Infection and Immunity

Infection and Immunity

Enzyme-Linked Immunosorbent Assay (ELISA) refers to a diagnostic technique that exploits immunological principles to examine the presence of antibodies (Ab) (Doctorndtv.Com, 2008). ELISA tests are used in the diagnosis of various diseases such as hepatitis B Ag and Ab, human immunodeficiency Virus (HIV), Entamoeba histolytica Abs. However, ELISA test varies depending on the disease tested. HIV ELISA test involves screening for the presence of Abs against the disease to ascertain the presence of the virus in the body. Cichocki (2009) explain that the application of this test is very prevalent due to its cost effectiveness and has high sensitivity. The high sensitivity if the disease is due to the low rate of false positives (Van Dyk, 2008).

The use of ELISA test in the diagnosis of HIV has been used for a long time and has proved critical in saving lives. HIV ELISA test allows for infection surveillance and protection of an individual against infection in cases of organ transplant and transfusion (Constantine & Zink, 2005). The detection of HIV often takes place after 3-6 weeks after infection (Sharma & Marfatia, 2008; Van Dyk, 2008).  The duration of detection since infection depends on the test used. The development of HIV ELISA test has evolved to allow for early detection of Abs against the virus. The first generation of the tests required at least 42 days while the latest third generation requires about 23 days for them to be sensitive against the Abs against the virus. This study explores the application of ELISE tests in the diagnosis of HIV.

Material and Methods

The study involved taking a blood sample from 8 women who had unprotected sexual intercourse with HIV-positive men. The inner arm was cleaned using an antibacterial solution. A tourniquet was then applied around the arm to allow filling of the arm’s veins with blood. A needle was then used to obtain small blood sample after which a bandage was placed over the area of injection. The blood samples were then placed in Petri dishes with HIV antigens separately and allowed to react.

Sample selection

Before the tests were given, a briefing was done to inform the patients of the experiment. All factors of ethics such as anonymity and confidentiality were ensured. Moreover, all the participants were required to fill a consent form. Patient I (P1) had unprotected sexual intercourse 18 months before the test. P2, P3 & P4, P5 and P6, P7 and P8 had sexual intercourse 10, 7, 2, 3 and 1 months respectively.


The seropositivity results from the examination showed P1, P2, P4, P5 and P6 were positive. On the other hand, P3, P7 and P8 were negative.


The following table summarizes the results of the experiment.

Patient Time span between sexual intercourse and the test Seropositivity
P1 18 months Positive
P2 10 months Positive
P3 7 months Negative
P4 7 months Positive
P5 2 months Positive
P6 2 months positive
P7 3 months Negative
P8 1 month Negative


The Western Blot antibody test is an additional test that can be done to confirm HIV- seropositivity. It is also an antibody test; that means that it relies on the emergence of antibodies that come about as a result of the HIV, so as to ensure the positivity result (Van Dyk, 2008). The ELISA test is preferred to the Western blot test as it is less expensive compared to the latter. Also, it also never used as a screening test, rather it is used a confirmatory test in special circumstances but this depends mostly on the laboratory performing the test. A positive result from the Western blot test infers the presence of the HIV, therefore, inferring the possibility of developing AIDS. However, the reliability and accuracy of this test are questionable as, the antigens used in this test are identical to those in other human proteins. This factor implies that a positive result from the Western Blot analysis may not necessarily mean that there is the presence of HIV infection. A disease may interfere with the Western Blot test for HIVinclude TB (Mullis, 1993).

The PCR (Polymerase Chain Reaction) technique is among the most valuable confirmatory test techniques to detect the presence of HIV. This test technique works by detecting the nucleic acid present in the HIV. The nucleic acid may be RNA or DNA of the virus. The PCR technique is very sensitive as it detects very little amount/fragment of the HIV; to the specificity of 1 fragment in 100,000 hosts cells. This test can be used as both the screening test as well as confirmatory test. The qualitative PCR test can also be used for early diagnostic purposes; for example testing babies that have been delivered to HIV-positive mothers, or in the cases of post-rape cases.

CD4 counting technique can also be used as an HIV test that works by analyzing the blood concentration of CD4-lymphocytes. CD4 lymphocytes and their amount are regarded as a signifying factor of the robustness and the functionality of a person’s immune system, as well as the ability to guard the body against diseases. The HIV destroys the CD4 cells, therefore depleting them immensely. This phenomenon reduces the immunity of a person’s body to the disease. The greater the HIV viral load, the lower the concentration of CD4 cells.

HIV-seronegative case

In cases where the ELISA test shows negative results, of a patient who had unprotected sex with an HIV-positive person, they should undergo a confirmatory test. The significance of this test is to confirm that the first test was not faulty. A more sensitive test should be performed such as a PCR test, which is a more reliable test as discussed earlier. Besides, the patient should wait for a few months; say three, as some of the patients do not exhibit enough antibodies in their blood to show HIV infection (Spivak, et al., 2010).

The diagnostic reasons for using ELISA as a test method for HIV include the fact that it is a sensitive test; meaning that it detects a very little amount of antibodies present in the blood. Another reason is the fact that it is reliable and last, but not least the reliability and sensitivity of the test renders it not to produce false positives (Doctor NDTV book series, 2008).

One may add blood sample to the sensitivity testing medium in cases where the viral load is below 50 copies of the antibodies per 1 ml. This activity results in the exaggerated result but does not represent the actual viral load of a patient’s body (Nam, 2015).

Antagonistic activity is the opposition of a certain body activity facilitated by a chemical agent. For example, an agent that opposes a drug whose role is to cause an action on the nervous system. An antagonistic activity may be through inhibition or blockage of the whole process. Antibiotic combination refers to the use of two antibiotic agents so as to complete a certain wanted process. One of the antibiotic agent involved cannot complete the process required until the other agent is introduced into the system [Leekha, et al., 2010].

According to Public Health England (2015) the essence of isolating a gram positive becterium from a normally sterile site would be the indication of a posible infection. Such an infection might be life threatening. Moreover, the isolation allows for the screening of the suceptibility of the organisms to antibiotics. On the other hand, Williams, Ketley and Salmond (1998) explain that the essence of isolation of the gram positive bacteria from a non-sterile site is that it indicates a possible contamination or colonization that may also result to a health problem.


ELISA test is the most preferred screening test for the HIVdue to its inexpensive nature, as well as its sensitivity and reliability. However, a positive test cannot be guaranteed without confirmatory tests from other methods, which can be any of the techniques described in the previous section. The sensitivity of the test may also vary depending on various factors, such as the type of antigens used and the concentration of the HIV in the patient’s blood.






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