INTRODUCTION
Paediatric diarrhoea remains one of the major causes of death in young children. This is especially so in Asia, Africa and Latin America where it causes millions of deaths in the age group 0-4 years.
The main factors for high incidence and mortality are unsafe water or inadequate sanitation, requiring social, economic and political solutions. The immediate causes are often of an infectious nature and include a variety of pathogenic micro-organisms. A range of bacteria and parasites has been identified = enterotoxigenic Escheritia coli, salmonella, shigella, cholera, other vibrio bacteria, as well as cryptosporidium, but these account for well below half of investigated cases.
A number of different viruses cause diarrhoea, of which the most important is the family of ROTAVIRUSES.
Two strains of adenovirus (40 and 41) have also been associated with diarrhoeal disease.
A group of "small round viruses" (discovered by electron microscopy)
have been linked by genetic techniques as closely related to the previously
described "Norwalk" agent, associated with vomiting and diarrhoea.
VIRUS MORPHOLOGY:
Particles are 70 nm round, double shelled, enclosing a genome of 11
segments of double stranded RNA.
The virus is hardy and may even survive in sewage, despite stringent
treatment.
Human rota virus has proved difficult to culture in vitro, but the
serologically related monkey and calf rotaviruses grow easily in cell culture.
CLINICAL:
Essentially an ingestion disease (faecal-oral route)
Incubation is short : 1 to 3 days.
Illness: Sudden onset watery diarrhoea, with or without vomiting.
May last up to 6 days (or longer if immunocompromised). The disease is self
limiting.
Complications: Dehydration may result, this can be severe and
life threatening in young children.
Treatment: No specific treatment of viral infection is available
nor is it really required.
Treatment is aimed at prevention and/or treatment of dehydration by
oral and/or intravenous fluids and electrolytes
Diagnosis: Detection of virus in stools (peaks at day 3 or
4 of diarrhoea):-
(Antibody can be detected but is not clinically useful)
Prevention:
Non specific factors: improved hygiene, education, clean water
Specific - Breast feeding helps to provide passive immunity in the
newborn (from maternal antibodies),
Vaccination is still experimental.
EPIDEMIOLOGY
Infection is found world-wide.
All ages can be infected and reinfection can occur (usually asymptomatic).
Age: Infections at < 6 months age and > 5 years of age
tend to be asymptomatic and give degrees of protection against diarrhoeal
infection.
Maternity hospitals commonly have resident strains which readily cause
asymptomatic infections of new- borns.
Seasons: In temperate '1st world' populations rota virus is
the main cause of winter gastroenteritis .
In tropical and developing countries, rotavirus diarrhoea occurs all the
year round ,but with a peak in summer. However, it is only one of
a variety of pathogens causing diarrhoea.
Vaccine: In view of the major role of dehydration from diarrhoea
as a cause of childhood death, the World Health Organisation has waged an
intensive campaign for
No vaccine is currently used routinely, but several candidate vaccines are
being evaluated in children: e.g. animal strains, attenuated human strains,
animal-human recombinant strains, designed to cover all 4 main human pathogenic
strains.
The prevention of severe dehydration is the main aim, rather than
totally preventing infection.
A limited number of strains of ADENOVIRUS have been causally related to childhood
diarrhoea.
They do not grow in cell cultures and were discovered by Electron Microscopy.
( Recently there has been limited success in special cell culture systems).
They are classified in the 40/41 serogroup of adenoviruses.
Viruses can be isolated from stools,as well as throat and respiratory secretions.
Adenoviruses in stools can be detected by latex agglutination, and the 40/41
strains can be detected by specific molecular techniques.
The exact role or significance of these strains in the global picture of
childhood diarrhoea, especially in developing countries, is not yet fully
established.
Apart from this 40/41 group, other adenoviruses may be found in the stools of asymptomatic children. .
Apart from the severe problem of diarrhoea in young children there have been
outbreaks of infectious gastro-enteritis in adults. Electron microscopy
(of the stools) has revealed two main groups of virus particles which do
not grow in cell culture.
NORWALK agent (33nm in size)
'Common source' type of explosive outbreaks of gastroenteritis, with
limited secondary spread to household contacts, have been described. These
often occur in institutions, or follow common source ingestion episodes e.g.
celebratory feasts.
Vomiting with cramps are more common symptoms than the diarrhoea.
At first, the virus was seldom identified as there were no easy diagnostic tests - only expensive electron microscopy of stools. Serology was limited, as the only antigen available was prepared from known infected stools - not in plentiful supply!
Recently, molecular techniques have shown that many of these agents from different parts of the world are essentially similar. Molecular techniques have also enabled the expression of viral antigens that can be used in serological surveys. For example, a 1993 survey in the UK has shown that Norwalk infection is apparently a common silent infection in childhood. Antibody prevalence rises to about 16 years of age and then begins to level off, with 80% of persons above 30 years being seropositive. It was hitherto believed that Norwalk infections were rare, - it now seems that the disease is rare, not the infection.
Illustrations and layout by Linda Stannard, 1999 ©