Blood borne infections

Blood borne infections are those in which the infectious agent is transmitted from one person to another in contaminated blood. Infections of the blood can occur as a result of the spread of an ongoing infection, such as with bacteria including bacteria such as Yersinia pestis, Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pyogenes. However, the latter re considered to be separate from true bloodborne infections.

Bacterial blood borne infection can occur, typically in the transfusion of blood. Such infections arise from the contamination of the site of transfusion. While information on the rate of such infections is scarce, the risk of transmission of bacterial infections via transfusions is thought to be at least equal to the risk of viral infection. For example, figures from the United States Food and Drug Administration indicate that bacterial infections comprise at least 10% of transfusion-related deaths in the United States each year.

Another route of entry for bacteria are catheters. For example, it has been estimated that the chances of acquiring a urinary tract infection (which can subsequently spread to the blood) rises by up to 10% for each day a hospitalized patient is catheterized.

While bacteria can be problematic in blood borne infections, the typical agents of concern in blood borne infections are protozoa and viruses . The protozoan Trypanosoma brucei is transmitted to humans by the bite of the tsetse fly. The subsequent infection of the blood and organs of the body produces sleeping sickness , al illness that still afflicts millions each year in the underdeveloped world.

With respect to viral blood borne diseases, hepatitis A, hepatitis C, and the Human Immunodeficiency Virus (HIV ; the cause of acquired immunodeficiency syndrome) are the focus of scrutiny in blood donors and in the setting of a hospital. Exposure to the blood from an infected person or the sharing of needles among intravenous drug users can transmit these viruses from person to person. In Canada, the contamination of donated blood and blood products with the hepatitis viruses and HIV in the 1980s sickened thousands of people. As a result the system for blood donation and the monitoring guidelines for the blood and blood products was completely overhauled. For example, in the 1980s, monitoring for hepatitis C was in its infancy (then only a few agencies in the world tested blood for what was then termed "non-A, non-B hepatitis"). Since then, definitive tests for the hepatitis C virus at the nucleic acid level have been developed and put into routine use.

Within the past 20 years, emerging diseases such the lethal fever and tissue destruction caused by the Ebola virus have been important blood borne threats. These so-called hemorrhagic fevers may have become more prominent because of human encroachment onto formerly wild regions, particularly in Africa.

Health care workers are particularly at risk of acquiring a blood borne infection. Open wounds present an opportunity for blood to splatter on a cut or scratch of a doctor or nurse. Also, the use of needles presents a risk of accidental puncture of the skin to doctors, nurses and even to custodial workers responsible for collecting the debris of hospital care.

Another group particularly at risk of blood borne infections are hemophiliacs. The necessity of hemophiliacs to receive blood products that promote clotting leaves them vulnerable. For example, in the United States, some 20% of adult hemophiliacs are infected with HIV, about 56% are infected with the hepatitis B virus, and almost 90% are infected with the hepatitis C virus. HIV is the most common cause of death among hemophiliacs.

Other viruses pose a potential for blood borne transmission. Human herpesvirus 6 and 7, Epstein-Barr virus and cytomegalovirus require close contact between mucous membranes for person-to-person transfer. Abrasions in the genital area may allow for the transfer of the viruses in the blood. Parvovirus, which causes the rash known as fifth disease in children, can be transferred between adults in the blood. In adults, particularly women, the resulting infection can cause arthritis

At least in North America, the increasing urbanization is bringing people into closer contact with wildlife. This has resulted in an increase in the incidence of certain blood borne diseases that are transmitted by ticks. Mice, chipmunks, and deer are two reservoirs of Borrelia burgdorferi, the bacterium that causes Lyme disease . The increasing deer population over the past 35 years in the state of Connecticut has paralleled the increasing number of cases of Lyme disease, over 3,000 in 1996 alone.

Other blood borne disease transmitted by ticks includes Rocky Mountain Spotted Fever, human granulolytic ehrlichiosis, and babesiosis. While these diseases can ultimately affect various sites in the body, their origin is in the blood.

The institution of improved means of monitoring donated blood and blood products has lowered the number of cases of blood borne infections. However, similar success in the hospital or natural settings has not occurred, and likely will not. Avoidance of infected people and the wearing of appropriate garments (such as socks and long pants when walking in forested areas where ticks may be present) are the best strategies to avoid such blood borne infections at the present time.

See also AIDS; Hemorrhagic fevers and diseases; Transmission of pathogens