communicable diseases

32 Pages·2017·10.57 MB·English

communicable
diseases
Cover:
Beware: person-to
person infection !
Original design by
Peter Davies
IX ISSN 0043-8502
World Health is the official illustrated
magazine of the World Health Organization.
Editor:
John Bland
Deputy Editor:
Christiane Viedma
This Month's Theme Editor:
Catherine Dasen
Art Editor:
Peter Davies
News Page Editor:
Peter Ozorio
World Health appears ten times a year in English,
French, Portuguese, Russian and Spanish, and
four times a year in Arabic and Farsi. The German
edition is obtainable from German Green Cross,
Schuhmarkt 4, 3550 Marburg, FRG.
Articles and photographs not copyrighted may be
reproduced provided credit is given to the World
Health Organization. Signed articles do not necess
arily reflect WHO's views.
World Health, WHO,
Av. Appia, 1211 Geneva 27, Switzerland.
Contents
Communicable diseases
by Giorgio Torrigiani and William Parra . 3
Vaccines and vaccination
by Gordon L. Ada . . . . . . . . . . . . . . . . . . 5
Influenza is preventable
by Yuri Ghendon . . . . . . . . . . . . . . . 8
Hepatitis B : eradicable?
by Wolfgang Jilg and Friedrich Deinhardt. 10
Leprosy: light at the end of the tunnel
by John Maurice 13
"Information may be their only defence"
by Martha Leslie-Harwit and
Andre Meheus . . . . . . . . . . . . . . . . . . 16-17
AIDS in Mexico
by Jaime Sepulveda 18
Yellow fever gains ground
by Thomas P. Monath . . . . . . . . . . . . . . . 20
Sleeping sickness-re-awakes
by Pierre Cattand 24
From surviving smallpox to
preventing measles
by Edna Adan lsmail . . . . . . . . . . . . . . 26
Cooperation with industry
by John F. Dunne . . . . . . . . . 27
Talloires: a quiet revolution
by Robert Walgate . . . . . . . . . . . . . . . . . 28
News Page . 30
2 W ORLD HEALTH, July 1988
Communicable diseases
by Giorgio Torrigiani and William Parra
Or Giorgio Torrigiani is Director of WHO's Division of Communicable Diseases and
Mr William Parra is Management Support Officer for the same division
C
ommunicable diseases, in global scale, and put the brake on the increase throughout the world,
WHO's parlance, are those attempts to develop many tropical with a general shift towards youn
which are transmitted either areas. Efforts to control them may ger age groups. And even while the
from human to human, from ani drain a sizeable proportion of the number of pathogens found to be
mals to people, carried to us by in available resources in countries sexually transmitted has been in
sects or other "vectors," or con where these diseases are endemic. creasing in recent years, the disease
veyed to us in the air we breath, the An estimated 17.5 million people spectrum in this area has been fur
water we drink and the very ground are infected with onchocerciasis ther complicated by the emergence
we tread on. (river blindness) and about 340,000 of acquired immunodeficiency syn
A large number of them are so are blind as a result; an additional drome (AIDS) and its various dis
firmly entrenched in human com ease manifestations.
munities that we tend to take them A matter of persistent concern is
for granted-infections like the the increasing resistance of mi
common cold, or influenza, or crobes to drugs as well as resistance
chickenpox. It is easy to forget that, of insects and other vectors to
for at least two millennia to our chemical pesticides-trends that im
knowledge, smallpox too was "tak pede progress in disease reduction
en for granted" by generation upon and increase the costs of control
generation ; yet just 13 years of operations. Rapid expansion of the
global effort sufficed to wipe it cities, the boom in travel and popu
from our planet. lation movements, and increasing
Many of these communicable dis trade in human and animal foods
eases, in fact, are fostered by low within and between countries-all
standards of environmental sanita these have increased the risk of dis
tion, malnutrition, inadequate so eases being rapidly transmitted
cial and economic development, from one country or region to
and general ignorance of simple another.
changes in behaviour that could The burden of many communi
help to avoid infection. And some cable diseases could undoubtedly
diseases contribute to levels of sick be reduced by environmental man
ness, disability and death-parti agement, by which we mean pro
cularly in children aged under five viding safe water supply and the
in the developing world-that are Vaccination has proved to be one of the sanitary disposal of refuse, waste
most cost-effective methods of protect
simply unacceptable in the closing water and excreta, ensuring ade
ing human health.
decades of the 20th century. quate housing, safeguarding the en
· Acute diarrhoea! diseases alone vironment from chemical pollution
Left: A household put at risk by inade
(including cholera) represent the and other control technologies. But
quate housing in the Western Pacific.
primary cause of child mortality in building up these control measures
Photos WHO/Zafar
developing countries and contri is, of necessity, a slow process. In
bute to one-third of the 15 million big cities, they require a large capi
deaths in this age group each year. one million individuals are consid tal investment, while in the vast ru
Another one-third result from ered to have suffered significant ral areas of the Third World, envi
acute respiratory infections, pri loss of sight, leaving them partially ronmental management can only
marily pneumonias. In addition, disabled. take place as part of the overall
these infections are the leading Tuberculosis and leprosy still social and economic development.
cause of sickness in virtually all constitute significant public health So emphasis will continue to fall
countries. problems, while viral haemorrhagic on traditional methods of prevent
Parasitic diseases, in particular fevers continue to have a major im ing and controlling communicable
malaria, filariasis, schistosomiasis pact, particularly during epidemic diseases. These methods include
and trypanosomiasis, remain as se outbreaks, in many countries. Sex setting up and maintaining surveil
rious public health problems on a ually transmitted diseases are on lance systems to enumerate and
WORLD HEALTH, July 1988 3
Communicable diseases
evaluate all cases that occur, a ma to avoid disease, to actively seek though no reliable figures on immu
jor first step in determining the health and maintain healthy life nization coverage were available at
distribution, responsible factors, styles, all of which will directly con that time, it could be estimated
severity and extent of each com tribute to the prevention or early from the total quantities of vaccines
municable disease. This in turn treatment of many communicable being used, that fewer than five
provides the necessary base-line diseases. percent of children in their first
information for setting the right Research is another important year of life were receiving the vital
priorities for applying disease con component of disease prevention third dose protecting them from
trol strategies. and control activities, and thanks to polio, as well as diphtheria, whoop
Other control efforts include modern biotechnology the hunt is ing cough and tetanus (DPT). As a
building up manpower resources on for new and inexpensive drugs, result, some five million children
through training programmes in diagnostics and vaccines. It is par died each year from vaccine-pre
technical and managerial areas, in ticularly important to develop new ventable diseases; another five mil
creasing the number of skilled per drugs to counter the many disease lion more were crippled, blinded or
sonnel engaged in communicable causing organisms which are be mentally damaged.
disease control activities, and de coming increasingly resistant to Today, immunization coverage in
veloping simple diagnostic tech existing antibiotics. the developing countries (excluding
niques and inexpensive means of Vaccines, by contrast, have China) had increased to 50 percent
treatment that primary health care proved in recent history to be one of in 1987 for a third dose of DPT or
workers can deliver even in remote the most cost-effective methods of polio vaccine. The stage is now set
villages. And today there is re protecting human health. The in to add newly available vaccines to
newed interest in "health promo tensive immunization programme existing immunization schedules,
tion" aimed at showing people how mounted by WHO was the key to the and to further strengthen national
global eradication of smallpox by managerial capabilities to ensure
1977. Inspired by this success, WHO immunization and other kinds
Tuberculosis remains a significant pub initiated, in 1974; the Expanded of health care for mothers and
lic health problem in many countries.
Programme on Immunization, a children.
This young Burmese mother is being
programme designed to immunize WHO continues to promote and
treated for TB in her own home.
the children of the world against six support several programmes aimed
Photo WHO common childhood diseases. AI- at developing vaccines, whether to
control more effectively those dis
eases for which vaccines do not ex
ist, or to improve the efficiency of
existing vaccines. Theoretically at
least, it should now be possible to
design vaccines which provide long
term protection without any of the
side effects observed in the past.
Despite encouraging results, new
vaccines for general use are not go
ing to be available overnight.
So WHO is not slackening its ef
forts to prevent and control com
municable diseases by existing and
conventional means. But a research
and development effort of this mag
nitude, and the introduction of
improved disease prevention and
control strategies, cannot be under
taken without encouraging coun
tries to build up still further their
national capabilities in such fields
as epidemiology, biological re
search and health systems research.
In turn the essential elements of
these new strategies have to be in
corporated rapidly into the curri
cula of training institutions, and
health staff will need continuing
education and complementary train
ing facilities. It goes without saying
that WHO will continue to do its ut
most to collaborate with Member
States and strengthen their capacity
and efficiency in all these fields. •
4 WORLD HEALTH, July 1988
Vaccines and vaccination
by Gordon L. Ada
Professor Gordon L. Ada is visiting Professor at Johns Hopkins University, USA
I n ancient times, it was observed the basis of the vaccine but it had to Measles, rubella ("German mea
that those who survived an in be inactivated in a special way be sles"), yellow fever and polio vac
fectious disease seldom suffered fore it could be safely administered. cines can give life-long protection
a second, similar sickness; and this The six vaccines against the com from these diseases. Though vac
was particularly apparent in the mon childhood diseases which form cine administration may cause
case of a disease like smallpox the basis fo WHO's Expanded Pro some side-effects, a comparison of
which left characteristic pockmarks gramme on Immunization are pre the incidence of complications fol
on the skin. Sometimes a mild in pared by one or other of these lowing infection with the wild-type
fection could be related to the site three procedures : the measles and measles virus versus the vaccine
of the disease symptoms, and this polio vaccines are attenuated dramatically demonstrates the ad
led to the practice of deliberate in strains of these viruses, and an inac vantage of vaccination. In the Uni
fection with the disease agent at tivated preparation of polio virus is ted States, immunization of chil
these sites-a hazardous procedure. also available; BCG against tuber dren with measles vaccine prior to
The first demonstrably safe pro culosis is an attenuated form of the school entry is now required by
cedure for preventing infection tubercle bacillus; the pertussis vac law, with the result that indigenous
-the process now called vaccina cine is an inactivated preparation of measles has virtually disappeared
tion-was carried out in 1796 by the bacteria that cause whooping from that country. Though widely
Edward Jenner. He inoculated a cough; the diphtheria and tetanus used, BCG has given variable re
boy with infectious material from vaccines are composed of the inac sults. It has proved to be an effec
cows (cowpox virus) and then tivated poisons (toxins converted to tive vaccine for infants but has giv
showed that he was immune from toxoids) secreted by those bacteria. en variable results in adults. A trial
smallpox by injecting him with ma of this vaccine in South India
terial from a victim's smallpox showed such poor protection
scab! Louis Pasteur later developed against tuberculosis that, because
(initially by chance) the means of of the continuing global importance
changing the properties of microbes of this disease, it was clear that we
so that their potential for causing needed more detailed knowledge of
disease (a property called viru the biology of the bacterium and of
Lence) was much reduced without the immune responses that would
greatly affecting their ability to in give immunity from infection. This
duce an immune response. This Cowpox sores on a milkmaid's led to the establishment, in 1984, of
process of attenuation was subse hands inspired Dr Edward Jenner the WHO Vaccine Development Pro
quently used to develop some of to develop the vaccine that eventu gramme which supports research
our most successful vaccines, par ally eradicated smallpox. on a number of viral and bacterial
ticularly to control diseases caused Photo WHO diseases for which new or improved
by viruses. vaccines are needed.
Viruses and many bacteria cause These vaccines have reduced the
disease by damaging or killing the There are about 50 vaccines for burden of infectious disease to a
cells they infect; consequently, a human use currently approved or much greater extent in developed
vaccine aims to prevent infection of under trial. With few exceptions, than in developing countries, partly
these cells by the virus or bacteri they are for the control of viral or because of wider coverage of the
um. Many vaccines consist of the bacterial diseases, and those in population in the former but also
live, attenuated organism; or, if common use vary in their efficacy. because the other infections are
such a preparation is either not The live attenuated viral vaccines much more prevalent in the latter
available, or cannot be made, the are generally the most effective. countries. The wHo Programme on
virus or bacteria is inactivated World-wide use of the smallpox Tropical Diseases Research (TDR)
(killed) before being administered. vaccine, based on vaccinia virus was established to support research
Other bacteria secrete powerful (vacca is the Latin for a cow) and aimed at controlling one bacterial
poisons which damage the host's progressively developed since Jen (leprosy) and five parasitic diseases
cells, so protection against these ner's day, achieved the ultimate prevalent in these countries. At
bacteria called for a different strat goal of a vaccination programme present, a vaccine to control lepro
egy. The isolated poison was made the eradication of the disease itself. sy and several preparations aimed
W ORLD HEALTH, July 1988 5
Above : To remain potent vaccines must
be kept cold: in a hospital in Thailand,
a user's guide is printed on the
refrigerator.
Photo WHO/Zafar
Left : At a research centre on influenza
in the United Kingdom, nasal washings
are obtained from patients in order to
isolate viruses.
Photo WHO/D. Henrioud
Far right: There are about 50 vaccines
for human use; bacterial vaccines are
produced by fermenting bacteria in
these huge vats.
Photo Swiss Serum and Vaccine Institute ©
at different stages of the life-cycle Broadly speaking, there are two the DNA coding for antigens,
of the malaria parasite are under main new approaches towards vac transforming cells with the DNA so
trial. Similarly, WHO's Diarrhoea! cine development. The first at that the antigen is now produced by
Diseases Control Programme tempts a synthetic approach by these cells and can be used as a vac
(CDD) aims to develop means of making in the test tube those parts cine. A variation of this approach is
controlling diseases of the gastro of the virus or bacteria or parasite to incorporate this DNA into an ex
intestinal tract, while new vaccines which are thought to be the most isting vaccine, such as the smallpox
to control rotaviral infections, important for stimulating the im vaccine, so that this well-tried vac
which cause serious diarrhoea in in mune response. The synthetic pre cine can be used to protect against
fants, and cholera are being tested. paration, composed of peptides, another disease, such as malaria.
The need for these and other vac should provide an entirely safe vac The smallpox vaccine did however
cines is great. A third of the world's cine, by contrast with existing vac cause side-effects, with occasional
population is at risk of malaria cines which may cause side-effects, deaths. Fortunately, novel ways of
infection and millions suffer from sometimes serious, in a very small making such a "hybrid vaccine"
simultaneous infection by several proportion of recipients. However, both more safe and more effective
parasites. The appearance of AIDS the as-yet-unresolved question is: than the parent vaccine have re
due to infection by the human im will such vaccines be as effective cently been described, but such
munodeficiency virus, HIV, is al in preventing disease as the con preparations have yet to be licensed
ready of major concern in devel ventional approach? If used by for human use.
oped countries but seems certain to themselves, the answer is No! There have also been advances in
have devastating consequences in They must be combined with other developing oral vaccines. A "gene
some developing countries. What molecules and administered with tically-disabled" form of a Salmo
can the new knowledge of immuno an adjuvant (a preparation which nella organism, which can be taken
logical processes and the new tech enhances the immune response to orally, has been successfully used to
niques of the molecular biologists the peptide). protect against typhoid fever in tri
contribute to making effective vac The second approach is to use als in Egypt. DNA coding for an
cines to control these diseases? techniques which involve isolating important antigen of the organism
causing cholera has been incorpo
rated into this Salmonella, and tri
Serious reaction For every
als are in progress to establish
following 100,000 cases
whether this hybrid vaccine will
Measles Pneumonia Convulsions Brain damage Early death now also give protection against
infection 5,000 720 280 10
cholera. If so, it can readily be ap
preciated that such hybrid vaccines
Measles ' offer the possibility of developing
vaccination 1 60 0.1 0.02
multivalent vaccines. In other words,
6 WORLD HEALTH, July 1988
Vaccines and vaccination
some day a single vaccine may pro
tect against several diseases-a pre
cious boon in tropical countries
where there is so much infectious
disease.
Scientists working in these areas
are justifiably confident that apply
ing these new approaches should
lead to the development of vaccines
against many diseases, particularly
such parasitic diseases as malaria.
But the future is not entirely rosy.
Infectious micro-organisms have
eo-evolved with man over millen
nia, and the "cleverest" micro-or
ganisms have developed means of
by-passing man's defences so that
they continue to survive and to
plague us. One example i.s the influ
enza virus. By continually changing
its properties, this virus escapes
pre-existing antibodies and infects
susceptible cells. This is why the
currently available vaccines are
only partially successful. The virus
can be controlled at a later stage,
but not before it has caused the
Or Barry Bloom, in his Presidential
Address to the American Associa
tion of Immunologists in 1986, pre
sented a graphic summary of the
situation in tropical and other
developing countries. "This is the
Third World, in which 75 per cent of
the planet's population lives, where
86 per cent of all children are
born and 98 per cent of all infant
and child deaths occur, and where
10 kids die of vaccine-preventable
illness every minute."
symptoms of influenza and has
spread to other people. It is the
"perfect" virus; most people easily
survive an attack and the virus con
tinues to flourish!
In the process of adapting to hu
man hosts, HIV is still a major kill
er and, unfortunately, it seems to
have nearly all the cards on its side.
As well as the trick of changing its
properties, like the influenza virus,
it infects and destroys those cells
which are an essential part of the
immune system. For these reasons,
it is difficult to develop a vaccine
which would protect those at risk
from infection by this virus. Our
hopes for controlling AIDS rest on
educating people about transmis
sion of the virus, and on the not un
realistic hope that an effective drug
to control the infection will speedily
be developed. •
WORLD HEALTH, July 1988
Influenza is preventable
by Yuri Ghendon
Or Yuri Ghendon is Senior Virologist with WHO's section of Microbiology
and Immunology Support Services
I nfluenza-'flu-is for most people enza infection. In fact, 10,000 or tality is not only a direct result of
an unpleasant illness that sends more excess deaths have been do pneumonia, but also of cardio-pul
them to bed for a few days and cumented in the USA during each monary or the chronic diseases that
leaves them feeling weak. But it is of 18 different epidemics from 1957 are exacerbated during influenza
also a potential killer. to 1985. infection. In addition, the days lost
In the United States alone for ex Some 80 to 90 per cent of the ex from school and work, and the hos
ample, in 1957, the Asian strain of cess deaths attributed to pneumo pital care required for complica
influenza virus caused an estimated nia and influenza during epidemics tions, result in a very high cost of
70,000 deaths; the Hong Kong have occurred among persons of 65 influenza to society.
strain that appeared in 1968 caused years of age or more, although 'flu Three types of human influenza
about 30,000 deaths in the same associated deaths among children viruses, A, B and C, were discov
country. Even in years not associat or previously healthy adults under ered in 1933, 1940 and 1947 respec
ed with antigenic shift in the virus, 65 years of age are reported during tively. Only type A is associated
many people die as a result of influ- major epidemics. This excess mor- with pandemics.
8 WORLD HEALTH, July 1988
Manufacturing influenza vaccines in
In fact there is plenty of evidence phylactically and therapeutically
Switzerland. But doubts still linger
to show that influenza vaccines can (administered between 24 and 48
about their efficacy.
protect individuals and indeed, if hours after the onset of symptoms).
Photo Swiss Serum and Vaccine Institute ©
used properly, may protect 70 to In prophylactic use, a 70 to 90 per
Below: For most people, 'flu means a
80 per cent of vaccinees in the com cent reduction in infection has been
bout of sneezing and a few days in bed.
munity as a whole. achieved. It is unfortunate that
But it is a potential killer.
Vaccination strategies have two these drugs have been so little used
Photo WHO/D. Henrioud
main objectives: to protect individ to protect against influenza
These viruses are variable and uals who are at particular risk from A infections.
can change the antigenic specificity disease (the elderly, the chronically On the other hand, chemopro
of their envelope proteins-haemag sick, people living in institutions phylaxis with these drugs is not a
glutinin and neuraminidase. They under crowded conditions and so substitute for vaccination, because
thus escape the neutralising anti on) ; and to protect other defined there is no protection against the B
bodies that we have developed sectors of the population (such as virus, and also because patients
through previous infections or vac schoolchildren, or factory work may fail to take the drug for the full
cinations and that ought to protect ers). In the last case, vaccination 6 to 12 weeks of an epidemic peri
us. That is why the strains of may have direct benefit for the indi od. Aerosolised ribavirin has been
viruses used for the production of viduals involved and for the com recommended against influenza B,
influenza vaccines have to be munity as a whole. But it should be but its usefulness would possibly be
changed every one or two years. noted that in closed or semi-closed restricted to patients confined in
WHO's influenza programme essen settings, maximum benefit from im hospital.
tially consists of rapidly isolating munization is likely to be achieved Influenza is not a trivial disease.
and characterising all new strains in when more than about 75 per cent It kills many thousands of patients
order to make available for produc of the population are vaccinated, so every year and the cost of its
tion laboratories those that show as to exploit the advantages of depradations to any country's econ
substantial variation from the cur "herd immunity. " omy is enormous. But influenza
rent strains. WHO Collaborating Besides vaccines, there are good is preventable. By means of the
Centres for influenza in London antiviral preparations against the vaccines and antivirals now avail
and in Atlanta, USA, together with disease. Amantadine and rimanta able it is possible to protect indivi
110 national institutions for influen dine have proved in many con duals both in the high-risk groups
za in 79 countries all carry out sur trolled trials to be effective against and in defined sectors of the
veillance activities. Each year, to influenza A infections, both pro- population. •
wards the end of February, WHO
holds a consultation to draw up rec
ommendations for the composition
of influenza vaccines for the forth
coming season. It is now possible to
recombine the new antigenic vari
ant with a strain that has been
trained to grow rapidly in chickem
bryos, or with the cold-adapted at
tenuated master strain, and this re
duces the time needed to get into
large-scale vaccine production.
Two sorts of vaccines are now
available: those that are inacti
vated, concentrated and purified
for administration by injection and
live, attenuated, cold-adapted vac
cines destined for instillation or
pulverisation into the upper respi
ratory passages.
Even though this disease is a
widespread problem in many coun
tries, the existing 'flu vaccines are
among the least used vaccines avail
able. The need for annual revacci
nation, misconceptions about the
capabilities of the vaccines-many .
recipients expect them to prevent
all respiratory infections-and ques
tions about their efficacy have led
many physicians to conclude that
vaccination against influenza is not
worth the effort.
W ORLD HEALTH, July 1988
B;
Hepatiti~
eradicaBle ?
by Wolfgang Jilg
and Friedrich Deinhardt
Drs Wolfgang Jilg and Friedrich OeiQhardt are with)the
Max van Pettenkofer Institute, University of Munich
R ecent progress in developing it is a disease of particular risk to four weeks. This typical course
hepatitis B vaccines has groups, such as medical personnel, of acute hepatitis B has several
brought much closer the ul patients needing frequent blood variations. In about one per cent of
timate goal of controlling and elimi products (for instance, haemophi cases, acute fulminant hepatitis de
nating this disease- much as that liacs and chronic haemodialysis pa velops with an often lethal out
other viral disease, smallpox, was tients), persons with close contacts come; by constrast, many infec
eradicated. to HBV carriers, drug abusers who tions cause a mild illness without
Hepatitis B today remains one of share contaminated needles, male jaundice ("anicteric hepatitis") or
the most important global infec homosexuals and prostitutes. The may even occur without any symp
tious diseases ; every year, around prevalence of HBV infection toms at all.
40 million people die from the con ranges from about 20 per cent in Two characteristics make infec
sequences of chronic hepatitis. medical personnel to more than 90 tion with HBV so important: the
About six million people develop per cent in haemophiliacs who have development of chronicity (persis
hepatocellular carcinoma, a disease received frequent treatments with tence over a long period of time),
which is also associated with hepati non-inactivated clotting factors pre and the association of HBV with a
tis B virus (HBV). Between 200 pared from unscreened human type of cancer called hepatocellular
and 300 million people carry HBV blood. carcinoma. Most patients recover
chronically, and they constitute the The acute disease caused by from acute hepatitis, but five to ten
major reservoir of this infectious HBV does not differ from hepatitis per cent continue to carry the virus
agent. due to other viral agents, such as in their livers for a long time, even
Hepatitis B is highly endemic in hepatitis A virus or the hepatitis for a lifetime. And even patients
South-East Asia and in Central and non-A, non-B viruses. In a typical without any signs of acute hepatitis
Southern Africa. Some 70 to 80 per case, the disease starts after an in may develop chronic infections.
cent of people living in these re cubation period of two to six These chronic HBV carriers may
gions have had contact with the vi months. For several days, there are remain asymptomatic or they may
rus, of whom five to ten per cent (in only vague symptoms similar to develop chronic hepatitis, of which
certain areas even 20 per cent or those of other viral infections. They there are two forms : chronic persis
more) are chronic virus carriers. In include fever, anorexia, weakness tent hepatitis, which may eventual
industrialised countries, such as the and headache ; a more specific ly resolve itself; and chronic active
United States and the western and symptom is right upper quadrant hepatitis, which usually proceeds to
northern parts of Europe, the hepa pain with local tenderness. This so cirrhosis, chronic liver failure and
titis B prevalence is rather low, not called "prodromal" phase is fol death.
exceeding five or ten per cent, with lowed typically by jaundice (yellow Irrespective of the clinical condi
a chronic carrier rate well below ing of the skin and mucous tion, all chronic carriers are a po
one per cent. In these countries, membranes) lasting for about two tential source of infection to others,
10 WORLD HEALTH, July 1988