CBER Presentation
Global Problem of Malaria, Biology of Malaria Parasites and Implications for Transfusion-Transmitted Malaria and Detection Methods
Sanjai Kumar, Ph.D.
Center for Biologics Research and Review
Food and Drug Administration
Malaria Workshop
July 12, 2006
Epidemiology
- Plasmoidum falciparum, P. vivax, P. ovale, P. malariae
- Occurs in more than 100 countries throughout Africa, Asia, Latin America, and on certain Caribbean and Pacific Islands
- 3.2 billion inhabitants at risk
- 300 - 500 million clinical cases
- ~ 1 - 2 million per year
World Malaria Report, WHO 2005
Representative Distributions of the Four Recognized Species of Human Malaria Parasites in the World Today
Distribution of species (%) in following areas (total no. of cases) | |||||
---|---|---|---|---|---|
Species | Sub-Saharan Africa | Asia (all) (863) |
Central America and Caribbean (178,242) |
South America (859,480) | |
West and Central (858) |
East and Southern (297) |
||||
P. falciparum | 88.2 | 78.8 | 4.2 | 12.9 | 29.2 |
P. vivax | 1.2 | 9.8 | 95.6 | 87.1 | 70.6 |
P. malariae | 2.2 | 3.0 | 0.0 | 0.0 | 0.2 |
P. ovale | 8.4 | 8.4 | 0.2 | 0.0 | 0.0 |
Carter and Mendis, Clin Microbiol Rev 2002
Global Reach of Malaria
- In today's interconnected world, no country is immune from the hazards of malaria
- The problem of malaria is rising. There are more cases of malaria today than 30 years ago
- Major factors attributed to rise in malaria transmission
- Environmental
- Human activities
- Drug resistance in malaria parasites
- Vector populations
Malaria Mortality: Summary Statistics at the Beginning and End of the 20th Century
Region | Year | Total no. of deaths from malaria | % of all deaths due to malaria |
---|---|---|---|
Europe and North America | |||
Caribbean, Central and South America | |||
Asia, China and Western Pacific | |||
Sub-Saharan Africa | |||
World minus Sub-Saharan Africa | |||
Total World | |||
Total World Annual Deaths/10,000 | |||
Carter and Mendis, Clin Microbiol Rev 2002
Source: Tom Wellems, NIH
Projected Risk of Malaria Transmission in the year 2020 based on a global temperature increase of 2ºF and no human efforts to contain the spread of malaria. Source: Pim Martens (http://www.exploratorium.edu/climate/global-effects/data3.html)
Drug resistance to P. falciparum from studies in sentinel sites, up to 2004. World Malaria Report, WHO 2005
Malaria Life Cycle and Biology
- Liver stage: 6 - 14 days
- Blood stage: 48 - 72 hrs
- Incubation period: 21 days
- Primary infections: Clinical disease of varying manifestations
- Adults from endemic areas develop clinical immunity but carry low-grade parasitemia
Malaria Parasite Biology, Clinical Disease, Immunity, and implications for TTM
- Incubation period: Time between infection to first appearance of blood form parasites (varies between species). P. vivax and P. ovale have dormant liver form stage causing relapse infection (months to a year or more)
- Chronicity of infection: P. malariae can be present in a host for up to 40 years
- Asymptomatic carriers: Multiple exposures in individuals born in endemic countries or expatriates with prolonged residence develop partial immunity while carrying low-grade parasite burden
- Parasite burden in asymptomatic carriers is not known
- Infectious dose of blood form malaria parasites is very low
Donor populations that cause TTM and Implication for a Donor Screening Test
Travelers
- No prior immunity
- Infection can be acquired shortly before departure
- Infection with a strain of Plasmodium with prolonged latency
Residents
- Born in an endemic country or had a prolonged residence
- Asymptomatic carriers
- Parasite burden in asymptomatic carriers is not known
History of clinical malaria
- Inadequate treatment
- Relapse from liver form parasites
Considerations for laboratory tests to detect malaria parasites in blood donors
- Direct parasite demonstration (microscopy or DNA detection) is most suitable for all donor groups
- Window period of exposure in travelers before testing should be allowed and low-parasite burden in asymptomatic carriers
- A surrogate of exposure such as the presence of anti-malaria antibodies can be indicative of a current infection or a previous exposure
- Time lapse between parasite exposure and first appearance of antibodies in travelers and assay sensitivity in donors with primary infections and asymptomatic carriers
- A few reports suggest that seroconversion occurs within a few weeks after appearance of blood form parasites
- A screening test should be able to detect all Plasmodium species that frequently cause TTM
Methods to Detect Malaria Parasites
- Direct parasite demonstration
- Antigen detection
- Indirect demonstration of parasite exposure
- Microscopy- Thick blood film
- QBC method
- HRP, LDH etc. based dip sticks
- Nucleic acid based methods- PCR test, TaqMan assay, Real-time PCR and Microarray
- Antibody based methods: IFAT, ELISA
Plasmodium falciparum: Blood Stage Parasites Thick Blood Smears
Sensitivity limit: 5 - 500 parasites per µL of blood. Source: CDC http://www.dpd.cdc.gov/dpdx/HTML/ImageLibrary/Malaria_il.htm
The Quantitative Buffy Coat (QBC) Test
- A high precision glass hematocrit tube, pre-coated with acridine orange is filled with 55-65 µl of blood
- Centrifugation at 12, 000 rpm separates cells based on their densities
- Sensitivity is claimed to be as good as a thick smear
Source: http://www.malariasite.com/malaria/QBC.htm.
Antigen Detection Tests for Malaria
|
Source: http://www.malariasite.com/malaria/rdts.htm#parasight
Nested PCR Amplification of 18 S rRNA Gene Fragment from P. falciparum Spiked in 1 µL of Human Blood
|
Indirect Fluorescent Antibody Test
|
Pan-Plasmodium reactivity of sera from malaria patients detected against individual & combination recombinant antigens in ELISA
PfCSP |
PfAMA1 |
PfMSP142
|
PfCSP/PfAMA1/PfMSP142 |
Cross-species recognization of recombinant P. falciparum antigens with sera from P. falciparum, P. vivax, P. malariae and P. ovale infected patients by western blot
Acknowledgements
- CBER
- WRAIR
- CDC
- NIAID
Hong Zheng
Babita Mahajan
Hira L. Nakhasi
David Haynes
Monica Parise
Marriana Wilson
Malaria Vaccine Development Branch