Viral Diseases

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Viral Diseases

  1. 1. What is an Arbovirus? acronym for arthropod-borne virusArboviruses are a large group of viruses that are spread by certain invertebrate animals (arthropods), most commonly blood- sucking insectsEPIDEMIOLOGY found throughout the world depends on the availability of specific types of mosquitoes that can carry it and specific birds or animals that can be infected
  2. 2. PREVENTION If possible, stay inside between dusk and dark. This is when most types of mosquitoes are most active in their search for food. When outside in mosquito- infested areas, wear long pants and long-sleeved shirts. Spray exposed skin with an insect repellents, e.g. Permethrin, DEET Screen homes to prevent mosquitoes from entering. Remove old tires and other water-holding containers from around homes. These can provide breeding sites for mosquitoes.
  3. 3.  Alphaviruses  Bunyaviruses Eastern Equine  LaCrosse encephalitis encephalitis  Reoviruses Western Equine  Colorado tick fever encephalitis Venezuelan equine  Orbivirus encephalitis  Colorado Tick Fever Flaviviruses  African Horse Sickness St. Louis encephalitis  Blue Tongue Viruses Japanese encephalitis Yellow fever Dengue
  4. 4. ERADICATED IN 1980.. one of the success stories of medicinePATHOGENESISVirus invades through broken skin, replicates at the site of inoculation and causes dermal hyperplasia and leucocyte infiltration.This causes lymphadenopathy and elicits an immune responseThe lesion of molluscum is circumscribed by a connective tissue capsule and the dermis
  5. 5.  Human monkeypox is usually acquired via the respiratory tract During the 12th day of incubation period viraemia distributes infection to internal organs which get damaged by viral infection Spread to skin initiates the clinical phase and the lesions progress to classic stages of macule to papule to vesicle to pustule to crust Lymphadenopathy usually involving the cervical and inguinal areas is often marked
  6. 6. TREATMENTSmallpox vaccination within three days of exposure will prevent or significantly lessen the severity of smallpox symptoms in the vast majority of peopleOther than vaccination, treatment of smallpox is primarily supportive, such as wound care and infection control, fluid therapy, and possible ventilator assistanceNo drugs available currentlyAnti-virals like cidofovir, intravenously administered might be useful
  7. 7. The family Poxviridae is classified into 2 sub- families : Chordopoxvirinae and EntomopoxvirinaeChordopoxvirinae, the poxviruses of vertebrates, are classified into 6 genera: Orthopoxvirus Parapoxvirus Capripoxvirus Leporipoxvirus Avipoxvirus Suipoxvirus
  8. 8. EPIDEMIOLOGYUpper respiratory tract infections are the most common infectious diseases among adults, who have two to four respiratory infections annuallyChildren may have six to ten colds a year (and up to 12 colds a year for school children)..CAUSATIVE ORGANISMRhinoviruses, of the Picorna group
  9. 9. PATHOPHYSIOLOGYThe major entry point -the nose, but can also be the eyes (via the nasolacrimal duct). From there, it is transported to the back of the nose and the adenoid area. The virus then attaches to a receptor, ICAM-1, which is located on the surface of cells of the lining of the nasopharynx.The receptor fits into a docking port on the surface of the virus. Large amounts of virus receptor are present on cells of the adenoid.After attachment to the receptor, virus is taken into the cell, where it starts an infection, and increases ICAM-1 production, which in turn helps the immune response against the virus.Rhinovirus colds do not generally cause damage to the nasal epithelium.Macrophages trigger the production of cytokines, which in combination with mediators cause the symptoms. Cytokines cause the systemic effects. The mediator bradykinin plays a major role in causing the local symptoms such as sore throat and nasal irritation
  10. 10. PREVENTION Hand washing with plain soap and water is recommended. The mechanical action of hand rubbing with plain soap, rinsing, and drying physically removes the virus particles off the hands. Alcohol-based hand sanitizers provide very little protection against upper respiratory infections, especially among children. Because the common cold is caused by a virus instead of a bacterium, anti-bacterial soaps are no better than regular soap for removing the virus from skin or other surfaces. Aqueous iodine has been found to reliably eliminate the cold virus on human skin, however iodine is not acceptable for general use as a virucidal hand treatment because it discolors and dries the skin.TREATMENTHelp alleviate symptoms: simple analgesics and antipyretics such as ibuprofen and acetaminophen / paracetamol
  11. 11. CAUSATIVE ORGANISM: Haemophilus influenzaeEPIDEMIOLOGYInfluenza reaches peak prevalence in winter Because the Northern and Southern Hemispheres have winter at different times of the year, there are actually two different flu seasons each year An alternative hypothesis to explain seasonality in influenza infections is an effect of vitamin D levels on immunity to the virus - Robert Edgar Hope-Simpson in 1965
  12. 12. PATHOPHYSIOLOGY The viral hemagglutinin protein is responsible for determining both which species a strain can infect and where in the human respiratory tract a strain of influenza will bind Strains that are easily transmitted between people have hemagglutinin proteins that bind to receptors in the upper part of the respiratory tract, such as in the nose, throat and mouth. In contrast, the highly lethal H5N1 strain binds to receptors that are mostly found deep in the lungs.This difference in the site of infection may be part of the reason why the H5N1 strain causes severe viral pneumonia in the lungs, but is not easily transmitted by people coughing and sneezing.
  13. 13. PREVENTION Inactivated influenza virus vaccines are used for old people Vaccine contains the strains of type A and B and early October to mid-November is the best time to get vaccinatedTREATMENT Drugs like amantadine and rimantadine hydrochloride are used against type A but not against type B viruses These drugs interfere with virus uncoating and transport by blocking transmembrane M2 ion channel
  14. 14. EPIDEMIOLOGY According to the WHO, measles is a leading cause of vaccine-preventable childhood mortality. Worldwide, the fatality rate has been significantly reduced by a vaccination campaign led by : the American Red Cross, the United States Centers for Disease Control and Prevention (CDC), the United Nations Foundation, UNICEF and the WHO. Globally, measles fell 60% from an estimated 873,000 deaths in 1999 to 345,000 in 2005
  15. 15. PATHOPHYSIOLOGY The respiratory route and conjunctiva acquire rubeola (measles) virus After replicating in the upper respiratory tract, it spreads to lymphoid tissues and eventually spreads throughout the body Secondary infections that measles- infected people are susceptible to include those of the middle ear and lungCONTROL Young children are vaccinated with MMR vaccine (pre-school children too)
  16. 16. The mumps virus belongs to the family ParamyxoviridaeIt targets the parotid gland, causing painful swelling of one or both glandsEPIDEMIOLOGYHumans are the only natural hosts of mumps and natural infection confers lifelong immunityPATHOPHYSIOLOGY Portal of entry- the respiratory tract Multiplies in the tract and local lymph node in neck and viraemia results Symptoms surface only after infecting parotids and meninges It eventually destroys the salivary duct epithelium and testicular tissue until host’s immune system eliminates the infection
  17. 17. PREVENTIONMost common preventative measure against mumps is immunization with a mumps vaccine, invented by Maurice Hilleman at MerckMay be given separately or as part of the MMR immunization vaccine which also protects against measles and rubellaTREATMENT no specific treatment for mumpsOnly symptomatic relief by warm water gargles, soft foods, extra fluids, acetaminophen/paracetamol
  18. 18. Progressively reduces the effectiveness of the immune system and leaves individuals susceptible to opportunistic infections and tumorsPATHOPHYSIOLOGY HIV causes AIDS by depleting CD4+ T helper lymphocytes The mechanism of CD4+ T cell depletion differs in the acute and chronic phases:During the acute phase, HIV-induced cell lysis and killing of infected cells by cytotoxic T cells accounts for CD4+ T cell depletion, although apoptosis may also be a factor.During the chronic phase, the consequences of generalized immune activation coupled with the gradual loss of the ability of the immune system to generate new T cells appear to account for the slow decline in CD4+ T cell numbers.
  19. 19. PREVENTION Avoiding sexual contact with HIV-infected individuals Avoiding sharing of shaving materials Avoiding drug abuse Screening of blood before transfusion Using condoms during sexual contactTREATMENT Highly Active Anti-Retroviral Therapy (HAART) – zidovudine, lamivudine, tenofovir Azidothymidine (AZT)- for prophylaxis against progression of disease
  20. 20. PATHOPHYSIOLOGYHerpes is contracted through direct contact with an active lesion or body fluid of an infected person Herpes labialis Virus enters into susceptible cells via entry receptors such as nectin-1, HVEM and 3-O sulfated heparan sulfate. Infected people showing no visible symptoms may still shed and transmit virus through their skin asymptomatically Antibodies that develop following an initial infection with a type of HSV prevents reinfection with the same virus type—a person with a history of orofacial infection caused by HSV-1 cannot contract herpes whitlow or a genital infection caused by HSV-1
  21. 21. Causative Organisms: herpes simplex viruses, type 1 and 2 HSV-1: Oropharyngial lesions HSV-2 : lesions on Genital mucosaEPIDEMIOLOGY Worldwide in distribution No animal reservoirs involved in human infection transmissionTREATMENT DNA synthesis inhibiting drugs Vidarabine triphosphate inhibits DNA polymerase
  22. 22. PREVENTION Primary prophylaxis: Avoidance of direct contact with lesion or infected secretions Barrier protection Anti-virals like acyclovir, valacyclovir Vaccination for herpes is the ideal preventive measure
  23. 23. Hepatitis is the term used for any condition where there is inflammation of the liverJaundice and Hepatitis are not the sameA heterogenous group of viruses called hepatotrophic viruses causes viral hepatitis and damage to liver: HAV – Transmitted by fecal-oral route HBV – Transmitted by blood transfusion HCV – Post-transfusion Hepatitis HDV – Occurs only in HBV-affected HEV The most important type is Hepatitis B
  24. 24. HEPATITIS BEPIDEMIOLOGY This disease occurs throughout the world HBV causes more than a million deaths worldwide every yearPATHOPHYSIOLOGY Involves 3 steps:1. Entry : Blood transfusion Sexual transmission Infected mother to neonates Contaminated syringes and needles Rarely by arthropods
  25. 25. 2. Multiplication and Spread: The HBV target the hepatocytes, integrate their DNA into host genome and exocytose complete virions3. Liver cell damage: By activation of cytotoxic immune mechanisms causes cell-degeneration and release of liver- associated enzymes into bloodstreamPEVENTIONTwo types of vaccines currently available: Recombinant HB vaccine synthesized from yeast cells are safe, effective and provides 90% protection Plasma-derived vaccineTREATMENT Interferons in combination with ribavirin – stimulates body’s defence

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