MYCOPLASMA-ASSOCIATED POLYARTHRITIS IN FARMED CROCODILES (CROCODYLUS-NILOTICUS) IN ZIMBABWE

Outbreaks of polyarthritis in farmed crocodiles (Crocodylus niloticus) on five farms in Zimbabwe are described. Cases were reported only amo ng the rearing stock aged 1-3 years. No breeding stock suffered. Morbi dity was about 10% and the mortality even lower. All the sick animals consistently displayed swollen limb joints as well as progressive lame ness and paresis. The synovial structures in subacute cases contained mycoplasmas and excess turbid mucus which, at a later stage of the dis ease, became yellowish, inspissated and sterile. cellular changes in t he joint capsule included oedema, necrosis of the superficial layers o f membrane, lymphocytic infiltration and fibrosis. Evidence of pneumon ia was observed only at necropsies. Fifteen isolates of Mycoplasma wer e cultured from the clinical specimens collected from the four sick an d three dead crocodiles. The affected joints of all these animals yiel ded Mycoplasma in pure culture, but the culture from lungs yielded pos t-mortem invaders also. The sick animals were treated with a single in tramuscular injection of long-acting tetracycline(10 mg/kg), and oxyte tracycline mixed in feed at 550 mg/kg was fed for 10 d. The treatment appeared to be effective in ameliorating the clinical signs, but in so me cases inflammatory swelling persisted. All 15 the isolates conforme d to the characteristics of the genus Mycoplasma, and were serological ly indistinguishable in growth-inhibition (GI) tests. Although these i solates shared the main biochemical characteristics of Mycoplasma capr icolum, they differed serologically. Also goats were refractory to exp erimental infection with crocodile strains. In crocodile yearlings, ho wever, the disease was reproduced with an isolate from one of the affe cted farms. The source of infection remained elusive. The farmers susp ected poultry meat fed to the crocodiles to be the source. However, GI tests failed to identify the isolates as one of the pathogenic glucos e-metabolizing avian mycoplasmas. This appears to be a first of isolat ion of Mycoplasma from crocodiles and also of its association in disea se.