Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using direct contact with electrical or electromagnetic...
Reexamination Certificate
1999-04-27
2003-05-20
McKane, Elizabeth (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using direct contact with electrical or electromagnetic...
C422S023000, C210S748080
Reexamination Certificate
active
06565803
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for inactivating
Cryptosporidium parvum
in water and in particular to a method for the prevention of
Cryptosporidium parvum
and other protozoans, such as
Giardia muris,
from establishing infection in human hosts, as measured by the ability to infect neo-natal mice, using low doses of ultraviolet light.
BACKGROUND OF THE INVENTION
It has been generally well recognized that it is necessary to kill or inactivate protozoan oocysts so that they cannot infect susceptible hosts. This is especially important in drinking water. One such method is the use of ultraviolet (“UV”) light. The prior art teaches that a UV dose of at least 3000 mJ/cm
2
is required to inactivate
Cryptosporidium parvum
(Lorenzo-Lorenzo et al., J. Parasitol. 1993, 79, 67-70) and
Giardia muris
(E. L. Jarol, “Effect of Disinfectants on Giardia Cysts”, CRC Critical Reviews in Environmental Control, 1988, 18, 1-28). Snowball and coworkers (UK Patent Application #9416287.2, Nov. 8, 1984; Wat. Res., 1995, 29, 2583-2586) developed an apparatus that first filtered out Cryptosporidium oocysts and then exposed them to UV doses of 700-800 mJ/cm
2
. The patent teaches the use of 2 &mgr;m screen filters to trap Cryptosporidium oocysts which are then irradiated with a bank of low-pressure Hg lamps for a UV dose of 350-400 mJ/cm
2
. The filter is then backwashed onto a second filter and the irradiation is repeated for a total dose of 700-800 mJ/cm
2
. The patent discloses that the treatment “kills” the organisms.
M. J. Lorenzo-Lorenzo, M. E. Area-Mazea, I. Villacorta-Martinez de Maturana and D. Duran-Oreiro [“Effect of Ultraviolet Disinfection of Drinking Water on the Viability of
Cryptosporidium parvum
Oocysts”,
J. Parasitol.
1993, 79(1), 67-70] report the prevention of infection in mice after exposure to at least 150 min. of UV from a (presumably) low-pressure Hg lamp. Although the paper is not clear, it can be inferred that the UV dose applied was over 5000 mJ/cm
2
to obtain better than 2 logs reduction in infectivity. The authors claim that exposure to UV for 150 min. or more “eliminates” infectivity, but they give no mechanism other than to say “UV radiation disrupts DNA by causing formation of thy[ia]mine dimers, and high levels may lead to cell death”. At the UV doses they applied, the effects observed almost certainly arose from cell death.
In a paper by A. Bushnell, W. Clark, J. Dunn and K. Salisbury [“Pulsed Light Sterilization of Products Packaged by Blow-Fill-Seal Techniques”,
Pharm. Engin.
1997, September/October, 74-83], a pulsed UV technique for “sterilizing” surfaces containing bacteria, fungi, spores, viruses, protozoa and oocysts is described. The required UV doses were reported to be over 1000 mJ/cm
2
. The effectiveness of the method was assayed using mouse infectivity. At the reported UV doses, the effects were believed to be due to cell death.
In a paper by R. LaFrenz [“High Intensity Pulsed UV for Drinking Water Treatment”,
Proc. AWWA WQTC Conference,
Denver, Colo., November, 1997], a similar pulsed system was described. While very few details were given, it appears that mouse infectivity assay was used and 6 logs of “inactivation” of Cryptosporidium was obtained at energy levels of approximately 200 mJ/cm
2
and greater. The paper claims that the pulsed UV overcomes the “DNA repair mechanism”; however, the UV doses applied are much larger than required with either a steady-state medium pressure or low pressure Hg lamp, as shown herein.
From the references cited above, we infer that the prior art teaches that very large UV doses (>200 mJ/cm
2
and up to 5000 mJ/cm
2
) are required to inactivate Cryptosporidium by “killing” the organisms. Accordingly, it is an object of the invention to provide a method using ultraviolet light to treat water in an effective way so that Cryptosporidium oocysts cannot infect susceptible hosts or, in other words, to “disinfect” the water in regard to Cryptosporidium oocysts that may be present. It is another object of the invention to provide a method using ultraviolet light from a medium-pressure mercury lamp to render the Cryptosporidium oocysts unable to infect. It is yet another object of the present invention to provide a method using ultraviolet light that is cost-effective in treating drinking water to eliminate the potential for infection by Cryptosporidium oocysts and Giardia cysts. The final object of the invention is to provide a method using ultraviolet light from a low-pressure mercury lamp to render Cryptosporidium oocysts and Giardia cysts unable to infect.
SUMMARY OF THE INVENTION
Generally it has been discovered that it is not necessary to “kill” pathogens, such as
Cryptosporidium parvum
or
Giardia muris
with ultraviolet light in order to prevent infection; one need only apply enough ultraviolet light to prevent the organism from “replicating”. The method of the present invention prevents replication (cell mitosis) by inactivating the DNA to prevent infection. The UV doses required to prevent replication are orders of magnitude lower than required to “kill” the oocysts. This means that the cost of UV treatment to prevent infection by Cryptosporidium oocysts will be markedly lower.
It has been found that when biological organisms are exposed to ultraviolet light (UV) in the range of 200-300 nm, the UV can be absorbed by DNA, RNA, and proteins. Absorption by proteins can lead to rupture of cell walls and death of the organism. Absorption by DNA or RNA (specifically by thymine bases) is known to cause inactivation of the DNA or RNA double helix strands through the formation of thymine dimers. If enough of these dimers are created in DNA, the DNA replication process is disrupted and hence, in mitosis, the cell cannot replicate. Cells that cannot replicate cannot infect. The present invention utilizes UV doses substantially lower (to achieve the state of hindered replication) by orders of magnitude than those required to cause oocyst death.
The present invention preferably utilizes a broad band (200-300 nm) medium-pressure mercury UV lamp to achieve the disinfection. In another embodiment of the invention, a low-pressure mercury (essentially monochromatic) UV lamp can be used. The dose required with a medium-pressure lamp was measured to be 11 mJ/cm
2
to achieve better than 5.9 log disinfection. From this it can be inferred that a dose of 7 mJ/cm
2
will achieve better than 4 log disinfection (99.99%) and 3.6 mJ/cm
2
will achieve better than 2 log disinfection (99%). For low pressure lamps a dose of 8 and 16 mJ/cm
2
was required to achieve 4.1 and 4.3 log disinfection, respectively. Thus, the dose levels of UV are significantly lower than those used before resulting in significantly lower power levels needed to achieve the results. It has been found that inactivation of Cryptosporidium and similar organisms such as Giardia occurs at dosages from about 1 mJ/cm
2
. Accordingly, the method provides a substantial improvement in the cost effectiveness of UV for the disinfection of contaminated drinking water as regards to Cryptosporidium oocysts and Giardia cysts that may be present. Other advantages will become apparent from a perusal of the following detailed description of a presently preferred embodiment of the invention.
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patent: 4265747 (1
Bolton James R.
Dussert Bertrand
Stevens R. D. Samuel
Calgon Carbon Corporation
Cohen & Grigsby P.C.
McKane Elizabeth
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