Evaluation of a Neonatal Rat Model for Prediction of Mumps Virus Neurovirulence in Humans

Abstract

Neurovirulence of several mumps virus strains was assessed in a prototype rat neurovirulence test and compared to results obtained in the monkey neurovirulence test. The relative human neurovirulence of these strains was proportional to the severity of hydrocephalus in rats but not to lesion scores in the monkeys.Neurovirulence testing is performed to demonstrate that attenuated mumps virus seeds used in the manufacture of vaccine lack the neurovirulence properties of wild-type mumps virus strains. Mumps virus neurovirulence testing as currently performed in monkeys has failed to discriminate between strains with known differences in human neurovirulence (2,8,27,28). Similarly, tests in hamsters have also failed to reliably discriminate neurovirulent from nonneurovirulent human mumps virus strains (12,19,22,34). The difficulty in evaluating the neurovirulence potential of mumps viruses may be reflected in reports of mumps virus central nervous system (CNS) infection causally linked to vaccination with some mumps virus vaccines (e.g., Urabe-AM 9, Leningrad-3, and Sofia-6) (3,9,10,23,24,32). Thus, a validated mumps virus neurovirulence test with greater relevance to human disease remains an important public health objective.Because neonatal rat brain is particularly sensitive to damage following perinatal virus infection (5,6,11,13,16,25,26,31), it was hypothesized that neuropathology in rats neonatally inoculated with mumps virus may serve as a sensitive indicator of neurovirulence potential in the human CNS. Litters of 1-day-old Lewis rats were inoculated intracranially with 0.02 ml containing 10 2 PFU of the following mumps virus strains: (i) Jeryl Lynn vaccine (JL) (15); (ii) RIT 4385 vaccine (JL-RIT), cloned from JL by limiting dilution (33); (iii) Urabe-AM 9 vaccine (Ur-AM9) (35); (iv) Ur-1004, a cerebrospinal fluid isolate from a case of Ur-AM9 meningitis (7); (v) Kilham, a wild-type strain isolated from human breast milk and serially passaged in suckling hamster brain (20); (vi) Lo1, a wild-type strain isolated from the saliva of a patient with uncomplicated parotitis (1); and (vi) 88-1961, a wild-type strain isolated from the saliva of a patient with parotitis and symptoms of CNS infection.Rats were euthanized on days 3, 6, 9, and 30 postinoculation, and brains were removed and either homogenized to determine viral titer by plaque assay (26) or fixed in 10% formalin for histological analysis. Two 3-to 4-mm-thick sagittal slices were selected at a standard distance from either side of the anatomical midline from a fixed brain, paraffin embedded, sectioned, and stained with hematoxylin and eosin. The severity of hydrocephalus was determined as the percentage of the total brain cross-sectional area (excluding the cerebellum) occupied by the lateral ventricle on each of the two sections per rat using Image Pro Plus image analysis software (Media Cybernetics, Silver Spring, Md.). The mean percentage of hydrocephalus in each experimental group of rats was calculated and designated as the rat neurovirulence test...

Oncolytic activities of approved mumps and measles vaccines for therapy of ovarian cancer

“…Toxicity was minimal but clinical responses were very encouraging, including partial response or total regression in 37 out of 90 patients 47 and disappearance of ascites in 26 out of 37 patients. 50 Despite the very encouraging clinical data, it is not clear why the studies did not result in widespread testing of Urabe mumps as an oncolytic. 38 It could be due to possible safety concerns with the Urabe strain.…”

Identification of genetic mutations associated with attenuation and changes in tropism of Urabe mumps virus

“…The former site has been shown to be particularly susceptible to mutation after passage in Vero cells [Sauder et al, 2006], so there is a possibility that the mutation here in 1004-10/2 may have occurred after isolation of the virus from the patient. The mutation in Gw7 observed at nt 15,328 is also present in the published sequence for 87-1004, and a stock of this virus, like 1004-10/2, has been shown to have intermediate virulence in the RNVT [Rubin et al, 2000], suggesting that this mutation on its own does not confer attenuation.…”

“…In the RNVT, there is no threshold value that discriminates a virulent virus from an attenuated virus, and the test is designed to compare the virulence or attenuation of one strain to another within a single experiment. Although the absolute scores determined for 1004-10/2 and the original stock of 87-1004 were different, the hydrocephalus score for the latter was shown to be intermediate when compared to 88-1961 and JL in a separate assay [Rubin et al, 2000].…”

“…Fixed brains were processed, embedded in paraffin and sectioned sagitally at 8 mm. Two sections from each rat brain taken at anatomical midline were stained with hematoxylin and eosin and assessed for neurovirulence as described previously [Rubin et al, 2000]. Briefly, the percentage of the total brain cross sectional area (excluding cerebellum) occupied by the lateral ventricle was determined for each pair of brain sections for each rat using Image Pro Plus TM image analysis software (Media Cybernetics, Silver Spring, MD).…”

“…Recently, a rodent model has been developed that is predictive of neurovirulence of mumps isolates in humans [Rubin et al, 2000[Rubin et al, , 2005. In this system, the severity of hydrocephalus developing in brains of neonatal rats after intracranial (i.c.)…”