Outbreaks of polyarthritis in farmed crocodiles (Crocodylus niloticus) on five farms in Zimbabwe are described.
Cases were reported only among the rearing stock aged 1-3 years. No breeding stock suffered. Morbidity was
about 10% and the mortality even lower. All the sick animals consistently displayed swollen limb joints as well as
progressive lameness and paresis. The synovial structures in subacute cases contained mycoplasmas and excess
turbid mucus which, at a later stage of the disease, became yellowish, inspissated and sterile. Cellular changes
in the joint capsule included oedema, necrosis of the superficial layers of membrane, lymphocytic infiltration and
fibrosis. Evidence of pneumonia was observed only at necropsies.
Fifteen isolates of Mycoplasma were cultured from the clinical specimens collected from the four sick and three
dead crocodiles. The affected joints of all these animals yielded Mycoplasma in pure culture, but the culture from
lungs yielded post-mortem invaders also. The sick animals were treated with a single intramuscular injection of
long-acting tetracycline(10 mg/kg), and oxytetracycline 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 some cases inflammatory swelling persisted.
All 15 the isolates conformed to the characteristics of the genus Mycoplasma, and were serologically indistinguishable
in growth-inhibition (GI) tests. Although these isolates shared the main biochemical characteristics of Mycoplasma
capricolum, they differed serologically. Also goats were refractory to experimental infection with crocodile
strains. In crocodile yearlings, however, the disease was reproduced with an isolate from one of the affected farms.
The source of infection remained elusive. The farmers suspected poultry meat fed to the crocodiles to be the source.
However, GI tests failed to identify the isolates as one of the pathogenic glucose-metabolizing avian mycoplasmas.
This appears to be a first report of isolation of Mycoplasma from crocodiles and also of its association in disease.
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