The conducted studies made it possible to establish previously unknown microscopic changes in dry and mixed forms of infectious peritonitis of cats, to detail the morphogenesis of the disease in the temporal aspect and to supplement the morphological diagnosis of the disease during life and postmortem examination.
In our studies, the mixed form of the disease was registered in 78.8 % of cases (26 cats out of 33), and the dry form in 21.2 % of cases (7 cats out of 33). The wet form of infectious peritonitis in our work was not encountered.
At the dissection, it was established that the corpses of cats that had been suffering from infectious peritonitis for more than a month were emaciated. In all animals with a mixed form of the disease, a different degree of abdominal distension was registered. In both dry and mixed forms of the disease, pallor and jaundice of visible mucous membranes and subcutaneous tissue were recorded.
In a part of cats that had infectious peritonitis for less than 3 weeks before death
(19.2% of animals with mixed and 42.9% of animals with dry forms of the disease), all lymph nodes were enlarged.
In the abdominal and thoracic cavities of cats with a mixed form of infectious peritonitis, a clear, straw-yellow liquid was found.
The kidneys in all cases, both at the dry and mixed forms of infectious peritonitis,
were enlarged and unevenly colored – with numerous grayish areas of various sizes
and shapes. The spleen appeared unchanged or somewhat flaccid.
Macroscopic changes in the liver of all cats did not depend on the form of the disease, but depended on the duration of the infection.
The mucous membrane of the stomach and small intestine was hyperemic in 19.2 % of cats with a mixed form of the disease and in 28.6 % of cats with a dry form.
In all cases, the brain and spinal cord were grossly unchanged, and in the heart, the right ventricle was enlarged.
At the histological examination, it was found that the cellular infiltrate and granulomas in various organs and tissues in both forms of infectious peritonitis of cats contain mainly lymphocytes.
It was demonstrated for the first time that the mesothelium, which covers the organs of the abdominal and thoracic cavities, undergoes pronounced metaplasia in both forms of infectious peritonitis – only in some areas it was not changed.
Discomplexation of the adjacent metaplastic cells of the mesothelium and their separation into the lumen of the abdominal and thoracic cavities was also established, which indicated significant violations of intercellular connections. Part of the changed
cells of the mesothelium was destroyed.
For the first time, a detailed microscopic study of the mesentery of the small and large intestines of cats was carried out.
For the first time, it was found that at the infectious peritonitis of cats in the mesentery of the small and large intestines, regardless of the form and duration of the disease, necrosis and destruction of the mesothelium and the underlying layer of thick bunches of collagen fibers are detected.
It has been shown that dry and mixed forms of infectious peritonitis in cats are characterized by generalized damage to the walls of all blood vessels.
It has been established that microscopic changes in the brain and spinal cord, in the stomach, small and large intestines, somatic and visceral lymph nodes, pancreas, lungs and heart do not depend on the form of the disease or on the duration of its course. Spasm of blood vessels, edema of the brain substance and basophilia of nerve cells are established in the brain and spinal cord.
In each cat, the microscopic changes in all examined lymph nodes were similar. At the same time, such changes were somewhat different in different animals, regardless of the form of the disease, age, sex of the animals, and the duration of the disease, which reflected the individual characteristics of the state of the immune system.
In the gastrointestinal tract, the most significant microscopic changes occurred in the muscle sheath.
In the pancreas was established granular dystrophy of insular cells and destruction of part of the secretory cells of the acini. In the myocardium – granular dystrophy of cardiomyocytes. In the lungs, there is venous congestion and edema, and directly under the fibrinous-necrotic overlays, there is also pronounced infiltration of the walls of the alveoli by lymphocytes and monocytes.
Microscopic changes in the spleen, liver and kidneys do not depend on the form of the disease, but differ depending on the duration of its course.
In the liver of cats whose disease lasted up to 3 weeks, congestive hyperemia, granular dystrophy and destruction of hepatocytes, hypertrophy of Kupffer cells, slight infiltration by lymphocytes and monocytes, and edema and foci of necrosis are recorded. Portal hepatitis and necrosis of most of the hepatocytes are diagnosed in cats whose illness lasted more than 3 weeks.
