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Posts Tagged ‘virus’

How many bacteria/viruses are actually removed by the body’s natural defenses while we are sick?

March 10, 2015 Leave a comment

The answer to this question is completely dependent on the context of infection. For instance, when you brush your teeth, you introduce bacteria from your mouth into your blood stream and become temporarily bacteremic. Fortunately, the immune system clears these bacteria quickly. In this daily event, thousands of bacteria enter the bloodstream. After brushing, bacteria in the blood were below 104 cfu/ml, as estimated by PCR, and exact numbers are nearly impossible to quantify (Lockhart et al. 2008).

In contrast,  Ebolavirus replicates to ~107 – 108 virions/ml in the blood of non-human primates (Bente et al. 2009). The average person has ~5 liters of blood. Very conservatively, an Ebola survivor will have cleared ~5 x 1010 virions from just the blood. That’s 50 billion virions.

Keep in mind that this is also just a snapshot of a moment during infection. Viruses are constantly propagating, and a single virally infected cell can produce thousands of viral particles in a single day. It’s possible that over the course of a 2 week infection, 1011 – 1012 virions may be produced and cleared (it’s probably much higher). While this number is staggering, it somehow pales in comparison to the magnitude of the U.S. debt, which currently stands at ~$18 trillion, or $1.8 x 1013.

Geisbert et al. 2004 Nat. Med.

Geisbert et al. 2004 Nat. Med.

I also estimated the rough number of virions from the liver and spleen, two organs with significant ebola titer, and the total is nowhere near the magnitude of virions in the blood.* Additionally, ebola virus is being shed through mucosa and other bodily fluids. People generate ~ 4 liters of mucus daily in the gastrointestinal tract. I could not find an accurate estimate of Ebola viral titers in the mucus, but it’s unlikely to be near the levels of that in the blood. Granted, mucus could still contribute significantly to viral titer. There’s also the possibility that other organs harbor high titers of ebola virus, especially the gut.

*Approximately 104 – 105 virions/gram were detected in the liver and spleen using a mouse model for Ebola (Bray et al. 1996). Given that the average mass of a human liver is 1.5kg and a spleen is 140g (Molina et al. 2012), and using conservative estimates, about 1.6 x 107 virions from the spleen and liver alone, over 1000 times less than that from the blood.

Measles: Thinning the Herd

January 22, 2015 Leave a comment

CDC Measles51 confirmed cases of measles. Really? Measles? John Franklin Enders first isolated measlesvirus in 1954, and immediately began work to develop a cure. In 1960, Enders began to test his measles vaccine, and a year later he announced that the vaccine was 100% effective.

Now, more than half a century later, we have a problem. There hasn’t been a failure with the vaccine, or in the scientific process. The measles vaccine is still ~100% effective. We continue to dive deeper into molecular mechanisms of disease and come up with clever cures. A paper published just two days ago demonstrates stem cell therapy as a treatment for multiple sclerosis.  However, we do have a social problem that unfortunately bleeds into global health.

It’s interesting that a lot of diseases have been well characterized and would not be an issue if not for social dysfunction. Take polio for example. The polio vaccine is extremely effective. There are enough doses of polio vaccine to go around and in fact the WHO actively sends teams of vaccinators to the last three countries where polio is endemic: Pakistan, Nigeria, and Afghanistan. Despite vaccine efficacy, there are uneducated radicals opposed to vaccination, and often these groups are violently hostile. Efforts to eradicate polio have been undermined, and it’s because of social problems. In the U.S., we may not have violent extremists opposed to vaccination, but we do have major social issues.

herd-immunity1. We take for granted herd immunity (or ignore it completely).

People hear about the 0.01% chance of adverse reaction to a vaccine, in contrast to the low odds of contracting measles in the U.S., and choose not to vaccinate their children. As far as I’m aware, there is no scientific fix for ignorance. The only real solution is education.

2. Ignorance often trumps scientific evidence.

Let’s start with Andrew Wakefield. In the late 90’s, this guy published a fraudulent paper that drew a link between vaccines, autism, and gastrointestinal disease. The paper was disproven, and after an investigation, many signs of misconduct came to light. Sure, fraud happens, and it would have been okay if not for what happened next.

Normally the conclusions of a disproven paper are disregarded. But the torch had already been lit and the anti-vaccine movement had begun. Jenny McCarthy used her public position to advocate the anti-vaccine movement, claiming her child developed autism due to vaccines. People empathize with anecdotes. (Please allow this brief interruption for an introduction to the Jenny McCarthy Body Count: Deaths attributable to the anti-vaccine movement) The torch is now a wildfire. Again, we have an example of social dysfunction that could be effectively fixed with education.

Sometimes it takes a disaster to develop a fix. Unfortunately, this problem can’t be solved with any technology or scientific advancement. Alas, social science may be relevant, thanks to measles.

Your odds of contracting Ebola vs. Chikungunya

August 12, 2014 1 comment

Sure, Ebola is scary. However, the issue with Ebola is primarily a social one where misinformation, a lack of infrastructure, and general government mistrust have thrown the epidemic out of control (I suggest reading a historical perspective on Ebola response and prevention). Unless you’ve recently traveled to west Africa to eat bushmeat or treat Ebola patients, there is little cause for concern. You are very unlikely to contract Ebola, but recently your odds of getting Chikungunya have significantly increased.

On June 17, 2014, the CDC announced the first case of Chikungunya acquired in the continental US. Previously, Chikungunya in the US had only been identified in travelers coming from the Caribbean where over half a million people have contracted Chikungunya (Caribbean Chikungunya Cases Climb 8%, top 500,000). In late 2013, Chikungunya was introduced to the Caribbean from Africa or Asia, where the disease has been endemic since its discovery in the 1950s. This rapid spread of Chikungunya is particularly alarming, and has been heavily influenced by the increase in international travel.

They're gonna have to change this map.

They’re gonna have to update this map.

What’s Chikungunya?
Chikungunya is a disease caused by chikungunya virus, which is transmitted by Aedes mosquitos. Infection by Chikungunya may result in a fever, rash, insomnia, headache, and joint pain. While Chikungunya is rarely fatal, it is incredibly debilitating, causing symptoms for weeks to months. Chikungunya also presents with other symptoms such as leg swelling and ocular inflammation. Chikungunya pathology is not well understood, and as a result antivirals and vaccines have not been developed.

800px-Aedes_aegypti_feeding

Avoid Aedes mosquitos.

Ebola is not likely to cause a pandemic.
Ebola is one of the deadliest diseases on the planet, but with the proper infrastructure can be controlled. Additionally, the likely reservoir of Ebola is in bats, which are often eaten as bushmeat in villages in Africa (Africans still eating bushmeat despite Ebola). 1. Here in the US we rarely come in contact with or eat bats. 2. Even if we were more bat oriented, the Ebola reservoir is likely specific to animals in Africa. 3. Education plays a major role in the spread of the disease. African tribes are notorious for rejecting help from Doctors without Borders and the like (Superstitions play a role). 4. Ebola transmission requires contact with bodily fluid such as blood, vomit, or diarrhea. It is not a respiratory infection and close contact with a patient is unlikely to cause transmission.

In contrast, Chikungunya transmission is nearly impossible to avoid. Aedes albopictus and Aedes aegypti, reservoirs of Chikungunya virus, are invasive species of Asian tiger mosquito that are now firmly seated in the US. Importantly, on August 7th, Chikungunya was found in mosquitos in the US. The West African outbreak of Ebola is certainly devastating, but Chikungunya is far more widespread and is transmitted with relative ease. So while it is important to be mindful of the current state of Ebola, overlooking other potential outbreaks may have devastating consequences.

An introduction to emerging infectious diseases

July 17, 2013 Leave a comment

Viral_infections_and_involved_speciesWhile most of my research is directed toward antibiotic resistance in bacteria, the vast majority of the news in the popular media suggests that the most prevalent diseases are caused by cancer and viral agents. While concerns of bacterial drug resistance are on the rise, the fear of an influenza pandemic or an ebola outbreak creates excellent headlines.

Additionally, bacteria are relatively slow killers and infections are generally treatable (although some are not). A virus may have an incubation period of about two or three weeks with mild flu-like symptoms. During this time you may believe you have acquired the seasonal flu, and that it will pass. You hug your kids, and walk around the office touching doorhandles, shaking hands, and using the company copier. By the time you’re hemmorhaging and you realize it’s not just the flu, it’s too late, and you may have infected others.

The first thing you learn in microbiology is that bacteria are ubiquitous, but these single celled organisms are not alone in their pervasiveness. There’s a saying that for each bacterial species, there exists at least one virus that is capable of infection. Viruses are extremely prevalent. In a single milliliter of sea water, there are roughly 10 million viral particles, and about 15 times as many viruses as bacteria (a fun read). Despite the prevalence of viruses, most are incapable of infecting humans. Many bacterial infections are closely associated with immunocompromised individuals, and immunosuppression is often caused by a virus, such as HIV (opportunistic infections and AIDS).

Viral research has lead to incredible advances in medicine. Because general hygiene has decreased the incidences of bacterial caused diseases such as plague and tularemia, scientific efforts have been directed toward understanding viruses. Vaccines for smallpox and polio have saved an immeasurable number of lives. Viruses may even be key to a future cure for cancer or other genetic diseases, as viruses have been engineered as tools to deliver gene therapies (an easy to read microbe wiki link on viral based gene therapies). Hopefully I can shed light on some interesting aspects of emerging infectious diseases.

*I began writing this as a brief introduction to highlight some of the research in the field of microbiology, virology and immunology. I had too much to say, and hopefully my next post will cover this paper about how ebola evades the immune response.