It has also been shown that transmission of nvCJD may be facilitated, within blood transfusion, by leukocytes (B – Lymphocytes), (Murphy 1999), as the PrP (prion protein) is associated with cell membranes and the buffy coat has been shown to be infectious in some experimental studies, (Cervenakova et al, 2003). For this reason, leucodepletion of blood products, including platelets, fresh frozen plasma and cryoprecipitate, has been introduced in the UK as it has been shown that this reduces the risk of infection/transmission. Leucodepletion as a precautionary measure has also been shown to reduce transmission rates of cytomegalovirus, (Dumont et al, 2001).
In view of all these concerns, the UK blood transfusion service (BTS) and regulatory authorities have chosen to apply other precautionary principles in evaluating strategies, which could also reduce the risk of transmission of nvCJD. Apart from leucodepletion of blood products, these measures include donor selection and exclusion and a ban on using UK plasma for the manufacture of fractionated products, such as albumin, clotting factor and immunoglobulin.
Overall, the precautionary measures mentioned above and a promotion of the appropriate use of blood products throughout the National Health Service is thought to ensure the best way of preventing transmission of nvCJD from blood transfusion.
Part 2:
New-variant Creutzfeldt Jakob Disease (nvCJD) was initially described in 1996 in the UK. It is a rare, neurological illness believed to be caused by a prion, a newly identified type of disease-causing agent or protein. It is different from a virus in that there is no immune response to infection and there is a very long time between infection and onset of symptoms. nvCJD is a very serious and life threatening disease and patients with nvCJD differ greatly from patients with the classical form of CJD.
Primary symptoms can include insomnia (difficulty sleeping), depression, confusion, personality and behavioral changes, and problems with eyesight, memory, and coordination. As the disease progresses patients develop rapid dementia followed by involuntary muscle jerking known as myoclonus. In the end stages of the disease, muscle weakness and coordination worsen and patients lose their eyesight and ability to talk. Prior to death, patients lose all mental and physical functions, leading to coma. Also, nvCJD tends to manifest in younger people, between the ages of 19 – 41.
The clinical and scientific data all point to nvCJD being caused by the same strain of Prion as Bovine Spongiform Encephalopathy (BSE) or ‘mad cow disease’, therefore suggesting that nvCJD resulted due to human consumption of BSE infected cattle. To date there have been just over 120 definite and probable cases of nvCJD in the UK, however, the estimation of the number of individuals within the UK population likely to develop nvCJD remains unpredictable. One of the reason for this is that the incubation period, the period between infection and actual clinical detection of the disease, is still unknown and is thought to be very prolonged, around 30 years or so, and in this period a patient would show no obvious signs of infection.
A number of features of nvCJD suggest that transmission is possible by blood transfusions or transfusions of other blood products. The primary and convincing feature of this is the prion protein that causes nvCJD is known to be found primarily on the white blood cells. This therefore suggests, theoretically at least, that blood from patients with nvCJD is infective and possesses possible risk of transmission through blood transfusion. Even though this has been proven in some animal models, it is not yet known whether nvCJD will prove to be transmissible between humans by blood transfusion, but the risk cannot be excluded and for this reason, the UK blood services have taken certain specific precautionary measures to safe guard against or reduce the risk of nvCJD infection by blood transfusion. These include:
- Donor selection and exclusion: High risk individuals are excluded.
- Leucodepletion (removal of white blood cells) of all blood components.
- Promotion of appropriate use of blood and blood products through the NHS
- Withdrawal and recall of any blood components obtained from any individual who later develops nvCJD.
Overall, the chance of acquiring nvCJD from a blood transfusion is extremely low and the benefits of having a blood transfusion when needed have to be weighed against the disadvantages. In the UK, further precautionary measures are also being revised and considered and ultimately, the responsibility to ensure that patients are treated with blood only when there is a real benefit so it is weighted against the uncertain risk of transmitting nvCJD falls on the medical professionals involved in the treatment.
References:
1. . 1998 Dec;24(6):476-86
Prion protein immunohistochemical staining in the brains of monkeys with transmissible spongiform encephalopathy.
Baker HF, Ridley RM, Wells GA, Ironside JW.
2. Lancet 1996; 347: 921 - 925.
A New Variant Creutzfeldt-Jakob Disease in the UK.
Will RG, Ironside JW, Zeidler M, Cousens SN, Estibeiro K, Alperovitch A, Poser S, Pocchiari M, Hofman A, Smith PG.
3. British Journal of Hameatology. 1999 Sep;106(4):842-50
The impact of new-variant Creutzfeldt-Jakob disease on blood transfusion practice.
Turner M.
4. Lancet. 1997 Jan 11;349(9045):99-100.
Diagnosis of new variant Creutzfeldt-Jakob disease by tonsil biopsy.
Hill AF, Zeidler M, Ironside J, Collinge J.
5. Blood Reviews. 1998 Dec;12(4):255-68.
New-variant Creutzfeldt-Jakob disease: the risk of transmission by blood transfusion.
Turner ML, Ironside JW.
6. The Journal of Hospital Infection. 2000 Sep;46(1):78-9.
Infectivity in the blood of mice with a BSE-derived agent.
Taylor DM, Fernie K, Reichl HE, Somerville RA.
7. Lancet. 2000 Sep 16;356(9234):999-1000
Transmission of BSE by blood transfusion in sheep.
Houston F, Foster JD, Chong A, Hunter N, Bostock CJ.
8. Nature Medicine. 2001 Mar;7(3):261.
Scientists race to develop a blood test for vCJD.
Bonetta L. Bethesda
9. Transfusion Medicine Reviews. 1999 Apr;13(2):75-83.
New variant Creutzfeldt-Jakob disease (nvCJD): the risk of transmission by blood transfusion and the potential benefit of leukocyte-reduction of blood components.
Murphy MF.
10. Transfusion. 2003 Dec;43(12):1687-94.
Similar levels of infectivity in the blood of mice infected with human-derived vCJD and GSS strains of transmissible spongiform encephalopathy.
Cervenakova L, Yakovleva O, McKenzie C, Kolchinsky S, McShane L, Drohan WN.
11. Blood. 2001 Jun 1;97(11):3640-7.
The effect of leukocyte-reduction method on the amount of human cytomegalovirus in blood products: a comparison of apheresis and filtration methods.
Dumont LJ, Luka J, VandenBroeke T, Whitley P, Ambruso DR, Elfath MD.
