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
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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
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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
arthropod borne viruses, such as Yellow fever virus, Dengue viruses, Rift
Valley fever virus.
Transmission ways of viruses
MODE
Respiratory transmission
VIRUSES
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 HIV, HTLV-1, hepatitis B,C and D virus,
blood, fluids
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
 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.
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 .
Current viral infections and diseases
 Congenital Viral Infections.
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Foetal and neonatal viral infections
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Childhood viral infections and diseases
 Acute Viral Respiratory Infections.
 Viral Infections of the Gastrointestinal Tract.
 Viral skin Infections
 Viral Infections of the CNS
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 infections
 B 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:
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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
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 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, GBC/VH-G et TTV.
All these viruses belong to different families
Hepatitis causative agents
Virus
Family
Genome of
Types
transmission
of
HVA
Picornaviridae
Heparnavirus
RNA
Enteral ou oro-fecal
HVB
Hepadnavirus
DNA
Parenteral, motherneonatal
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:
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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
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 type 1
(HTLV1) an Oncornavirus belonging to Retroviriday family
– AIDS dementia associated to Human Immunodeficiency Virus type 1 or 2,
HIV 1 and 2, species of genera Lentivirus and Retroviridae family