Infections, causes, types, signs, symptoms, diagnosis, prevention, treatment

1. INFECTIONS
By FOTSO BENNIS Mounir
Medical student at Belarusian State Medical University
Faculty of General Medicine

2. DEFINITION
Infection is the invasion of an organism's
body tissues by disease-causing agents, their multiplication,
and the reaction of host tissues to these organisms and
the toxins they produce. Infectious disease, also known
as transmissible disease or communicable disease,
is illness resulting from an infection.

3. CAUSES OF INFECTION
Infections are caused by infectious agents :
• Viruses;
• Viroids;
• Prions;
• Bacteria;
• Nematodes such as parasitic roundworms and pinworms;
• Arthropods such as ticks, mites, fleas, and lice;
• Fungi such as ring worm;
• Other micro parasites such as tapeworms and other helminths.

4. VIRUSES
A virus is a small
infectious agent that replicates only
inside the living cells of other
organisms. Viruses can infect all types
of life forms, from animals and plants
to microorganisms, including bacteria
and archaea.

5. VIROIDS
Viroids are the smallest infectious pathogens known, consisting solely
of short strands of circular, single-stranded RNA without protein coats.
They are mostly plant pathogens, some of which are of economical
importance. Viroid genomes are extremely small in size, ranging from
246 to 467 nucleobases. In comparison, the genome of the smallest
known viruses capable of causing an infection by themselves are
around 2,000 nucleobases in size. The human pathogen Hepatitis D
virus is a defective RNA virus similar to viroids.

7. PRIONS
A prion is a protein that can fold in multiple,
structurally distinct ways, at least one of which is transmissible to other
prion proteins. It is this form of replication that leads to disease that is
similar to viral infection. The word prion, coined in 1982 by Stanley B.
Prusiner, is short for “proteinaceous infectious particle” derived from
the words protein and infection in reference to a prion's ability to self-
propagate and transmit its conformation to other prions.

9. BACTERIAS
Pathogenic bacteria are bacteria that can cause infection. One of
the bacterial diseases with the highest disease burden is tuberculosis,
caused by the bacterium Mycobacterium tuberculosis, which kills about
2 million people a year, mostly in sub-Saharan Africa. Pathogenic
bacteria contribute to other globally important diseases, such
as pneumonia, which can be caused by bacteria such
as Streptococcus and Pseudomonas, and foodborne illnesses, which can
be caused by bacteria such as Shigella, Campylobacter, and Salmonella.
Pathogenic bacteria also cause infections such as tetanus, typhoid
fever, diphtheria, syphilis, and leprosy. Pathogenic bacteria are also the
cause of high infant mortality rates in developing countries.

10. NEMATODES
The nematodes or roundworms constitute the phylum Nematoda.
They are a diverse animal phylum inhabiting a very broad range of
environments. Nematode species can be difficult to distinguish, and
although over 25,000 have been described, of which more than half
are parasitic, the total number of nematode species has been
estimated to be about 1 million. Unlike the phylaCnidarians and
Platyhelminthes (flatworms), nematodes have tubular digestive
systems with openings at both end.

12. ARTHROPODS
An arthropod (from Greek arthro-,
joint + podos, foot) is an invertebrate
animal having an exoskeleton
(external skeleton), a segmented body,
and jointed appendages. Arthropods
form the phylum Arthropoda, and
include the insects, arachnids,
myriapods, and crustaceans.
Arthropods are characterized by their
jointed limbs and cuticle made of
chitin, often mineralized with calcium
carbonate. Louse
(Fahrenholzia
Pinnata)
Castor Bean Tick
(Ixodes Ricinus)
Peacock Mite
(Tuckerella Sp.)

13. FUNGI
A fungus is any member of the group
of eukaryotic organisms that includes unicellular
microorganisms such as yeasts and molds; as well as
multicellular fungi that produce familiar fruiting forms
known as mushrooms. Dermatophytosis is a clinical
condition caused by fungal infection of the skin in
humans, pets such as cats, and domesticated animals
such as sheep and cattle. The term "ringworm",
commonly used to refer to such infections, is a misnomer,
since the condition is caused by fungi of several different
species and not by parasitic worms. The fungi that
cause parasitic infection (dermatophytes) feed on keratin,
the material found in the outer layer of skin, hair, and
nails.
Dermatophytosis on a
human leg.

14. TYPES OF INFECTION
Bacterial infections are classified by the causative agent, as well as
the symptoms and medical signs produced. Symptomatic infections
are apparent, whereas an infection that is active but does not produce
noticeable symptoms may be called unapparent, silent, subclinical or
occult. An infection that is inactive or dormant is called a latent
infection. A short-term infection is an acute infection. A long-term
infection is a chronic infection.

15. SIGNS AND SYMPTOMS
The symptoms of an infection depend on the type of disease. Some signs of
infection affect the whole body generally, such as fatigue, loss of appetite,
weight loss, fevers, night sweats, chills, aches and pain. Others are specific to
individual body parts, such as skin rashes, coughing, or a runny nose.
In certain cases, infectious diseases may be asymptomatic for much or even
all of their course in a given host. In the latter case, the disease may only be
defined as a "disease" (which by definition means an illness) in hosts who
secondarily become ill after contact with an asymptomatic carrier. An
infection is not synonymous with an infectious disease, as some infections do
not cause illness in a host.
Bacterial and viral infections can both cause the same kinds of symptoms. It
can be difficult to distinguish which is the cause of a specific infection. It's
important to distinguish, because viral infections cannot be cured
by antibiotics.

17. DIAGNOSIS
Diagnosis of infectious disease sometimes involves identifying an infectious
agent either directly or indirectly. In practice most minor infectious diseases
such as warts, cutaneous abscesses, respiratory system infections
and diarrheal diseases are diagnosed by their clinical presentation.
Conclusions about the cause of the disease are based upon the likelihood
that a patient came in contact with a particular agent, the presence of a
microbe in a community, and other epidemiological considerations. Given
sufficient effort, all known infectious agents can be specifically identified.
The benefits of identification, however, are often greatly outweighed by the
cost, as often there is no specific treatment, the cause is obvious, or the
outcome of an infection is benign.
As methods of diagnosis, we have symptomatic diagnosis, microbial
structure, microscopy, biochemical tests, molecular diagnosis, indicators.

18. PREVENTION
Techniques like hand washing, wearing gowns, and wearing face masks can help prevent infections
from being passed from the surgeon to the patient or vice versa. Frequent hand washing remains
the most important defense against the spread of unwanted organisms.Nutrition must be improved
and one has to make changes in life style- such as avoiding the use of illicit drugs, using a condom,
and entering an exercise program. Cooking foods well and avoiding foods that have been left
outside for a long time is also important. Antimicrobial substances used to prevent transmission of
infections include:
• Antiseptics, which are applied to living tissue/skin;
• Disinfectants, which destroy microorganisms found on non-living objects;
• Antibiotics, called prophylactic when given as prevention rather as treatment of infection.
However, long term use of antibiotics leads to resistance and chances of developing opportunistic
infections like clostridium difficile colitis. Thus, avoiding using antibiotics longer than necessary
helps preventing such infectious diseases.
There is also immunity. Infection with most pathogens does not result in death of the host and the
offending organism is ultimately cleared after the symptoms of the disease have waned. This
process requires immune mechanisms to kill or inactivate the inoculum of the pathogen. Specific
acquired immunity against infectious diseases may be mediated by antibodies and/or T
lymphocytes.

19. TREATMENTS
When infection attacks the body, anti-infective drugs can suppress the
infection. Four types of anti-infective or drugs exist: antibacterial
(antibiotic), antiviral, anti-tubercular, and antifungal. Depending on
the severity and the type of infection, the antibiotic may be given by
mouth, injection or may be applied topically. Severe infections of
the brain are usually treated with intravenous antibiotics. Sometimes,
multiple antibiotics are used to decrease the risk of resistance and
increase efficacy. Antibiotics only work for bacteria and do not affect
viruses. Antibiotics work by slowing down the multiplication of
bacteria or killing the bacteria. The most common classes of
antibiotics used in medicine include penicillin, cephalosporins,
aminoglycosides, macrolides, quinolones and tetracyclines.