P.vivax malaria: the neglected malaria and why it matters...Kamini Mendis P.vivax malaria: the...
Transcript of P.vivax malaria: the neglected malaria and why it matters...Kamini Mendis P.vivax malaria: the...
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Kamini Mendis
P.vivax malaria: the
neglected malaria and why
it matters
MMV Stakeholders’ Meeting
6-8 November 2012, Delhi, India
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RBC Duffy negativity >95%
Plasmodium vivax “0%” in endemics
~ 1% in travellers
Guerra, CA et al. PLoS Negl Trop Dis 2010 4 (8), 774
Global spatial limits of P.vivax transmission
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Proportion of P.vivax infections increase as malaria is controlled
(annual data from Sri Lanka 1980 – 2012)
50
55
60
65
70
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85
90
95
100
0
100,000
200,000
300,000
400,000
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1980 1985 1990 1995 2000 2005 2010 2015
Pro
po
rtio
n (
%)
of
P.vi
vax
Tota
l mal
aria
cas
es
Year
Total malaria cases
Proportion of P.vivax
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The proportion of P.vivax higher in countries where transmission intensity
is low – SEARO countries, 2009
0.1
1
10
100
1000
0 10 20 30 40 50 60 70 80 90 100
An
nu
al P
aras
ite
Inci
den
ce o
f M
alar
ia (
per
100
0)
Proportion of P.vivax infections
MMR
MMR
BHU
TLS
BAN
THA
INO
IND
SRL NEP
KRD
R2 = 0.444
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0.01
0.10
1.00
0.000 0.001 0.010 0.100 1.000 10.000
Annual malaria incidence rate (%)
Pro
po
rtio
n o
f P
.viv
ax
: :
% P
las
mo
diu
m v
iva
x
100
10
1
Total Annual Malaria Incidence Rate (%)
0.000 0.01 0.001 0.1 1.0 10.0
(blue) Asia: Bangladesh, Bhutan, Cambodia, China, India, Indonesia, Lao PDR, Malaysia, Myanmar. Nepal, Papua New Guinea, Philippines, Solomon Islands, Sri Lanka, Thailand, Vanuatu and Vietnam,
(green) Eastern Mediterranean: Afganistan, Iran, Iraq, Oman, Pakistan, Saudi Arabia, Syria and Yemen.
(pink) Latin America: Argentina, Belize, Bolivia, Brasil, Colombia, Costa Rica, Dominican Republic, Ecuador, El Salvador, Guatemala, French Guyana, Guyana,Haiti, Honduras, Mexico, Nicaragua, Panama, Peru, Suriname and Venezuela.
(orange) Central Asia & the Caucasus: Armenia, Azerbaijan, Tajikistan and Turkey.
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Persistent liver forms cause relapses – GENERATION OF CASES WITHOUT INOCULATION
Preferentially invades reticulocytes – LOWER PARASITE DENSITIES
CONTINUOUS IN VITRO CULTURE STILL NOT POSSIBLE
Mature gametocytes appear in peripheral blood simultaneously with asexual stages – PARASITE HAS ESCAPED EVEN BEFORE PATIENT PRESENTS FOR TREATMENT
Shorter development in mosquitoe – LESS SUSCEPTIBLE TO VECTOR CONTROL MEASURES WHICH REDUCE THE MOSQUITO LIFE SPAN.
Distinctive biological features of P.vivax
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Thrives in highly favourable transmission conditions to outcompete P.vivax
Also more vulnerable to any form of malaria control
Does poorly in well managed human environments
Can persist under a variety of less favourable conditions
Less amenable to current control methods sp., early treatment than to transmission control
P.falciparum
P.vivax
As more powerful antimalaria campaigns are put into effect,
primarily against P.falciparum, the residual burden of malaria
will become increasingly that of P.vivax
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Pro
po
rtio
n (
%)
of
P.v
ivax
Outside of Africa Africa
P.falciparum
P.vivax
P.vivax malaria: 75 - 90 million cases annually Mendis K et al., 1998
Other estimates: 132 - 391 million (Hay et al., 2004, Price et al., 2007)
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Global distribution of Plasmodium vivax cases
(1993 – 1997)
C.America &
Caribbean
(4%) [84%]
Asia
56% [48%]
C.Asia &
Caucasus
(<1%) [99%]
Africa
13% [4%]
The World Health
Report 1999
Travellers
(0.02%)
[10-30%] Korea
(<1%)
[100%]
S.America
(11%) [70%]
Eastern
Mediterranean
15% [80%]
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Clinical burden of P.vivax malaria
Acute infection
– extremely debilitating febrile illness
Reputation of being a benign, non-life threatening
– but severe and fatal infections have and are being reported
– high TNF-alfa levels, transiently even higher than those in severe and
complicated P.falciparum infections
Anaemia – main pathological consequence, both acute and chronic
Effects on pregnancy
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• Vivax malaria occurs characteristically in low endemic
situations.
• Both adults and children suffer from vivax malaria.
• Where vivax prevails, males (15-50 yrs) are at high
risk
• School children suffer high absenteeism and impaired
learning
• Massive economic and social costs, and cost to human
and nation development
Hallmarks of vivax epidemiology
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Current, key antimalarial interventions
Prevention
Insecticide-treated bednets/
/Long-lasting ITNs
Indoor Residual Spraying
Selective methods of VC
Diagnosis & Treatment
•Microscopy
•Rapid Diagnostic Tests
•Chloroquine/Artemisinin-based
combination therapies (ACTs)
+ primaquine
Effective surveillance and
response system
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Source:
2010
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Currently effective medicines against P.vivax
Against asexual blood stages
Chloroquine
Mefloquine
All current ACTs (except AS-SP)
Against dormant liver stages
Primaquine o Risk of AHA in G6PDd patients
o Long course of therapy
Tafenoquine – phase II b trials
MEDICINES NEEDED a medicine directed against pre-erythrocytic stages which is
short-course therapy,
safe
long half-life or as implants?
• medicines against the blood stages of P.vivax – which synergise with anti-
relapse medicines
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Global distribution of Plasmodium vivax
maximum distribution 19th century (pink)
late 20th century (purple)
Prepared by R Carter In
Mendis, K.N. et al.
Am.J.trop.Med.Hyg.(2001)
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“the ghost of a man, a sufferer from his cradle to his
grave; aged even in childhood and laying down in misery
that life which was but one disease”
John Macculloch, 1827
- and he or she laid down that life, on average, by
around 20 to 25 years of age.
An allegory of malaria