Apoptosis in canine distemper

Abstract

Canine distemper is a systemic viral disease characterized by immunosuppression followed by secondary infections. Apoptosis is observed in several immunosuppressive diseases and its occurrence on canine distemper in vivo has not been published. In this study, the occurrence of apoptosis was determined in lymphoid tissues of thirteen naturally infected dogs and nine experimentally inoculated puppies. Healthy dogs were used as negative controls. Samples of lymph nodes, thymus, spleen and brain were collected for histopathological purposes. Sections, 5 microm thick, of retropharingeal lymph nodes were stained by HE, Shorr, Methyl Green-Pyronin and TUNEL reaction. Shorr stained sections were further evaluated by morphometry. Canine distemper virus nucleoprotein was detected by immunohistochemistry. Retropharingeal lymph nodes of naturally and experimentally infected dogs had more apoptotic cells per field than controls. In addition, DNA from thymus of infected dogs were more fragmented than controls. Therefore, apoptosis is increased in lymphoid depletion induced by canine distemper virus and consequently play a role in the immunosuppression seen in this disease.

Morphometric analysis of the thymus of puppies infected with the Snyder Hill Strain of canine distemper virus

“…The only consistent post-mortem finding in uncomplicated CD is the thymus atrophy (Appel, 1969;Appel, 1987;Moro et al, 2003b). In some puppies, the thymus is not demonstrable grossly (Mccullough et al, 1974).…”

“…CDV infection causes lymphopenia and immunosuppression in dogs during the early phase of the disease (Iwatsuki et al, 1995;Moro et al, 2003b). Lymphopenia probably occurs due to the ability of the virus to replicate in and destroy the lymphoid tissues (Mccullough et al, 1974).…”

“…Lymphopenia probably occurs due to the ability of the virus to replicate in and destroy the lymphoid tissues (Mccullough et al, 1974). The infection induces lymphoid cells apoptosis (Moro et al, 2003b) that can also be observed in blood smears (Moro et al, 2003a;b).…”

“…In gnotobiotic dogs, at post inoculation day 6 corticomedullary ratios of thymus decrease, together with the loss of distinct demarcation between cortex and medulla. The decrease in thymic size is due both to loss of cortical thymocytes in the absence of necrosis (Krakowka et al, 1980) and inflammation, and in the presence of apoptosis (Moro et al, 2003b).…”

“…Deregulation of this process, resulting in either too much or too little cell death, can cause both developmental defects and a wide variety of disease states (Verhagen and Voux, 1999). Apoptosis has been observed in various immunosuppressive diseases of humans and animals (Ameisen and Capron, 1991;Lam and Vasconcelos, 1994;Sarli et al, 1998;Moro et al, 2003b). Ito et al (1997) suggested that apoptosis induced in stimulated MV-infected cells could be one mechanism of immunosuppression that occurs in natural MV infection.…”