Tropical Health Matters

March 3rd marks the annual World Health Day. The World Health Organization explains that the purpose of this day is to raise awareness on how to prevent deafness and hearing loss and promote ear and hearing care across the world. WHO notes that, “Unless action is taken, by 2030 there will be nearly 630 million people with disabling hearing loss.”

Factors associated with health loss and disability include ageing of the population, environmental noise exposure, certain medications, and infectious diseases. It is the latter that we address here.

Globally there are several infectious diseases associated with hearing loss. In children these include congenital rubella infections a direct result of bacterial meningitis infections, although with improved immunization rates these are less of a problem. In contrast Congenital cytomegalovirus infection has been on the increase.

Continuing study of Ebola, Lassa Fever and Zika point to infectious tropical diseases as another serious concern.  The large scale of infection and survisorship in Ebola outbreak in West Africa made it possible to study on a large scale reported symptoms of “post-Ebolavirus disease syndrome” (PEVDS) that include, “chronic joint and muscle pain, fatigue, anorexia, hearing loss, blurred vision, headache, sleep disturbances, low mood and short-term memory problems.” A study of 277 Ebola Survivors in one Sierra Leone community found the following clinical sequelae were common: arthralgias (76%), new ocular symptoms (60%), uveitis (18%), and auditory symptoms (24%).

Lassa Fever has unfortunately made a strong showing in West Africa this dry season. Mateer and colleagues noted an association between Lassa fever (LF) and sudden-onset sensorineural hearing loss (SHNL) was confirmed clinically in 1990. Their literature review found that, “Although LF-induced SNHL has been documented, the prevalence and economic impact in endemic regions may be underestimated.”

Finally, while much of the focus on the complications of Zika have focused on microcephaly, other problems occur.  Zare Mehrjardi et al. documented that Zika Virus may cause “other central nervous system abnormalities such as brain parenchymal atrophy with secondary ventriculomegaly, intracranial calcification, malformations of cortical development (such as polymicrogyria, and lissencephaly-pachygyria), agenesis/hypoplasia of the corpus callosum, cerebellar and brainstem hypoplasia, sensorineural hearing-loss, and ocular abnormalities as well as arthrogryposis in the infected fetuses.”

The benefits of vaccines for rubella and meningitis should spur on immunization research for Ebola, Zika and Lassa Fever. In the meantime there are some preventive measures. One would not have thought that using personal protective equipment by health workers would protect hearing, but it is a practice that should be enabled and encouraged for multiple reasons. Household and community control of Aedes aegypti and rodent breeding to prevent Zika and Lassa, respectively, can also help. By protecting our communities from infection we can also protect their hearing.

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