Biology Reference
In-Depth Information
infections have a higher reported case-fatality rate among patients with
severe malaria than seen with either species alone ( Yadav et al., 2012 ;
Manning et al., 2011 ).
11. PATHOPHYSIOLOGY OF DISEASE IN VIVAX
MALARIA
11.1. Comparative Pathobiology of P. vivax
There are a number of differences in pathobiology between P. vivax and P.
falciparum that are important in understanding the pathophysiology of vivax
malaria (see Kitchen, 1949b ; Anstey et al., 2009 for reviews).
11.1.1. Parasite Biomass
Plasmodium falciparum invades RBC of all ages, and progresses to high para-
site burdens if uninhibited by treatment or host immunity, with parasite
biomass a major independent determinant of the risk of death ( Dondorp
et al., 2005 ; Yeo et al., 2008 ). In contrast, P. vivax has a very strong predilec-
tion for infecting RBCs that have emerged from the bone marrow within
the last 14 days ( Kitchen, 1949b ; Simpson et al., 1999 ), particularly early
in the course of infection ( Kitchen, 1938 ). This property contributes to
the lower parasite biomass seen in P. vivax infections. Unlike P. falciparum
infections, parasitaemias in vivax malaria rarely exceed 2% of circulating
RBCs ( Ross and Thomson, 1911 ; Kitchen, 1949b ; Field and Shute, 1956 ).
Although a high P. vivax parasite burden (140,000/µl) compared to that
usually observed has been reported in a fatal case of vivax ARDS ( Valecha
et al., 2009 ), this appears to be exceptional. Although the series reporting
parasite counts in severe vivax malaria have documented relatively high par-
asitaemias for P. vivax , all have been <100,000/µl (about 2% parasitaemia),
ranging from 6000 to 90,400 ( n = 11) ( Kochar et al., 2005 ), 680 to 28,847/
µl ( n = 17) ( Alexandre et al., 2010 ), 8400 to 60,000/µl ( n = 40) ( Kochar
et al., 2009 ) and 7600 to 60,000/µl ( Kochar et al., 2010 ). None of these
studies presented comparative data of parasitaemia between patients with
uncomplicated and severe vivax malaria. The correlation of P. vivax parasi-
taemia and disease severity has been limited by the use of semi-quantitative
measures (grading 1+-4+) frequently used in endemic areas, extensive pre-
treatment, lack of reporting and lack of comparison with uncomplicated
vivax malaria. Nevertheless, two recent studies have demonstrated an asso-
ciation between disease severity and semi-quantitative parasitaemia in P.
vivax infection ( Nurleila et al., 2012 ; Lanca et al., 2012 ).
 
Search WWH ::




Custom Search