Scientists in the Virus Identification Laboratory
have investigated the survival of HIV when it is exposed to a
range of temperatures and to ultraviolet (UV) light. The current
procedures used in Victoria to decontaminate surgical equipment
such as cardiac catheters have also been evaluated (Druce
2003).
The temperatures at which survival of the virus was examined were
4°C, 20-24°C (room temperature ) and 37°C. In order
to represent the conditions under which the virus is likely to
be found in different body fluids, the studies were conducted
on both cell-free virus and cell-associated virus. Cell-associated
virus was that contained within chronically infected human lymphocytes
(H9/HTLVIIIB cells).
Briefly, aliquots of either cell-free virus (starting titre of
10^4.5 TCID50) or chronically infected cells (starting titre of
10^7 TCID50) were stored at each of the three temperatures for
up to 28 days. Individual aliquots were removed during this time
and stored at -70°C. At the end of this procedure, quantitation
of infectious HIV was undertaken in human T-lymphocytes (MT-2
cells). Replication of HIV was observed by the presence of HIV-specific
cytopathic effects (cpe) and by detection of specific antigen
(p24).
For the experiments involving UV light, survival of HIV suspended
in culture medium or blood was examined. Five µl of suspensions
containing HIV in either culture medium or blood were placed at
3 distinct sites within a class II biological safety cabinet,
then exposed to UV light for up to one hour. The strength of UV
light ranged from 150 to 220 µW/cm2 at these sites. Isolation
of HIV was attempted immediately after exposure.
Results
Effect of Temperature: Following exposure to a temperature
of 4°C, the HIV titre reduced by approximately one log per
week. At room temperature the HIV titre reduced by approximately
3 log per week. At 37°C the titre reduced by approximately
3.5 log per week. The rate of reduction in titre was similar for
both cell-free (fig. 1a) and cell-associated HIV (fig. 1b). The
apparently longer overall survival time of cell-associated HIV
is likely to be due to its higher starting titre compared to cell-free
virus.
Effect of Exposure to UV Light: Following exposure
to UV light in a class II biological safety cabinet, cell-free
and cell-associated HIV suspended in culture medium was inactivated
within 5 to 20 minutes, depending on the site in the cabinet at
which the virus was exposed. This reflects differences in the
strength of UV light at different sites within the cabinet. Noteably,
when cell-associated HIV was suspended in blood, complete inactivation
was not achieved after one hour exposure at any site within the
cabinet (fig. 2).
Conclusion
HIV can retain infectivity for extended periods
of time. However, the duration that the virus remains infectious
is related to the temperature and the initial starting titre of
the material (other untested factors may be involved). Extreme
care should be taken at all times when handling potentially HIV-infected
or contaminated material. It should be noted that when stored
in biological material such as blood or serum, HIV may still be
infectious after weeks or even months of refrigeration.
| Exposure Time
|
Position A |
Position B |
Position C |
|
Cell-Free HIV |
| 5 minutes |
+ |
- |
+ |
| 10 minutes |
- |
- |
- |
| 15 minutes |
- |
- |
- |
|
Cell-associated HIV |
| 15 minutes |
+ |
+ |
+ |
| 20 minutes |
+ |
- |
+ |
| 30 minutes |
- |
- |
- |
|
Cell-Associated HIV in blood |
| 30 minutes |
+ |
+ |
+ |
| 60 minutes |
+ |
+ |
+ |
|
Controls |
| control cells |
- |
- |
- |
