Infectious arthritis is a common problem in young Australian sheep and occasionally affects older sheep. In sheep practice, we see three distinct syndromes, Erysipelas arthritis, Chlamydophila polyarthritis and purulent arthritis caused by a range of pyogenic bacteria. These disease entities will be discussed as will a fourth syndrome, neonatal arthritis caused by Streptococcus dysgalactiae. Occasional and exotic causes of arthritis in sheep will be mentioned.
Erysipelas arthritis is a very common disease in NSW sheep flocks. In my experience, it usually occurs at less than 1% prevalence. Occasionally it affects up to 10% of lambs and in these flocks is a significant cost to the enterprise as affected sheep are often stunted and unsaleable. While I have once seen it as a neonatal disease and have sometimes seen it in older sheep, it usually becomes obvious at and subsequent to weaning.
In my experience, the disease most commonly affects the stifle, hock and carpus and less commonly the metatarsal and metacarpal joints. Affected lambs are lame with a fluid swelling of one or more joints. These swollen joints are not conspicuously painful and contain clear liquid the consistency of synovial fluid. In chronic cases this fluid is resorbed but the joints fibrose causing affected lambs to appear thin and crippled, especially if more than one leg is involved.
Erysipelothrix insidiosa has also been isolated from the joints (presumably) of sheep and lambs affected by post-dipping lameness. Cole in 1948 reported a case in which apart from the 1500 sheep dipped on the first day, almost 100% of the remaining six thousand sheep were sick and 40% were lame. Fortunately most recovered although approximately 30 died from secondary infection. Post dipping lameness is at least in my experience now a rarity no doubt due to the increased awareness of the need for dip hygiene and for allowing sheep to recover from shearing wounds before. The widespread use of pour-on lousicides and non-recycled jetting fluids has contributed.
Chlamydophila pecorum infection usually presents as a striking syndrome of rapid onset, high prevalence (20-40% of the flock) polyarthritis in young rapidly growing crossbred lambs post weaning. Dorset lambs are also frequently affected but I have seen the condition only twice in Merino lambs. I have however seen Chlamydophila arthritis as a sporadic disease of low prevalence in some prime lambs flocks. It is my recollection that this disease primarily occurs in the spring and early summer in autumn and winter drop lambs after weaning. This comment is however verging on a data free opinion. I have never seen this condition in mature sheep.
Affected lambs are lame on several legs and often lie under trees to avoid walking. However if exercised they can warm out of this lameness and so cases are more difficult to detect when mustered into yards. Affected lambs are usually febrile although I am not sure how to interpret a body temperature of over 40 C in lambs on a warm day after travelling into yards. Affected joints are moderately painful but are not conspicuously swollen. Lambs respond rapidly to oxytetracycline but I am not sure of the consequences of leaving affected lambs untreated.
Jensen and Swift (1982) describe chlamydial polyarthritis in sheep in the US as 'an acute contagious but nonfatal disease of feedlot and nursing lambs' characterised by fever, lameness, arthritis, serositis, conjunctivitis and emaciation. They comment that it is a major disease of the US sheep industry especially for feedlot enterprises. In the US, the strains of Chlamydia that cause abortions are distinct from the strains causing conjunctivitis. However, neither conjunctivitis nor abortions are a feature of the Australian strains.
I have seen several cases of purulent arthritis affecting about 10% of lambs 2-3 weeks post-mulesing. I have also seen sporadic cases. Affected lambs are markedly lame with hot joints that are sometimes massively distended with pus. A range of pyogenic organisms can be cultured from these joints including Fusobacterium necrophorum, Staphylococcus spp, Histophilus somni, Mannheimia haemolytica (Radostits et al 2007) and Arcanobacter.
As these outbreaks are not anticipated appropriate antibiotic therapy is often not commenced until significant joint damage has occurred. Sometimes, euthanasia is the preferred option. I have mostly seen these outbreaks in lambs mulesed in the spring and they may be associated with small black fly (Musca spp) worry to the wounds delaying healing.
Neonatal arthritis caused by Streptococcus dysgalactiae is the most common form of arthritis encountered in Europe (Watkins and Sharp, 1998). Affected lambs develop a purulent arthritis from two days to about three weeks of age. The disease virtually never occurs in lambs older than about one month of age. A case will be reported (Refshauge and Watt, in preparation) in which 10% of flock of 600 crossbred lambs born in a closely supervised research flock at Cowra, NSW developed neonatal Streptococcal arthritis.
Affected lambs were markedly lame often choosing to lie rather than walk. In early cases, affected joints contained a brownish fluid and a thick yellowish pannus. Later cases may have contained purulent material. All lambs treated with a benzathine procaine penicillin mix responded rapidly and with minimal long term effects.
A wide range of organisms including several exotic to Australia, are capable of causing arthritis in sheep. Histophilus ovis (and previously organisms resembling H. ovis) has been isolated from synovitis and septicaemia cases in southern Australia and New Zealand (Rahaley and White, 1977). They reported on twelve outbreaks of septicaemia, synovitis and/or abscessation in lambs and from two cases of neonatal lamb mortality in Western Victoria from June 1973 to June 1974.
Worldwide, Brucella melitensis is the major cause of brucellosis in sheep and goats and an important zoonosis. It behaves much like the bovine version of brucellosis and so causes spectacular abortion storms in naive animals and occasional mastitis, orchitis and arthritis (Geering and Forman, 1987).
Maedi-visna is a retrovirus, which while exotic to Australia, behaves similarly to the endemic closely related arthritis-encephalitis virus (CAE) in goats. While the maedi form of the disease is characterised by a chronic diffuse interstitial pneumonia and the visna form of the disease is characterised by wasting and neurological signs, both mastitis and arthritis have been reported in association with this virus (Geering and Forman, 1987).
While staphylococci are responsible for occasional cases of purulent arthritis in sheep in Australia, they are a common cause of arthritis in European sheep subsequent to infection by the tick borne protozoa, Anaplasma phagocytophila. This organism selectively destroys white cells (as the name suggests) leading to immune suppression and a susceptibility to infection. The resulting syndrome is named tick pyaemia (Watkins, 2000).
Melioidosis is endemic to tropical Australia and has caused outbreaks featuring lameness and respiratory distress in sheep. While the disease is characterised by multiple abscesses in most organs, in experimental cases the causative bacteria Burkholderia pseudomallei (Pseudomonas pseudomallei) has produced an acute purulent polyarthritis (Thomas 1980).
I am not aware of Mycoplasmas causing arthritis in sheep in Australia. However, Mycoplasma capricolium is reported to cause a septicaemia with subsequent pneumonia and arthritis in kids and lambs. Other Mycoplasma species have caused a similar syndrome again in goats and lambs (Radostits et al, 2007).
Foot abscess is in part an osteo-arthritis of the interphalangeal joints. It is a common condition of heavy sheep grazing on wet pastures. While affected sheep recover, they are often left with permanent damage including ankylosis of the affected joints.
Occasionally lambs with hygroma, a bilateral, painless, fluid filled swelling anterior to the carpii are seen. Hygroma is of no consequence except that it may be mistaken for arthritis.
Farquharson (2008) in an analysis of data from export abattoirs between July 1 2000 and June 30 2006 found that approximately 0.02% of both sheep and lambs were condemned for arthritis. This represented 25% of lamb carcase condemnations but only 6.8% of adult sheep carcases (due to the higher condemnation rate in adult sheep). He then surveyed sheep producers across the southern states of Australia and concluded that arthritis was three times more prevalent than the abattoir data suggested. This is because many affected sheep are culled on farm. Farquharson also summarised NSW laboratory submissions requesting joint culture from sheep from the 1987 to 2005. Chlamydiae were detected in from 20-33% of submissions, Erysipelas from 6-20% of submissions and the pyogenic bacteria from 28-42% of submissions. No organisms were isolated in from 28-42% of submissions.
I contend that these figures should not be taken as a reflection of the true prevalence of these diseases. Erysipelas arthritis for example is readily diagnosed on clinical and gross pathology appearance while Chlamydophila is often diagnosed on history, clinical findings and serology. It is useful to culture the joints of lambs affected by an outbreak of pyogenic bacterial arthritis to help in selecting the most appropriate antibiotic although in practice antibiotic therapy is commenced immediately.
In many flocks, Erysipelas arthritis occurs at such low levels that preventative vaccination of ewes is uneconomic. However, on current lambs prices the break-even on vaccination (assuming 100% efficacy) is about 0.5% prevalence. While I have not seen data on the efficacy of vaccinating ewes pre-lambing to prevent Erysipelas arthritis I have heard anecdotally that it is effective. While at Condobolin, I have on two occasions attempted to assess the effectiveness of a single dose of vaccine administered to lambs at marking. I found no differences between treated and control lambs but in both instances the prevalence was low. Others have also observed the effectiveness of organising a vaccination trial in reducing the prevalence of Erysipelas arthritis (Edmonstone, pers. comm.).
While we as veterinarians assume that improved hygiene at marking and mulesing should reduce the prevalence of Erysipelas arthritis, a large Western Australian case control study does not support this. These authors concluded that any practice that breaks the skin of lambs predisposes to Erysipelas arthritis and if possible lambs should not be mulesed or shorn prior to sale (Paton et al, 2003). Chlamydophila polyarthritis is an enigmatic disease. Little is known of its epidemiology and to my knowledge, the reservoir of the infection is unknown.
I find it peculiar that a disease organism should selectively infect young, otherwise healthy, rapidly growing crossbred lambs after weaning. It is also intriguing that neonatal Streptococcus dysgalactiae arthritis has not previously been reported in Australia. The organism is present and has been reported to cause arthritis in calves (Ryan et al, 1991). However if the disease occurred at a low prevalence on many broad acre Australian sheep farms it may pass unnoticed as affected lambs would be susceptible to predation.