VIRAL DISEASES AND EPIDEMIOLOGY - PowerPoint Presentation

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VIRAL DISEASES AND EPIDEMIOLOGY

Claude MUVUNYI M.D., Ph.D.

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

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.

Infants

are especially prone to more serious presentation of

Paramyxovirus

respiratory infections and gastroenteritis.

However

, children generally do not mount as severe

an

immunopathological

response 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.

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).

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.

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

noncontrolled

contamined

organ,

more

often by respiratory and

oral-fecal

routes.

They may also be transmitted by

a maternal-neonatal transmission

during

foetal

live

or the delivery.

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

a

rthropod

b

orne

v

iruses, such as Yellow fever virus, Dengue viruses, Rift Valley fever virus.

Transmission ways of viruses

MODE

VIRUSES

Respiratory transmission

Paramyxoviruses, influenza viruses, picornaviruses, Varicella-zoster virus.

Fecal oral transmision

Picornaviruses, rotaviruses, Reovirus, calicivirus, Norwak virus,adenovirus

Contact (lesions, saliva, fomites)

Herpes simplex viruses, poxviruses, adenoviruses

Zoonoses ( animals, insects)

Togaviruse, flavivirues, bunyaviruse, arboviruses, arenaviruses, rabies virus

Transmission via non-controlled blood, fluids

HIV, HTLV-1, hepatitis B,C and D virus, cytomegalovirus

Sexual contact

Blood-borne viruses,

herpes simples 2, humanpapilloma virus

Maternal-neonatal transmission

Rubella virus, cytomegalovirus, B 19

virus,echovirus

, herpes simplex virus 2, Varicella-zoster virus, HIVs

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

Enterovirus

and 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

Viral infection epidemiological types

We account three epidemiological

types:

sporadic

,

epidemic,

pandemic

Sporadic

C

oncern 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:

E

xample is that HBV chronically people infected form a reservoir of the virus and establish the

endemicity

of that infection.

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)

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 .

Congenital Viral Infections.

Foetal

and 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

Current viral infections and diseases

Main

foetal

and neonatal viral infections

Rubella virus

causes in utero infections

Cytomégalovirus

with 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

and

zoster virus

that cause in utero and perinatal infectionsB 19 Parvovirus cause in utero infections.HIVs can cause in utero and peri-natal infections,HBV may cause peri-natal infections

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

Paramyxoviridae

family

,

Rubella

caused by a RNA virus, belonging to genus

Rubivirus

of

Togaviridae

family,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 Varicellovirus genera of Alphaherpesvirinae sub-family from Herpesviridae family. 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.

Respiratory

tract viral infections

Those called respiratory virus share an exclusive tropism for respiratory

epithelial ciliated

cells. We account with

:

flu

Influenza

A and

B

Para-influenza

1, 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, laryngitis by Parainfluenza virus, bronchiolitis by Syncitial respiratory virus flu by influenza virus. But also different viruses can cause a same clinical syndrom

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

Hepatitis causative agents

Virus

Family

Genome of

Types of transmission

HVA

Picornaviridae

Heparnavirus

RNA

Enteral ou oro-fecal

HVB

Hepadnavirus

DNA

Parenteral, mother-

neonatal

sexually

HVC

Flaviviridae

RNA

Parenteral

HVE

Calciviridae

RNA

Enteral or oro-fecal

GB-A

GB-B

GB-C/VHG

Flaviviridae

RNA

Parenteral

TTV

Parvovirus

DNA

Parenteral

Gastroenteritis causative agents

Those

viruses are:

Rotavirus

Astrovirus

enteric

Adenovirus

serotypes 39,

40

Norwack

agent

Coronavirus

All

these gastroenteritis associated viruses are not detected at

same frequency.

Rotavirus

and new enteric

Adenovirus are the more frequently detected from newborn gastroenteritis

. Others interest children

and adults are rarely isolated.

A

new vaccine is available against

Rotavirus

Central

nervous system viral infections

These

acute clinical syndromes may

be:

Aseptic

meningitis or AAP for Acute anterior poliomyelitis that is

caused

by

Polioviru

s;

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 PapovirusTropical spastic paralysis (T.S.P) due to human T leukemia virus type 1 (HTLV1) an Oncornavirus belonging to Retroviriday familyAIDS dementia associated to Human Immunodeficiency Virus type 1 or 2, HIV 1 and 2, species of genera Lentivirus and Retroviridae family