as frequently accompanying chlamydial polyarthritis although I have seen a number of cases in which conjunctivitis was not obvious.
Barry Kemp, in his comprehensive 1986 paper noted the association between rapid growth and clinical polyarthritis. He described at least two occasions when properties ran similar lambs on either dryland or irrigated pastures. While serology indicated a comparable prevalence of chlamydia in each mob, clinical disease was only seen on the lambs grazing irrigated pastures (Kemp, 1986).
Chlamydial polyarthritis is most commonly seen in prime lambs and the lambs of British breds and in particular Dorsets. However, I have seen it in merinos and Greg McCann (pers. comm.) reports that the disease is a problem in merinos on irrigated lucerne. It is my impression that in NSW the disease is more prevalent in sheep on the western slopes and plains than on the tablelands.
Chlamydial polyarthritis responds rapidly to oxytetracycline. However, treating individual lambs is time consuming especially in high morbidity outbreaks and difficult because not all affected lambs are readily identified. Occasionally producers medicate the entire mob.
Chlamydial polyarthritis has been reproduced experimentally as noted by Kemp (1986). Infective material, inoculated into four cross bred lambs produced a fever on day three, lameness on days 6 to 9 and recovery after 20 days. Antibodies were detected on day 8, declining at day 26 and at low levels by day 56.
Keratoconjunctivitis is occasionally reported as accompanying polyarthritis in chlamydial outbreaks in lambs (Littlejohns 1976, Kemp 1986). Affected lambs present with a clear to purulent ocular discharge and conjunctival hyperaemia. However, in several of the cases I have seen keratoconjuctivitis is not a feature of the disease. If polyarthritis can occur without keratoconjunctivitis, can keratoconjunctivitis occur without polyarthritis?
CHLAMYDIAL PNEUMONIA AND MASTITIS
ExperimentallyChlamydia abortus caused mastitis in ewes when inoculated into the teat canal (Papadopoulos and Leontides, 1972). However, I am not aware of chlamydia being isolated from a clinical case of mastitis in Australia. Chlamydia are also potential causes of pneumonia in most animal species (Radostits, et al) However, TD St George (1972) in a comprehensive study of pneumonia in sheep, found no cultural or serological evidence implicating chlamydia.
CHLAMYDIAL ABORTION (AND ORCHITIS)
John Seaman isolated C. psittaci from two cases of placentitis and late term abortions in ewes. He noted that C. psittaci has previously been incriminated in ovine abortions in Australia although this is rare (Seaman, 1985).
However, it appears that Chlamydia abortus, the cause of enzootic abortion of ewes (EAE) is absent. A recently published serological survey of 891 sheep from 109 properties across southern Australia supports this (McCauley, Lancaster, Butler and Ainsworth, 2010). Interestingly, they found that 4% of ewes reacted (cross-reacted) at CFT titres of 1:4 (but none at 1:32) while 10% of rams reacted at 1:4 and 4% reacted at 1:32. The authors considered that these results support the present belief that C. abortus is not enzootic within Australia and thus EAE is not present. However, these cross-reactions have the potential to hamper the export of Australian sheep especially rams.
In Britain, EAE causes necrotic placentitis, so ewes abort in late term or deliver weak lambs. It is uncommon in extensively managed hill flocks but occurs more often on farms that lamb intensively. In endemic flocks, a proportion of sheep carry C. abortus in the reproductive tract and the intestines. Of lambs infected neonatally, up to one third develop subsequently develop placentitis and some abort. As the bacterium survives in the environment for several days (longer in cold conditions), the contamination provided by abortions and discharges is important in disease transmission.
Rams, infected either venereally or orally by C. abortus can develop orchitis. Some develop chronic palpable lesions and some secrete the organism in semen.
While it is apparent that the organism survives from one year to the next in carrier animals, the relative important of intestinal versus genital tract carriers in the epidemiology of the disease has not yet been elucidated.
On infected farms, ewes that abort may be segregated and joined to quarantined rams. Oxytetracylines are used to manage outbreaks and vaccines are available. Britain has an accreditation scheme enabling farmers to purchase sheep tested negative for EAE (Aitken and Longbottom, 2007).
Chlamydial arthritis is currently diagnosed on history, clinical presentation and serology. It is advised to collect blood from 5- 10 sheep when seeking a diagnosis to overcome the problem of inadvertently collecting blood from early or convalescent cases.
Chlamydial polyarthritis is a significant disease to prime lamb producers causing distress and weight loss on otherwise rapidly growing animals. It can also be a serious and recurring problem for ram breeders, most notably breeders of Dorsets. However, the disease remains poorly understood. It has been suggested that birds might be the reservoir for the organism. Given that chlamydia can be readily isolated from the faeces of normal animals, it seems most likely that 'carrier' sheep harbour it in the gastro-intestinal tract. However, given the predilection of chlamydia for mucous membranes, it is possible that the respiratory tract, oro-pharynx or the eyes are reservoirs.
Current control measures rely on antibiotics administered either to individual sheep or occasionally to the affected mob. Vaccination would be a desirable option for many affected producers.
Field veterinarians need to remain aware that while C. pecorum can occasionally cause abortions in Australian sheep, C. abortus appears to be exotic and therefore should be kept under surveillance.