| Background Element |
| Malaria Genetics and Epidemiology |
Richard Culleton Email: Richard.culleton@gmail.com
Malaria
Natural history of the malaria parasite
The four human malaria parasites are members of a genus that includes some 180 species (Ash and Orihel, 1990). The genus
Plasmodium is thought to have evolved from a coccidian ancestor that was parasitic on an insect host (Garnham, 1966).The
Plasmodium genus is a member of the phylum Apicomplexa, the extant members of which are obligate intra-cellular animal
parasites. The Apicomplexa are themselves members of the Alveolata superphylum which includes ciliates, dinoflagellates,
perkinsida and marine alveolates. The phylum consists of 5000 described species, but there may be as many as 60,000 still to
be described (Escalante and Ayala, 1995). All members of the Apicomplexa contain a vestigial plastid called an apicoplast - a
discrete organelle bound by three or four membranes (Kohler et al., 1997). The origin of this organelle is likely to have been
in a “secondary endosymbiotic event” in which the ancestor of all Apicomplexans engulfed a photosynthetic unicellular alga
and retained the algal plastid (which was itself the product of a previous endosymbiotic event) (Palmer and Delwiche, 1996;
Wilson et al., 1996;Kohler et al., 1997). Supporting this theory is the evidence that present day Apicomplexa such as
Plasmodium and Toxoplasma have highly organized cytoplasmic compartments which are associated with organisms of a
phagotrophic nature (Robibaro et al., 2001).
The Apicomplexa phylum is thought to be very ancient, and may have originated earlier than the multicellular kingdoms of
plants, fungi and animals. The Plasmodium lineage may have diverged several hundred million years ago (before the
appearance of vertebrates), with the radiation that gave rise to human parasites beginning around 130 million years ago
(Escalante et al., 1995). Digenetic parasitism, a feature of Plasmodium and other Apicomplexa may have independently
evolved several times within the phylum (Barta, 1989; Escalante et al., 1995). The phylogenetic relationship of the extant
human parasites is somewhat contentious, with debate ongoing about the origin and age of P. falciparum in particular (see
Tanabe et al. (2004).
References
Ash,L.R. and Orihel,T.C. (1990). Atlas of Human Parasitology. ASCP press, Chicago.
Garnham,P.C.C. (1966). Malaria Parasites and other Haemosporidia. Blackwell, Oxford.
Escalante,A.A. and Ayala,F.J. (1995). Evolutionary Origin of Plasmodium and Other Apicomplexa Based on Ribosomal-Rna Genes. Proceedings of
the National Academy of Sciences of the United States of America, 92, 5793-5797.
Kohler,S., Delwiche,C.F., Denny,P.W., Tilney,L.G., Webster,P., Wilson,R.J.M., Palmer,J.D., and Roos,D.S. (1997). A plastid of probable green
algal origin in apicomplexan parasites. Science, 275, 1485-1489.
Palmer,J.D. and Delwiche,C.F. (1996). Second-hand chloroplasts and the case of the disappearing nucleus. Proceedings of the National Academy of
Sciences of the United States of America, 93, 7432-7435.
Wilson,R.J.M., Denny,P.W., Preiser,P.R., Rangachari,K., Roberts,K., Roy,A., Whyte,A., Strath,M., Moore,D.J., Moore,P.W., and Williamson,D.
H. (1996). Complete gene map of the plastid-like DNA of the malaria parasite Plasmodium falciparum. Journal of Molecular Biology, 261, 155-172.
Robibaro,B., Hoppe,H.C., Yang,M., Coppens,I., Ngo,H.M., Stedman,T.T., Paprotka,K., and Joiner,K.A. (2001). Endocytosis in different lifestyles
of protozoan parasitism: role in nutrient uptake with special reference to Toxoplasma gondii. International Journal for Parasitology, 31, 1343-1353.
Barta,J.R. (1989). Phylogenetic Analysis of the Class Sporozoea (Phylum Apicomplexa Levine, 1970) - Evidence for the Independent Evolution of
Heteroxenous Life-Cycles. Journal of Parasitology, 75, 195-206.
Tanabe,K., Sakihama,N., Hattori,T., Ranford-Cartwright,L., Goldman,I., Escalante,A.A., and Lal,A.A. (2004). Genetic distance in housekeeping
genes between Plasmodium falciparum and Plasmodium reichenowi and within P-falciparum. Journal of Molecular Evolution, 59, 687-694.. In
Sherman,I.W. (Ed.), Malaria:Parasite biology, Pathenogenesis and Protection, . ASM Press, Washington DC.
The four human malaria parasites are members of a genus that includes some 180 species (Ash and Orihel, 1990). The genus
Plasmodium is thought to have evolved from a coccidian ancestor that was parasitic on an insect host (Garnham, 1966).The
Plasmodium genus is a member of the phylum Apicomplexa, the extant members of which are obligate intra-cellular animal
parasites. The Apicomplexa are themselves members of the Alveolata superphylum which includes ciliates, dinoflagellates,
perkinsida and marine alveolates. The phylum consists of 5000 described species, but there may be as many as 60,000 still to
be described (Escalante and Ayala, 1995). All members of the Apicomplexa contain a vestigial plastid called an apicoplast - a
discrete organelle bound by three or four membranes (Kohler et al., 1997). The origin of this organelle is likely to have been
in a “secondary endosymbiotic event” in which the ancestor of all Apicomplexans engulfed a photosynthetic unicellular alga
and retained the algal plastid (which was itself the product of a previous endosymbiotic event) (Palmer and Delwiche, 1996;
Wilson et al., 1996;Kohler et al., 1997). Supporting this theory is the evidence that present day Apicomplexa such as
Plasmodium and Toxoplasma have highly organized cytoplasmic compartments which are associated with organisms of a
phagotrophic nature (Robibaro et al., 2001).
The Apicomplexa phylum is thought to be very ancient, and may have originated earlier than the multicellular kingdoms of
plants, fungi and animals. The Plasmodium lineage may have diverged several hundred million years ago (before the
appearance of vertebrates), with the radiation that gave rise to human parasites beginning around 130 million years ago
(Escalante et al., 1995). Digenetic parasitism, a feature of Plasmodium and other Apicomplexa may have independently
evolved several times within the phylum (Barta, 1989; Escalante et al., 1995). The phylogenetic relationship of the extant
human parasites is somewhat contentious, with debate ongoing about the origin and age of P. falciparum in particular (see
Tanabe et al. (2004).
References
Ash,L.R. and Orihel,T.C. (1990). Atlas of Human Parasitology. ASCP press, Chicago.
Garnham,P.C.C. (1966). Malaria Parasites and other Haemosporidia. Blackwell, Oxford.
Escalante,A.A. and Ayala,F.J. (1995). Evolutionary Origin of Plasmodium and Other Apicomplexa Based on Ribosomal-Rna Genes. Proceedings of
the National Academy of Sciences of the United States of America, 92, 5793-5797.
Kohler,S., Delwiche,C.F., Denny,P.W., Tilney,L.G., Webster,P., Wilson,R.J.M., Palmer,J.D., and Roos,D.S. (1997). A plastid of probable green
algal origin in apicomplexan parasites. Science, 275, 1485-1489.
Palmer,J.D. and Delwiche,C.F. (1996). Second-hand chloroplasts and the case of the disappearing nucleus. Proceedings of the National Academy of
Sciences of the United States of America, 93, 7432-7435.
Wilson,R.J.M., Denny,P.W., Preiser,P.R., Rangachari,K., Roberts,K., Roy,A., Whyte,A., Strath,M., Moore,D.J., Moore,P.W., and Williamson,D.
H. (1996). Complete gene map of the plastid-like DNA of the malaria parasite Plasmodium falciparum. Journal of Molecular Biology, 261, 155-172.
Robibaro,B., Hoppe,H.C., Yang,M., Coppens,I., Ngo,H.M., Stedman,T.T., Paprotka,K., and Joiner,K.A. (2001). Endocytosis in different lifestyles
of protozoan parasitism: role in nutrient uptake with special reference to Toxoplasma gondii. International Journal for Parasitology, 31, 1343-1353.
Barta,J.R. (1989). Phylogenetic Analysis of the Class Sporozoea (Phylum Apicomplexa Levine, 1970) - Evidence for the Independent Evolution of
Heteroxenous Life-Cycles. Journal of Parasitology, 75, 195-206.
Tanabe,K., Sakihama,N., Hattori,T., Ranford-Cartwright,L., Goldman,I., Escalante,A.A., and Lal,A.A. (2004). Genetic distance in housekeeping
genes between Plasmodium falciparum and Plasmodium reichenowi and within P-falciparum. Journal of Molecular Evolution, 59, 687-694.. In
Sherman,I.W. (Ed.), Malaria:Parasite biology, Pathenogenesis and Protection, . ASM Press, Washington DC.
