Subject: Solar UV Radiation and the Risk of Infectious Disease

From: [email-masked] (Bruce Hamilton)
Date: Sun, 9 Apr 1995 08:40:24 GMT

This post is a little brief, I have a feeling that the last couple may
not have escaped from this site, thus a shorter one to check the system.

As this is was a workshop, I will only mention two selected papers, but
readers should be assured that all papers were interesting and worthy
of perusal. This review is sufficiently unusual that the editors of
P&P have chosen to depart from their standard format, and provide
a footnote explaining why they chose to depart from thier rules.
This is an interesting series of brief reviews...

"Solar Ultraviolet Radiation and the Risk of Infectious Disease:
 Summary of a Workshop"
Photochemistry and Photobiology. v.61. p.223-247. (1995)
R.S.Chapman. USEPA; K.D.Cooper. Uni.Mich.; E.C.De Fabo. George Washington
Uni.; J.E.Frederick. Uni.Chicago.; K.N.Gelatt. Uni.Florida.; 
S.P.Hammond. SPA-AFEAS.; P.Hersey. Uni.Newcastle(Oz); H.S.Koren. USEPA.;
R.D.Ley. The Lovelace Institutes.; F.Noonan.George Washington Uni.;
G.M.Rusch. Allied Signal Inc.; A.Sarasin. Cancer Research Institute(Fr);
M.J.Selgrade. USEPA; I.Sobolev. Chemical and Polymer Tech.,; B.J.Ward.
McGill(Ca or Qe); T.E.Werkema. UMAP.

Background.

Photoimmunology, the newest of the disciplines dealing with the effects
of ultraviolet radiation(UVR) on biological systems, has been attracting
increasing attention. The initial finding in laboratory experiments that
Ultraviolet B radiation (UVB; 280-320nm) could have immunosuppressive
effects in animals has led to speculation that changes in stratospheric
ozone might affect human immune response functions. It has been suggested 
that increases in ambient UVB associated with ozone depletion could 
exacerabte the course of infectious diseases. Some of the background of 
this theory was discussed in connection with the 1991 review of the 
Montreal Protocol on substances that Deplete the Ozone Layer.

Because of the paucity of direct evidence linking changes in ambient
UVB to infectious diseases, a workshop was jointly sponsored by the
Health Effects Research Laboratory (HERL) of USEPA and the Ultraviolet
Monitoring and Assessment Program Panel (UMAP), an interantional industry
science committee headquartered in Washington, DC. The workshop was held
on 1-2 March 1994 at Miami Beach, FL. Its objectives were:

1) To identify and assess the available evideence on potential effects
   of ecologically relevant UVR changes on infectious diseases in humans.
2) To assess the available data on quantitative dose-response relationships
   for such effects.
3) To identify the remaining scientific uncertainties.

******************

First selected review

Ultraviolet Climatology - J.E.Frederick.

Summary statements
1) UV-B radiation consists of only about 1.5% of the incident sunlight
   energy; visible and infrared represent 91.7%. UV-B radiation shows
   wide latitude cvariations, the highest levels being found within 25

   degrees of the equator and lowest at the higher latitudes. For example,
   the summertime, DNA-weighted irradiance in Miami is 54% greater than
   in Boston.
2) The most important factor in estimating ground levels of UVB is to
   develop a model to correct for scattering by clounds and aerosols. 
   Depending on location, backscattering by clounds attenuates the monthly
   mean UV irradiance to levels of 50-80% of the values expected for 
   clear skies. Atmospheric pollutants can add an additional 10% 
   attenuation.
3) Monthly average irradiances can vary by 10-20% from year to year just
   due to clound cover. This difference can be either positive or negative
   and can, if viewed from one year to another, give the appearance of a
   dramatic increase in UV-B, which is, in fact, transitory and unrelated
   to column ozone levels. Downward trends in summertime ozone at 45 degrees
   north total only 3% for the decade ending 1990: This change is small
   when compared to a natural annual cycle of approx. 205 in column ozone.

****************************

Second selected review

Effect of Solar UV radiation on Humans: Biological Consequences of
Unrepaired Solar-induced DNA Damage.
A.Sarasin

Sunlight is one of the major environmental carcinogens in humans leading
to skin tumours on exposed parts of the body. The number of skin cancers
has increased dramatically, especially for melanoma, in the last 10 years.
Moreover, several human genetic diseases are characterised by 
hypersensitivity to UV - usually due to nucleotide excision repair defect
of UV-induced lesions.....

Discussion Highlights.

The question of whether UVR is the only human carcinogen in UV-sensitive
children is not readily resolved. Ultraviolet radiation can be classed as
a carcingogen if XP or the mutation spectra in oncogenes and the tumour
suppressor genes in skin tumours are included. It does not appear as a
carcinogen, on the other hand, if other DNA repair-deficient diseases
not directly associated with cancer are considered, such as Cockayne
symdrome and trichothiodystrophy.

DNA repair deficiencies may affect the risk of infectious disease,
possibly through free-radical processes. Free radicals can destroy
neurons, and they may also destroy other types of cells involved in 
immune response. In XP patients, development of skin tumours appears
to be associated with a deficiency in NK cells and also in Interferon
production.

              Bruce Hamilton

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From: [email-masked] (FMims)
Date: 9 Apr 1995 12:41:36 -0400

In prior post Bruce Hamilton ([email-masked]) discusses attenuation
and scattering of UV-B by clouds and aerosols. It is important to
understand that certain clouds can cause a significant increase in UV-B. I
have measured as much as +27% caused by cumulus clouds in a very clear
sky. See my note in Nature (22 Sept 94). Also, increasing aerosols reduce
direct and global UV-B, but they significantly increase diffuse UV-B. Thus
organisms in shady regions now receive considerably more UV-B than before
the industrial era. See my essay on this in New Scientist (24 Dec 94).

Forrest M. Mims III
Sun Photometer Atmospheric Network (SPAN)