DNA from pre-erythrocytic stage malaria parasites is detectable by PCR in the faeces and blood of hosts.
Following the bite of an infective mosquito, malaria parasites first invade the liver where they develop and replicate for a number of days before being released into the bloodstream where they invade red blood cells and cause disease. The biology of the liver stages of malaria parasites is relatively poorly understood due to the inaccessibility of the parasites to sampling during this phase of their life cycle. Here we report the detection in blood and faecal samples of malaria parasite DNA throughout their development in the livers of mice and before the parasites begin their growth in the blood circulation. It is shown that parasite DNA derived from pre-erythrocytic stage parasites reaches the faeces via the bile. We then show that different primate malaria species can be detected by PCR in blood and faecal samples from naturally infected captive macaque monkeys. These results demonstrate that pre-erythrocytic parasites can be detected and quantified in experimentally infected animals. Furthermore, these results have important implications for both molecular epidemiology and phylogenetics of malaria parasites. In the former case, individuals who are malaria parasite negative by microscopy, but PCR positive for parasite DNA in their blood, are considered to be "sub-microscopic" blood stage parasite carriers. We now propose that PCR positivity is not necessarily an indicator of the presence of blood stage parasites, as the DNA could derive from pre-erythrocytic parasites. Similarly, in the case of molecular phylogenetics based on DNA sequences alone, we argue that DNA amplified from blood or faeces does not necessarily come from a parasite species that infects the red blood cells of that particular host.
Malaria Unit, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan; Laboratory of Molecular Biology of Infectious Agents, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
Hussein M
HM
Abkallo
Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Weimin
W
Liu
Malaria Unit, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
Sarina
S
Hokama
School of Biological Sciences, Nanyang Technological University, Singapore.
Pedro E
PE
Ferreira
Department of Protozoology, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
Shusuke
S
Nakazawa
Department of Virology and Parasitology, Fujita Health University School of Medicine, Aichi, Japan.
Yoshimasa
Y
Maeno
Khanh Phu Malaria Research Unit, Medical Committee Netherlands-Vietnam, Khanh Hoa, Viet Nam.
Nguyen T
NT
Quang
Laboratory of Molecular Biology of Infectious Agents, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
Nobuyuki
N
Kobayashi
Department of Protozoology, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
Osamu
O
Kaneko
Department of Ecology and Social Behaviour, Primate Research Institute, Kyoto University, Inuyama, Japan.
Michael A
MA
Huffman
Laboratory of Tropical Medicine and Parasitology, Dokkyo University School of Medicine, Tochigi, Japan.
Satoru
S
Kawai
Khanh Phu Malaria Research Unit, Medical Committee Netherlands-Vietnam, Khanh Hoa, Viet Nam.
Ron P
RP
Marchand
Institute of Evolutionary Biology and Center for Immunity, Infection and Evolution, University of Edinburgh, United Kingdom.
Richard
R
Carter
Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Microbiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
Beatrice H
BH
Hahn
Malaria Unit, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan. Electronic address: richard@nagasaki-u.ac.jp.
Richard
R
Culleton
D000818:Animals; D016054:DNA, Protozoan / Q000097:blood* / Q000235:genetics; D005243:Feces / Q000469:parasitology*; D008251:Macaca; D008288:Malaria / Q000453:epidemiology / Q000469:parasitology / Q000662:veterinary; D051379:Mice; D008969:Molecular Sequence Data; D010802:Phylogeny; D010967:Plasmodium yoelii / Q000235:genetics* / Q000502:physiology*; D014744:Vietnam / Q000453:epidemiology
D016054:DNA, Protozoan
Bile; Diagnosis; Faeces; Liver stage; Malaria; Plasmodium yoelii; Pre-erythrocytic stages; Submicroscopic parasitaemia