Document Type : Original Articles
Authors
1
Human Viral Vaccines Department, Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, P.O. Box 14831975, Iran.
2
Department of Animal Pathology and Epidemiology, Razi vaccine and Serum Research Institute, Agricultural research, education and extension organization (AREEO), Karaj, Iran.
3
Master's student in Pharmaceutical and Industrial Biotechnology, Faculty of Natural Sciences, Martin Luther University (MLU), Halle(Saale), Germany.
4
Department of Pathology and Experimental Animals, Razi vaccine and Serum Research Institute, Agricultural research, education and extension organization (AREEO), Karaj, Iran.
10.22092/ari.2025.369465.3696
Abstract
Since the 1960s, when the first live-attenuated vaccine against the mumps virus was developed, the mumps outbreaks have dramatically decreased. Monkey-based neurovirulence test has been developed and used to assess the safety of the attenuated mumps virus strains. However, the monkey-based test may not necessarily reflect the neurovirulence behavior of the Mumps virus when administered to the vaccinees. A neonatal rat-based MuV neurovirulence safety test has been developed and recommended by reference institutions in recent years. This test in Lewis rats was first introduced in 1998. This study aimed to evaluate the suitability of neonatal Sprague-Dawley rats for the neurovirulence test of an Iranian Mumps virus vaccine strain, RS-12. One-day-old Sprague-Dawley newborn rats were intracranially injected with MRC-5 cell supernatant (assigned as “C” for control group), the RS-12 attenuated strain (assigned as “V” for vaccine group), and the RS-12 wild-type strain (assigned as “W” for wild-type group), respectively. The animals were observed for 30 days post-injection regarding the weight gain, viral titer in the brain tissue, and appearance of hydrocephalus in the brain sections. The mean weight gain in groups C and W was the highest and lowest, respectively. Regression analysis of Log weight values revealed a significant difference between group C and group W. A significant difference between group V and group W was seen. There was no significant difference between the weight gain of group C and group V. No Mumps viruses were detected in the homogenized brain samples of group C, and in groups V and W, the viral titers showed a continuous decrease during the observation period. In the microscopic view of brain sections, the hydrocephalus started to form on day 15 post-injection and reached its highest extent on day 30th. On day 30 post-injection, the hydrocephalus area was determined as a maximum of 1%, 5%, and 10% for the C, V, and W groups, respectively. This study introduced the newborn Sprague-Dawley rat model capable of demonstrating the neurovirulence potential of mumps viruses in vaccinees and distinguishing between wild-type and attenuated RS-12 strains. Further experiments are needed for optimization and validation of the test procedures.
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