HumanContactDiseases

What are contact diseases

“These are diseases caused by microorganisms that are spread by person-to-person contact or indirect contact

with contaminated objects.”

Kinds of contacts:• Droplet contact – coughing or sneezing on another

person• Direct physical contact – touching an infected person,

including sexual contact• Indirect physical contact – usually by touching soil

contamination or a contaminated surface• Fecal-oral transmission – usually from contaminated

food or water sources

Types of diseases according to the kind of invaders:• Diseases caused by viruses and prions• Diseases caused by Bacteria• Diseases caused by fungi and protists

Diseases Caused by Viruses and Prions

Cold Sores

Cause & Transmission:• Caused by Herpes Simplex Virus, which is a double stranded DNA Virus. Often spread with direct contact.

Infection:• Blister develop at the inoculation site and resulting in the tissue destruction, mostly on gums, lips and mouth(gingivostomatitis).• It heals within week but virus often doesn’t exit and stays in trigeminal nerve for may be life time.• If infection reappears due to stressful stimuli (sunlight, fever, trauma, chilling, emotional stress, and hormonal changes) then virus transfers to the peripheral nerves and may also affects the cornea (herpetic keratitis) along with lips and mouth.

Diagnosis:•By ELISA and direct fluorescent antibody screening of tissue.• It may also be made through the recovery of viral nucleic acid by PCR.

Common ColdCause:• About 50% of the cases are caused by rhinovirus (rhinos: nose), which

are non-enveloped single stranded viruses.• There are over 115 distinct serotypes, and each of these antigenic types

has a varying capacity to infect the nasal mucosa and cause a cold.

Transmission:• Include infected individuals excreting viruses in nasal secretions,

airborne transmission over short distances by way of moisture droplets, and transmission on contaminated hands or fomites (towels etc.).• Hand-to-hand contact between a rhinovirus “donor” and a susceptible

“recipient” is more vulnerable.

Infection:• Viral invasion of the upper respiratory tract is the basic mechanism in

the pathogenesis of a cold.• The virus enters the body’s cells by binding to the adhesion molecule

ICAM-1.• ICAM-1 (Intercellular Adhesion Molecule 1) is a protein that in humans

is encoded by the ICAM1 gene. This gene encodes a cell surface glycoprotein which is spoiled by rhinovirus.

Clinical manifestations:• Nasal stiffness• Sneezing• Scratchy Throat• Watery discharge which becomes yellow after several days• Though fever is absent, but a low grade (100-102°F) may occur in

infants or kids.• Diagnosis is often occur by observing the symptoms.

Cytomegalovirus Inclusion Disease

Cause:• Caused by human cytomegalo virus, a member of family Herpes

viridae.

Transmission:• Mostly caused by personal contact with an actively infected individual.• Blood transfusion.• Organ transplantation.“it is shed for several years in saliva, urine, semen, and cervical

secretions”

Infection:• It infect the cell and divide hence swelling produces in the size of cell

(cytomegalo).• Interferes with many host immune mechanisms like MHC, cytokine

production and NK cell activity.• Infected cells contain the unique intranuclear inclusion bodies and

cytoplasmic inclusions.• Fatal cases cause damage of different organs.

Genital HerpesCause:• Caused by the herpes simplex virus type 2 (HSV-2). The HSV-2 virus is

classified in the alpha herpes subfamily of the family Herpes viridae.

Transmission:• Mostly caused by sexual contact (Sexually transmitted disease).

Infection:• Begins when the virus is introduced into a break in the skin or mucous

membranes.• The virus infects the epithelial cells of the external genitalia, the

urethra, and the cervix.• Rectal and pharyngeal herpes are also transmitted by sexual contact.• Infection is splitted in two phases:

Active Phase: • Virus multiplies explosively—between 50,000 and 200,000 new

virions are produced from each infected cell.• HSV-2 inhibits its host cell’s metabolism and degrades its DNA.

• Cell dies as a result blisters appear on the skin containing infectious liquid.• Fever, headache, burning sensation and genital soreness are symptoms of this phase.• blisters may heal after sometime but virus retreat to sacral plexus of spinal and remain in latent form.

• Latent Phase:• Viral genome incorporates into host genome.• Periodically the viruses multiply and migrate down nerve fibers to the skin or mucous membranes that the nerve supplies, where they produce new blisters.•Activation may be due to sunlight, sexual activity, illness accompanied by fever, hormones, or stress.

Cure:• No special cure, but some antiviral diseases like ancyclovir or fanciclovir are seen effective against blisters.• Idoxuridine and trifluridine are used to treat herpes infections of the eye.

LeukemiaCause:• Caused by two retroviruses:

Human T-cell lymphotropic virus I (HTLV-I)HTLV-II

• Both are members of viral family Retro viridae. They have a nuclear core containing two positive-strand RNA genomes.

Transmission:• Sharing needles among drug addicts.• Sexual contact• Across placenta• Breast feeding• Mosquitoes

Infection:• Once a cell is infected, RNA genome is converted by reverse

transcriptase to DNA and integrates into the host’s chromosome.

Hairy cell leukemia:• This leukemia is a chronic, progressive lympho proliferative disease.

Caused by HTLV-II.

• Originate in a stage of B-cell development.• The bone marrow, spleen, and liver become infiltrated with

malignant cells, lowering the person’s immunity.

Diseases caused by Bacteria

Inclusion ConjunctivitisCause:• Caused by Chlamydia trachomatis serotypes D–K.

Transmission:• Chlamydia is acquired during passage through an infected birth canal.• Adult inclusion conjunctivitis is acquired by contact with infective genital

tract discharges.

Infection:• Characterize by:

Mucous discharge from the eye An inflamed and swollen conjunctiva Presence of large inclusion bodies in the host cell cytoplasm

• The disease appears 7 to 12 days after birth. • If the Chlamydia colonize an infant’s nasopharynx and trachea bronchial

tree, pneumonia may result.

Cure:• Recovery usually occurs spontaneously over several weeks or months• Erythromycin eye drops prevent ophthalmia neonatorum also prevents

Chlamydia inclusion conjunctivitis.

• Therapy involves Tetracycline Erythromycin Sulfonamide

Diagnosis:• The specific diagnosis of C. trachomatis can be made by

Direct immunofluorescence Giemsa stain Nucleic acid probes Culture

Bacterial VaginosisCure:• It has a polymicrobial etiology

Gardnerella vaginalis Mobiluncus spp. Various anaerobic bacteria

Transmission:• Sexually transmitted disease.• Presence in vagina and rectum indicates that it is also an

autoinfection.

Infection:• Mild disease, but a risk factor for

Obstetric infections Various adverse outcomes of pregnancy Pelvic inflammatory disease.

• Characterized by a copious, frothy, fishy-smelling discharge with varying degrees of pain or itching.

Cure:• Treatment for bacterial vaginosis is with metronidazole, a drug

that kills anaerobic streptococci and the Mobiluncus spp.

Diagnosis:• Diagnosis is based on

Fishy odor from vaginal secretion Microscopic observation of clue cells in the discharge. Clue

cells are sloughed-off vaginal epithelial cells covered with bacteria, mostly G. vaginalis.

ChanchroidCause:• Caused by the pleomorphic gram-negative bacillus Haemophilus

ducreyi.

Transmission:• Sexually transmitted disease.

Infection:• Enters in skin through broken epithelium.• After incubation of 4-7 days, papular lesion develops within the

epithelium, causing swelling and white blood cell infiltration.• A pustule forms and rupture causing producing a painful,

circumscribed ulcer with a ragged edge.

Cure:• Chemotherapeutically by azithromycin or ceftriaxone.

Diagnosis:• Isolating H. ducreyi from the ulcers

TetanusCause:• Caused by Clostridium tetani, an anaerobic, gram-positive,

endospore-forming rod.

Transmission:• Associated with skin wounds. Any break in the skin can allow C.

tetani spores to enter. (if environment is exposed to its spores)

Infection:• If oxygen tension is low, spores germinate and release the

neurotoxin tetanospasmin.• Tetanospasmin is an endopeptidase that selectively cleaves the

synaptic vesicle membrane protein synaptobrevin.• This prevents its release from the cell and also of inhibitory

neurotransmitters (gamma-aminobutyric acid and glycine) at synapses within the spinal cord motor nerves. • The result is uncontrolled stimulation of skeletal muscles (spastic

paralysis). A second toxin, tetanolysin, is a hemolysin that aids in tissue destruction.

Course of disease:• Causes tension or cramping and twisting in skeletal muscles

surrounding the wound• Tightness of the jaw muscles. With more advanced disease, there is

trismus (“lockjaw”), an inability to open the mouth because of the spasm of the masseter muscles.• Facial muscles may go into spasms, producing the characteristic

expression known as risus sardonicus.• Spasms or contractions of the trunk and extremity muscles may be

so severe that there is board like rigidity, painful tonic convulsions, and opisthotonos.• Death usually results from spasms of the diaphragm and

intercostal respiratory muscles.

Prevention:• Active immunization with toxoid.• Proper care of wounds contaminated with soil.• Prophylactic use of antitoxin.• Administration of penicillin.

TrachomaCasue:• Chlamydia trachomatis serotypes A–C.• It is one of the oldest known infectious diseases of humans and is the

greatest single cause of blindness throughout the world.

Transmission:• By contact with inanimate infected objects such as soap and towels• By hand-to-hand contact that carries bacteria• From an infected eye to an uninfected eye• By flies

Infection:• Begins abruptly with an inflamed conjunctiva, leading to an

inflammatory cell exudate and necrotic eyelash follicles.• Spontaneously heals• With reinfection, secondary infections, vascularization of the cornea,

or pannus formation, scarring of the conjunctiva can occur. • If scar tissue accumulates over the cornea, blindness results.

Diagnosis & treatment are as same as inclusion conjuctivitis.

Diseases caused byFungi & Protists

Superficial MycosesCause:• Black piedra is caused by Piedraia hortae• White piedra is caused by the yeast Trichosporon beigelii• Tinea versicolor is caused by the yeast Malassezia furfur

Piedras:Spanish for stone because they are associated with the hard nodules formed by mycelia on the hair shaft.Called superficial because they are limited to the skin surface.

Infection:• Black piedra forms hard, black nodules on the hairs of the scalp• White piedra forms light-colored nodules on the beard and mustache• Tinea versicolor forms brownish-red scales on the skin of the trunk, neck, face, and arms.

Treatment:• Removal of the skin scales with a cleansing agent• Removal of the infected hairs

Subcutaneous MycosesCause:• Caused by subcutaneous mycoses are normal saprophytic inhabitants of

soil and decaying vegetation.

Transmission:• Most infections involve barefooted agricultural workers when they are

wounded on infected surface.

Infection:• Because they are unable to penetrate the skin they are called

subcutaneous.• The disease develops slowly, often over a period of years.• During this time the fungi produce a nodule that eventually ulcerates and

the organisms spread along lymphatic channels, producing more subcutaneous nodules.

• Chromoblastomycosis: Caused by the black molds Phialophora verrucosa and Fonsecaea

pedrosoi. Most infections involve the legs and feet

•Maduromycosis: Caused by Madurella mycetomatis

Because the fungus destroys subcutaneous tissue and produces serious deformities, the resulting infection is often called a eumycotic mycetoma, or fungal tumor.

• Sporotrichosis: Caused by the dimorphic fungus Sporothrix schenckii. Infection occurs by a puncture wound from a thorn or splinter

contaminated with the fungus. The fungus can be found in the soil, on living plants, such as

barberry shrubs and roses, or in plant debris, such as sphagnum moss, baled hay, and pine-bark mulch.

After an incubation period of 1 to12 weeks, a small, red papule arises and begins to ulcerate

New lesions appear along lymph channels and can remain localized or spread throughout the body, producing extracutaneous sporotrichosis.

ToxoplasmosisCause:• Caused by the protist Toxoplasma gondii.• It has been found in nearly all animals and most birds• Cats are the definitive host and are required for completion of the sexual

cycle.

Transmission:• Animals shed oocysts in the feces; the oocysts enter another host by way

of the nose or mouth; and the parasites colonize the intestine.• Toxoplasmosis also can be transmitted by:

Ingestion of raw or undercooked meat Congenital transfer Blood transfusion Tissue transplant

Infection:• Most cases of toxoplasmosis are asymptomatic.• Adults usually complain of an “infectious mononucleosis-like” syndrome.• In immunoin competent or immune suppressed individuals, it frequently

results in fatal disseminated disease with a heavy cerebral involvement.

• Acute toxoplasmosis is usually accompanied by lymph node swelling (lymphadenopathy) with reticular cell hyperplasia (enlargement).• Pulmonary necrosis, myocarditis, and hepatitis caused by tissue

necrosis are common.• Toxoplasma in the immune compromised, such as AIDS or

transplant patients, can produce a unique encephalitis with necrotizing lesions accompanied by inflammatory infiltrates.

Treatment:• With a combination of pyrimethamine and sulfadiazine.

Prevention and control:• It require minimizing exposure by the following

Avoiding eating raw meat and eggs Washing hands after working in the soil Cleaning cat litter boxes daily Keeping household cats indoors if possible and feeding them

commercial food.

TrichomoniasisCause:• Caused by the protozoan flagellate Trichomonas vaginalis

Transmission:• Sexually transmitted disease

Infection:• In response to the parasite, the body accumulates leukocytes at the site of the

infection.• In females this usually results in a profuse, purulent vaginal discharge that is

yellowish to light cream in color and characterized by a disagreeable odor.• The discharge is accompanied by itching.• Males are generally asymptomatic because of the trichomonacidal action of

prostatic secretions.• Burning sensation occurs during urination.

Diagnosis:• In females by microscopic examination of the discharge and identification of

the protozoan.• Infected males demonstrate protozoa in semen or urine.Treatment:• By administration of metronidazole (Flagyl).

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