Malaria is primarily transmitted by an
insect vector specifically the female mosquito of the Anopheles genus. Thus, males do not transmit the disease. The
female insect prefers to feed at night. They usually start searching for a meal
at dusk and will continue throughout the night until they succeed. When a
mosquito bites an infected person, a small amount of blood is taken. This
contains microscopic malaria parasites. About one week later, when it takes its
next blood meal, these parasites mix with the mosquito saliva and are injected
into the person bitten.
However malaria parasites can also be
transmitted by blood transfusion (Marcucci
et al., 2004).This is a rare occurrence but potentially is a source of
concern for blood recipients. During 1958-1998 a total of 103 cases of
transfusion transmitted malaria were reported to the centre for disease control
(CDC) in the United States.
The frequency of post transfusion malaria has been estimated to vary from less
than 0.2 cases per million in non-endemic countries to 50 or more cases per
million in endemic countries (Bruce-Chwatt, 1985)
Thus the frequency of reported
transfusion malaria is relatively low in non-endemic countries. For instance,
there have only been about 8 cases in the United
Kingdom in 50 years; 26 cases in the United States of America in 10 years from 1972
to1981 and in France,
110 cases in 20 years (Bruce-Chwatt, 1985). But in Saudi Arabia there have been 12
cases in just four years in one centre in Ridyadh as well as at least 20
unreported cases from other centres in the kingdom.
In another study carried out in 1987, it was reported that P. falciparum was present in the blood
of donors who were exposed to malaria 20 months to 3 years previously. P.vivax has been transmitted by
transfusion from donors infected four years previously and P. malariae from donors infected 17 years earlier (Chikwen, et al., 1997). Also McClure and Lam
(1945) reported that quartian malaria (P.
malariae) has been accidentally transmitted in blood previously stored for
five days (McClure et al., 1993) and
in yet another case reported by Black (1960), a donor had carried P. malariae parasite for 10 years
(Button et al., 1993).
These cases clearly implicate blood
transfusion and qualify it as a second source of malaria transmission. The transmission
of malaria by blood transfusion is a serious risk as the diagnoses of malaria
in the recipient is unexpected and this is often missed (Kinde-Gazard et al., 2000). Asymptomatic carriers
are generally the source of transfusion transmitted malaria. Since healthy
blood donors are often selected for blood donation, density of parasites is
usually very low, if present and hence may be missed (Kaur et al., 2005).
In another report it was stated that
donors who have been implicated as infection source in transfusion-transmitted
malaria cases typically present with very low level of parasitemia that may be
undetectable, even with microscopic examination of several thick films. Out of
the 60 cases reported in United States during 1963-1998 where a blood smear was
obtained, only 18 (30%) of implicated donors had Plasmodium parasites
detected on the blood smear. Detection of malaria antibodies provides
evidence of an immune response to current and past infection, but these tests
may remain positive for more than 10 years long after parasitemia has resolved;
therefore the use of malaria antibody detection to screen blood donors would
result in the exclusion of otherwise healthy volunteers. However, polymerase
chain reaction (PCR) has increased the sensitivity over blood film examination,
positively indicating current malaria infection (Vu et al., 1995).
Thus, to fully and accurately determine
the actual risks posed by blood transfusion in the transmission of malaria
parasite, a more sensitive screening technique other than microscopic
examination of thick blood films is required and the use of PCR may be a
helpful tool for investigation. The reviews of several works done outside Nigeria have
proved that there is a significant potential risk of malaria transmission via
blood transfusion. Consequently, Okocha et
al., (2005) recommended that all pints be screened for malaria parasite
(post-donor screening) and marked negative or positive as the case may be
(Okocha et al., 2005). Perhaps what
is left is to develop a more sensitive screening method that will accurately
determine the magnitude of the risk of transfusion malaria. This may raise the
necessary alarm required to expand hemovigilance to include screening of blood
for malaria parasites prior to transfusion.
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General Distribution of Malaria
The Transmission of Malaria Parasite
The Plasmodium Life Cycle
Aetiology of Malaria Infection
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