A reviewer of this article stated that influenza viruses are designed to grow at 37 degrees C (Celsius) [98.6 degrees F (Fahrenheit)] and to replicate using mammalian cell enzymes and that a long period of host and pathogen co-evolution is required.

The following graphs are provided as a first step in checking up on whether or not a suitable temperature, pressure, and chemically friendly environment for the production or replication of viruses exists in the Venusian atmosphere.

So, in spite of the surface temperature of Venus being on the order of 864 degrees Fahrenheit, there is a region in the Venusian atmosphere which approximates that of Earth with respect to temperature and pressure. But there may be problems.

52.5 kilometers above the Venusian surface turns out to be in the middle of the Venusian cloud blanket which is made up largely of sulfuric acid droplets. (The cloud bottoms are estimated to be 30 to 35 km above the surface and the tops are estimated to be from 60 to 75 km above the Venusian surface.) This upper altitude limit is perhaps a fuzzy estimate. The cloud tops temperature has been reported to be 260 K (-13 degrees C or 9 degrees F). According to the temperature profile above (green line) this temperature corresponds to an altitude of 58 km (36 miles) for the cloud tops. (For stratus clouds there will be thermal equilibrium between the atmosphere and the cloud tops.)

Is this acidic cloud environment good or bad for the formation of viral precursors and/or virus building processes? (Do sulfuric acid droplets in a reducing atmosphere assist or preclude the formation or preservation of amino acids and other RNA building blocks? Can sufficient solar ultraviolet energy penetrate the clouds to this depth? ) If either answer is harmful to the hypothesis then we can ask whether or not the Venusian atmosphere above the clouds, say 60 km (37 miles) and up, could be (or not be) a candidate region for the biological processes in question. Ultraviolet penetration will not be a problem above the clouds. So, what are the lowest temperature and pressure constraints for reasonable biological activity?

The article Looking for clues to our mineral wealth, published by the Australian Academy of Science, describes unusual life forms associated with oceanic subsurface volcanic chimneys (black smokers).

"The environment around black smokers forms the habitat for a number of highly specialized animals. Species of tube worms, bivalves, gastropods and crustaceans are capable of surviving in complete darkness, under extreme pressures and at water temperatures that range from 10°C to 400°C. These organisms survive by eating bacteria that use hydrogen sulfide as their primary energy source."

Hydrogen sulfide powered bacteria, if they can actually make it at 400° C (720° F), might, with special conditioning, qualify for life on the "ocean floor" of the Venusian atmosphere. Dietary considerations would, of course, be in order.

Here is a diagram showing blackbody radiation for 750 K, which is approximately equal to the surface temperature of Venus.
[Added 11 Feb 2010.]

The temperature and pressure graphs on this web page (before my modifications) were originally published by J.M. Jenkins, P. G. Steffes, D.P. Hinson, J.D. Twicken, and G.L. Tyler in their article, Radio Occultation Studies of the Venus Atmosphere with the Magellan Spacecraft, Icarus, Vol. 110, 79-94, 1994. (The kind permission to use the graphs does not constitute endorsement of the hypothesis under evaluation in this article.) See: Venus Temperature and Pressure Profiles - Jenkins, et.al.

According to Velikovsky(1), the high temperatures of Venus's lower atmosphere and surface result primarily from [the energetics involved with] its recent expulsion from Jupiter. See Velikovsky Pages.
[Added 19 Jan 2006. Modified 12 Feb 2010.]

Acidic clouds of Venus could harbour life - NewScientist.com 26 Sep 2002.

Chemical that could power microbes is found at Jupiter moon. The "signature" for sulfuric acid, found in acid rain and car batteries on Earth, has been found on Europa. ... Ken Nealson, head of JPL's astrobiology unit said the acid's presence excited him about the possibility of life on Europa. ... Bacteria are very good at exploiting chemical energy sources, even inorganic sources like sulfuric acid, NASA's Mark Anderson said.
Source: CNN.com sci-tech > space > story page 01 Oct 1999. [Page no longer available.]

Defining Life "We can conceive of chemistries that might occur in sulfuric acid as a solvent as on Venus." Astrobiology Magazine 5 Aug 2002.

Prospecting for Viruses "Under scalding acidic conditions, scientists wonder, how do life processes function?" ... "To me, the most interesting aspect is why the RNA does not hydrolyse, as it should quite rapidly according to general phosphate chemistry if at 90 degrees C and pH 2." Astrobiology Magazine 5 Aug 2002.