Thursday, October 11, 2018

Eradication of Pinworm Eggs with Chlorine Dioxide

Pinworms are common contaminants of laboratory animal facilities. Pinworm infections can have adverse effects on behavior, growth, intestinal physiology, and immunology of experimental rodents, making effective pinworm surveillance and eradication important for many facilities. However, eradication of such infections is complicated by the ova’s ability to aerosolize and remain viable in the environment for lengthy periods. Pinworm eggs are microscopic and have been found on equipment, shelving, in dust, and in ventilation air intake ducts. The University of Tennessee at Knoxville performed a study on chlorine dioxide gas’ effect on pinworm eggs to see if it was a viable option for treating contaminated spaces.

Prior to this study, only ethylene oxide gas and dry heat had been proven to eliminate pinworm eggs.  Ethylene oxide is not used for space fumigation due to its carcinogenic and explosive properties, and it is very difficult to uniformly establish and maintain the high temperatures needed for dry heat (212° F held for 30 minutes) to be effective. In a controlled study, Syphacia spp. ova were affixed to a slide and exposed to a set concentration of chlorine dioxide gas for varying amounts of time. After being exposed to chlorine dioxide gas, the ova were placed in petri dishes, covered with a hatching medium, and incubated at 37° C for six hours. Positive control ova not exposed to chlorine dioxide gas were also processed and incubated.

The parameters to achieve a 6 log level kill of viruses, bacteria, fungi, and spores are normally 1 mg/L chlorine dioxide gas (360 parts per million or ppm) for 2 hours of exposure contact time.  This equates to a 720 ppm-hours (360 ppm x 2 hours) chlorine dioxide gas dosage.  It was found that a dosage twice as long (1440 ppm-hour) was needed in order to eliminate all viable ova from hatching. All ClO2 treatment times significantly decreased the hatching rates of the ova. Below is a table showing the results of the study: 

Exposure time
Chlorine DioxideGas Dosage
% of Syphacia, spp. ova hatched
Treated with CD Gas
Untreated(Positive Control)
1 hour
360 ppm-hour
2 hours
720 ppm-hour
3 hours
1080 ppm-hour
4 hours
1440 ppm-hour

To learn more about gaseous chlorine dioxide's effectiveness against pinworm eggs, visit Booth #1903 at this month's AALAS National Meeting or read the complete Journal of the American Association for Laboratory Animal Science article here.

Tuesday, October 2, 2018

Case Study: Electron Microscope Decontamination

An electron microscope can be used to study dangerous biological organisms. Occasionally, the organism can be sucked into the internals of the microscope making it hazardous to repair with concern for the maintenance technician’s health. To mitigate these concerns, decontaminating the inside components of the microscope can be accomplished using gaseous chlorine dioxide with no adverse effect on the equipment.

The normal sterilization process is automated and consists of 5 steps:
1. Precondition: Raising of humidity to make spores susceptible to gas
2. Condition: Holding of raised humidity level for spore softening
3. Charge: Injection of gas into chamber
4. Exposure: Holding of gas concentration for the set amount of time
5. Aeration: Expulsion of gas and humidity

Some microscope manufacturers add a sixth step which is a pre-purge of the system with nitrogen. If a Pre-Purge step is used, the valves are opened and nitrogen is passed through the system.

In 2009, ClorDiSys was approached by JEOL USA as they set forth to find a suitable decontamination method for their electron microscopes. They wanted a method to decontaminate the interior chambers to protect their service workers from the pathogens being studied within. Identical sets of parts were sent for material testing against chlorine dioxide and hydrogen peroxide vapor. According to “Construction and Organization of a BSL-3 Cryo-Electron Microscopy Laboratory at UTMB” in the December 2012 Journal of Structural Biology, their early attempts to use VHP with JEOL microscopes were not successful because of unacceptable level of corrosion of some parts inside the microscope column. Some showed visible discoloration and corrosion after the level of exposure necessary for a single decontamination cycle. Chlorine dioxide gas has a lower oxidation potential than ozone, peracetic acid, bleach and hydrogen peroxide, making it scientifically less corrosive than those other decontaminating agents. Our chlorine dioxide gas was selected due to its success in the material compatibility trials and is used with the $3 million TEM.

Read more about the process and benefits of using chlorine dioxide for Electron Microscope decontamination in our application note.

Eradication of Pinworm Eggs with Chlorine Dioxide

Pinworms are common contaminants of laboratory animal facilities. Pinworm infections can have adverse effects on behavior, growth, intestina...