Article Index
Transfusion Diseases
Infectious agents transmissible through blood
Laboratory diagnosis of HIV infection
Competitive ELISA Method
Interpretation of results
Serological Findings
Hepatitis D (Delta virus)
All Pages

Transfusion Diseases

Florence Nightingale, more than 100 years ago said “No stronger condemnation of any hospital or ward could be pronounced than the single fact that zymotic (infectious) disease has originated in it, or that such a disease has attacked other patients than those brought in with them”.

It should, therefore, be obligatory on those who are involved in transfusion of blood to a patient for saving his life, that the blood transfusion does no harm to the patient. Nothing could be worst than the fact that in an attempt to save life, blood & blood products having transmissible infectious agents have been given. Many of these infectious agents may cause death or prolonged illness. Hence it is necessary to understand the organisms which could be transmitted through blood transfusion and means by which this could be prevented.

Infectious agents
There are four main groups of micro-organisms known to cause infections namely viruses, bacteria, protozoa and fungi. Only first three groups of microbes - viruses, bacteria and protozoa - have been reported to be transmitted by blood transfusion. Individuals with fungal infections are usually too sick to be accepted as blood donors. Viruses are most commonly transmitted by transfusion.
Recently, a new form of infectious agent - the prion - has been identified. At this time, there is no evidence to suggest that they could be transmitted by blood transfusion.

Viruses
Viruses are the simplest forms of life. They infect all forms of life, they lack certain components needed to live and their growth hence depend on the host cell that they infect to provide these missing components.
Following are some of the viruses which are known to be transmitted through blood:

• Human immunodeficiency virus (HIV)
• Hepatitis B virus
• Hepatitis C virus
• Hepatitis A virus
• Hepatitis G virus
• Non - A, Non - B Hepatitis
• Epstein Barr Virus
• Cytomegalo virus (CMV)
• Human T Lymphocytic virus (HTLV - 1 & HTLV - 2)

Some viruses have the property of latency. This is the ability of a virus to join its own nucleic acid with the nucleic acid of the host cell without taking complete control of the host cell as a virus would normally do. Latency usually occurs after an active infection when the individual has recovered and immunity is building up. The viral nucleic acid exists in an inactive form that does not seem to harm the host cell. When the host cell divides, the cell nucleic acid is copied, together with the viral nucleic acid. In this way, the viral nucleic acid becomes part of the cell nucleic acid and is copied every time the cell divides.

Latency is usually indefinite and without any harmful effects on the host cell. However, at any time, the latent nucleic acid could become active and take over the cell functions, resulting in an active infection. This is called a reactivation of infection (recrudescence), which is caused by the reactivation of virus already present in the individual.

Transmission of infectious agents by Blood Transfusion
In order to be transmitted by blood transfusion, an infectious agent must be present in the donated blood. Each blood transfusion service or blood bank or laboratory should, therefore, screen for evidence of the microbes that are known to cause infections with this route of transmission.
There are three basic conditions that will determine whether an infectious agent is likely to be transmitted by transfusion:

• The agent must be capable of using the blood stream as a route of entry in host.
• The infected donor must be essentially free of any noticeable signs and symptoms of disease, otherwise, they would have been identified during donor screening and the donor would have been excluded or deferred.
• The agent must exist naturally for a period of time, either free in the plasma or present in a cellular component in the blood stream of an infected donor.

Any infectious agent meeting all these conditions can be transmitted by blood transfusion. However, whether transmission actually occurs or not depends on a number of other factors, particularly on the immune status of the patient and the amount of infectious agent transfused.

It is known that the transmission of certain infectious agents through blood transfusion can, and do occur, and it can be an important route of infection, however, the key point to remember here is that there are a number of ways by which risk can be reduced.

Strategies to reduce the risk of transfusion - transmitted infections.
he careful selection of donors to ensure that, as far as possible, blood is not collected from people who are likely to be carriers of infectious agents. Safe blood donation depends on, building a panel of regular, voluntary, non - remunerated donors as the first step in ensuring a safe and adequate supply of blood. In our country where most of the blood is collected from family/replacement donors, the risk of transfusion transmissible infection is higher.

The direct screening of the blood for evidence of the presence of infectious agents or markers produced by them.

The removal of specific components of blood thought to harbor infectious agents, for example, by the filtration of blood to remove white blood cells.

The physical/ chemical inactivation of any contaminating agent that may be present: for example, heat treatment of 5 % albumin during production.

Not all infectious agents can be detected directly in donated blood. Blood is often screened for evidence of previous infection by looking for the presence of specific antibodies raised against the infectious agent. Clearly, it is only by understanding what markers of infection are produced by the infectious agent that screening for the correct marker can be introduced.