Trachoma

So I went to an interesting talk on the role of water and sanitation on incidence of Trachoma, and for the first time in recent memory, somebody besides me used the word “fomites”.  So I naturally wanted to blog all about it.

Trachoma is an infectious eye disease caused by Chlamydia trachomitis.  [Side note: inour lab safety training, the safety coordinator tells a story about how she got Chlamydia in her eye when she was working in the lab]  A typical infection, which lasts for 5-12 days, causes conjunctivitis-like symptoms, with eye inflamation leading to irritation and discharge.  If you visited the poorest of regions in Africa, Asia, the Middle East, and/or Latin America, and ended up with Trachoma, it’d be no big thing.  Your doctor would hand you antibiotics like he always does and you’d keep on walking.  But the locals who are continually re-infected with Trachoma end up with permanent blindness.  The constant inflamation from repeat infections leads to entropian, a painful form of blindess, which (according to Wikipedia) is the leading cause of infectious blindness.

Gross.

So trachoma is spread through contact with eye, nose, and throat secretions.  Either by direct contact, indirect contact via fomites, or indirect contact via vectors (like flies and cattle).  People who like the F-diagram say it is spread through feces, flies, fomites, and fingers.

The fomites in question are thought to be items like towels, but the speaker mentioned that the cloths women use to wrap and hold their babies [is kitenge the right word?  When i Googled it, i just got a bunch of photos of the whitest people wrapping random African-looking cloths around themselves and their sun-deprived babies,  so there's probably a better word out there] rubs right against the baby’s eyes, allowing discharge from one infection to continually cause reinfection.

So secretions appear to be the main form of transmission, but the speaker’s premise for the talk was that sanitation would reduce incidence of Trachoma because it would remove feces from areas where individuals and flies had access.  In general, promoting sanitation is always a great thing, but I’m not completely sold on its usefulness in combating an infectious disease spread through secretions.

And, perhaps, neither are the individuals at WHO working on its elimination who apparently rely heavily on the use of antibiotics to treat individuals, instead of trying to interrupt the transmission pathway.

 

Triclosan – Where Microbiology and Toxicology Collide.

Hitting the innerwaves today, care of ES&T,  is an article on EPA’s approval of Triclosan.   Triclosan is found in a large number of consumer products (e.g.  soaps, detergents, deodorants, mouth wash, and toothpaste).  Colgate Total, for example, contains triclosan to prevent gingivitas.

Triclosan is an antibacterial that binds to an enzyme in bacteria that is used to build fatty acids, a necessary component in bacterial cell membranes.    Notice, I said that it is an antibacterial and not an antibiotic.

Triclosan’s efficacy in hand soap is debatable.  Some studies have shown that hand washing is not improved with the addition of triclosan, if the recommended 30 second social hand wash is followed.  Others contend that triclosan provides a residual on the hands that continues to work against bacterial contamination, useful in settings where people do not wash their hands completely or correctly.  Most consumer products, like cutting boards, table tops, and children’s toys, that bear the term antibacterial likely have triclosan imbedded in the surface.

Additionally, soap with high concentrations of triclosan (think 2% compared to the 0.5% found in consumer soaps) are used to decontaminate individuals exposed to MRSA.

So why is it news that the EPA extended triclosan’s approval?

1) There is some (ok, very little) concern about antibacterial resistance developing, which seems unlikely unless organisms currently resistant (such as P. aeroginosa) are able to transfer resistance to other species.

2) Triclosan degrades in sunlight to form byproducts in a class of compounds known as Dioxins, which bioaccumulate in fatty tissue and pose a threat to the reproductive, sexual development, and immune systems and are probable carcinogens.  With household use sending triclosan directly down the drain to the waste water treatment plant, it frequently ends up in surface waters where it becomes an environmental pollutant.

and 3) The ES&T article mentions, through Cathy Propper at NAU, that triclosan bioaccumulates and impacts nitrogen fixation in microbial communities and plants.

My take?  Totally not necessary.  Just wash your hands well.  Wash your cutting board well.  Your table top…  Why contribute to a problem we have no idea of the magnitude of for the sole benefit of maybe, possibly, protecting ourselves environmental bacteria?

We’ll see what the EPA says when it comes up again in 5 years…

 

VF481

Purell has busted out the “Original Formula” label to distinguish the infamous hand gel from its successor.  The active ingredient of the original formula is 62% Ethyl Alcohol, which primarily acts to denature/coagulate proteins.  Bacteria, those evolving little buggers, can not become resistant to this mode of inactivation.  Ethyl Alcohol also dissolves lipids, so it works better on enveloped virus (e.g. influenza) then nonenveloped virus (e.g. norovirus, adenovirus, rotavirus).

The new formulation, Purell VF481, is showing a 4 log reduction of norovirus and adenovirus using the fingerpad test with infected stool to artificially inoculate fingers.  Concentrations of adeno-/noro- are determined using quantitative reverse-transcriptase, with the log reduction a comparison of concentrations on fingers before and after ABHS use.  Since this is working so well against non-enveloped virus, I wonder how it does against spore-formers.

I have no idea what the active ingredient is for VF481.   A Google Search of “Purell VF481″ only turns up about 170 listings.  The method of ethyl alcohol inactivation doesn’t mesh with increased virucidal activity.  I think there’s something else in there.

According to “Disinfection, Sterilization, and Preservation” by Seymour Block: for both bacteria and virus: methanol < ethanol < isopropanol < propan-1-ol.  Maybe that has something to do with it…

Anyway they’re already selling it (in Europe at least)… so I imagine the ingredient is listed right on the packaging.