CONSIDERACIONES GENERALES PARA LA PUESTA EN

The distribution o f macroscopic and microscopic l esions m possums mfected following conJunctival i nfection \Yith the m edium and high doses, or by the i ntratracheal route, were compared with that reported in

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1 905 ). there \\ as only one possum \Vith lesions after low dose infection, no analysis ''as

conducted. Overall there was p oor correlation b et\veen the distributions o f macroscopic lesions b etween the naturally infected and experimentall y i n fected possums. The intratracheal group had the h ighest correlation (0. 5 3 ), with the medium dose group (0.2 1 )

and high dose group ( -0. 1 0) shov�ing no correlation. The correlati on \Vas higher 1.vhen the distributions of microscopic l esions w ere compared. The i ntratracheal and medium dose groups were simil ar (0.7() and 0 72 respectively) but the high dose group showed poor correlat ion (02 1 ).

DISCUSSION

Tuberculosis in captive possums was induced by instilling a suspensi on of M. bovis into

the conjunctival sac. The proportion of possums that became diseased, the rate of

development and severity of lesions, the severity of clinical signs, and distribution of

macroscop ic and microscopic lesions, \Vere all dependent on the dose of M

bovis.

visible lesions developed on the conjunctivae of infected possums.

Increasing dose rate produced an increase in the severity of the infection and the time course of disease was shortened. The medium dose group in Experiment 2 lead to the development of tuberculosis in nine out of l 0 possums. The disease in these possums progressed slowly, compared with those i nfected by the intratracheal route, and was

characterised by the development of palpable lesions in superficial lymph nodes in fi ve possu ms and a draining si nus in one. Lower and higher dose rates gave different results. A

five fold lower dose (400 cfu) lead to disease in only t\vo of 1 0 possums and a five-fold higher dose ( 1 0,000 cfu) lead to a more rap i d disease process.

Conj uncti val infection produced disease v,rith the characteristics that were desired: a

slowly developing disease, with superficial lymph node lesions and widespread evidence of microscopic infection. The disease resulting from conj unctival infection had a less

dramatic effect on the general health of the possums than did i ntratracheal i nfection. Even

with the highest dose rate the diseased possums did not become debil itated and the

maj o rity gained body weight The highest dose lead to the rapid development of superficial

lymph node lesions and the development of draining sinuses. That group was euthanas ed in the ninth week after infection because there was a high risk of transmission of disease from

open draining sinuses. By about eight weeks after intratracheal infection the possums had either died or were severely debilitated. The disease in these possums was characterised by

extensive lung lesions.

The optimum dose for conj unctival infection was between 1 000 cfu and 2000 cfu. This

dose resulted in disease with a course that reflected tuberculosis as seen in naturally

infected possums. The possums had progressing infection and i n the second

experiment half of the group receiving this dose developed cli nically detectable swellings by nine weeks and 90% had pulmonary disease. At 1 5 weeks one possum d ied from

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