Wednesday, February 17, 2016

On to the Next One

Jay Z, image from Newsweek

Isn't it phenomenal that there's always a newer, more pressing issue on the horizon? In the words of Jay Z:

"Ya'll should be afraid of what I'm gonna do next"

Now that the WHO has declared the ebola outbreak completely over (with a new case reported the very next day, whoops!)...

This is the first thing I thought of when I saw the declaration of the end of the ebola outbreak.

The new focus is on the Zika virus (ZIKV) outbreak in South and Central America. I've been waiting to write this post for weeks because the news coverage is so heavy, and I didn't feel like being redundant. Everyone has heard about this "new" virus, the "new" link to microcephaly, and most recently, the anti-GMO tie to Monsanto. But, what do we really know about ZIKV? Let's break it down:

ZIKV is not a new virus.
ZIKV is a single-stranded RNA virus of the Flaviviridae family. It is related to dengue virus (DENV), West Nile virus (WNV), yellow fever virus (YFV), and Japanese encephalitis (JE) virus.

ZIKV structure, thanks to St. George's University in Grenada
While newly introduced to South and Central America, ZIKV has been endemic in specific regions of Africa and Asia for quite some time. ZIKV was first discovered in Uganda in 1947, yet phylogenetic analysis of the viral genome estimate that ZIKV originated sometime between 1892 and 1947 (most likely in the 1920s). Early reports stem back to the 1950s, but with evolution of arthropod-borne viruses (arboviruses), the general and non-specific symptoms reported may have been caused by a similar virus (more on that later). Both urban and sylvatic, or rural/forest-based, transmission has been reported, and ZIKV is also seen in monkeys.

Yet, the recent and substantial outbreak in South and Central America (most notably in Brazil, which reported more than 14,000 cases in a matter of months) is new and a big deal. Prior to outbreak in 2015, ZIKV was wreaking havoc on islands like French Polynesia (2013-2014) and Easter Island (2014-2015). In fact, the outbreak in French Polynesia illustrated the link between ZIKV infection and chronic neurological conditions, specifically Guillain-Barré Syndrome

Pregnant women are always seen as an "at risk" or "high risk" group.
The human body goes through a plethora of changes and adaptations when pregnant, mostly because survival of the mother is imperative for survival of the fetus. Development of the fetus is directly dependent on the numerous resources that the mother's developed body provides. The most relevant to this blog is "immunological priming", that continues after birth through contact with the mother's microbiome during the birthing process and during breast feeding.  
Given the sensitivity of this relationship, pregnant individuals are always seen as a high risk group, as some pathogens can travel across the placenta, exposing the fetus during development and before birth. Trans-placental transmission/exposure to ZIKV is currently being investigated by a number of different institutions. With the increase in microcephaly cases during the ongoing ZIKV outbreak in South and Central America, it is understandable why a potential link would cause alarm. 

One important thing to note is that Brazil is one of the few places that already had baseline incidence and prevalence data for microcephaly, making the increase in cases easier to identify. That type of data hasn't been readily available during previous outbreaks in other regions, which makes it difficult to determine whether or not ZIKV is the immediate cause. 

A mosquito bite does not guarantee disease.
Unlike it's relative, dengue virus, it is estimated that only 20% of people infected with ZIKV will become ill and experience symptoms. That means 80% of people infected are asymptomatic (meaning, they do not have any symptoms and often do not know they are infected). Symptom of ZIKV are, much like the symptoms of other arboviruses, general and non-specific. This means you experience fever, headache, rash, and joint or muscle pain. ZIKV also commonly causes conjunctivitis, or redness and swelling of the eye and skin around the eye. 
Arboviruses have been threatening to spread to North America with increasing persistence for years.
Graphic from the Institute of Medicine's presentation on Zika by Dr. Victor Dzau (2/15/2016)
North America is an anomaly in the infectious disease world. Since clearing most of the natural forests to favor rapid urbanization and industrial usage of land and resources, most hosts and vectors for many infectious diseases just won't survive in these areas. Part of that is because a majority of infectious diseases are perpetuated by tropical climates that are hospitable to the hosts and vectors (think jungles and warm/wet environments). But, some of the hosts and vectors are durable, and have taken advantage of changes in climate and global travel. 

Many of the mosquito species that are required to spread these viruses have already established residency in California and Florida. So, as these viruses come closer to our geographical borders, and travel to/from endemic regions becomes more frequent, we may see some locally-acquired cases. But, the spread of a virus into a new region is a complicated process and so many factors have to overlap.

Sexual Transmission can occur, but is not common.
There have been isolated cases of sexual transmission, but the uptick in news coverage is only a result of the ZIKV madness people have seen to caught, and is most likely the mass media's way of "helping" figure out whether microcephaly is linked to ZIKV infection. Despite what you've heard, having sex with someone that has ZIKV on the head of their penis will not cause microcephaly in all of your future children. Thanks, internet.
It is common sense, from an evolutionary standpoint, if you think about it. If you are in a region where mosquitoes are plentiful and looking for a bloodmeal, you are more likely to be exposed to ZIKV by a mosquito. Yet, these viruses "survive" when they are passed from one person to the next. Without transmission, our immune systems would clear the infection or we would die, and that would be the end of the story. Your mucosal membranes are a perfect environment for transport from one human to the next, especially when small tears may occur, giving access to blood. 

Just because there is a statistical possibility for sexual transmission to occur doesn't mean it can be considered a main method of transmission. There have only been 3 confirmed cases to date of male to female transmission through unprotected sexual contact. 

When babies are at risk, money is dedicated to the cause.
In hearing that there may be a link between ZIKV infection and an increased risk for microcephaly, President Obama dedicated $1.8 billion to ZIKV research. This funding will go to the development of faster, cheaper, and more specific and sensitive diagnostic tests, vaccine development, immune profiling and characterization of ZIKV disease, and studies to definitively determine whether microcephaly in newborns can result from ZIKV infection in pregnant women.
If you are traveling to an endemic or high-risk area, you can protect yourself.
Arboviruses are some of the least feared diseases, from what I can tell based on my friends' reactions when I tell them to pack DEET and other mosquito repellents when traveling. Basically, if they are not at risk of getting malaria, they aren't worried. 
If you are worried and have travel scheduled, there is a page dedicated just to the prevention of ZIKV exposure and transmission on the CDC website.
Cartoon by Rob Rogers and (c) the Pittsburgh Post-Gazette
Now, let's all hold our breaths and see what happens during the 2016 Summer Olympics, which are being hosted in Brazil.