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Environmental Transmission of
Pathogens
What is a Pathogen?
Pathogen: A disease causing organism
Host: the organism which is attacked and becomes diseased
Disease: the disease is a complex process and is the result of host-pathogen interaction
- In simpler terms, disease is an abnormal condition
Infection: The process in which a microbe multiplies or grows in or on the host and causes
disease
Incubation Time: the time between infection and appearance of the symptoms
Pathogenicity: refers to the ability of a parasite to gain entry into the host tissue and brings
about a change (anatomical or physical) resulting in a change of health and thus disease
- It is used in a qualitative sense
Parasitism: refers to a relationship between two living organisms in which one partner is
benefitted and the other is in loss
Opportunistic Pathogens: these microbes exist as commensals in the body until normal defense
mechanism is suppressed, when they invade the tissue and act as pathogens
- E
...
Streptococcus pneumoniae
Virulence: it is used in a quantitative sense giving a measure of the extent of pathogenicity of a
parasite
Moderately Virulent: when a pathogen causes disease moderately, not severe
Highly Virulent: when a pathogen causes disease and severe conditions; symptoms are
dominant
Any microbe has the ability to change genetically and become virulent
- For example, E
...
Invasiveness
2
...
Herpes virus, smallpox
Indirect transmission: through different factors of the environment
- Air droplets
- Water
- Soil
- Contaminated food
- Formities
Pathogens come out of infected hosts through respirations, feces, urine, saliva, and tears

Enteric Pathogens
Microorganisms that are transmitted by fecal-oral route are usually referred to as “Enteric
Pathogens”
Water-Related Diseases of Man
Class

Transmission

Examples

Water-borne

Transmitted by ingestion

Cholera, Typhoid fever

Water-washed

Transmitted by contact

Diarrhea

Water-based

By inhalation

Legionella

Water-related

Through insects

Yellow fever, Dengue, Malaria

Microbial Diseases of Human Beings

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Bacterial diseases
Viral diseases
Fungal diseases
Diseases due to protozoa
Diseases due to helminths (Nematodes)

Bacterial Diseases
Air-borne Diseases:
- Diphtheria
- Tuberculosis
- Whooping cough (Pertussis)
Food-borne & Water-borne diseases
- Botulism
- Food poisoning
- Typhoid fever
Soil-borne diseases
- Tetanus
Tuberculosis
- Bacterial infection
- Caused by Mycobacterium tuberculosis
- Damages a person’s lungs or other parts of the body
- Fatal if not treated properly
Transmission (Air-borne)
Spreads through air when a person with active tuberculosis (TB)
- Coughs
- Speaks
- Laughs
- Sneezes
- Sings
Another person breathes in the bacteria and becomes infected
TB in other parts of the body, such as the kidney or spine, is usually not infectious
Inside the Body
- Breathed in infected air and bacilli go to lungs through bronchioles
- Bacilli infect alveoli
- Macrophages attack bacteria, but some survive

-

Infected macrophages separate and form tubercles

Active vs
...
It may survive for a longer period in fresh water and
foods
Infection occurs by injection of bacteria
Incubation period is 10-14 days
Pathogenesis
- Colonizes small intestine
- Penetrate epithelium
- Spread to lymphoid tissue, blood, liver, gallbladder
Symptoms
- Fever
- Headache
- Abdominal pain
- Last several weeks
- Carrier for up to three months (except chronic carriers: gallbladder)

Treatment
- Antibiotics: Chloramphenicol, Amoxicillin
Resistant strains of bacteria are found
Recovery: permanent immunity
Precautionary measures
- Purification of drinking water
- Pasteurization of milk
- Prevention of food handling by carriers
- Complete isolation of patients
Botulism
-

It is the most dangerous food-borne disease
The exotoxin of the bacteria is very powerful
One ounce of the purified material may eliminate the entire population of many countries
The disease is caused by: Clostridium botulinum, gram positive rod, as spores in
intestine of many fish, birds, cows, horses, and human intestine

The bacteria are less important as they do not grow further, it is the exotoxin which causes harm

Exotoxin is a high molecular weight protein, which is activated by the enzyme trypsin in the
intestine and is absorbed in the bloodstream
- Within hours the patient feels paralytic symptoms
Symptoms
- Blurred vision
- Impaired speech
- Difficulty in chewing
- Muscle weakness
- Diarrhea
- Vomiting
Clostridium botulinum
- Gram positive rods
- Spore forming
- Anaerobic bacteria
- Produces toxin that causes botulism
- Seven neurotoxic subtypes
Food-borne Botulism
- Second most common form
- Caused by eating food contaminated with toxin produced by Clostridium botulinum
- Non-commercially canned food is at higher risk for being contaminated
- Dangerous because most contaminated foods cannot be detected until too late
Treatments
- Sometimes antibiotics are not effective
- Large doses of botulinum antitoxin are given
- There are three types of botulism:
- Infant botulism
- Wound botulism
- Limberneck in animals (Fodder disease)

Diphtheria
Bacterium is gram positive
Produces exotoxin
Symptoms and Causes
- Tonsillitis is inflammation of the tonsils most commonly caused by a viral or bacterial
infection

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Symptoms of tonsillitis include sore throat and fever
The infection may also be present in the throat and surrounding areas, causing
inflammation of the pharynx
This is the area in the back of the throat that lies between the voice box and the tonsils

Characteristic of Bacteria (Corynebacterium diphtheria)
- Gram positive, nonmotile
- Don’t forms spores and capsules
- Production of very strong exotoxin
- Firm to low temperature, highly responsive to heating and disinfection solutions
Epidemiology
- Source →Sick person or carrier
- Ways of transmission → airborne, contact-household (occasionally)
- Sensibility is high, adults more often become sick (80%)
- Outbreaks are possible
- Immunodefence antitoxic
- Seasonal character →autumn-winter

Cholera
Symptoms: an intestinal disease
- Dysentery
- Vomiting
- Violent cramps
- Loss of fluids
Organism: Vibrio cholerae, gram negative rods the bacteria produce toxins
Treatment:
- Restore water balance in the body
- Intravenous injection of Tetracycline
Prevention:
- Sanitation, personal hygiene, and care in food preparation

Tetanus
-

Caused by bacterium: Clostridium tetani, gram positive rods
This bacterium exists in air, water, animal, human intestine, and soil

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The bacteria enters through wounds and produce powerful toxin
In severe cases, death may occur
The bacteria exists in intestine of many animals and enters the soil through feces

Symptoms:
- The symptoms develop very rapidly within hour of entry
- The spores produce a toxin called “Tetanospasmin”
- The toxin spreads through the bloodstream
- Causes muscle contractions and muscle stiffness
Treatment:
- Vaccination and antitoxin injection

Viral Diseases of Human Beings
Viral diseases of human beings can be classified into 4 groups on the basis of the organs on or
in which typical symptoms are produced
1
...
Influenza and common cold
2
...
Measles and chickenpox
3
...
Yellow fever, hepatitis
4
...
Rabies, polio

Influenza Virus
Cause: RNA Virus
- The influenza virus, commonly known as the flu
- It is an infectious disease of birds and mammals caused by RNA viruses
- Commonly confused with a cold, the flu is a much more severe disease and is caused by
a different virus
Symptoms
- Chills

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Body aches, especially throat and joints
Coughing and sneezing
Extreme fever
Fatigue, headache, and nasal congestion

Though similar symptoms occur with a cold, they are much more severe with the flu
Prevention & Treatment
-

Annual flu vaccine
Personal hygiene
Covering the mouth while sneezing to prevent the spread of the virus (spreads through
aerosols)

Since the flu is a virus, antibiotics won’t work unless there is a secondary bacterial infection

Herpes Viruses
These remain silent for many years only to be reactivated
Human Herpes Viruses
- Herpes simplex virus (HSV) type 1
- HSV type 2
- HSV-6 (causative agent of roseola)
- HHV-7
- HHV-8
Once a patient has become infected by herpes virus, the infection remains for life
The initial infection may be followed by latency with subsequent reactivation
Herpes viruses infect most of the human population and persons living past middle ages usually
have antibodies to most of the above herpes viruses with exception of HHV-8
Herpes Simplex
- It is a collection of diseases
- It may occur as cold sores in the mouth, skin, encephalitis in newborns, or urogenital
infections in adults
- There are two major types Herpes Simplex Virus:
- Type-1 called HSV-1 usually infecting areas above the waist
- Type-2 called HDV-2: Often below the waist
- Both are dsDNA enveloped viruses with spikes

The viruses multiply rapidly in the nucleus of infected cells forming inclusion bodies used for
diagnosis
The virus remains for a longer time in the body
In each case, the initial lesion looks the same
- A clear vesicle containing infectious virus with a base of red (erythematous) lesion at the
base of the vesicle
- This is often referred to as a ‘dewdrop on a rose petal’
- From this pus-containing (pustular), crusted lesions and ulcers may develop

Herpes Viruses 1 & 2
Affect primarily the oral and genital areas
Disease is typically a manifestation of reactivation
- Triggers for clinical reactivation are not well understood
Herpes simplex Type-1 (HSV-1)
- Largely involves mouth/oral cavity
- Can cause urogenital infections
Herpes simplex Type-2 (HSV-2)
- Most common cause of genital ulcers in developing world
HSV-1
Primary infection may be asymptomatic
Vesicles form moist ulcers after several days
- If untreated, epithelialize over 1-2 weeks
Recurrences
- Tend to be labial
- Heal faster
- Induced by stress, fever, infection, sunlight
HSV-2
Genital herpes is usually the result of HSV-2 with about 10% of cases being the result of HSV-1

Primary infection is often asymptomatic, but many painful lesions can develop on the glans or
shaft of the penis in men and on the vulva, vagina, cervix, and perianal region of women
HSV - Treatment/Prevention
Urogenital, encephalitic or disseminated disease
- Acyclovir (Zovirax) & related compounds for genital simplex
Recurrent mucocutaneous disease is most effectively treated with Acyclovir
Recurrent genital disease also requires barrier precautions during sexual activity

Chickenpox
This is among the most communicable of diseases caused by varicella-zoster virus (VZV)
The virus belongs to herpes virus group
It is a dsDNA virus
In adults, the same virus causes Herpes Zoster (shingles)
The virus is transmitted chiefly by droplets and skin contact
Symptoms
- Fever in the beginning
- Headache
- Vesicles are formed in case of cutaneous infection
- The vesicles are filled with fluid which is highly infectious
- The lesions are larger than smallpox
- The disease becomes serious if lungs and brain are involved
- Shingles in adults is painful
Varicella Complication
- Interstitial pneumonia
- More common in adults than children
- Hepatitis
- Reye’s syndrome
- Usually in childhood/associated with aspirin use
- Congenital malformation
- Congenital varicella syndrome which leads to scarring of the skin of the limbs,
damage to the lens, retina and brain and microphthalmia

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Secondary bacterial infection
- Group A beta-hemolytic streptococci common

Smallpox (Variola)
-

The virus has brick-shaped DNA particles and largest in size … 270 nm, non-enveloped
virus
Transmission is by contact with skin or any of the body fluid including blood, urine or
droplets
The causative agent, variola virus, is a member of the genus Orthopoxvirus
- Other members of the genus include cowpox, camelpox, and monkeypox

The oropharynx served as the reservoir for virus spread
Contracts become infected by inhaling virus
Multiplication occurred within lymphoid organs leading to secondary development of viremia
Virus localized with small dermal blood vessels produced endothelial swelling and
intraepidermal vesicles
- Extension of infection into sebaceous glands produced pock marks
Infectivity
- Persons carrying the virus during the incubation period cannot infect others
- The frequency of infection is highest after face-to-face contact with a patient after fever
has begun and during the first week of rash, when the virus is released via the
respiratory tract
- Although patients remain infectious until the last scabs fall off, the large amounts of virus
shed from the skin are not highly infectious
- Exposure to patients in the late stages of the disease is much less likely to produce
infection in susceptible contacts
Transmission
- Non-immunized humans universally susceptible to infection with smallpox virus
- No animal reservoir
- Insects play no role in transmission
- Transmission occurs from person to person by infected aerosols and air droplets,
specially if symptoms include coughing
- Variola virus is relatively stable in the natural environment
Can be transmitted via contaminated clothes and bedding, risk of infection is much lower
Patients with variola bed ridden - spread limited to close contacts in a small vicinity

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Variola minor was so mild that these patients remained ambulatory and spread the virus
far more widely

Epidemics developed comparatively slowly
- The interval between each generation of cases was 2-3 weeks
Treatment
- Vaccine administered up to 4 days after exposure to the virus, and before and can
prevent infection or ameliorate the severity of th disease
- No effective treatment, other than the management of symptoms, is currently unavailable

Major Vaccine-Preventable Viral Infection
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Measles
Mumps

Measles (Rubeola)
-

It is highly communicable respiratory disease of children, whose symptoms develop on
skin
Caused by a ssRNA virus closely related with mumps
It contains envelope spikes
Measles may lead to many complications
Infection is via an aerosol route and the virus is very contagious
It is caused by virus

Symptoms
- Fever of 101 degrees Fahrenheit or above
- Respiratory tract symptoms: running nose (coryza) and cough
- Koplik’s spots on mucosal membranes - small (1-3 mm), irregular, bright red spots, with
bluish-white speck at center
- The patient may get an enormous number and red areas may become confluent
- Rash which extends from face to the extremities
Prevention
- Vaccination
Treatment
- Isolation one week following onset of rash
- Symptomatic
- Vitamin A 200,000 units/d orally reduce pediatric morbidity rates (maintenance of GI and
respiratory mucosa, immune enhancement)

Mumps
- It is a disease of children’s salivary glands… technical name is “Parotitis”
- The disease is transmitted by droplets, contact and fomites
- The virus is present in urine, blood and cerebrospinal fluid
- The disease may begin on one side of the mouth but both glands are affected in most
cases
This virus occurs mostly in humans and is found both in males and females
In adults, mumps represents a threat to reproductive organs
It is ssRNA virus
Mumps is very contagious and is probably usually acquired from respiratory secretions and
saliva via aerosols or fomites
The virus is secreted in urine and so urine is a possible source of infection
Pathogenesis of Mumps
- Virus infects upper/lower respiratory tract leading to local replication
- The virus spreads to lymphoid tissue which, in turn, leads to viremia
- The virus thus spreads to a variety of sites, including salivary glands, other glands and
other body sites
Symptoms of Mumps
- Parotitis: Infection of salivary glands
- Orchitis in males: swelling of testicles to 3-4 times of normal size
- Sperm count is reduced
- Oophoritis in females: lower back pain, and enlargement of ovary
- Fever
- Deafness (rare)
Prevention
- Vaccination
- Isolation

Poliovirus
-

It is one of the smallest viruses
Its diameter is 27-30 nm
It multiplies rapidly in nerve cells
The virus enters the body through contaminated food and water

Paralytic Polio
- About 4 days after the end of the first minor symptoms, the virus has spread from the
blood to the anterior horn cells of the spinal cord and to the motor cortex of the brain
- The degree of paralysis depends on which neurons are affected and the amount of
damage that they sustain
- The disease is more pronounced in very young and very old patients
- In bulbar paralysis cranial nerves and the respiratory center in the medulla are affected
leading to paralysis of the neck and respiratory muscles
- There is no sensory loss associated with the paralysis
- In spinal paralysis one or more limbs may be affected or complete flaccid paralysis may
occur
Treatment
- Proper vaccination
Adenovirus
- Almost half of adenoviral infections are subclinical
- Most infections are self-limited and induce type-specific immunity
- Incubation period is 2-14 days; for gastroenteritis usually 3-10 days
Adenovirus symptoms
- Eye
- Epidemic keratoconjunctivitis (EKC), acute follicular conjunctivitis,
pharyngoconjunctival fever
- Respiratory system
- Rhinitis
- Pharyngitis (with or without fever)
- Tonsillitis
- Bronchitis
- Pharyngoconjunctival fever
- Acute respiratory disease (LRI)
- Pertussis-like syndrome
- Genitourinary
- Acute hemorrhagic cystitis, orchitis, nephritis, oculogenital syndrome
- Gastrointestinal
- Gastroenteritis
- Mesenteric adenitis
- Intussusception
- Hepatitis
- Appendicitis
Epidemiology
- Endemic, epidemic and sporadic infections occur

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-

Outbreaks have been noted in military recruits, swimming pool users, residential
institutions, hospitals, daycare centers, etc

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