First the bad
news . . .
J. Dick MacLean, MD; Brian J. Ward, MD
CMAJ 1997;157:1675-6
Drs. MacLean and Ward are with the McGill Centre
for Tropical Diseases, Montreal, Que.
© 1997 Canadian Medical Association
See also:
ropical
medicine is an ill-defined profession caught
philosophically between public health and clinical
medicine and geographically between the economically
constrained tropics and the well-heeled temperate
world. The literature describing the successes and
failures in this profession ranges from social policy
to microbial biology. The news from the tropics this
year has been cause for both celebration and
discouragement.
Public health
Bad news
The past year has seen the continued expansion of
several multinational epidemics and the emergence of
new ones. Dengue continues to reclaim territory
throughout the Caribbean and Central America, with
increased reports of dengue hemorrhagic fever in
countries that have not seen this problem for years.
The explosive cholera epidemic of 1991 continues to
grumble in large areas of South and Central America.
The malignant interaction between HIV and
tuberculosis is a dominant health issue in
sub-Saharan Africa and is beginning to have a
significant detrimental effect on tuberculosis
control programs in Southeast Asia. Tobacco products
continue to be aggressively marketed around the
globe, and cigarettes now kill more people in the
world than malaria or diarrheal disease.
Closer to home, the Canadian Red Cross is now
screening donors for a history of residence in west
Africa or areas where Chagas disease is endemic, in
an attempt to keep variant strains of HIV (i.e.,
those undetectable by routine screening) and Trypanosoma
cruzi out of the Canadian blood supply. Salads,
fresh fruit, meats and fish are now becoming
international travellers themselves; sporadic cases,
small outbreaks and epidemics of "developing
world" infections are increasingly linked to
food importation rather than foreign travel. For
example, the summer of 1997 was marked by a North
American epidemic of Cyclospora cayatanensis
diarrhea caused by raspberries imported from
Guatemala. Ciguatera fish poisoning was reported as a
result of the ingestion of barracuda imported from
the Caribbean.
In the face of clear evidence of increasing
microbial internationalism, an important piece of bad
news is the continued shrinkage of global and
Canadian resources devoted to international
development assistance in general and health
development initiatives in particular. In Canada, the
International Development Research Centre (IDRC) has
closed its health division. Recent important
contributions by this division included major
initiatives in malaria control strategies in Africa
(such as insecticide-treated bed nets) and the
launching of a much-needed evaluation, in Tanzania,
of the World Bank's controversial strategy for health
development. The Canadian International Development
Agency (CIDA) continues to cut Canada's overseas
development assistance, now at its lowest level in a
quarter of a century (0.31% of GNP).1 CIDA
claims to support evidence-based sustainable
development but has been too slow to pick up the
torch dropped by IDRC and provide adequate support
for the researchers who produce that evidence.2
Good news
The number of vaccines available and both
corporate and government interest in vaccination
appear to be increasing. Improved surveillance and
mass vaccination campaigns in 1997 have had a
dramatic impact on polio throughout the world and on
measles in the Americas. A decade of work
demonstrating the health benefits of supplemental
vitamin A has finally led to global implementation
efforts. Although the mechanism(s) by which vitamin A
influences health remain to be determined, an
analysis of studies in the developing world suggests
an overall benefit of approximately 30% in child
survival. There were increased efforts in 1997 to
control malaria through programs based on the
demonstrated efficacy of insecticide-treated bed
nets. The recent Canadian-backed international
agreement to ban the production, sale and use of
anti-personnel land mines is a notable accomplishment
in terms of both its result and the grass-roots
process that propelled the campaign. Web
communications systems (e.g., the ProMED email
discussion group and Web pages for WHO, the US
Centers for Disease Control and Prevention, the World
Bank and the Laboratory Centre for Disease Control)
have brought public health onto computer monitors
worldwide. We now follow the evolution of epidemics,
such as hand-foot-and-mouth disease in Malaysia and
meningococcal meningitis in the Sahel, by means of
daily bulletins. Because of this immediacy and the
abundant evidence that microbes care little for
international borders a great deal of attention has
been focused on the so-called emerging pathogens.
Clinical sciences
Bad news
Malaria prophylaxis for travellers is again in the
news. Highly visible and in some cases sensationalist
adverse publicity about the neuropsychologic side
effects of mefloquine are leading many travellers to
reject this drug. Although published studies clearly
demonstrate the benefits of mefloquine (it is indeed
the best prophylactic drug for many regions of the
world), the basis of the current debate is
unfortunately not scientific. Travel clinics will
need to renew their efforts to inform the travelling
public about the risks of both malaria and malaria
prophylaxis. Although new drugs for malaria
prophylaxis (including double-dose primaquine and the
combination of atovaquone and proguanil) are being
tested, the available data do not justify a great
deal of optimism. On another front,
multidrug-resistant tuberculosis continues to be a
major clinical threat to both patients and
caregivers.
Good news
Amebiasis has become much less confusing. It had
long been suspected on clinical grounds that Entamoeba
histolytica might have a split personality. New
antigen-capture tests are now available to
distinguish between pathogenic E. histolytica
and its more common, morphologically identical and
non-pathogenic "cousin," Entamoeba
dispar.3 Similar antigen-capture tests
have also been introduced for the diagnosis of
lymphatic filariasis (caused by Wuchereria
bancrofti) and African sleeping sickness (caused
by Trypanosoma brucei), culminating more than
a decade of basic science research. From 1995 to 1996
the reported prevalence of leprosy decreased from 2.3
to 1.7 per 100 000 in response to aggressive and
well-coordinated multidrug therapy programs. The
continued success and rapid expansion of "direct
observation of therapy" programs for
tuberculosis control make the point that we should
never hesitate to relearn things we already know.
Basic sciences
As far as tropical medicine is concerned, the
basic sciences have yielded mostly good news in the
year just past. Despite the dwindling resources of
the past decade,3 research in this area
continues to yield new insights and tools that permit
cautious optimism about some of the world's ills. New
vaccines against 2 of the major international
killers, rotavirus and respiratory syncytial virus,
are in the final testing stages. However, the high
development costs of these vaccines and other
products continue to challenge us to find ways to
ensure that the entire world benefits. Several groups
have generated convincing evidence in animal models
that cytokine manipulation will eventually help us to
treat and prevent leishmania infections.
Investigators have found a way to genetically
manipulate leishmania through the stable insertion of
transposable elements. Zhang and Matlawshewski4
have just discovered (and knocked out) a potent
leishmania virulence gene, and a number of
laboratories are racing ahead with leishmania
vaccines based on interleukin 12. Finally, a great
deal of data are being generated worldwide suggesting
that "naked DNA" vaccination (i.e.,
injection of plasmids containing defined proteins or
peptide sequences) will eventually help us address
health problems as diverse as chronic viral
hepatitis, HIV infection and malaria.
References
- Tomlinson B. Canada. In: Randel J, German T,
editors. The reality of aid 1997/8. An
independent review of development cooperation.
London: Earthscan Publications; 1997. p.
42-8.
- Hamilton R. The need for centres of health
research excellence in the developing world. Policy
Sci 1997;30:25-46.
- World Health Organization. Amoebiasis. Wkly
Epidemiol Rec 1997;72:97-100.
- Zhang WW, Matlawshewski G. Loss of virulence
in Leishmania donovani deficient in an
amastigote-specific protein, A2. Proc Natl
Acad Sci U S A 1997;94:8807-11.
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