AREAS DE VALOR PAISAJISTICO Y TURISTICO

Transfusion-transmitted malaria (TTM) occurs when the infection in the patient is caused by the same parasite that was present in the donated blood. The first case of TTM was reported by Woolsey in 1911 (93). This was due to the blood in the syringe flowing back when the direct method of transfusion from artery to vein was used (94).

2.2.1 Epidemiology of transfusion-transmitted malaria Transfusion-transmitted malaria in non-endemic countries

Most of the published data on TTM are from non endemic countries for malaria. This may be due to the ease of diagnosis in non-endemic countries compared to endemic countries where it cannot be readily proven whether malaria which

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develops post-transfusion is from the blood received or from a re-infection or recrudescence.

Excluding deliberate infections for malaria therapy or for experimental purposes, there were about 350 cases of accidentally induced human malaria reported between 1911 and 1950 (94). During the period 1950-1972, 1,756 cases were reported to have occurred in 49 countries. The role of surveillance activities of the global malaria eradication programme from various countries and the reports forwarded to the WHO were of considerable value in providing reliable data (95). There is still the possibility that some cases of TTM were missed or not reported. As transfusion of blood and its components increased, more cases of TTM were expected. However, with an increased awareness of this problem, more interventions have been introduced to reduce its occurrence including screening tests and deferral of donors who have travelled to malaria endemic countries. . Currently, there is about one case of TTM every 3 years in France (96,97). In the UK, only 2 confirmed cases of TTM have been reported since 1996 (98). Three cases of TTM were reported in the US in 2009. Prior to 2009, the last case of TTM was reported in 2007 (99). In Japan, there have been 22 cases of TTM since 1945 (100).

Incidence of transfusion-transmitted malaria in sub-Saharan Africa

There are no published studies on the incidence of TTM in malaria endemic regions. This may be due to the use of malarial prophylaxis in recipients, making it difficult to follow up patients to determine incidence. A study in Sudan found that the prevalence of post transfusion malaria in transfusion recipients was 3.5%, four days after transfusion (101). All patients in the study (twelve) who received malaria positive blood became malaria positive (by microscopy). There were also two patients who did not receive malaria positive blood but still developed malaria parasitaemia 4 days after transfusion. Genotyping was not done to determine if the parasites in the patients were the same as the ones received from the donated blood. In malaria endemic countries post transfusion malaria cannot be equated to TTM because there are other sources of transmission. In non endemic countries however, post transfusion malaria is likely to be the same as TTM because the

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transfusion is likely to be the only source of parasitaemia in a recipient who has had no previous exposure to malaria.

Prevalence of malaria in blood donors in sub-Saharan Africa

The prevalence of malaria in blood donors depends on the endemicity in the country or region and the transmission season. For example, during a high transmission season in a high endemic area, the prevalence of asymptomatic parasitaemia is high in all age groups, reaching up to 94% (102). Similarly it is reasonable to expect a high prevalence of asymptomatic donors in endemic countries (103). Our recent review of published prevalence studies shows a wide variability of malaria prevalence across sub-Saharan Africa (104). The prevalence of malaria varied from 0.7% in Nairobi, Kenya (low malaria endemicity) to 55% in Anambra, South-eastern Nigeria (high malaria endemicity). The prevalence of malaria varies across Africa and even within countries.

Asymptomatic donors with parasitaemia may be a source of transmission but it is unknown whether presence of parasitaemia in donors translates into infection or disease for the recipient. The presence of parasitaemia in donated blood raises some important issues including

1. How much parasitaemia in donors translates to infection or disease in recipients

2. Whether blood banks can afford to discard all malaria positive blood that is donated and

3. What is the best screening method to detect malaria parasitaemia?

Incubation period for transfusion-transmitted malaria

The incubation period for TTM is variable (105) but for falciparum, it ranges from seven to 27 days. This variability may depend on factors such as inoculum size and the intrinsic factors of the recipient such as age, level of immunity, presence of protective red cell abnormalities such as sickle cell etc. Recent observations from TTM cases indicate that the incubation period may last several months (99). Determination of incubation periods is based on the ability of the patient to recollect exactly when the symptoms started and on knowing the date of the

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implicated transfusion. This is not always known. In an observation from non- immune subjects in Yugoslavia, 3 children who received blood from the same source had varying incubation periods of 7, 15 and 23 days. Assuming that they each received the same dose of parasites then, it was the recipient’s immunity that played the major role in determining the incubation period (106). Inoculum size in a transfused unit of blood can be huge. When one parasite /µl is found, that translates to about 500,000 parasites in a unit of blood.

Parasite viability

Plasmodium parasites can survive refrigeration for up to 18-20 days (59,93) but a recent study shows that refrigeration is detrimental to their survival (107). There was a 7.1 fold reduction after 14 days but parasites remained detectable by microscopy for 28 days when stored in blood at 4°C. Parasites also did not show in vitro replication when cultured after 14 days storage. This may be an indication of the parasite losing viability after prolonged refrigeration. More studies are needed to authenticate this.

Presentation of transfusion-transmitted malaria

It is not expected that symptoms of TTM should be different from the usual symptoms of malaria which include fever chills, myalgia, headache, vomiting and diarrhoea. In a study by Ali et al who found 14 patients with post transfusion malaria after receiving P. falciparum positive blood, there was no clear clinical presentation of TTM except for the presence of fever (101).