Seroprevalence of anti-Chlamydia trachomatis IgA antibody in a Nigerian population: diagnostic significance and implications for the heterosexual transmission of HIV.
B Nwanguma, I Kalu, L Ezeanyika
chlamydia trachomatis, hiv, nigeria, seroprevalence
B Nwanguma, I Kalu, L Ezeanyika. Seroprevalence of anti-Chlamydia trachomatis IgA antibody in a Nigerian population: diagnostic significance and implications for the heterosexual transmission of HIV.. The Internet Journal of Infectious Diseases. 2008 Volume 7 Number 2.
The prevalence of
Additional attention is being paid to a number non-viral, sexually transmitted infections (STIs) because of recent thinking that they predispose to heterosexual transmission of HIV infection by a variety of mechanisms. For example, the lesions created by the ulcerative STIs, like syphilis, are believed to serve as portals that facilitate the entry of HIV during heterosexual intercourse between an infected person and an uninfected partner . On the other hand, the non-ulcerative STIs, for example, trichomoniasis, gonorrhoea and chlamydia
Whereas syphilis, trichomoniasis and gonorrhoea have since been known and treated as serious public health problems amongst sexually active people,
On the contrary, across-the-board data on the prevalence of genital
In this paper, we report the findings of a study on the prevalence of anti
Materials And Methods
Subjects and Location
The subjects used for the study were Nigerian residents of two cities, Owerri (urban) and Nsukka (semi – urban), both in South – Eastern Nigeria. The subjects were aged between 17 and 42 years and comprised 69 volunteers of unknown HIV status (group 1), 17 screened HIV-positive subjects (group 2) and 16 screened HIV-negative subjects.
The volunteers of unknown HIV status were recruited from students of Federal University of Technology Owerri and University of Nigeria, Nsukka, while the screened HIV-positive and HIV – negative groups were recruited from the HIV monitoring unit of the Federal Medical Centre, Owerri. Socio - demographic data were collected on a standard questionnaire together with information on their sexual behaviour and knowledge of
Anti – Chlamydia trachomatis ELISA
Detection of the HIV antibodies in the sera of patients was done with the use of commercial ELISA kits. The initial screening was done with HIV Q spot, Biosystems Nigeria and the positive results were counterchecked with another commercial ELISA kit, Immunocomb (Orgenics Israel).
The results of the prevalence experiments in all three groups of subjects are shown in table 1. Out of the 69 volunteers of unknown HIV status (group 1) included in the study, 23 (33.33%) were positive for Chlamydia antibodies. Within this group, the highest prevalence of 50% was observed in the 17 – 24 – year group, followed by the 25 – 33-year olds amongst whom the prevalence was 35.3% and the 34 – 42-year old group in which the lowest prevalence of 14.7% was recorded. On the other hand, the prevalence in the HIV-positive (group 2) and HIV – negative (group 3) subjects was 50% (8/16) and 17.6% (3/17), respectively.
The result of the questionnaire survey on some behavioural risk factors for genital
The association of untreated non-viral sexually transmitted infections with some long-term health implications as well as the heterosexual transmission of HIV has resulted in an upsurge of interest on the prevalence of these diseases, especially
The prevalence of 33.0% reported in this study on asymptomatic volunteers falls within this range, but such relatively high prevalence values are usually reported in subjects drawn from hospital settings, mostly those attending STI clinics . The high prevalence thus observed in this study could be due in part to the age distribution of the subjects, many of whom were adolescents or young adults - the age groups usually associated with the highest prevalence rates of Ct infection. A number of behavioural risk factors, which were revealed in the questionnaire that accompanied this study (Table 3), are also partly responsible for the relatively high prevalence reported in the study. These include intercourse with multiple sex partners (35.8%), non-use of barriers (25.45%) and previous history of STI (10.3%).
In addition, the high prevalence reported could also be due to the antibody detection method of assay, which is reputed to detect many more cases than the other methods of screening. The apparent inability of antibody-detection methods to differentiate between active and non-active Ct infections in prevalent studies is thought to be partly responsible for the much higher prevalence figures reported with them. Other unresolved issues concerning the diagnostic significance of results obtained with antibody detection methods in Ct screening include the apparent lack of knowledge on how long Ct antibodies remain in the serum after an infection has been resolved and the questions about the level of correlation between results of EIA assays and other methods. Recently, Siemer
The high prevalence figures reported in this study could have far-reaching health implications for both the individuals and for the larger society. Since most cases of genital Chlamydia remain asymptomatic , these subjects may have been or could remain infected for extended periods of time without seeking diagnosis and treatment. This opinion is supported by information gathered from the questionnaire that accompanied this study, which revealed that 68.0% of the subjects had no previous knowledge of the existence of
One of the consequences of the inflammatory and immune responses elicited by Ct infection in persons with active cases of untreated infection is that they could face an increased risk of heterosexual transmission of HIV by mechanisms involving the preferential aggregation of the virus on immune cells expressing CD4+ proteins. The prevalence of
However, the implication of this observation for the individual and the population could be viewed in two perspectives (figure 1).
When Chlamydia pre-exists before HIV infection, it predisposes the subjects to HIV infection through the initiation of inflammatory and immune responses which facilitate the entry of HIV . When HIV pre-exists before Chlamydia infection, the immune suppression typical of HIV infection increases the risk of Chlamydia infection occurring as an opportunistic infection. In subjects concurrently infected by both infections, the inflammation caused by untreated Chlamydia will increase the population of HIV-bound lymphocytes and macrophages present. This will in turn increase the viral shading in the HIV-infected individuals, thereby increasing the probability of HIV transmission during intercourse with an uninfected partner . The possible synergy that can occur between the infections is illustrated in figure 3. The possibility that HIV and any such concurrently existing STIs can be co-transmitted in the affected individuals has also been recognised .
In conclusion, a relatively high prevalence (33.5%) of Ct IgA antibody was observed in the population used for the study. Although these may not all represent active Ct infections, it can be inferred that a high percentage of the population has been exposed to Ct infection and many of them may still be habouring the active infection unknowingly. Based on the implication of untreated Ct infection for HIV transmission, such cases of untreated C. trachomatis may contribute to the alarming rate of heterosexual spread of C. trachomatis experienced in Nigeria, and by inference, the rest of sub-Saharan Africa. Because of the adverse implications of this observation for the individual and the larger society in terms of HIV transmission, amongst other health complications, there is an urgent need to promote the establishment of diagnostic centres for C. trachomatis in addition to promoting awareness on the existence and implications of C. trachomatis. In the interim, reducing the prevalence of chlamydia infection in the population could be achieved through treating patients infected by other STIs, such as gonorrhoea, with an effective anti-chlamydial regimen. Ideally, this should be part of a wider programme to reduce the incidence of all STIs.