Biology Reference
In-Depth Information
Group III is the temperate or St Elizabeth-type strain that has a long period
of latency between the primary attack and the first relapse. Group II is inter-
mediate between these two types'. This intermediate group has not been
well characterised. The ratio of short- to long-latency relapse phenotypes
in Aligarh, Uttar Pradesh was estimated as 4:1 ( Saifi et al., 2010 ). A similar
ratio was observed recently in Kolkata ( Kim et al., 2012 ) ( Fig. 2.7 ). Overall
relapse rates from India have been relatively low by comparison with South
East Asia ( Gogtay et al., 1999 ; Singh et al., 1990 ; Prasad et al., 1991 ; Sinha
et al., 1989 ; Srivastava et al., 1996 ; Luxemburger et al., 1999 ; Silachamroon
et al., 2003 ). Data from travellers returning from the Indian sub-continent
have suggested that long-incubation-period P. vivax may be common in
the Punjab, which is consistent with evidence in the past from Northern
India, Pakistan and Afghanistan ( Warwick et al., 1980 ; Walker, 1983 ). There
are few data on temporal patterns of relapse in travellers in recent years
although studies in Eritrean immigrants to Israel, Turkish immigrants to
Germany, and US soldiers returning from Somalia all suggest the presence
of long-latency phenotypes in the countries of origin ( Kopel et al., 2010 ;
Eichenlaub et al., 1979 ; Smoak et al., 1997 ). Most travellers receive radical
treatment for vivax malaria in temperate countries, which may be more
effective against the long-incubation or long-latency infections than against
the tropical frequent-relapse phenotypes ( White, 2011 ).
In South East Asia, there is no evidence as yet for long-latency pheno-
types. Luxemburger et al. studied 342 children with acute vivax malaria
treated with chloroquine on the north-western border of Thailand
( Luxemburger et al., 1999 ). The 28-day cure rate was 97% [95% confidence
interval (CI) 95-99%] but by day 63, the relapse/re-infection rate was 63%
(95% CI 57-69%). Most reappearances of parasitaemia (85%; 121/143) were
symptomatic. Silachamroon et al. studied 316 adult patients in Thailand
with acute vivax malaria who were treated with artesunate monotherapy
( Silachamroon et al., 2003 ). Half the patients relapsed within 28 days. The
timing of the relapses suggested that very few, if any, relapses emerged
from the liver before the eighth day after starting anti-malarial treatment.
In Papua, Indonesia, 38% of patients relapsed within 6 weeks following
artemether-lumefantrine treatment (the total number may well have been
higher because of later emerging relapses) ( Ratcliff et al., 2007 ). In French
Guiana, the relapse rate in children was 70% (nearly all relapses occurred
within 3 months) but both recrudescence and reinfection could not be
excluded ( Hanf et al., 2009 ). Although South American P. vivax is generally
regarded as 'tropical frequent relapsing' in phenotype, a recent report from
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