Microbes: Enemy and Friend
- Nowhere is biologic diversity demonstrated more
dramatically than by microorganisms. Clearly by now, we have observed how viruses,
bacteria and other microorganisms can upset the balance of our ecosystem. Our initial image of breakouts is that these
minute organisms are nothing but trouble, and, not only that, they do it big
time. We see that they can easily evolve and adapt to our own defense
mechanisms, then strike in an insidious manner. Right when we think it’s over,
they mutate and defeat us in a couple of ways. But first, let’s review the
basic differences between a bacterium and a virus.
- To be fair, there are
species of microorganisms that serve a useful purpose. One example is Bti (Bacillus thuringiensis serovar israelensis), a gram-positive soil bacterium that produces crystalline inclusions with a
highly specific insecticidal activity. It produces toxins which are effective
in killing various species of mosquitoes, fungus gnats, and blackflies, while
having almost no effect on other organisms. Bti strains possess the pBtoxis plasmid which
encodes numerous Cry and Cyt toxins, including Cry4, Cry10, Cry11, Cyt1 and
Cyt2. They have been used as a larvicide for many years and is
now becoming widely available for you to buy and use yourself at home. - Formulations
include small, donut-shaped form "Mosquito
Dunks"/"Mosquito Bits". It is also available in bulk liquid or
granular formulations for commercial and public agency use. A home gardener’s
spray,“GET OFF ME! Natural Bug Spray”, is also available. These Bti solutions can
be produced in small batches making them practical for local area mosquito
control. Another natural solution is made from efficacious isolates of Bacillus
sphaericus Neide. B. sphaericus has been shown to persist longer
than Bti in polluted habitats and under certain circumstances. A
disadvantage of B. sphaericus has been the development of resistance in
certain populations of Culex quinquefasciatus Say and Culex pipiens
Linnaeus.
- The factors for their larvicidal
action depend on the nature of the breeding potential of the environment, type
of mosquito, their respective feeding strategies, rate of ingestion, age and
density of larvae, habitat factors (temperature, solar radiation, depth of
water, turbidity, tannin and organic content, presence of vegetation, etc.),
and the different aspects of the formulations. Let us remember though, that the
best way to control mosquitoes is still to get rid of standing water on your
property. Prevention and control begin with understanding disease transmission
and insect vector life cycle. This is probably the most neglected aspect in
the control of disease. The seasonal pattern of WNV parallels the proliferation
(life cycle) of the insect. This makes this quite relevant to our current West
Nile Virus-mosquito epidemic connection.
Back to Bacterial Basics
- Eukaryotes are organisms containing a membrane-bound nucleus.
Among the groups of eukaryotic microorganisms are the algae, the protozoa,
the fungi, and the slime molds. On the other hand, prokaryotes
are organisms in which DNA is not physically separated from the cytoplasm. Eukaryotes
and prokaryotes are organisms because they contain all of the enzymes required
for their replication. Furthermore, they possess the biologic equipment
necessary for the production of metabolic energy. Bacteria are a large domain of prokaryotic
microorganisms.
Typically a few micrometres in length, and have a wide range of shapes,
ranging from spheres
to rods and spirals. They thrive in soil, plants, water, as well as in the gut
flora and integument.
Gram Positive Bacterium
A diagram of a typical prokaryotic
cell.
March 2008; Author Mariana Ruiz
Villarreal
- There are approximately ten times as many bacterial cells
in the human
flora as there are human cells in the body.
Bacteria display a wide diversity of shapes and sizes. Most bacterial species are either spherical (cocci), or
elongated (bacilli). They are broadly classified as Gram positive (no outer membrane), and Gram negative (outer membrane present). Gram stain primarily detects peptidoglycan, which is present in a thick layer in Gram positive bacteria. They exist simply as single cells, others associate in
characteristic patterns. Neisseria, (e.g. gonococcus), form diploids
(pairs). They have a cell wall and
self-preserving intracellular structures, responsible for the respiration and
metabolism of the organism. The bacteria’s outer lipid membrane, or cell
membrane, encloses the contents of the cell and acts as a barrier to hold
nutrients, proteins
and other essential components of the cytoplasm
within the cell. Biochemical reactions, such as energy generation, occur by concentration
gradients across membranes. Internally, there is a lack of membranes which means reactions such as electron transport occur across the cell
membrane between the cytoplasm and the periplasmic
space (region bordered by two selective permeable barriers, i.e. biological membranes, which are the inner membrane (i.e. cytoplasmic membrane) and the outer membrane in Gram-negative bacteria). They may need oxygen (aerobic
bacteria), or not (anaerobic bacteria). They thrive on extracellular ions and
the like, and do not need a host to give it the ability to multiply.
Going Viral
- In 1892, Dimitri Ivanovsky described a
non-bacterial pathogen infecting tobacco plants. Then in 1898 Martinus
Beijerinck eventually identified the tobacco mosaic virus. a positive-sense single stranded RNA virus that infects plants, especially tobacco and other members of the family Solanaceae, known as the nightshade or potato family. Since that time, at
least 5000 viruses have been described, quite a few of which still have to be
properly studied in detail. The unique properties of viruses set them apart
from living creatures.
Electron microscopy of West Nile virus, taken from lab,
rights retained to displayed author.
20 November 2007 (first version); 10 June 2010 (last version)
Original uploader was PhD Dre
[Magnification in a Scanning Electron Microscope ]
- There are seven classes of viruses. (The term virus is
from the Latin, virulentus, meaning poisonous.) Viruses are not cells,
but rather particles consisting of 2 to 3 things, i.e. genetic material made
from DNA or RNA, the protein coat that protects these genetic materials, and in
a few cases a lipid envelope that that surrounds the protein coat when the
virus is not inside a host cell. The virus is of an extremely smaller size, at 1/100 the size of the usual bacterium. Viruses can
be shaped as a helix, or can be icosahedral (20 identical equilateral triangular faces, 30 edges and 12 vertices), and in some still more complex
geometries. Of course, because of its minute size, they cannot be seen using
the optical microscope commonly found in labs.
They can be visualized usually through special imaging techniques such an electron microscope such as a
SEM (scanning electron microscope) which can render a magnification over a range of up to 6 orders of magnitude from about 10 to 500,000 times. Polymerase Chain Reaction (PCR) is another method for studying bacteria. This technique enhances (amplifies) the DNA sequence wherein a short region of the DNA (fragments containing a few copies) is amplified up to ~10 kilo base pairs (kb). The underlying mechanism for PCR is called thermal cycling.
- The range of host cells that a virus can infect is called
its "host range". This is how viruses can be transmitted from
plant to plant, plant to arthropod, arthropod to animal, or man, and this is carried
out by a vector like an insect feeding on the infected plant’s nutrients. Virus
transmission is also often times effected through droplets such as sneezing, and
that is exemplified by respiratory viral illnesses. Still others are
transmitted through blood products. Viruses lack many of the attributes of
cells, including the ability to replicate.
- Viruses are obligatory parasites,
meaning they need a host cell to invade and where they then hijack the host
cell’s genetic material. There the virus redirects the host's enzymatic
machinery to functions associated with replication of the virus. As they
infiltrate the host’s immune cells, they have the ability to knock out the
immune system resulting in severe and long-term disease. Viral infections
however, are also capable of inducing immunity of the host. This way, the host’s
immune system protects against future infection. A number of transmissible
plant diseases are caused by viroids, which are small, single-stranded,
covalently closed circular RNA molecules existing as highly base-paired
rod-like structures; they do not possess capsids. The extracellular form of the viroid is naked
RNA—there is no capsid of any kind. The RNA molecule contains no
protein-encoding genes, and the viroid is therefore totally dependent on host
functions for its replication.
- Antibiotics have no
effect on viruses, unlike bacteria that are usually eliminated by this drug
class by different mechanisms. It is asked, where and when did viruses begin to appear? Are they
primitive genetic molecules that have evolved into infectious agents? One might
ask, “Were they remnants of decaying plant or animal tissue, remnant particles that became a rogue
part of the environment, very much like plants and animals?” One thing seems
sure, and that is, viruses need the host to exist, multiply, and thrive. Recent developments involve using viruses as vectors for delivery of therapeutic substances.
-
The Virus-Mosquito-Bacteria Circle
- On a lighter note, horticulturists as well as ornamental
plant growers can both use Bti to control mosquitoes that may thrive in irrigation
water barrels and pails. In a big plot of land, good drainage should be
encouraged thereby limiting the mosquitoes and the use of any control agent.
Those who own dipping or swimming pools should keep them clean with the
appropriate disinfectants (e.g. sodium hypochlorite and copper sulfate).
17 June 2007
by Steffen Dietzel
- As far as the Preventive Medicine principles are concerned, the measures used to control the West Nile Virus carriers are also measures for other mosquito-borne diseases.
For U.S. West Nile Virus outbreak demographics, visit this page for updates
- As far as August 14, there appears to be no new case of WNV. This is good. At least the proper surveillance and control methods are paying off, albeit a tad slow at first.Total number of cases as of Aug. 14, 2012 is 693. Since 1999, more than 30,000 people in the United States have been reported as getting sick with West Nile virus.
- In the meantime, awareness and surveillance continues so as not to miss the patient with atypical clinical presentation. Travelers need to be cautious especially in going to areas with swamps, stagnant rivers, and other areas where their is an outbreak. So it would be wise to consult the map as noted in aforementioned page
- As newer technology and better preventive methodology develops, it is hoped that the big brothers in healthcare, eg., WHO and CDC, will be able to prepare us in any eventuality. In this outbreak alone, we have seen the melding of clinical acumen, public health/preventive medicine and various areas of bioinformatics. Sometimes, in all the hustle of the situation, we tend to overlook the role of the computer scientist and physician in their untiring efforts to keep us healthy.
- Keep smart, keep safe. Til another day...
- Fernando Yaakov Lalana, M.D.
- P.S. If you would like to see some interesting Scanning Electron Microscope images do visit this page.
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