INFECTIOUS DISEASES: VIRAL, CHLAMYDIAL RICKETTSIAL,
BACTERIAL, FUNGAL, PROTOZOAL, HELMINTHIC
1) possible pathways of infection
 contagious infections- direct spread by contact or by airborne particles, by contaminated water, food
 transplacental infections -infections may be transmitted from mother to fetus via placenta- lead to prenatal and perinatal infections
 zoonotic infections - transmitted from animal to humans

2) factors influencing a development of infection
-mechanisms of barriers against infection
-virulence of agent and resistance of the host
-response to infection by inflammation
VIRAL INFECTIONS.
-upper respiratory tract infections -rhinitis, sinusitis, otitis media, pharyngitis,
tonsillitis
-lower respiratory tract infections -bronchiolitis, laryngotracheobronchitis, interstitial pneumonia, pleuritis
-viral infections of digestive tract- viral enteritis- acute onset, watery diarrhoea- viruses are major causes of acute diarrhoeal disease, mostly in children
 HERPES SIMPLEX (HSV-1) AND HERPES GENITALIS (HSV-2)
INFECTIONS
-herpesvirus lesions are characterized by marked cytopathic effect and by distinct intranuclear inclusions
-large acidophilic inclusions within slightly enlarged nucleus is composed of live and dead virions
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gingivostomatitis- painful vesicular eruptions in oral mucosa
-
genital herpesviral lesions- painful ulcerations in mucosa- possible cause of infection of baby in the course of delivery
-herpesvirus keratoconjunctivitis- recurrent infections, serious clinical consequence, because prone to bacterial superinfection, possible cause of blindness
herpes simplex encephalitis- rare, highly lethal disease, in patients with severe immunodeficiency
 CYTOMEGALIC INCLUSION DISEASE (CID)
-viral infection caused by cytomegalovirus
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-highly frequent in adults- in healthy persons the infection is always
latent, on the other hand in immunodeficiency may cause severe even lethal infections -AIDS, patients after bone marrow transplantation, etc
-in neonates - CID belongs to congenital infections usually benign presentation of the infection, in rare cases may cause neonatal
hepatitis, brain damage or haematological disorders microscopically:
-characteristic findings are markedly enlarged cells with prominent large nuclei- with distinctive visible inclusions, that are surrounded by clear halo
-mostly affected organs are
kidney (renal tubular epithelia), - lungs (interstitial pneumonia )
brain (lethal infection)
 INFECTIOUS MONONUCLEOSIS is a benign self-limited lymphoproliferative disease caused by Epstein-Barr virus it is characterized by
-fever
-generalized lymphadenopathy
-sorethroat appearance of atypical activated T-cells in the blood (mononucleosis cells)
-infectious mononucleosis occurs in late adolescence, its incidence is higher in developed countries, in higher social economic classes
EBV is transmitted by contact between persons, often by kissing morphologic findings:
1) lymph nodes
-are enlarged (lymphadenopathy)- lymphoproliferative reaction may partly efface the normal lymph node architecture
-striking proliferation of paracortical areas, less prominent follicular hyperplasia
-occasionally large bi-nucleated cells, resemble Sternberg-Reed cells which are diagnostic Hodgkin s disease- distinct form of malignant lymphoma
2) spleen- enlarged microscopically:
-prominent lymphoid follicles- hyperplasia of white pulp
-heavy accumulation of stimulated lymphocytes and plasma cells
3) liver may be severely affected, cause elevation of serum level of liver enzymes microscopically: portal infiltration by atypical mononuclear cells, invasion of sinusoids by the same cells, scattered necrosis of hepatocytes
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CHLAMYDIAL INFECTIONS.
1) Trachoma
-is a chronic suppurative eye disease with follicular keratoconjunctivitis - one of the leading global causes of blindness it is caused by Chlamydia trachomatis
2) Lymphogranuloma venereum is a venerally transmitted disease caused by some serotypes of Chlamydia
trachomatis
-it is a chronic inflammation- suppurative granulomatous lymphadenitis and perilymphadenitis – abscesses
3) Chlamydial ureteritis- sexually transmissible disease
RICKETTSIAL DISEASES.
-rickettsiae are transmitted by insects- lice transmits epidemic typhus,
ticks transmit Rocky Mountain spotted fever, and mites transmit scrub typhus
-by injuring the endothelial cells- rickettsiae cause a hemorrhagic vasculitis- visible skin rash
MYCOPLASMAL DISEASES.
- mycoplasmas - tinist free-living organisms
mycoplasma pneumoniae spread from person to person by air- cause atypical pneumonia-characterized by peribronchiolar infiltrates composed of plasma cells and lymphocytes of filamentous structures
FUNGAL DISEASES.
-fungi- have thick cell walls- frequently grow by extension and branching
-fungi that cause human infections can be divided to two groups- surfaces
-superficial- such as dermatophytes restricted to the epidermal these include Tinea species that may cause infection of fingernails, cause local ckin depigmentations, focal hair loss, etc.
-deep fungi- most important are so called opportunistic deep fungi- these cause infections only in immunosupressed persons, producing widespread necrosis with minimal inflammatory infiltrate and frequent hemorrhages
-patients with AIDS, and those receiving chemotherapy may suffer of recurrent oral infections caused by Candida, and by systemic infections caused by other fungi, such as Aspergillus, and Mucor
Pneumocystis carinii- fungus-like organism that causes a diffuse and severe pneumonia, in which alveolar spaces are filled by foamy, proteinaceous edema fluid containing 4-6 um- long organisms
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-AIDS patients
PROTOZOAN PARASITIC DISEASES.
-parasitic protozoa are monocellular eukaryotes- are among the foremost causes of infectious disease in developing countries
- in industrialized countries are widely distributed, but less often lethal
-Trichomonas- simple protozoan parasite is sexually transmitted- colonizes vaginal and urethra
-Giardia lamblia, (duodenum)- malabsorbtion, asymptomatic in some patients -
Entamoeba histolytica- large intestine- ulcerative colitis, in some patients the parasites enter blood- hepatic abscess
-both occur in motile form that attach to the intestinal epithelium, and in immobile cysts that are infectious when eaten
-Trypanosoma (gambiense, rhodiense)- they cause African sleeping sickness
(African trypanosomiasis)- they proliferate as extracellular forms in the blood, and cause fever, lymphadenopathy, splenomegaly and progressive brain dysfunction, cachexia and death
-Plasmodia (falciparum, vivax and malariae)- cause malaria
-parasitic disease that kills 1-1.5 million persons per year
-plasmodia are transmitted by Anopheles mosquitoes- plasmodia infect erythrocytes- thus cause anemia by destruction of infected RBCs.
-Toxoplasma Gondii- is an obligate intracellular protozoan parasite, that causes
-mild lymphadenopathy with fever in normal adults
-severe opportunistic infections in immunosupressed persons, such as those receiving chemotherapy, AIDS patients, patients receiving bone marrow and organ transplants
HELMINTHIC DISEASES-
-helminths are multicellular worms that have strict specificities for the
definitive host- in which sexual reproduction takes place, and intermediate host- in which the reproduction is asexual there are three major classes of helminths:
 the roundworms (Nematodes), including ascaris, hookworms, -cause severe anemia, and Trichinella species- that infect skeletal muscles
 the flat worms (Cestodes), including fish, pork and beef tapeworms, and echinococus
 flukes (Trematodes), that include important schistosomes oxyuriasis, filariasis
ECTOPARASITES. are insects (lice, bedbugs, fleas) or arachnids (mites, ticks) that attach and live on or in the skin
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insects- may cause excoriations, itching, etc. or insects may be vectors for the other pathogens, such as spirochete Borrelia burgdorferi- transmitted by deer ticks- causes Lyme disease
-is named for the Connecticut town where in the mid-1970s there was an epidemic of arthritis associated with skin erythema, caused by B. burgdorferi
-Lyme disease has three stages:
1.
an expanding area of redness with an indurated or necrotic center at the site of the tick bite- erythema chronicum migrans
2.
early hematogenous spread of spirochetes, resulting in annular skin lesions, lymphadenopathy, migratory joint and muscle pain, cardiac arythmias
3.
two or three years later after initial skin bite, a chronic arthritis appears, and sometimes encephalitis and various neurological disturbances
BACTERIAL DISEASES.
-streptococcal infections- scarlet fever, skin, streptococcal pharyngitis
-gram-negative rods- sepsis- DIC, septic shock
-Legionella pneumophila- causes Legionnaires disease
Legionella is a gram-negative bacterium
-causes mini-epidemics of severe pneumonia in susceptible individuals exposed to aerosols from cooling systems of buildings
L- is a facultative intracellular parasite –within macrophage
 SYPHILIS is a venereal disease caused by spirochete Treponema pallidum
1) ACQUIRED SYPHILIS neither primary stage (takes a form of ulcer) nor the secondary stage (the form of rash) is accompanied by disturbing clinical symptoms. The disease then enters a long period of latency and after years, the tertiary stage follows- that is serious and often fatal disease
1-primary stage: follows an incubation period of average 3 weeks is characterized by development of specific ulcer at the site of treponema invasion, that is called chancre the chancre usually occurs on the glans penis in males and on the vulva or uterine cevix in females in 10 per cent- the chancre may develop in extragenital sites, such as in lips, oral mucosa, fingers, or some other sites morphological findings: the chancre begins as a solitary slightly elevated firm papule then it undergoes a superfitial ulceration- hard chancre (ulcus durum)
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superimposed secondary bacterial infection may give rise to a suppurative exudation histological findings:
1- the chancre is characterized by a heavy infiltration composed mainly of plasma cells and scattered macrophages and lymphocytes obliterative endarteritis with endothelial cell proliferation is often present in the inflammed area treponemas may be visualized by special staining using silver impregnation
2- the regional lymph nodes- are usually enlarged and show nonspecific acute or chronic lymphadenitis- plsma cell-rich infiltrate or may contain focal epithelial cell granulomas the chancre usually heals in 3 to- 12 weekswith (antibiotics) or without therapy the patient seems to be entirely well specific tests for antibodies against treponemas are usually negative
2-secondary stage:
-is characterized by widespread mucocutaneous lesions that are often generalized over the whole body- including the mucous membranes of oral cavity
 rash is polymorphic- macules, in other places follicular, pustular, annular and ulcerative lesions histologically: within these skin lesions- heavy infiltrate mostly composed of plasma cells
 condylomata lata- flat, red-brown elevations, usually in genital or perianal regions, up to 3 cm in diameter, less commonly on the lips or in oral mucosa histologically: condylomata lata are heavily infiltrated by plasma cells, as well as there are vessels with obliterative endarteritis, abundant spirochetes
-serological anti-treponemal tests are positive following the secondary stage the patient again enters a period ofapparent wellbeing, referred to as latent syphilis
3-tertiary stage: this became very rare the cardiovascular system is most commonly affected
 aorta- syphilitic mesoaortitis- inflammatory scarring of the tunica media - leads to dilatation and weakening of the wall of aorta- results in aneurysm formation- risk of rupture and death of exsanguination- massive retroperitoneal hemorhage
 CNS- neurosyphilis- leading to severe neurologic disorders including general paresis and progressive dementia
 syphilitis gumma- is characterized by distinctive necrosis of firm, rubbery consistency single or multiple, variable in size, most commonly found in liver, bones, testes
histologically:
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center of coagulative necrosis, margins are composed of palisaded macrophages and fibroblasts with plasma cells
2) CONGENITAL SYPHILIS congenital syphilis may develop in fetus from infected mother via placenta the more recent the infection of the mother, the more certain involvement of the fetus by congenital syphilis
1.) perinatal, infantile forms of syphilis
-most striking lesions affect the mucocutaneous tissue and bones- diffuse rash, particularly on palms and soles and about the mouth
-generalized luetic osteochondritis and periostitis- may cause destruction of cartilage of nose- characteristic saddle nose deformity widespread disturbance in endochondral bone formation
-liver is severly affected- diffuse fibrosis
-lungs- diffuse interstitial fibrosis- called pneumonia alba (grossly - pale, firm, airless tissue)
-diffuse interstitial inflammatory reaction virtually in all organs
2.) delayed congenital syphilis among most typical signs are: interstitial keratitis- blindness, Hutchinson teeth, eight nerve deafness
TUBERCULOSIS- chronic communicable disease caused by M. tuberculosis, is characterized by necrotizing (caseating) granulomas
SARCOIDOSIS
-is relatively common disease of unknown etiology, most likely caused by atypical mycobacteria, charaterized by noncaseating granulomas in virtually any tissue
-females are affected more frequently than males
 -s. can be entirely asymptomatic- discovered only incidentally at autopsy
 or it may present as isolated cutaneous or ocular lesions, or as peripheral lymphadenopathy, or/and hepatosplenomegaly
 or may present with acute fever, polyarthritis, erythema nodosum
(inflammatory lesions in subcutaneous tissue often in lower extremities)
 lung is commonly involved- diffuse scattered granulomas- that heal by hylinized scars
 lymph nodes are very commonly affected- hilar and mediastinal- microscopic granulomas composed of epithelioid cells, Langhans cells
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