Detection Overview
HIV/HCV detection: an overview (1), (2)HIV and HCV are large epidemics that are spreading throughout the world. Since the mode of spread is via blood and sexual contacts, one of the most important modes of curtailing the epidemic is good HIV and HCV diagnostics.
This can ensure that no tainted blood units are used for transfusion, and when screening high-risk populations all those infected are detected, and thus treated and educated.
Today, using standard serology tests, many infected individuals are missed, and thus more new infections, that could have been avoided, via direct education, happen daily.
Due to the current limitations of the serology antibody tests some infectious blood units are transfused into needing individuals, spreading the infection even further.
This is due to the “window period” of weeks, months and sometimes years from the time of HIV or HCV infection to the time of sero-conversion.
The window period is due to suppression of the immune response against the virus.
Current status of HIV and HCV Diagnostics.
Tests for the detection of carriers are conducted all over the world.
o The most common way to identify the carriers is by detecting the antibodies against the virus.
o Antibodies against HIV and HCV take weeks or months after infection to develop in the body.
The infected yet sero-negative period is called the “window period”.
Other tests are based on detecting the virus itself, by its proteins or its genetic material.
HIV
HIV (Human Immuno-deficiency Virus) is the virus that causes AIDS. In the initial period of the HIV infection the carrier is asymptomatic and thus does not know that he / she is infected. It takes years before AIDS develops. HIV is transmitted mainly by sexual contact, blood and blood products, and from mother to the fetus.
The national blood banks test every blood donation for the presence of HIV, and these tests account for the largest portion of the HIV testing (~60% of the total tests carried out in the west). Currently the diagnosis of HIV is based on the detection of HIV antibodies in the serum.
The time between exposure/infection and the detection of antibodies in the serum is called the “window period”. According to the CDC (Center for Disease Control), only 50% of those infected will seroconvert within 3 months of the exposure, and 95% will become seropositive within 6 months. Thus, HIV antibodies in the serum are often not detectable in the early stages of the infection, shortly after exposure, leaving infected units in the blood supply.
Since the virus goes up in the blood some time before the antibodies appear, developing sensitive molecular biology techniques to detect the virus in the blood have been able to shorten the window period by 10-12 days.
Since every day counts these methods have been introduced into the blood banks, as an additional screening tests for blood units, making every possible effort to make the blood supply as safe as possible. As sensitive as these methods and tests are, the weeks and months prior to this ‘rise in virus levels’, when the virus is not in the blood in measurable levels, are still left undetectable. It is this gap that still needs resolving
An antibody enhancing method that enables the test to be positive throughout the whole infection period, is easy to perform and is relatively inexpensive could fill in the gaps.
HCV:
Hepatitis C is a liver disease caused by the hepatitis C virus (HCV), which is found in the blood of persons who have this disease. HCV is spread by contact with the blood of an infected person. The hepatitis C virus (HCV) is one of the most significant health problems affecting the liver.
More than 4 million Americans (1.3% of the U.S. population) and 170 million individuals in the world (3% worldwide) are infected with hepatitis C virus.
The prevalence (number of cases in a population at a specific time) of hepatitis C virus infections varies in different parts of the world. For example, the prevalence of hepatitis C virus in Scandinavia is less than 0.5% of the population, whereas the prevalence in Egypt is over 20%. In the U.S. and Western Europe, the complications of hepatitis C virus chronic hepatitis and cirrhosis are the most common reasons for liver transplantation.(3)
Usually people with HCV do not know they have the disease until the virus has already done some damage to the liver. This is one of the reasons that HCV advocate groups try to raise public awareness of this disease.(4)
Some statistics and trends (5):
o Number of new infections per year has declined from an average of 240,000 in the 1980s to about 30,000 in 2003.
o Most infections are due to illegal injection drug use.
o Transfusion-associated cases occurred prior to blood donor screening; now occurs in less than one per 2 million transfused units of blood.
o Estimated 3.9 million (1.8%) Americans have been infected with HCV, of whom 2.7 million are chronically infected.
o The risk for prenatal HCV transmission is about 4%. o If coinfected with HIV the risk for prenatal infection is about 19%.
o A single positive PCR test indicates infection with HCV. A single negative test does not prove that a person is not infected. Virus may be present in the blood and just not found by PCR. When hepatitis C is suspected and PCR is negative, PCR should be repeated.
o HCV accounts for "most" liver transplants.
o Another reason for public awareness is that at least 4 million people in the United States presently have HCV.