An Observational Study of the Effect of Hemoglobinopathy, Alpha Thalassemia and Hemoglobin E on P. Vivax Parasitemia

BACKGROUND: The protective effect of α-thalassemia, a common hematological disorder in Southeast Asia, against Plasmodium falciparum malaria has been well established. However, there is much less understanding of the effect of α-thalassemia against P. vivax. Here, we aimed to investigate the proportion of α-thalassemia including the impact of α-thalassemia and HbE on the parasitemia of P. vivax in Southeast Asian malaria patients in Thailand. METHODS: A total of 210 malaria patients, admitted to the Hospital for Tropical Diseases, Thailand during 2011–2012, consisting of 159 Myanmeses, 13 Karens, 26 Thais, 3 Mons, 3 Laotians, and 6 Cambodians were recruited. Plasmodium spp. and parasite densities were determined. Group of deletion mutation (--(SEA), −α(3.7), −α(4.2)deletion) and substitution mutation (HbCS and HbE) were genotyped using multiplex gap-PCR and PCR-RFLP, respectively. RESULTS: In our malaria patients, 17/210 homozygous and 74/210 heterozygous −α(3.7) deletion were found. Only 3/210 heterozygous −α(4.2) and 2/210 heterozygous--(SEA) deletion were detected. HbE is frequently found with 6/210 homozygotes and 35/210 heterozygotes. The most common thalassemia allele frequencies in Myanmar population were −α(3.7) deletion (0.282), followed by HbE (0.101), HbCS (0.013), −α(4.2) deletion (0.009), and --(SEA) deletion (0.003). Only density of P. vivax in α-thalassemia trait patients (−α(3.7)/−α(3.7), --(SEA)/αα, −α(3.7)/−α(4.2)) but not in silent α-thalassemia (−α(3.7)/αα, −α(4.2)/αα, αα(CS)/αα) were significantly higher compared with non-α-thalassemia patients (p=0.027). HbE did not affect P. vivax parasitemia. The density of P. falciparum significantly increased in heterozygous HbE patients (p=0.046). CONCLUSIONS: Alpha-thalassemia trait is associated with high levels of P. vivax parasitemia in malaria patients in Southeast Asia.