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Hearing Loss from Infectious Diseases: Malaria

HHTM staff writing

Now is the time to get the flu vaccination as a responsible health measure.  Flu is a virus which doesn’t cause hearing loss and and can be caught at home.  Today’s post addresses a different infectious disease that can cause hearing loss but is usually acquired away when traveling away from home.   

Those of us who travel by armchair may find the hardest part of “travel” is adjusting our TV volumes.  But those who journey out in search of worldwide adventure still face the threat of serious diseases in much of the world.  One of those diseases is malaria, which is endemic in countries where a specific parasite and mosquito thrive.  Hearing and balance problems are side effects in some cases.    

 Though rare in the US since it was virtually eradicated in the 1940s, malaria should hold particular interest to Audiologists because both the disease and the treatment pose threats to hearing that are not well known or understood AND the disease is reappearing.

 

What Is Malaria?

 

Malaria parasite invading and rupturing red blood cells
Malaria parasite invading and rupturing red blood cells

First and foremost, malaria is something you do NOT want to get.  It’s one of four plasmodium parasites that can enter the human bloodstream, lodge in the liver, and commence blood cell destruction. By name, the parasites are designated P. falsiparum, P. ovale, P. vivax and P. malarie.

Within the first two weeks, the parasite duplicates itself 10,000 times and then enters the blood stream.  Red blood cells are invaded and destroyed  through a gruesome process.

 [The parasite] digests a cell’s hemoglobin, multiplies inside to the point of rupturing the cell, and rapidly spreads a new generation of infection.

It acts like the flu, presenting with “wrenching cycle(s) of shivering cold, high fevers, and profuse sweats” and more.  But it’s a really bad version of flu, with fevers reaching as high as 107 degrees Fahrenheit.  The CDC describes malaria as a medical emergency, noting that symptoms recur at intervals, associated with anemia and jaundice in “uncomplicated” cases.  Severe cases bring on “seizures, mental confusion, kidney failure, acute respiratory distress syndrome, coma, and [even] death.”

 

Who Gets Malaria?

 

Those who are bitten by a female anopheles mosquito (shown above) are at risk. That is the only insect in the word that carries the human malaria (P. falsiparum) parasite.

http://science.nationalgeographic.com/science/photos/malaria/#/mosquito-nets_1104_600x450.jpg
Mosquito Nets are Good Barriers if They Don’t Have Holes and You Keep Hands and Feet Inside.

The mosquitoes feed at night while humans are in bed– most bites are in the 9pm to 5am– hence, the familiar (and effective) use of bed netting.  But symptoms are delayed, which makes it hard to know when/if one is infected.  Though some people show symptoms within 7 to 10 days post-infection, others do not develop symptoms until 4 weeks after the parasite has entered their bodies.

Travelers to West Africa and India are especially at risk. In addition, malaria is endemic to Haiti, the Dominican Republic, and most countries in Central and South America. Click here for world maps of endemic and non-endemic countries.

These countries lack the infrastructure and financial wherewithal to implement large-scale water drainage projects of the type used in the US  the 1930s which rid the US of malaria.  Plus, such large scale government projects come with other environmental costs.{{1}}[[1]]$1 Million Relief Work for New Mexico. Projects for Community Sanitation and Swamp Drainage.  Santa Fe New Mexican, August 28, 1935, p 1.[[1]]

About the only people who do not get malaria are those with sickle cell anemia and those who carry a single copy of the the sickle mutation.  That’s because the genetic mutation confers natural protection against the malaria parasite in humans.  Although the mechanism by which this happens remains unclear, promising research in mice is ongoing.

Why Worry About Such a Rare Disease?

 

Contracting malaria in the United States is highly unlikely.  In fact, there were only five cases reported to the CDC country-wide in 2011:  1 each from a lab accident and blood transfusion, 2 in babies born to mothers who had traveled abroad, 1 unexplained.

But bringing malaria home to the US is a rapidly growing problem — up 48% from 2008 to 2011.  According to an article in the CDC’s Mortality and Morbidity Weekly Report, US malaria cases  hit a 40 year high in 2011 due to travelers who imported malaria contracted abroad.  CDC Director Tom Frienden commented in a news release:

“The increase in malaria cases reminds us that Americans remain vulnerable and must be vigilant against diseases like malaria because our world is so interconnected by travel.”

 

What Links Malaria to Hearing Loss?

 

There are two links, the first indirect but well documented; the second, direct but tentative.

  1.  Antimalarial drugs have been linked to hearing loss for some time.  That topic will be addressed in a later post.
  2. A direct link between malaria itself and hearing loss, about which little is known.

According to a recent systematic literature search, malaria itself is “a rare case of hearing loss in various studies”  but there has been no serious investigation of the link to date.  The lack of data is in part due to confounding effects of treatment, but also because the disease ravages far more than hearing and the hearing effect is rare, or at least rarely measured. Descriptions of type, configuration and degree of hearing loss are lacking.

However, the authors of the literature search reported a handful of antimalarial drug trials in which hearing was tested prior to treatment and a subset of patients with “unexplained hearing loss which improved with elimination of the parasite.”  The idea of reversible hearing loss in one or both ears, especially if it is sensorineural in nature, associated with presence/absence of a parasite is intriguing and indicates the need to develop audiologic protocols for serial monitoring of hearing in those who present with a history of malaria.

Images courtesy of National Geographic Science photo gallery