PATHOLOGICAL STUDIES ON THE CHANGE IN THE LIVER AND LUNG OF THE DOGS IN DIFFERENT AGES CAUSED MAINLY BY THE LARVAE OF INFECTING ROUNDWORM (TOXOCARA CANIS)

Abstract

It is known that Toxocara canis does not parasitize in the adult dog but in minor. As to this point, some immunological studies are performed by many authors.
In this report, differences depending on the age of dogs in histological changes around the larbored in the liver or lung, and histological findings in the lung of the parasitized adult dog after the operation of anastomosis between portal vein and inferior vena cava, are described.
About ten thousand eggs of Toxocara canis per kilogram of body weight are given by catheter into the stomach of dogs which are 7 and 15 days old, 1, 2, 3 and 6 months old and over one year old, and above mentioned operated dog, respectively.
On the 5th, 10th, 15th, 20th, 25th and 30th day after giving the eggs, the liver and lung were studied histologically at autopsy.
In cases of the dog which were 7 or 15 days old, general symptom were almost normal after giving the eggs, that is, eosinophilic leucocyte did not increase, and visceral migration rate of the larva was prompt. On the 5th day, round cell infiltration around the larva was found in the liver and lung, but on the 10th day, this was almost entirely repaired.
In cases of the dogs which were 1_??_3 months old, marked general responses appeared, eosinophilic leucocyte count increased moderately, the visceral migration rate was lessened and the growth of larva was retarded. In the liver and lung, the reactions were found to be localized, the round cell infiltration around the larva changed into the proliferation of fibrocytes or reticulocytes on the 10th day after the infection, and into a perfect tubercle on the 30th day after.
In cases of the dogs which were over 6 months old, the general reactions were slight, a marked eosinophilia was found, the visceral migration rate was so slow that the majority of larvae remained in the liver even on the 10th day. The reaction in the liver and lung was a localized and productive one at the initial stage, and complete tubercles were found until the 20th day.
In case of the adult dog which was parasitized after making the anastomosis between portal vein and inferior vena cava, a comparatively strong exudative change was found around the larva in the lung, and a nearly complete tubercle was formed on the 35th day after the infection.
In conclusion, the defence power of hepatic and pulmonary tissues against the larva of Toxocara canis is thought to be established almost completely in 6 months of age.
The fact that adult dogs are scarcely parasitized by Toxocara canis is due to the strong defence power of their liver tissue and that of the lung tissue solely is not sufficient.