Adenovirus

Adenovirus

1. ADENOVIRUS BY- SANJU SAH ST. XAVIER’S COLLEGE, MAITIGHAR,KATHMANDU DEPARTMENT OF MICROBIOLOGY

2. Introduction: Adenoviruses were first isolated in 1935 from human adenoid tissues. Adenoviruses can replicate and produce disease in respiratory, gastrointestinal and urinary tract and in the eye. Many adenovirus infection are subclinical and virus persist in hosts for months. One third of 52 serotypes are responsible for most cases of human adenovirus disease. Whereas a few types serve as models for cancer induction in animal models

3. What are Adenoviruses Adenoviruses are a group of medium sized, nonenveloped, double stranded DNA viruses that share a common complement fixing antigen They infect humans and animals Classification: Family : Genus : Spec i es: Adenoviridae Mastadenovirus Human adenoviru

4. Classification: Family Adenoviridae is classified into two genera: Mastadenovirus , the adenovirus of mammals. Aviadenovirus ; adenovirus of birds At least 52 distinct antigenic types have been isolated from humans and many other types from various animals. Human adenovirus have been divided into seven groups (A-G) on the basis of their genetic, physical, chemical and biological properties. They are divided into serotypes on the basis of type specific antigens on penton bases and fibers. Serotypes are identified by neutralization tests. Different serotypes may cause infection or distinct diseases in different age groups or patient populations

5. Neutralization tests Neutralization of a virus is defined as the loss of infectivity through reaction of the virus with specific antibody. Virus and serum are mixed under appropriate condition and then inoculated into cell culture, eggs or animals. The presence of unneutralized virus may be detected by reactions such as CPE, haemadsorption/haemagglutination, plaque formation, disease in animals. The loss of infectivity is bought about by interference by the bound Ab with any one of the steps leading to the release of the viral genome into the host cells.

6. Classification: Classification schemes for Human Adenovirus

7. Chateristics of Adenovirus Adenoviruses are medium-sized (80 nm, nonenveloped (naked) icosahedral viruses composed of a nucleocapsid and a double-stranded linear DNA genome. There are over 52 different serotypes in humans, which are responsible for 5–10% of upper respiratory infections in children, and many infections in adults as well.

8. Adenovirus Genome The adenovirus genome is linear, nonsegmented double stranded (ds) DNA which is around 30–38 Kbp. This allows the virus to theoretically carry 30 to 40 genes. Although this is significantly larger than other viruses in its Baltimore group it is still a very simple virus and is heavily reliant on the host cell for survival and replication. An interesting feature of this viral genome is that it has a terminal 55 kDa protein associated with each of the 5' ends of the linear dsDNA. These are used as primers in viral replication and ensure that the ends of the virus‘ linear genome are adequately replicated

9. Morphology of Adenovirus Adenovirus are 80 nm in size No envelope The capsid contains 252 capsomers arranged as icosahedrons with 20 triangular facets and 12 vertices 240 are called as hexons 12 are called as pentons Each penton unit consists of penton base anchored in the capsid and projection or fibre consists of a rode like portion with a knob attached at the distal end The virus appears like a space vehicle.

10. Replication Adenoviruses possess a linear dsDNA genome and are able to replicate in the nucleus of vertebrate cells using the host’s replication machinery. Adsorption and entry into host Entry of adenoviruses into the host cell involves two sets of interactions between the virus and the host cell. Entry into the host cell is initiated by the knob domain of the fiber protein binding to the receptor. The two currently established receptors are: CD46 for group B human adenovirus serotypes and the coxsackievirus adenovirus receptor (CAR) for all other serotypes. There are some reports suggesting major histocompatibility complex (MHC) molecules and sialic acid residues functioning in binding of virus.

11. Once the virus has successfully gained entry into the host cell, the endosome acidifies , which alters virus topology by causing capsid components to disassociate. These changes as well as the toxic nature of the pentons result in the release of the virion into the cytoplasm . With the help of cellular microtubules , the virus is transported to the nuclear pore complex, whereby the adenovirus particle disassembles. Viral DNA is subsequently released, which can enter the nucleus via the nuclear pore. After this the DNA associates with histone molecules . Thus, viral gene expression can occur and new virus particles can be generated.

12. The adenovirus life cycle is separated by the DNA replication process into two phases: an early and a late phase . In both phases, a primary transcript that is alternatively spliced to generate monocistronic mRNAs compatible with the host’s ribosome is generated , allowing for the products to be translated. The early genes are responsible for expressing mainly non-structural and regulatory proteins. The function of these proteins are: To alter the expression of host proteins that is necessary for DNA synthesis; To activate other virus genes ; and To avoid premature death of the infected cell by the host-immune defenses.

13. Some Adenoviruses under specialized conditions can transform cells using their early gene products. E1A (binds Retinoblastoma tumor suppressor protein) has been found to immortalize primary cells in vitro allowing E1B (binds p53 tumor suppressor) to assist and stably transform the cells. Nevertheless, they are reliant upon each other to successfully transform the host cell and form tumors. The DNA replication separates the early and late phases. Once the early genes have liberated adequate virus proteins, replication machinery and replication substrates; the replication of the adenovirus genome can occur

14. A terminal protein that is covalently bound to the 5’ end of the adenovirus genome acts as a primer for replication. The viral DNA polymerase then uses a strand displacement mechanism as opposed to the conventional Okazaki fragments used in mammaliam DNA replication to replicate the genome of human Adenoviruses. The late phase of the adenovirus lifecycle is focused on producing sufficient quantities of structural protein to pack all the genetic material produced by DNA replication. Once the viral components have successfully been replicated, the virus is assembled into its protein shells and released from the cell as a result of virally induced cell lysis.

15. Pathogenesis The recognized diseases of Adenoviruses predominantly involve the respiratory tract, Gastrointestinal tract and eye . Virus may be introduced through contact, respiratory droplets or ingestion. The association of particular types with specific disease syndromes is striking. After recovery of illness, adenoviruses may maintain latent persistent infections in the tonsils, adenoids and other lymphoid tissues of n.

16. Pathogenesis: (contd…) Adenoviruses infect and replicate in the epithelial cells of the: pharynx, conjunctiva, urinary bladder small intestine. Infect and replicate in epithelial cells of respiratory tract, gastrointestinal tract, urinary tract and the eye. Do not spread beyond regional lymph nodes. Group C persists as latent infections for years in adenoids and tonsils and are shed in feces for many months after initial infection. Most adenovirus replicate in intestinal epithelium after ingestion but usually produce sub clinical infection than overt symptoms.

17. About 1/3 of human serotypes are commonly associated with human illnesses. Single serotype may cause different clinical diseases and conversely more than one serotype can cause same clinical illness. Adenoviruses 1-7 are more common types worldwide and account for most instances of adenovirus associated illness. Responsible for 5% of respiratory diseases in young children but account for much less in adults. Most infections are mild and self limited. Occasionally case disease in other organs particularly eye and gastrointestinal tract. Following are the clinical manifestation and disease caused by Adenovirus

18. Clinical Syndromes Respiratory diseases : Eye infections: Gastrointestinal disease Other diseases : Adenoviral infections of the immune compromised host

19. Respiratory Diseases: Typical symptoms: cough, nasal congestion, fever and sore throat. Symptoms most commonly manifested in infants and children and usually involves group C viruses. Adenoviruses particularly 3, 7 and 21 are thought to be responsible for about 10-20% pneumonias in childhood. Mortality rate of pneumonia 8-10% in very young. Also are cause of acute respiratory disease syndrome among military recruits. Characterised by fever, sorethroat, nasal congestion, cough and malaise; sometimes leading to pneumonia.

20. Occurs in epidemic form among young military recruits under conditions of fatigue, stress, and crowding soon after induction. Disease is caused by serotype 4 and 7 and occasionally by type 3. Outbreak of severe respiratory disease in 2007 caused by adenovirus 14 affects all age groups.

21. Eye Infections: Mild occular involvement may be part of respiratory pharyngeal syndrome. Pharyngoconjunctival fever occurs as outbreak such as in children’s summer camps (swimming pool conjunctivitis) and caused by type 3 and 7. Duration 1-2 weeks and complete recovery with no lasting sequela is common outcome. Epidemic keratoconjunctivitis more serious disease; occurs mainly in adults and is highly contagious. Source of infection: sinks and hand towel. Disease is characterises by acute conjunctivitis followed by keratitis ( inflammation of the cornea) that usually resolves in two weeks but may leave subepithelial opacities in the cornea for up to two years. Caused by serotypes 8, 19 and 37

22. Pharyngoconjunctival keratoconjunctivitis Keratoconjunctivitis is inflammation of the cornea and conjunctiva . When only the cornea is inflamed, it is called keratitis when only the conjunctiva is inflamed, it is called conjunctivitis Pharyngoconjunctival fever is a condition characterized by a fever, sore throat, and follicular conjunctivitis.

23. Gastrointestinal disease: Can often been isolated from feces but their relation to intestinal disease has not been conclusively established. However two serotypes (types 40 and 41) have been etiologically associated with infantile gastroenteritis. May account for 5-15% cases of viral gastroenteritis in young children. Adenoviruses 40 and 41 are abundantly present in diarrhoeal stools. Enteric adenovirus are very difficult to cultivate. Stool ELISA is often used for detection of these types.

24. Other Diseases: Cause variety of casual and severe diseases in immune compromised patients. Most common problem in transplant patients is respiratory diseases that may progress to pneumonia and may be fatal (usually types 1-7). Adenovirus hepatitis in children having liver transplant. AIDS patients mainly suffer from gastroenteritis due to adenovirus. Types 11 and 21 may cause acute hemorrhagic cystitis ( is an inflammation of the bladder) in children esp. boys.

25. Laboratory Diagnosis: Specimen: May be isolated from body fluids, eye swabs, throat swabs, throat washings, urine, faeces and CSF. Samples should be collected from affected sites as early as possible. Duration of excretion of the virus varies among various clinical illness; 1-3 days from throat of adults with common cold, 3-5 days for throat, stool and eyes, for pharyngoconjunctival fever, 2 weeks eye for keratoconjunctivitis, 3-6 weeks, throat and stool of children with respiratory illness, 2-12 months in stool, throat, urine of immunocompromised patients.

26. Isolation Viral isolation in cell culture requires human cells. Human epithelial cell lines such as Hep-2, HeLa and BK are sensitive but difficult to maintain. Primary monkey kidneV cells will permittee growth and isolation of AdV 40 and AdV41 strains. Isolates grown in these cells are identified by noting cytopathic effects or by immunofluorescence staining using anti hexon antibody , heamagglutination inhibition test and neutralization test. Shell vial techniques can also be employed for isolation of the virus. Can also be detected by electron microscopy, ELISA or by latex agglutination tests.

27. Serology Paired sera should be used to detect rise in antibody titre. Antibodies in patients sera can be detected by ELISA, complement fixatation test, heamagglutination inhibition and neutralization test. Molecular techniques: PCR, restriction endonuclease digestion, DNA hybridization. Treatment: no specific treatment

28. Adenovirus Treatment Antivirals against AdV: Potential targets: AdV DNA polymerase AdV cysteine protease receptors for binding host cells Antivirals in use: Ribavirin Cidofovir Ganciclovir (Vidarabine)

29. Prevention and control Careful hand washing is the easiest way to prevent infection. Disinfection of Environmental surfaces with hypochlorite's. The risk of water borne outbreaks of conjunctivitis can be minimized by chlorination of swimming pools. Epidemic keratoconjunctivitis can be controlled by strict asepsis during eye examination.

30. • Prevention of Adenoviral Infections Prevention: Vaccines were developed for adenovirus serotypes 4 and 7, but were available only for preventing among military recruits. Strict attention to good infection-control practices is effective for stopping nosocomial outbreaks of adenovirus-associated disease, such as epidemic keratoconjunctivitis. Maintaining adequate levels of chlorination is necessary for preventing swimming pool associated outbreaks of adenovirus conjunctivitis.

31. Epid e mio l ogy Worldwide in humans as well as in a variety of animals. Human Adenovirus are generally not pathogenic to animals and animal adenoviruses are pathogenic within the species . Infection varies from sporadic to epidemic Pattern often correlates with the viral serotypes and the age of the susceptible population Fecal oral transmission accounts for infections in young children. Initial spread by respiratory route Prolonged carriage in the intestine makes the feces a more common source The reservoir for adenovirus is in humans. Adenoviruses have a worldwide distribution, and they are ubiquitous in the environment where contamination of human feces or sewage has occurred.

32. Infections can occur throughout the year. Outbreaks have been more common in late winter, spring, and early summer. Though most adenovirus infections are mild, fatality and a number of sequelae are associated with immunocompromised patients. Adenovirus is a very common infection, estimated to be responsible for between 2% and 5% of all respiratory infections. All ages are susceptible to adenovirus infection, but infection usually occurs during childhood. Acute lower respiratory tract infection in children is a major worldwide health problem, and the virus is second only to rotavirus in terms of its significance as a cause of childhood gastroenteritis. In the winter, adenovirus has caused many cases of illness in military recruits, with about 25% requiring hospitalization for fever and lower respiratory tract disease. Some cases result in death.