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Rubella (German measles) is a contagious viral infection caused by
Rubella virus (RuV) and most frequently it occurs in the fetus during
pregnancy. Congenital rubella infection is one of the most common causes of
hearing loss in newborns. The aim of the present study is to systematically
review the audiological findings in congenital rubella syndrome. Based on the
audiological evaluation the degree, type and configuration of hearing loss
could be identified for both ears separately. The studies reported that degree
of hearing loss varied from mild to profound hearing loss and have bilateral
symmetrical hearing loss. They do often exhibit sensorineural or neural hearing
loss. Early intervention can diminish the consequences of hearing loss on child
development. Rubella antigen vaccination to all the mothers during their
gestation period must be essential in order to prevent congenital rubella
syndrome. Screening of all neonates before discharge from hospital should be
implemented in all the hospitals to identify congenital hearing impairment at
the earliest possible.
Keywords: Rubella virus, Hearing
loss, Congenital, Rubella syndrome
INTRODUCTION
Rubella (German measles) is contagious mild viral infection usually
manifests with fever and rash caused by Rubella virus (RuV) occurs in fetus
during pregnancy [1]. It is Togaviridae family of the genus Rubivirus which
affects multiple organs in the system [1]. The effect of rubella infection
varies depending on time of gestational period. Previous study reported that
the frequency of occurrence of congenital infection is greatest (80%) during
the fetus and reduces at the end of second trimester [2,3]. Congenital rubella
infection causes multiple congenital abnormalities with wide spectrum of
clinical manifestation in fetus, i.e., auditory deficits, vestibular deficits,
cataracts, cardiac defects, nerve deafness and cerebral lesion. The
complications in later stages include thyroid disease, diabetes, growth hormone
deficiency and pan encephalitis in newborns [1,4]. Rubella infection in
pregnant women may cause fetal death or congenital defects. Congenital deficits
in children due to rubella infection are diagnosed as congenital rubella
syndrome (CRS). Immunization is only treatment option for prevention of
congenital rubella syndrome [5]. The countries without having rubella
vaccination program are suffering with high prevalence of congenital hearing
loss due to congenital rubella infection as a major leading environmental
cause.
GLOBAL BURDEN OF CRS
AND HEARING LOSS
CONGENITAL RUBELLA SYNDROME AND HEARING LOSS
Congenital rubella
infection is one of the most common cases of hearing loss in newborns [2]. In
children with CRS sensorineural hearing loss is the second most commonly noted
among the various congenital abnormalities in CRS [4,9]. Previous studies
reported that the type of hearing loss generally exhibited by CRS are profound
degree with sensorineural hearing loss usually bilateral than unilateral
hearing loss [10]. Some studies also reported that the degree of hearing loss
may vary in range from mild to profound and audiometric configuration is
generally flat but few may exhibit sloping pattern and trough pattern
audiogram. The type of hearing loss is depending on site and extent of lesion
in cochlea and trimester of congenital rubella infection [10,11]. The mixed
type hearing loss is uncommon in children with congenital rubella syndrome
[11]. Recent study on profiling the audiological characteristics in early
infancy (before 6 months of age) by Sao and Navya [12]. In this study, the
infants underwent detailed audiological evaluation including otoscopic
examination, behavior observation audiometry (BOA), immittance audiometry,
otoacoustic emission (OAE) and auditory brainstem response (ABR) test. The
otoscopic examination revealed no structural abnormalities of ear canal and
tympanic membrane. In behavior observation audiometry, the auditory behavior
responses ex. eye blinking, startle responses etc. varies depending on degree
of hearing loss. Since, the BOA has poor sensitivity (66.7%) and specificity
(86.9%), the objective diagnostic test were adopted [13,14]. The immittance
audiometry findings suggestive of intact functioning of middle ear. The absent
of OAE suggestive of abnormal outer hair cell functioning in both ears in
infant with congenital rubella syndrome. The ABR test was used for threshold
estimation, suggestive of infant with CRS have mild to profound degree of
hearing loss. In the same study it was
also concluded that in CRS may have present OAE and absent of ABR, suggestive
of intact functioning of sensory hair cell, i.e., outer hair cell but
dysfunctioning of auditory nerve indicative of neural hearing loss in both
ears. Based on the audiological evaluation the infants with CRS were diagnosed
as having bilateral symmetrical sensorineural hearing loss which may range from
mild to profound hearing loss. Thus in this study, all administrated objective
test batteries will give valuable information regarding symmetry and severity
of hearing loss in infant with CRS before 6 months of age and audiological
outcomes in newborn with CRS by using state of art standardized technological
instruments for better understanding which aids in channelizing to accurate
diagnosis [12].
The newborn have high
risk of congenital hearing loss if rubella infection occurs before the 18th
week of gestations [10]. Histopathological studies reported that inner ear is
most susceptible to damage during sixth to twelve weeks of pregnancy [9]. Thus
sensorineural hearing loss in newborns with CRS can be attributed to
hemorrhagic damage of sensory end organ of hearing, i.e., organ of corti [15]
and interruption in further development of different parts of inner ear and
auditory nerve [16]. Bhandary et al. [17] reported that virus affects the blood
supply and cystic dilation of the stria vascularis and partial collapse of
reissner’s membrane of inner ear. It was also reported that the effect of
hearing loss resulting in delayed development of speech and language
milestone mental retardation and
cerebral palsy seen in newborns with CRS [18,19].
INITIATIVE OF GOVERNMENT OF INDIA FOR PREVENTION AND IDENTIFICATION
HEARING LOSS IN CRS AND MANAGEMENT
The Government of India
has launched the national program, i.e., National Program for Prevention and
Control of Deafness (NPPCD) and Rashtriya Bal Swasthya Karyakram (RBSK). This
program is also integrated with state and district level program, i.e.,
National rural health mission in India for early identification and early
management of hearing loss. In addition, Government of India has assign work to
Anganwadi (AWW) workers and Accredited Social Health Activist (ASHA) workers
for door to door survey of deafness maintain records and refer the cases of
hearing loss in district hospital/state medical colleges for detail
audiological evaluation and treatment [19]. The newborn screening program is
also started by All India Institute of speech and hearing funded by Ministry of
Health and Welfare. This program focuses on the early identification and
rehabilitation of hearing loss in newborns. The early identification of the
hearing loss with CRS in newborns will lay a path for the efficient
intervention program for the welfare of the child as early as before 6 months
of age itself [21].
CONCLUSION
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