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Global Problem of Malaria, Biology of Malaria Parasites and Implications for Transfusion-Transmitted Malaria and Detection Methods

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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)
SpeciesSub-Saharan AfricaAsia (all)
(863)
Central America
and Caribbean
(178,242)
South America (859,480)
West and
Central (858)
East and
Southern (297)
P. falciparum88.278.84.212.929.2
P. vivax1.29.895.687.170.6
P. malariae2.23.00.00.00.2
P. ovale8.48.40.20.00.0

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

 

RegionYearTotal no. of deaths from malaria% of all deaths due to malaria
Europe and North America
1900
80,000
0.8
1997
20
0.0001
Caribbean, Central and South America
1900
42,000
2
1997
4,000
0.05
Asia, China and Western Pacific
1900
2,800,000
9
1997
65,000
0.1
Sub-Saharan Africa
1900
210,000
6
1997
990,000
9
World minus Sub-Saharan Africa
1900
2,900,000
8
1997
69,000
0.08
Total World
1900
3,132,000
 
1997
1,059,020
 
Total World Annual Deaths/10,000
1900
19.4
 
1997
1.84
 

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

     

     

    - Microscopy
    - Thick blood film
    - QBC method

     

     

  • Antigen detection

     

    - HRP, LDH etc. based dip sticks
    - Nucleic acid based methods
    - PCR test, TaqMan assay, Real-time PCR and Microarray

     

  • Indirect demonstration of parasite exposure

     

    - 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

 

 
  • Antigen capture by mAb or polyclonal antibody
  • HRP-2, specific to Pf
  • Aldolase and pLDH: pan-Plasmodium recognization
  • Sensitivity: >83%
  • Less sensitive in non-immune travelers
  • Reactivity with auto-antibodies

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

 

 
  • 7-8 copies of 18 S rRNA
  • Genus and species specific identification
  • Potentially feasible for donor screening
  • Sensitivity: 0.25 parasite/µl or 250 parasites/ml of blood
  • 20-fold superior to thick blood film

Indirect Fluorescent Antibody Test

 

 
  • "Gold Standard" serology test
  • Possible to detect all four Plasmodium species
  • Highly effective in detecting antibodies in prior residents
  • Cumbersome and difficult to develop an automated format

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
    Hong Zheng
    Babita Mahajan
    Hira L. Nakhasi
  • WRAIR
    David Haynes
  • CDC
    Monica Parise
    Marriana Wilson
  • NIAID
    Malaria Vaccine Development Branch