Infectious Diseases: Introduction to Viral Diseases

Infectious Diseases:
Introduction to Viral Diseases

INTRODUCTION

Ever since pandora opened her mythical box, infectious diseases have plagued humanity. Even today, societies in densely populated developing countries are prone to tuberculosis, leprosy, malaria, filariasis, and schitosomiasis.

Medical practices too have altered panorama of infectious diseases. Since Jenner's time, vaccines curbed many infections including diphtheria, whooping cough, paralytic poliomyelitis, and measles. Later on, Fleming discovered penicillin, then antibiotics and microbial drugs have radically changed the prevalence and course of most diseases so they now appear in classical forms. However, we still lack information on other viral infections and their prevention or treatment.

TRANSMISSION OF INFECTIOUS DISEASES

  1. Direct transmission
  2. Transmission may also occur by the way of contaminated water food or soil from human or environmental reservoir.
  3. Can also be acquired prenatally passed from mother to fetus via placenta, or perinatally transmitted during or shortly after delivery
  4. Infection transmitted to humans from an animal host or reservoir are termed zoonotic

Information transmission of infection involves a number of factors including parasites biology, vector competence, human behavior, and environmental conditions.

FACTORS RELATING TO HOST
There are many host barriers to infection that prevent access of parasites to the required environment or can suppress infection it spread.

Barriers and differences take many forms:

  1. Intact integument and mucosal surfaces and secretions
  2. Phagocytic white cells that promptly marshaled to sites of entry
  3. The resident mononuclear-phagocyte (reticuloendothelial) system that effectively polices the internal environment for errant organisms
  4. All important immune system

The route by which infection enters may be:

  1. Respiratory
  2. Oral-fecal
  3. Transmucosal
  4. Transcutaneous

Most human pathogens follow a preferential route but this does not preclude other possible entry sites. For instance the bulk of tuberculosis infections arise by droplet aspiration that some may be going through the swallowing of infected milk or contaminated skin puncture. Moreover the site of entry does not necessarily conform to the site of disease.

The best example is tropism of many viruses. The poliovirus is first in sensibly replicate and permissive whole cells along the GI tract but then exert their destructive effects on neuronal targets— the anterior horn cells of the spinal cord.

HOST TISSUE RESPONSES TO INFECTION
Broadly speaking, there are five microscopic patterns of reaction:

  1. Exudative Inflammation
  2. Necrotizing Inflammation
  3. Granulomatous Inflammation
  4. Interstitial Inflammation
  5. Cytopathic-cytoproliferative Inflammation

VIRAL RESPIRATORY DISORDERS

Laryngotracheobronchitis and bronchiolitis

  • Often accompanied in the common chest cold or characterized by vocal cords swelling abundant glucose oxidation and mucosal changes analogous to those encountered in the URI.

Viral Pneumonia

  • like bacterial pneumonia, this take variety of anatomic forms, they may be patchy or disseminated interstitial, or consolidated compatible food restoration of normal structure responsible for permanent damage.

VIRAL DIGESTIVE TRACT DISORDERS

Mumps

  • this is an acute contagious childhood disease characterized by inflammation and swelling of the parotid glands and less often the other salivary glands. It may also involve the pancreas, testes, ovaries, and other organs. Although usually mild, this occasionally causes acute incapacitating, painful illness, especially in adult patients or malignant tissue destruction when it is awake.
  • this is commonly caused by paramyxovirus, usually acquired by respiratory droplet infection.

Viral Enteritis and Diarrhea

  • viruses are major causes of acute diarrheal diseases previously attributed to other or uncertain causes.
  • Two types of enteropathogenic viruses: rotaviruses and parvoviruses— have now been characterized by immunoelectron microscopy and may yet be more discovered.

Viral Hepatitis

  • infections caused by the human hepatitis viruses and their role in cirrhosis and liver cancer or discussed. Impairment of liver function may also occur in many other systemic viral infections most commonly those of the herpesvirus family both the CMV and EB virus produced focal hepatocellular necrosis with some regularity especially after transfusions or organ transplants.

EPIDERMAL-EPITHELIAL VIRAL DISORDERS

Epithelial Warty Growths

  • common features of these benign growths are exuberant but self-limited epithelial proliferation, cytopathic changes in maturing epithelial cells, and predominantly mononuclear stromal and base of inflammatory infiltration

Measles (Rubeola)

  • this is an acute febrile systemic viral infection usually beginning with coryza and conjunctivitis followed by typical spotty lesions inside the mouth, lymph reticular hyperplasia, and a blotchy generalized erythematous rash.
  • caused by RNA paramyxovirus. It is the measles virus that is highly contagious by droplet aspiration and is transmissible via placenta.

German Measles (Rubella)

  • sometimes called 3-day measles. It is a highly contagious but mild childhood system viral infection characterized by morbilliform rash and swelling of the posterior cervical lymph node.
  • caused by togavirus unrelated to measles virus.

Smallpox (Variola)

  • caused by a particle containing double-stranded DNA and terminal transcriptase has finally been confined to cold storage and a few high-security reference centers.

Chickenpox (Varicella) and Herpes Zoster

  • two seemingly disparate does orders are both caused by Herpes Zoster virus and are therefore closely related.

Chickenpox

  • this is an acute highly contagious but mild systemic viral infection with a vesicular generalized skin eruption. It is usually of little consequence in normal children but in those with immunodeficiencies may cause pneumonitis, encephalitis, and disseminated lesions including purpuric skin lesions.

Herpes Zoster (Shingles)

  • represents a reactivation of latent HZV virus that occurs with advancing age. Adults with shingles can transmit virus at the children but not vice versa.
  • the reactivated virus travel centrifugal from the ganglia to the skin of the corresponding dermatomes resulting in a localized vesicular eruption this is similar to that of chickenpox but differentiated by the often and teaching burning or sharp pain in the affected skin segment because of a simultaneous radiculoneuritis.

Ramsay Hunt Syndrome

  • this is an induced facial paralysis. In more than 50% of cases, only a single unilateral involved but several crops of lesions may arise or occur after long intervals.

Cytomegalic Inclusion Disease (CID)

  • this disease is an exceedingly protean viral disease caused by CMV, a member of the herpes virus group.

ARBOVIRUS DISEASES There are over 60 known diseases, some words spread, other strictly local caused by anthropol arboviruses.

Hemorrhagic fever

  • Korean and dengue hemorrhagic fevers caused fatalities among the military in southeast Asia. Disorder start suddenly with chills, headache, muscle and joint pains, followed by widespread skin and scleral bleeding, thrombocytopenia, proteinuria, and renal failure usually within 3 to 5 days.
  • shock and hypothermia are ominous preterminal science those who survived the first 7 to 10 days of illness gradually recover but proteinuria and oliguria persists for weeks.

Dengue

  • this is ordinarily a benign flu-like tropical disease well characterized by its popular name breakbone fever. However, a potentially lethal hemorrhagic variant occurs principally among children and countries of eastern pacific.
  • Example: Thailand and Pakistan

Yellow fever

  • It differs from other arbovirus infections and its profound effect on the liver and marked jaundice. However, the latter may complicate many viral and bacterial infections and perhaps for these reasons yellow fever outbreak sometimes remain undiagnosed until several deaths have occurred.

VIRAL CENTRAL NERVOUS SYSTEM DISORDERS

CNS is the direct target for the so-called neurotropic viruses. For example, polio, rabies, and encephalitis viruses that cause acute injury. It can also be acutely damaged by others the other systemic viral infections including those with prominent skin or visceral manifestations.

Rabies

  • Rabies alone among the neurotropic viruses induces diagnostic cell inclusions those agents that widely involve the brain often provide no histopathology clue to their etiology. Therefore virologic and serologic studies, and in some cases electron microscopy, or immunoperoxidase methods are essential diagnostic tools.

VIRAL HEART DISEASES
It is unusual for viral infections to present clinically with associated cardiac symptoms such as pericarditis, heart failure, or arrhythmias related to myocardial involvement in the absence of other systemic manifestations.

SUSPECTED VIRAL DISEASES

Cat-Scratch Disease

  • this is a self-limited condition usually manifested by localized lymphadenopathy. Seen in children than in adults. It usually takes the form of enlargement of lymph nodes most frequently in the axilla and neck
  • one or more weeks usually following a feline scratch but occasionally a splinter or inflammatory nodule may or may not appear at the site of the skin injury.
  • systemic manifestations are usually minimal such as fever, mild neutrophilia, and eosinophilia, and accelerated sedimentation rate
  • thrombocytopenia, pneumonia, and focal the mineralizing bone lesions have been reported, suggesting systemic spread.