Runting syndrome in neonatal rabbits infected with Treponema pallidum.

Infection of rabbits with prior to the 2nd week of life usually resulted in progressive runting leading to death about the 7th–13th week of age. The severity of the disease could be evaluated at any particular time by the percentage weight retardation. In this small series there was a suggestion that the runting index (R.I.) and the presence or absence of reagins might correlate with the prognosis of the disease. Weight retardation of more than 25% and a R.I. of less than 0·81 were usually associated with irreversible, pathological processes refractory to penicillin therapy. The disease occurred in degrees of severity. There was a mild form with a R.I. of about 0·90, reactive Malpighian corpuscles and increased number of histiocytic like cells in the spleen but with normal thymuses. A moderate form was described with a R.I. of about 0·81 and partial depletion of lymphocytes in the spleen with predominance of histiocytic like cells. The thymuses were normal. A severe form was characterized by a R.I. of 0·65–0·76, depletion of lymphocytes and increased number of histiocytic like cells in both spleen and thymus. The possibility that the syphilitic runting syndrome in baby rabbits is the result of a direct, or indirect action of the treponemes on the lymphatic system is advanced.