VIRAL DISEASES AND EPIDEMIOLOGY

1. VIRAL DISEASES AND EPIDEMIOLOGY Claude MUVUNYI M.D., Ph.D.

2. Viral diseases • The relative susceptibility of a person and the severity of the disease depend on factors such as: • the nature of exposure; • the immune status, • age, and general health of the person; • the viral dose and • the genetics of the virus and the host

3. Therefore: • new variant or viral strain would cause a viral outbreak (new influenza virus strain). • acute A hepatitis is more symptomatic in adulthood than in childhood. • Infantsare especially prone to more serious presentation of Paramyxovirusrespiratory infections and gastroenteritis. • However, children generally do not mount as severe an immunopathologicalresponse as adults, and some infections (Varicella caused by VZV a Herpesvirus) are more benign in children. • The elderly are especially susceptible to new viral infections and reactivation of latent viruses.

4. Stages of the viral disease • The initial period before the characteristic symptoms of a disease is termed the incubation period. • During that period, the virus is replicating but has not reached the target tissue or induced sufficient damage to cause disease. • The incubation period is relatively short if the infection of primary site produces the characteristic symptoms of the disease; e.g., 1-2 days for influenza. • This incubation period is longer for viral systematic infections such as • poliomyelitis ( 5-20 days), • measles (9-12 days), • rubella (17-20 days), • hepatitis (15-40 days for hepatitis A and 50-150 days for hepatitis B), • rabies (30-100 days), • AIDS for Acquired Immunodeficience Syndrome cause by HIVs (1-13 years).

5. Types of viral infections • Viral infections are usually self-limiting. Sometimes, however, the virus persists for long periods of time in the host. • Long-term virus-host interaction may take several forms: • 1- Chronic infections. • 2- Latent infections. • 3- Inapparent or subclinical infections.

6. Transmission ways of viruses • Viruses are transmitted • by direct contact, • sexual intercourses, • injection with contamined fluids or blood, • use of contamined injection materials (syringues, catheters), or prosthetic devices, • and the transplantation of noncontrolledcontaminedorgan, • more often by respiratory and oral-fecal routes. • They may also be transmitted by a maternal-neonatal transmission during foetal live or the delivery.

7. Transmission ways of viruses • Animals can also act as vectors that spread viral infection to other animals and humans. • They can also be reservoir for the virus that maintain and amplify the virus in environment. • Viral infections that are shared by animals or insects and humans are called zoonosis. • Arthropods include mosquitos, ticks can act as vectors for Togavirus, Flavivirus, Bunyavirus and Reovirus. • These viruses are often referred to as arboviruses because they are arthropod borne viruses, such as Yellow fever virus, Dengue viruses, Rift Valley fever virus.

8. Transmission ways of viruses

9. how viruses leave the body • Infectious agents leave body by many ways: • 1° with excreted products from epithelial cell mucous; with measles infection, conjunctival excretions; rhinopharyngeal excretions of flu infection; bronchal excretions of viral pneumonia. • 2° with glandular excretions for mumps and saliva for rabies • 3° with feces containing Enterovirusand other gastrointestinal viral infectious agents such as oral fecal transmitted hepatitis viruses A and E • 4° with fuids of cutaneous viral lesions such as vesicles or pustules that contain infectious agents(VZV). • All these excreted products are potential infectious; they are, also mainly used as specimens for biological diagnosis of viral infections and diseases

10. Viral infection epidemiological types • We account three epidemiological types: • sporadic, • epidemic, • pandemic

11. Sporadic • Concern one person or another with any relationship. • It cannot spread in all the population. • Those persons with sporadic infection act as reservoir if the infection may be persitent, latent or chronic: • Example is that HBV chronically people infected form a reservoir of the virus and establish the endemicity of that infection.

12. Outbreaks or epidemies • often occurs from the introduction of a virus in a new location. • The outbreak comes from a common source (e.g.,food preparation) or a new strain in a immunological naïve population, (new influenza virus strain). • Epidemy concern a wide population during the same time and in a location (e.g., influenza school outbreak)

13. Pandemic • are world-wide epidemics such as HIV 1 pandemy and Influenza A virus pandemy. • These epidemies spread from one continent to an other and may concern in a short time population of all the world • Pandemies of Influenza virus A have occurred approximately each 10 years as result of the introduction of a new strain .

14. Current viral infections and diseases • Congenital Viral Infections. • Foetaland neonatal viral infections • Childhood viral infections and diseases • Acute Viral Respiratory Infections. • Viral Infections of the Gastrointestinal Tract. • Viral skin Infections • Viral Infections of the CNS

15. Main foetal and neonatal viral infections • Rubella virus causes in utero infections • Cytomégaloviruswith in utero and peri natal infections →Those two foetal infections would be transferred through placenta from infected mothers; they are referred main severe congenital infections • Herpès simples 2, with perinatal infections, • Varicella andzoster virus that causein utero and perinatal infections • B 19Parvovirus cause in utero infections. • HIVs can cause in utero and peri-natal infections, • HBV may cause peri-natal infections

16. Main Childhood viral infections diseases During childhood, viral infections are dominated by exanthemous and other cutaneous manifestations. We can mention: • Measles caused by measles virus, a RNA virus, belonging to genus Morbillivirus of Paramyxoviridaefamily, • Rubella caused by a RNA virus, belonging to genus Rubivirusof Togaviridaefamily, • Varicella which is essential a benign disease with very rare complications in immunodeficienty children. It is caused by Varicella and Zoster virus or VZV ou HHV 3, DNA virus belonging to Varicellovirusgenera of Alphaherpesvirinae sub-family from Herpesviridaefamily. This virus may cause meningitis by immunodeprissive children • Mumps virus is responsible of parotiditis, a childhood benign disease. That’s a RNA virus of Paramyxoviridae family. It can sometimes cause neurologic disorders such as meningitis or meningo- encephalitis.

17. Respiratorytract viral infections • Those called respiratory virus share an exclusive tropism for respiratory epithelial ciliated cells. We account with: • flu Influenza A and B • Para-influenza1, 2, 3 and 4 • Respiratory syncytial virus or R.S.V • respiratory Adenoviruses • Rhinovirus, • Coronavirus. • Human Metapneumovirus • Each group of virus may cause different respiratory syndroms such as cold, laryngitis, tracheitis, bronchitis, bronchiolitis, pneumonia or flu. • Each clinical syndrome may be characteristict of a specific group of viruses. Such as • cold caused by Rhinovirus, • laryngitisby Parainfluenzavirus, • bronchiolitis by Syncitial respiratory virus • flu by influenza virus. • But also different viruses can cause a same clinical syndrom

18. Main gastro-intestinal tract viral infections • We deal with hepatitis and gastroenteritis • Hepatitis causative agents may be A, B, C, D and E virus with « new hepatitis virus »GB-A, GB-B, GB-C/VH-G et TTV. • All these viruses belong to different families

19. Hepatitis causative agents

20. Gastroenteritis causative agents • Those viruses are: • Rotavirus • Astrovirus • enteric Adenovirus serotypes 39, 40 • Norwackagent • Coronavirus • All these gastroenteritis associated viruses are not detected at same frequency. • Rotavirusand new enteric Adenovirus are the more frequently detected from newborn gastroenteritis. Others interest childrenand adults are rarely isolated. • A new vaccine is available against Rotavirus

21. Central nervous system viral infections • These acute clinical syndromes may be: • Aseptic meningitis or AAP for Acute anterior poliomyelitis that is caused by Poliovirus; • human or animal rabies caused by Rabies viruses • Four CNS chronic and degenerative diseases are associated with conventional agents. These diseases include: • Sclerotic sub-acute pan-encephalitis which may be caused by Measles virus • Progressive multiform leucoencephalitis due to J.C. virus a Papovirus • Tropical spastic paralysis (T.S.P) due to human T leukemia virus type1 (HTLV1) an Oncornavirusbelonging to Retroviridayfamily • AIDS dementia associated to Human Immunodeficiency Virus type 1 or 2, HIV 1 and 2, species of genera Lentivirusand Retroviridaefamily