Microbiology and Immunology

Blue-green algae WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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Another group particularly at risk of blood borne infec-

tions are hemophiliacs. The necessity of hemophiliacs to

receive blood products that promote clotting leaves them vul-

nerable. For example, in the United States, some 20% of adult

hemophiliacs are infected with HIV, about 56% are infected

with the hepatitis B virus, and almost 90% are infected with

the hepatitis C virus. HIV is the most common cause of death

among hemophiliacs.

Other viruses pose a potential for blood borne transmis-

sion. Human herpesvirus 6 and 7, Epstein-Barr virusand

cytomegalovirus require close contact between mucous mem-

branes for person-to-person transfer. Abrasions in the genital

area may allow for the transfer of the viruses in the blood.

Parvovirus, which causes the rash known as fifth disease in chil-

dren, can be transferred between adults in the blood. In adults,

particularly women, the resulting infection can cause arthritis

At least in North America, the increasing urbanization is

bringing people into closer contact with wildlife. This has

resulted in an increase in the incidence of certain blood borne

diseases that are transmitted by ticks. Mice, chipmunks, and

deer are two reservoirs of Borrelia burgdorferi, the bacterium

that causes Lyme disease. The increasing deer population over

the past 35 years in the state of Connecticut has paralleled the

increasing number of cases of Lyme disease, over 3,000 in

1996 alone.

Other blood borne disease transmitted by ticks includes

Rocky Mountain Spotted Fever, human granulolytic ehrlichio-

sis, and babesiosis. While these diseases can ultimately affect

various sites in the body, their origin is in the blood.

The institution of improved means of monitoring

donated blood and blood products has lowered the number of

cases of blood borne infections. However, similar success in

the hospital or natural settings has not occurred, and likely will

not. Avoidance of infected people and the wearing of appropri-

ate garments (such as socks and long pants when walking in

forested areas where ticks may be present) are the best strate-

gies to avoid such blood borne infections at the present time.

See alsoAIDS; Hemorrhagic fevers and diseases; Transmis-

sion of pathogens

BBlue-green algaeLUE-GREEN ALGAE

Blue-green algae are actually a type of bacteriathat is known

as cyanobacteria. In their aquatic habitat, cyanobacteria are

equipped to use the sun’s energy to manufacture their own food

through photosynthesis. The moniker blue-green algae came

about because of the color, which was a by-product of the pho-

tosynthetic activity of the microbes, and their discovery as a

algal-like scum on the surface of ponds. They were assumed to

be algae until their identity as bacteria was determined.

Although the recognition of the bacterial nature of the

microbe occurred recently, cyanobacteria are ancient. Fossils

of cyanobacteria have been found that date back 3.5 billion

years and are among the oldest fossils of any life from thus far

discovered on Earth. These microorganismsmust have devel-

oped very early following the establishment of land on Earth,

because the oldest known rocks are only slightly older at 3.8

billion years.

Modern day examples of cyanobacteria include Nostoc,

Oscillatoria, Spirulina, Microcystis, and Anabaena

Cyanobacteria were monumentally important in shap-

ing life on this planet. The oxygen atmosphere that supports

human and other life was generated by cyanobacterial activity

in the distant past. Many oil deposits that were laid down in

the Proterozoic Era were due the activity of cyanobacteria.

Another huge contribution of cyanobacteria is their role in the

genesis of plants. The plant organelle known as a chloroplast,

which the plant uses to manufacture food, is a remnant of a

cyanobacterium that took up residence in a eukaryotic cell

sometime in the Proterozoic or early Cambrian Era. The mito-

chondrion in eukaryotic cells also arose in this fashion.

The ability of cyanobacteria to photosynthetically uti-

lize sunlight as an energy source is due to a pigment called

phycocyanin. The microbes also contain the same chlorophyll

a compound used by plants. Some blue-green algae possess a

different photosynthetic pigment, which is known as phyco-

erythrin. This pigment imparts a red or pink color to the cells.

An example is Spirulina. The pink color of African flamingos

actually results, in part, from their ingestion of Spirulina.

Cyanobacteria tend to proliferate in very slow moving

or still fresh water. Large populations can result very quickly,

given the appropriate conditions of temperature and nutrient

availability. This explosive growth is popularly referred to as

a bloom. Accounts of blooms attributable to cyanobacteria

date back to the twelfth century. The toxic capabilities of the

organism have been known for over 100 years. Some species

produce a toxin that can be released into the water upon the

death of the microorganism. One of the cyanobacterial toxins

is damaging to the liver, and so is designated a hepatotoxin.

Another cyanobacterial toxin is damaging to cells of the nerv-

ous system, and so is a neurotoxin. Still other cyanobacterial

toxins cause skin irritation.

A toxin of particular note is called microcystin. This

toxin is produced by Microcystis aeruginosa. The microcystin

toxin is the most common in water, likely because of its sta-

bility in this environment. One type of microcystin, which is

designated microcystin-LR, is found in waters all over the

world, and is a common cause of cyanobacterial poisoning of

humans and animals.

At low levels, toxins such as microcystin produce more

of an uncomfortable feeling than actual damage to the body.

However, blue-green algae and their toxins can become con-

centrated in shallow, slow-moving bodies of water or in fish.

Ingestion of the fish or accidental swallowing of the water

while swimming can produce nausea, vomiting fever, and

diarrhea. Eyes can also become irritated. These symptoms can

be more exacerbated in children, because the toxin-to-body-

weight ratio is higher in children than in adults. Liver damage

can result in children exposed to the toxins.

In contrast to many other toxins, the cyanobacterial tox-

ins can still remain potent after toxin-contaminated water has

been boiled. Only the complete removal of the toxin from the

water is an assurance of safety. Some success in the removal

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