Infectious Disease: Nature, Transmission, and Prevention

This article provides an overview of infectious diseases, including their nature, transmission mechanisms, and prevention methods. It discusses the different types of microorganisms that cause infectious diseases and explores the role of hygiene and immune responses in preventing infections. The article also covers the use of drugs in treating infectious diseases and the mechanisms of drug resistance.

Running head: INFECTIOUS DISEASE
Name of the Student
Name of the University
Author Note

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Introduction:
An infectious disease is a disease which is caused by the invasion of a host by agents
whose activities are harmful to the host tissues and further can be transmitted to other
individuals. Microbes tahr are capable of causing disease is called pathogen. As discussed by
Crobach et al. (2016), there are 1400 human pathogens, 60% of which are transmitted to
human zoonotically and depends on the animal reservoir. Among emerging infections, 73% of
the infection are zoonotic infections, indicating the fact that human animal interaction is the
potential risk factor for the infections (Esposito et al. 2016). This paper will discuss the nature of
the infectious disease and how biological systems, behavioral, and the drug can prevent disease.
Discussion:
Ranges of microorganism:
Infectious disease can be devastating and fetal sometimes to the host. Although
microorganism that causes disease are under the spotlight of research, it is important to note that
not all microorganism are able to cause infection in host disease. As discussed by Crobach et al.
(2016), there are a variety of microorganisms which causes infectious disease resulted in an
increase in the mortality rate. The pathogenic microorganism is of four types which include
bacteria, virus, fungi, and protozoa.
 Bacteria are microscopic single cell microorganism which thrives in a diverse
environment and has the ability to cause infection by transmitting to the host (Nitzan et
al. 2015).
 Virus is an infectious agent typically consists of nucleic acid and protein coat that is able
to multiply to cause disease only within the living host.

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 Fungus is a member of eukaryotic organisms which include mold, yeasts.
 Protozoa is single-celled eukaryotes either free-living or parasitic. These different
ranges of microorganisms have a history of evolution which further induces potential
outbreaks.
Figure: Ranges of microorganism
Source: (Nitzan et al. 2015).
Mechanism of causing disease:
The infectious disease is usually characterized by the dominant organ involved. To be
infectious a microorganism must enter into the human body. However, the primary aim of the
microorganism is not causing disease, rather multiply for living. In order to multiply, a
microorganism is required to invade the human organism (Golding et al. 2016). The infection

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occurs when microorganism such as viruses, bacteria, protozoa, and fungus invades the human
organ to multiply and it potentially disrupts the normal function of human by damaging cells of
the body (Nitzan et al. 2015). Consequently, the damaged cells with disrupted functionality
exhibit in the signs and symptoms of the disease. These microorganisms are able to transmit
from one host to another host by direct or indirect contact, resulting in spreading of disease
Figure: Mechanism of causing disease
Source: (Golding et al. 2016)
Transmission through vector:
Semenza and Suk (2017), stated that a vector is a living organism which transmits an
infectious agent from an infected animal to a human or animal. The biological vectors such as
mosquitoes, ticks, fleas are able to carry infectious pathogens which can be transferred from one
to another. The microorganisms’ shelter in the saliva of the vectors and the transmission
mechanism usually occurs when these vectors bite the host. In the United Kingdom, there are
currently 14 vectors borne infectious diseases which are a national public health concern

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(Kraemer et al. 2016). Approximately 1.2 million around the globe are currently experiencing
vector born disease. 17% of all infectious diseases are vector born disease.
• The diseases such as West Nile virus, Dengue, Eastern equine encephalitis, Malaria are
the most common disease which is transmitted by the mosquito as a vector.
• Tick born disease includes Lyme disease, Babesiosis, Anaplasmosis, Spotted Fever
Rickettsia, and Tularemia.
• Flea born disease includes plague (Semenza and Suk 2017).
The vectors and host involved in the transmission of these infective pathogens are sensitive to
climate change and other factors such as vector and host survival, reproduction development,
activity, abundance and distribution, transmission, geographic range, human behavior, and
disease outbreak frequency.

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Figure: Transmission through vector
Source: (Semenza and Suk 2017).
Route of the entrance:
Microorganisms which are capable of causing disease usually enter our bodies through
the eyes, mouth, urogenital openings or through wounds or bites which breach the skin barrier.
• Some of the disease-causing pathogens enter the body through infected skin, body fluids,
blood or serum when an infected person is in direct contact with a healthy person (Cundell et al.
2016).
• The droplet containing infectious microbes coming from the sneezing and coughing or simply
talking of infected person are able to cause disease, highlighting indirect contact.
• As discussed by Cundell et al. (2016), the microorganisms can enter the body through
contaminated food, water.
• The microbes present in the dust remain suspended in the air for a longer period of time and
able to enter the body through inhalation where they invade mucous membrane and cause
disease.

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Figure: Route of entrance
Source: (Semenza and Suk 2017).
Nonspecific defense system in preventing disease:
Most microbes encountered in daily life are repelled before they exhibit detectable
signs. The nonspecific defense mechanism of the body includes physical barriers such as skin; a
chemical barrier such as antimicrobial proteins, cells that attack the foreign invades.

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• The skin contains keratin which serves as the barriers to the infection; the skin contains some
fatty acid, oleic acid, skin gland secreting lysozyme.
• The mucous membrane in the lining of the respiratory tract and genitourinary tract secrets
mucus which traps small particles of microbes. Other cells in the respiratory tract beat in a
sweeping movement eliminate the infection.
• Antimicrobial protein such as compliment can prevent infection through a complex
mechanism.
• Interferon’s such as alpha interferon, beta interferon, gamma interferon, provide protection
by inhibiting the replication of viral cells. Alpha produced by white blood cells, beta secreted by
fibroblast and gamma interferon is secreted by cytotoxic T lymphocytes (Mor, Aldo and Alvero
2017)
• The protein produced by gut microbes is able to prevent the infection.
• Phagocytotic cells such as macrophages destroy microbes by engulfing the cells.
• Natural killer cells randomly attack the cells that are harboring infectious microbes.
• Granulocytes containing digestive enzymes are able to break down proteins and induce
bacteriocidal proteins.
• Basophils, eosinophils and mast cells are able to release heparin, histamine to prevent the
microbes from causing infection.

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Figure: Nonspecific defense system in preventing disease
Source: (Mor, Aldo and Alvero 2017)
Hygiene control prevents infection:
Behavioral practice such good personal hygiene is able to prevent the infection and rapid
reduction of infection associated disease. The hygiene control practices in prevention of infection
are the following:

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• Hand hygiene is highlighted as the number one weapon in preventing the spread of microbes.
Alcohol based hand rubs and hand washing with soap and water are able to remove microbes
from the skin surface. (Khan, Baig and Mehboob, 2017).
• Using tissues when sneezing or coughing or turn away from other people prevent direct or
indirect transmission of microbes present in the sneeze or cough which further reduce infections
• Washing hands after sneezing or coughing prevent transmission of disease-causing microbes
from tissue to hand which further reduce infection (Bloomfield et al. 2016)
• Staying home when someone is sick is crucial for spreading of microbes from the infected
body fluid, blood or serum which further prevent infections.
• In house or hospital frequent cleaning of surface such as floors, walls or equipment’s can
prevent the transmission through droplet which further aid in reducing the infections
• In hospitals, promoting injection safety such as wearing gloves while using injections and
following the aseptic process can prevent infection by hindering transmission.
• Using gloves, masks, eyewear can prevent infection by creating barriers to protect skin,
clothing, and mucous membrane.
• Vaccinations against certain diseases can prevent infection by inducing antibodies against
certain microbes that can prevent infection by attacking microbial cells.

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Figure: Hygiene control prevents infection
Source: Khan, Baig and Mehboob, 2017).
Specific immune responses of humoral immunity and cell-mediated immunity:
Humoral immunity is the aspect of immunity which is mediated by macromolecules
found in an extracellular fluid such as secreted antibodies, complement proteins, certain body
fluids. The extracellular space of the body is protected by the humoral immune system.
• When the pathogenic microbes are detected in the body through their antigenic fragments
which are presented to the T cells in the form of the peptide on histocompatibility molecules of
antigen presenting cells. Helper T (CD4+) cell recognize the peptide and secrete cytokines to
induce B cell activation (Frie et al. 2016).
• B cells itself can detect soluble antigens and active itself.

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• The activation of B cells and their differentiation into plasma cells containing antibodies are
observed after induction by antigens and these antibodies destroy the antigen. The other
differentiated cells are stored as memory cells.
• Complement activation resulted from complement proteins adhere to the pathogen surface
and opsonize the pathogens by binding to the complement receptor on phagocytes.
Figure: Specific immune responses
Source: (Frie et al. 2016).

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Cell-mediated immunity:
• Cell-mediated immunity does not involve immune responses rather they involve activation of
phagocytic cells, antigen-specific cytotoxic T lymphocytes, and various cytokines in response to
the T cells of the body cells displaying epitope of foreign antigens (Sztein 2018).
• When antigens are detected helper T cell induces cytotoxic T cells via cytokines by the same
mechanism discussed for the humoral immune response which further induces phagocytosis of
the phagocytic cells and destroys pathogenic cells such intercellular bacteria, tumor and cancer
cells (Filipczak-Bryniarska et al. 2016).
Figure: Specific immune responses
Source: (Frie et al. 2016).

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Humoral responses give rise to acquired immunity:
As discussed above, a humoral immune response is mediated by antibodies which are
secreted by plasma cells. Antibodies protect against bacteria that present outside the body. The
antibody produces by B cell activation against the certain microbial cells give rise to acquired
immunity to fight against the microbial cells which will be observed after a reoccurrence of the
disease. The acquired immunity can be passive or activity immunity.
• Active is induced when the human body exhibits humoral immune response because of direct
exposure to the unknown pathogen. These responses are very specific to the antigen of particular
antigens (Filipczak-Bryniarska et al. 2016).
• Conversely, passively acquired immunity is humoral responses which involve the antibodies
obtained from outside of the body through the vaccination process.
Drugs in the prevention of disease:
Antimicrobial drugs have a certain inhibitory mechanism by which they target specific
parts of microbes and inhibit the replications. Generally, before bacteria started exhibiting signs
and symptoms, the immune responses of the human body typically kill them. When immune
responses are unable to prevent the infection then drugs are used to fight certain infection which
can be fatal sometimes. As discussed Ventola (2015) the drugs have a certain target of microbial
cells sites these sides include
• Cell wall synthesis
• DNA replication

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• RNA transcription
• Protein translation
• Transmembrane synthesis
For example, penicillin is an antibiotic which prevents bacterial infection such as strep throat by
preventing the synthesis of peptidoglycan of gram-positive bacteria streptococcus. Anti-
protozoal drugs include daraprime inhibit DNA replication by creating nicks or strand breaks in
DNA. Oseltamivir is an antiviral drug which prevents influenza A and B by inhibiting the
neuraminidase, the viral enzyme found in the surface of the viral coat and release progeny
produced virions (Wilson et al. 2016).
Drug resistance mechanism:
A considerate number of microbes show high resistance towards Antimicrobial drugs
after first application or frequent application, especially towards antimicrobial drugs. As
discussed by Brooun et al. (2016), microbes have evolved themselves after the first exposure to
the antimicrobials which further assists microbes to withstand the mechanisms of drugs.
• Few microbes evolve themselves to stop the antimicrobials to reach its target at a high
concentration. Few microbes decrease the permeability of the membrane surrounds microbial
cells. Few microbes develop efflux pump to push the drug out of cells. Few of the microbes
destroy microbes by developing enzymes (Blair et al. 2015).
• Few microbes modify or bypass the target site that the antimicrobial drugs act on. Few of the
microbes use alternative proteins for the drug target. Few of the microbes camouflage the targets
whereas few produce the variant structure of the target.

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Conclusion:
Thus it can be concluded that infectious diseases are the diseases which are caused by
pathogenic microbes when they transmitted directly or indirectly through vectors or any other
sources. A range of microbes such as bacteria, virus, protozoa, and fungus can cause infectious
disease when they invade body for multiplications. Usually, nonspecific immune defense
prevents the microbial infection before it started exhibiting signs and symptoms of the infection.
The human body has two kinds of the immune response such as cell-mediated involving
phagocytosis and humoral immune response involving antibodies. When the immune system
failed to prevent disease then drugs are consumed to fight the disease.

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