Microbiology and Immunology

Snow blooms WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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In general, the worldwide practice of smallpox immu-

nizationgreatly diminished the fear of an epidemic caused by

a deliberate release of the virus. Although the disease was

declared eradicated in 1980, stores of smallpox officially exist

at the two WHO-approved repositories. The first is at the

Centers for Disease Controland Prevention in Atlanta, USA.

The second is the State Research Center for Virologyand

Biotechnology(also known as Vector) at Koltsovo, in the

Novosibirsk region of Siberian Russia. In June 1995, WHO

inspected the Koltsovo facility and determined that it was an

acceptable storage facility after the virus stocks were moved

there from the original storage site at the Institute of Viral

Preparations in Moscow. All other laboratories around the

world were required to destroy their remaining stores of small-

pox virus. Concomitantly, WHO recommended that all coun-

tries discontinue vaccination against the disease.

Despite the provisions of the WHO and the 1972

Biological Weapons Convention, the former Soviet Union

maintained a sophisticated and large-scale research and devel-

opment program for biological weapons implementation. This

research was carried out at both military and civilian level. It

is now known that the Soviet Union successfully developed

and adapted smallpox virus for use in strategic weapons.

Considerable debate has ensued regarding the officially

remaining stores of smallpox virus. The WHO Ad hoc

Committee on Orthopoxvirus Infections has, since 1986, con-

sistently recommended destruction of the remaining reserves

of the smallpox virus. The initial proposal was to destroy the

remaining stocks in December 1990. However, the possibility

that smallpox has been, and might be, incorporated into bio-

logical weapons has encouraged the scientific community to

continue research on the pathogen. Although the tentative date

set for the destruction of all remaining smallpox stores is late

2002, a consensus among scientists and military strategists has

not yet been reached and in view of current political unrest in

areas such as the Middle East, total destruction of all stores is

not likely to happen.

Since many laboratories involved in biological

weapons research and development in the former Soviet

Union are now working with decreased funding, staff, and

support, there is concern that bioweapons resources and

expertise may spread to other countries. A report from the

Washington Center for Strategic and International Studies

states that at least 10 countries are involved in biological

weapon research programs. The ability of a group to acquire

variola and develop it as a biological weapon is limited by

several factors. Specialized skills are required to grow small-

pox in effectively large quantities and to adapt it for use as an

aerosol-based weapon. It is unlikely that small, technically

limited facilities or dissident groups would use smallpox as a

weapon. Also, the open use of a biological weapon by any

nation or political state would undoubtedly elicit severe retal-

iation. Lastly, the smallpox virus is not as readily available as

other agents of biological terrorism, such as anthrax(Bacillus

anthraci) or plague (Yersinia pestis).Therefore, analysis of

these and other factors have led bioweapons experts to con-

clude that well-financed and highly organized private groups

or politically/state financed terrorist groups would be the

most likely to use smallpox as a bio-weapon.

See also Bioterrorism; Bioterrorism, protective measures;

Epidemics, viral; Viruses and responses to viral infection

SSnow bloomsNOW BLOOMS

Snow bloom refers to the rapid growth and increase in num-

bers of so-called snow algae on the surface and interior of

snow fields. Typically occurring as the surface of the snow

warms in the springtime sun, the algal growth confers various

colors to the snow. Colors of different algal species include

yellow, red, green, and orange.

Blooms occur when nutrients are abundant and condi-

tions such as temperature are conducive to rapid growth. “Red

tide,” due to the growth of a diatomsin salt water, is another

example of a bloom.

There are some 350 species of snow algae. A common

species is Chlamydomonas nivalis.

Snow algae have been known for millennia. The Greek

philosopher Aristotle described red snow over 2,000 years

ago. The algal basis for the blooms was determined in the

early nineteenth century, when some red-colored snow

obtained by a British expedition near Greenland was analyzed.

Snow blooms occur most frequently in high altitude

areas where snow persists over a long time and accumulates to

great depths. Examples include the Sierra Nevada range in

California and the Rocky Mountains of North America.

The various colors of snow blooms reflect the presence

of various pigmented compounds in the algae. These com-

pounds, which are called carotenoids, confer protection

against the sunlight, particularly against the ultraviolet portion

of the spectrum. Red algae are more sunlight tolerant than are

green, orange, and yellow-pigmented algae. Non-red algae

tend to shield themselves from the sunlight by growing

beneath the snow’s surface.

In another adaptation, the algal membrane is adapted for

cold, in much the same way that cold-loving bacteriaare, via

the presence of lipids that remain pliable at low temperatures.

Another feature of snow algae that contributes to their

tolerance is their ability to form cysts. These are analogous to

bacterial spores, in that they provide the algae with a means of

becoming metabolically dormant during inhospitable periods.

During the winter, the cysts remain encased in snow. Indeed,

experiments have determined that cysts are not inactivated

even after a prolonged storage at -94° F (-70° C). As the snow

melts in the springtime, resuscitation of the cysts occurs. The

algal cells migrate to the surface of the snow in order to repro-

duce. After reproducing the cells drift down into the nutrition-

ally poor subsurface, where their transformationinto cyst

form is again stimulated. The following spring the cycle is

repeated.

See alsoPsychrophilic bacteria

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