Acanthamoeba keratitis

[jay87]

I wear contact lenses and am scared of acanthamoeba keratitis. It can cause blinding eye infections

It is quite common in natural waters, rivers, lakes, but contact lense wear is not recommended swimming for this reason. I think properly chlorinated pools have a low risk of it though.

Anyone encountered it before ? Is it difficult to kill?

 

[chem geek]

Acanthamoeba is an amoeba where some species form harder-to-kill cysts where this paper shows that for Acanthamoeba culbertsoni A-1 species had a CT value of around 4*24*60 = 5760 while Acanthamoeba polyphaga sp. 4A species had 8*24*60 = 11,520 (though at higher chlorine concentrations the CT was 16*1*60 = 960). This puts this protozoan oocyst closer to the chlorine-resistance of Cryptosporidium parvum so basically for practical purposes it won't be killed in chlorinated pools. Just note that other Acanthamoeba castellanii species had 3-log CT values of 0.5*5 = 2.5 for cultivability, but only 1-log reduction for permeability which may be a better measure of viability, but even so this would be easier to kill.

However, the cysts don't get blown in the air and instead come from the diarrhea of infected persons. So the risk in one's own private residential pool is exceptionally small. As for commercial/public pools, the risk would still be low, but not near zero unless secondary disinfection systems were used such as ozone or UV that are being added to some pools to combat Crypto.

 

[jay87]

thanks for that detailed and helpful response

I tend to swim in public pools , so think i'll wear goggles when possible. Makes me feel more relaxed about it in my hot tub. Shame I'm so blind really without them. I like to see peoples faces when swimming.

 

[jhalpinjr]

I am much more concerned about Naegleria fowleri which has been the cause of several deaths over the last couple years. The deaths occued in lakes. I've read conflicting information about them and chlorinated swimming pools.

http://en.wikipedia.org/wiki/Naegleria_fowleri

 

[chem geek]

Based on this paper, this isn't so bad:

In the current study, the chlorine Ct (chlorine concentration X time) values (at pH 7.5) for N. fowleri trophozoites were determined to be 6, 9, and 12, respectively, for a 99%, a 99.9 %, and a 99.99% reduction. As expected, the cysts were far more resistant and required chlorine Ct values (at pH 7.5) of 31, 42.5, and 53 to achieve the same reductions. These values for chlorine disinfection for N. fowleri are similar to those reported for Giardia.

So chlorinated pools are not expected to allow these cysts to survive. Person-to-person transmission of them is still possible, but even with an FC that is 10% of the CYA level there will be a 4-log (99.99%) reduction in cysts in under 9 hours. And again, the risk in a residential pool is near zero; it's commercial/public pools where there would be more issue, but more for individual transmission and less for larger outbreaks as with Crypto.

 

[jhalpinjr]

Thanks Chem- as always. Excellent, informative responses

 

[257WbyMag]

Although it is rare to see primary amebic meningioencephalitis (PAM) cases as a result of N. fowleri infection from swimming pools, the experts agree that it does occur (Shaw, 2008) and (Shakoor et al., 2011). It has even been found in indoor pools (Kadlec, Skvarova, Cerva, & Nebazniva, 1980). Still though, an amoeba is still much more sensitive to proper chlorination than microbial cysts such as those found in Giardia lamblia or Cryptosporidium parvum.

References
Kadlec, V., Skvarova, J., Cerva, L., & Nebazniva, D. (1980, February). Virulent Naegleria fowleri in indoor swimming pool. Folia Parasitologica, 27(1), 11-70. Retrieved from http://www.researchgate.net/publication ... b_srch_pub

Shakoor, S., Beg, M. A., Mahmood, S. F., Bandea, R., Sriram, R., Noman, F., ... Zafar, A. (2011, February 1). Primary amebic meningioencephalitis caused by Naegleria fowleri, Karachi, Pakastan. Emerging Infectious Diseases, 17, 258-261. Retrieved from http://web.ebscohost.com.ezproxy.ttuhsc ... =5&hid=108

Shaw, F. E. (Ed.). (2008, May 30). Primary amebic meningoencephalitis — Arizona, Florida, and Texas, 2007. CDC MMWR: Morbidity and Mortality Weekly Report, 57, 573-577. Retrieved from http://web.ebscohost.com.ezproxy.ttuhsc ... =5&hid=108

 

[chem geek]

In the first paper about a virulent strain in an indoor swimming pool it stated the following:

Renewed investigations revealed that the inside front wall in the deep end of the pool was cracked in several places.
:
The temperature in this space was between 27ºC and 30ºC and the water there was relatively isolated from the influence of any disinfectants.
:
For the purpose of competitive swimming, at weekly or monthly intervals, the water level was raised to about 40 cm above the usual level maintained for recreational swimming. We assume that this periodic fluctuation of the water level flushed some of the pathogenic amoebas from the space between the two walls and that these amoebas then infected the swimmers.

This situation with the pool with the gap in the wall with poor circulation where the water level was periodically raised and lowered which then flushed out its contents is unusual.

In the second link to the paper in Pakistan, the paper summarized the incidents as follows:

PAM is associated with freshwater swimming (5), and outbreaks have also been associated with poorly chlorinated swimming pools (6). However, all but 1 of the patients in this case series denied recent freshwater swimming or recreational water activities. Nevertheless, because all patients were Muslim, they routinely performed ritual ablution, which involves taking water into the nostrils. Infection acquired through this route has been reported (7). Because patients used domestic tap water for ablutions, we tested water from 2 patient’s homes and found N. fowleri amebae by culture. Additionally, N. fowleri DNA was identified by real-time PCR in a water sample from 1 patient’s home. PAM, resulting from aspiration of untreated ground water containing N. fowleri amebae, has been reported in 2 children from Arizona (8).

This quote above showed a reference (6) implying that poorly chlorinated swimming pools can harbor this amoeba, but the actual link to that paper simply says the following:

The amebae can also be found in coastal water, freshwater, sewage, heating and ventilation units, poorly chlorinated swimming pools, artificial lakes, and warm water near the discharge outlets of power plants (5).

where the reference (5) does not mention in the abstract anything about swimming pools and unfortunately I'm having trouble getting the original paper. I find it suspicious when there is such a long chain of references -- usually when one wants to make a point they should reference the original material whenever possible.

The last link to the CDC MMWR report lists all cases, not just swimming pools. In fact, "Exposure primarily occurred in untreated, warm, freshwater lakes or rivers" and only one had a tentative link to a swimming pool where "The youth had access to multiple drainage ditches and canals and to an apartment swimming pool during the 2 weeks before onset of symptoms; no location was conclusively identified as the source of exposure."

So properly chlorinated pools are not a risk for this amoeba.