1. Infectious Diseases
Abstract
Infectious diseases are a significant burden on global economies and public health.1,2,3
Their emergence
is thought to be driven largely by socio-economic, environmental and ecological factors[1,2,3,4,5,6,7,8,9]
, but
no comparative study has explicitly analysed these linkages to understand global temporal and spatial
patterns of EIDs. EID events have risen significantly over time after controlling for reporting bias, with
their peak incidence (in the 1980s) concomitant with the HIV pandemic. EID events are dominated by
zoonoses (60.3% of EIDs): the majority of these (71.8%) originate in wildlife (for example, severe acute
respiratory virus, Ebola virus), and are increasing significantly over time. We find that 54.3% of EID
events are caused by bacteria or rickettsia, reflecting a large number of drug-resistant microbes in our
database. Our results confirm that EID origins are significantly correlated with socio-economic,
environmental and ecological factors, and provide a basis for identifying regions where new EIDs are
most likely to originate (emerging disease ‘hotspots’). They also reveal a substantial risk of wildlife
zoonotic and vector-borne EIDs originating at lower latitudes where reporting effort is low. We
conclude that global resources to counter disease emergence are poorly allocated, with the majority of
the scientific and surveillance effort focused on countries from where the next important EID is least
likely to originate.
Introductions:
Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi;
the diseases can be spread, directly or indirectly, from one person to another. Many organisms live in and
on our bodies. They’re normally harmless or even helpful, but under certain conditions, some organisms
may cause disease. Zoonotic diseases are infectious diseases of animals that can cause disease when
transmitted to humans.
Signs and symptoms vary depending on the organism causing the infection, but often include fever and
fatigue. Mild infections may respond to restand home remedies,while some life-threatening infections may
require hospitalization. Many infectious diseases, such as measles and chickenpox, can be prevented by
vaccines.

2. Infectious diseases are one of the leading causes of death worldwide. Scientists are currently searching for
new approaches to treat infectious diseases, focusing on exactly how the pathogens change and drug
resistance. About infectious diseases that have a statistical data are given by Saudi Ministry of Hajj19 and
Central Department of Statistics and Information.10
.
Fig: Number of pilgrims attending the Hajj from 2003 to 2013 Data are from the Saudi Ministry of Hajj19
and Central Department of Statistics and Information.
Symptoms and Causes of Infectious Diseases
Each infectious disease has its own specific signs and symptoms. General signs and symptoms common to
a number of infectious diseases include:
 Fever
 Diarrhea
 Fatigue
 Muscle aches
 Coughing
Infectious agents:
An infectious agent is something that infiltrates another living thing. When an infectious agent hitches a
ride, you have officially become an infected host. There are four main classes of infectious
agents: bacteria, viruses, fungi, and parasites. This fab four[3,4,5]
can infect all sorts of living things.
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Infectious Diseases

3. Viruses
 Viruses are tiny infectious agents that replicate only in the living cells of other organisms.
 Viruses have a very simple structure consisting of genetic material in the form of DNA or RNA?
Within a protein? Capsule.
 They can infect all types of life forms, from animals to plants and bacteria? To amoebae?
Bacteria
 Bacteria are single-celled microorganisms.
 They come in many shapes including ball-, rod- and spiral-shaped.
 Most bacteria are not harmful and some are actually beneficial. Less than one per cent of bacteria
will actually make you ill.
 Infectious bacteria can grow, divide and spread in the body, leading to infectious disease.
 Some infectious bacteria give off toxins which can make some diseases more severe.
Fungi
 Fungi are microorganisms characterised by cell walls made from a substance called chitin.
 Most fungi are harmless to humans and some are edible.
 Other fungi can be infectious and may lead to life-threatening diseases.
 Fungi reproduce by releasing spores that can be picked up by direct contact or even inhaled.
 Fungal infections often affect the lungs, skin or nails. Some infections may also penetrate the body
to affect organs and cause whole-body infections.
Parasites
 Parasites are organisms that live in or on another organism and benefit by getting nutrients at the
expense of their host.
 Parasites can be found in many different body sites, for example in the blood, liver, digestive
system, brain and even the eyes.
Mechanism of infectious disease
Though each organism has a specific, unique signature of creating disease in human hosts, we can identify
common stages in the development of an infectious disease.
Symptoms of disease are usually caused by structural or functional changes in molecules in the cells that
make up our tissues. These changes result from physical or metabolic injury to a cell, which can be due to
a pathogenic organism.
Localised vascular response
These are the early stages of the inflammatory process. Local tissue damage or pathogens infecting our
tissue can set off this response. The roman doctor Aulus Cornelius Celsus who lived around the beginning
of the Christian era, described the 4 classical symptoms of inflammation:

4.  Redness
 Swelling
 Pain
 Increased temperature of inflamed tissue.
These symptoms can be explained by an increased blood flow to the inflamed tissue; causing redness and
increased temperature, as blood is warmer than our skin normally.
As the increased blood flow increases the pressure in the small capillaries, some of the plasma may leak
out of the blood vessels, causing swelling of the tissue and pain through pressure on the nerve endings.
These responses occur within minutes to hours after the initial damage. The increased blood flow allows
cells to travel to the place of damage to start making repairs.
Alteration and damage to cell of the tissue
Cells that migrate to the infected tissue have different functions. The first cells to arrive can recognize, kill
and remove foreign microbes. Others can kill infected cells. The destruction of cells by our own immune
system is one of the reasons that we suffer symptoms of a disease. Some organs, such as brain or lungs, are
more vulnerable to the effects of infection than others. For example, if our lung tissue is infected and the
defense system causes fluid leakage, then an organ such as the lungs suffer from decreased ability to
exchange oxygen.
Sometimes the response of the immune system is excessively strong, destroying also healthy surrounding
tissue, which also causes more severe symptoms. This is why the immune response depends on careful
regulation.
Clean up and repair of the damage
In the later stages of vascular response to infected tissue cells arrive that facilitate clean up and repair of
the damage. Repairs are important, because destroyed tissue is more susceptible to pathogens[5,6,7]
.
Routes of transmission
The spreading of microbes is called transmission.
Transmission involves the following stages
 Escape from the host or reservoir of infection (where the infectious agent normally lives and
multiplies).
 Transport to the new host.
 Entry to the new host.
 Escape from the new host.
Different pathogens have different modes of transmission. For example respiratory pathogens are usually
airborne and intestinal pathogens are usually spread by water or food.

5. The main routes of transmission[11,12,13]
are listed below:
Person-to-person
Touch
A cold can be caught by shaking the hand of a person who has a cold and who has just used their hand to
wipe their dripping nose. The mucus from the nose will be teeming with cold virus particles such as the
rhinovirus, which causes one third of colds in adults. Once the cold virus particles are on the hands of the
second person they are contaminated and the virus can be transferred into their nose by their fingers.
Contaminated blood or other bodily fluids
Hepatitis B and HIVcanbe spreadthrough sexual intercourse or sharing used syringe needles contaminated
with infected blood.
Saliva
A cold or the flu can be caught from the saliva of an infected person when you kiss them.
Air
Measles,mumps and tuberculosis can be spread by coughing or sneezing. A cough or a sneeze can release
millions of microbes into the air in droplets of mucus or saliva which can then infect somebody else if they
breathe in the infected particles.
Food
Microbes need nutrients for growth and they like to consume the same foods as humans. They can get into
our food at any point along the food chain from ‘plough to plate’. Therefore great care must be taken at
every stage of food production to ensure that harmful microbes are not allowed to survive and multiply. If
they do they can cause the unpleasant symptoms of food poisoning such as sickness and diarrhoea, when
the contaminated food is eaten.
Microbes can be spread from one food to another during the preparation process, for example by unclean
hands, or dirty kitchen utensils, and cause illness when those foods are eaten. This is known as cross-
contamination.
Water
Some diseases are caused by drinking water that is contaminated by human or animal faeces,which may
contain disease-causing microbes. Clean water,hygiene and good sewerage systems prevent the spread of
water-borne diseases such as typhoid and cholera.
Insects
Insects are responsible for spreading many diseases. Malaria is spread from person to person by certain
species of female mosquito carrying the protozoan Plasmodiumfalciparum. The parasite enters the human

6. host when an infected mosquito takes a blood meal. Bubonic plague (Black Death) is a bacterial disease of
rodents causedby Yersinia pestis.It can be spread to humans and other animals by infected rat fleas.People
usually get plague from being bitten by a rodent flea that is carrying the plague bacterium.
Insects can also transmit pathogens to food; house flies are very good at
spreading Salmonella and E.coli O157.Theyfeed on faecalwaste and transfer microbes from their feetand
other body parts to food. The microbe does not invade or multiply inside the fly.
Fomites
This is a non-living object such as bedding, towels, toys and barbed wire that can carry disease-causing
organisms. The fungus Trichophyton that causesathlete’s foot can be spread indirectly through towels and
changing room floors.
The fungus thrives in the damp warm environment found between the toes. The skin between the fourth
and fifth toe is usually affected first. A flaky itchy red rash develops. The skin becomes cracked and sore
and small blisters may appear. If the infection is left untreated it can spread to other parts of the body.
Diagnosis, Treatment and Prevention
 Many infectious diseases have similar signs and symptoms. Samples of patient’s body fluids can
sometimes reveal evidence of the particular microbe that’s causing their illness. This helps them
doctor tailor their treatment.
 Blood tests, Urine tests, Throat swabs, Stool sample and Spinal tap (lumbar puncture).
 Antibiotics: Antibiotics are grouped into “families” of similar types. Antibiotics are usually
reserved for bacterialinfections, because these types of drugs have no effect on illnesses caused by
viruses. But sometimes it’s difficult to tell which type of germ is at work. For example, some types
of pneumonia are caused by viruses while others are caused by bacteria.
 Antivirals: Drugs have been developed to treat some, but not all, viruses.
 Anti-parasitics: Some diseases, including malaria, are caused by tiny parasites. While there are
drugs to treat these diseases, some varieties of parasites have developed resistance to the drugs.
 Infection prevention and control demands a basic understanding of the epidemiology of diseases;
risk factors that increase patient susceptibility to infection; and the practices, procedures and
treatments that may result in infections.[7,8]
Infectious Diseases
Giardiasis
Giardiasis is a diarrheal disease caused by the microscopic parasite Giardia. A parasite is an organism that
feeds off of another to survive. Once a person or animal (for example, cats,dogs, cattle, deer, and beavers)
has been infected with Giardia, the parasite lives in the intestines and is passed in feces (poop). Once
outside the body, Giardia can sometimes survive for weeks or months. Giardia can be found within every
region of the U.S. and around the world.[10]

7. Sign and Symptoms
Giardia infection can cause a variety of intestinal symptoms, which include:
 Diarrhea
 Gas or flatulence
 Greasy stool that can float
 Stomach or abdominal cramps
 Upset stomach or nausea
 Dehydration
These symptoms may also lead to weight loss. Some people with Giardia infection have no symptoms at
all. Symptoms of giardiasis normally begin 1 to 3 weeks after becoming infected.
Etiology
Giardia parasites live in the intestines of people and animals. Before the microscopic parasites are passed
in stool, they become encased within hard shells called cysts, which allows them to survive outside the
intestines for months. Once inside a host, the cysts dissolve and the parasites are released.
Infection occurs when you accidentally ingest the parasite cysts. This can occur by swallowing
contaminated water, by eating contaminated food or through person-to-person contact.[12,13]
Pathogenesis of Giardia lamblia:
 Giardia is intestinal parasite and it is non-invasive.
 Once excystation occurs, trophozoites are releases and they uses their flagella to ‘swim’ to the
microvilli coveredsurface of duodenum and jejunum where they attachto the enterocytesusing their
adhesive disc.
 Lectins present on the surface of Giardia binds to receptor present on surface of enterocytes. This
attachment process damage microvilli, which interfere with nutrition absorption by villi.
 Rapid multiplication of trophozoites eventually creates a physical barriers between the enterocytes
and intestinal lumen, further interfering with nutrition absorption. This process leads to enterocytes
damage, villi atropy, crypt hyperplasia, intestinal hyperpermeability and brush boarder damage that
causes a reduction in disaccharide enzyme secretion.
 Lectins and othere cytopathic substance secretedby parasite also causesindirect damage to intestinal
epithelium.
 Trophozoites do not invade or penetrate surrounding tissue or enter blood stream. So, infection is
generally restricted to intestinal lumen.
 Giardiasis results in decreased jejunal electrolyte water and glucose absorptiom, and damages to
intestinal epithelium leads to malabsorption of electrolyte and fluids, resulting in osmotic diarrhea
known as giardiasis.[14,15]

8. Most risk of getting giardiasis:
Though giardiasis is commonly thought of as a camping or backpacking-related disease and is sometimes
called “Beaver Fever,” anyone can get giardiasis. People more likely to become infected include:
 Children in childcare settings, especially diaper-aged children
 Close contacts of people with giardiasis (for example, people living in the same household) or
people who care for those sick with giardiasis
 People who drink water or use ice made from places where Giardiamay live (for example,
untreated or improperly treated water from lakes, streams, or wells)
 Backpackers,hikers, and campers who drink unsafe water or who do not practice good hygiene
(for example, proper handwashing)
 People who swallow water while swimming and playing in recreational water where Giardiamay
live, especially in lakes, rivers, springs, ponds, and streams
 International travelers
 People exposed to human feces (poop) through sexual contact
Treatment for giardiasis:
 Metronidazole, trinidazole, nitroimidazole derivatives
 Nitrofurans- furazolidine
 Metronidazole is drug of choice. Dose- orally 250mg, 3 times daily for adults, 15mg/kg /day in three
divided dose for children for 7 days
Prevention of giardiasis:
 Improve water supply
 Proper disposal of human faeces
 Maintenance of good and proper personal hygiene
 Health education at individual as well as community levels
 Identifying the source of infection, particularly in outbreak situation.[14,15]
Trichomoniasis
Trichomoniasis is a common sexually transmitted infection caused by a parasite. In women, trichomoniasis
can cause a foul-smelling vaginal discharge, genital itching and painful urination.
Men who have trichomoniasis typically have no symptoms. Pregnant women who have trichomoniasis
might be at higher risk of delivering their babies prematurely.
To prevent reinfection with the organism that causes trichomoniasis, both partners should be treated. The
most common treatment for trichomoniasis involves taking one megadose of metronidazole (Flagyl) or
tinidazole (Tindamax). You can reduce your risk of infection by using condoms correctly every time you
have sex.[7]

9. Sign and Symptoms
Many women and most men with trichomoniasis have no symptoms, at least not at first. Trichomoniasis
signs and symptoms for women include:
 An often foul-smelling vaginal discharge — which might be white, gray, yellow or green
 Genital redness, burning and itching
 Pain with urination or sexual intercourse
Trichomoniasis rarely causes symptoms[8,9]
in men. When men do have signs and symptoms, however,they
might include:
 Irritation inside the penis
 Burning with urination or after ejaculation
 Discharge from the penis
Etiology
Trichomoniasis is caused by a one-celled protozoan, a type of tiny parasite that travels between people
during sexual intercourse. The incubation period between exposure and infection is unknown, but it's
thought to range from five to 28 days.[12]
Pathophysiology
T vaginalis is approximately the size of a white blood cell (WBC)—about 10-20 μm long and 2-14 μm
wide—though its size may vary with physical conditions (see the image below). It has 4 flagella projecting
from the anterior portion of the cell and 1 flagellum extending backward to the middle of the organism,
forming an undulating membrane. An axostyle, a rigid structure, extends from the posterior aspect of the
organism. [10, 11]
Diagnosis
The diagnosis of trichomoniasis can be confirmed by looking at a sample of vaginal fluid for women or
urine for men under a microscope. Growing a culture used to be the way to diagnose trichomoniasis, but
newer, faster tests, such as rapid antigen tests and nucleic acid amplification, are more common now.[13]
Treatment
The most common treatment for trichomoniasis, even for pregnant women, is to swallow one megadose of
either metronidazole (Flagyl) or tinidazole (Tindamax). In some cases, your doctor might recommend a
lower dose of metronidazole two times a day for seven days.
Both you and your partner need treatment. And you need to avoid sexual intercourse until the infection is
cured, which takes about a week.

10. Don't drink alcohol for 24 hours after taking metronidazole or 72 hours after taking tinidazole, because it
can cause severe nausea and vomiting. Your doctor will likely want to retest you for trichomoniasis from
two weeks to three months after treatment to be sure you haven't been reinfected. Untreated, trichomoniasis
can last for months to years.[13,14,15]
Conclusion
The substantial burden posed by chronic diseasesof likely infectious etiology demands global attention and
action. Evidence continues to mount implicating microorganisms as important etiologic agents of chronic
diseases that contribute substantially to morbidity and mortality. However, the identification and
confirmation of infectious causes of chronic diseases is complicated by several problems, including
frequent multifactor causation for many of these diseases and differences in the environmental background
and genetic composition of different populations. Recently developed molecular and immunological
techniques offer new approaches to addressing the technical barriers. However, improved coordination
among basic and clinical scientists, pathologists, and epidemiologists also will be critical to progress.
Standardization of case definitions and analytical assays combined with sound epidemiologic design will
help, aswill the development of broad, new strategiesfor creating carefully pedigreed specimen collections
and disease registries. Although the task is daunting, taking the practical and pragmatic pathways described
above could clarify many of the uncertain relationships between infectious agents and chronic diseases.
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