Clinical signs of trachoma are prevalent among Solomon Islanders who have no persistent markers of prior infection with Chlamydia trachomatis

Abstract

Background: The low population-prevalence of trachomatous trichiasis and high prevalence of trachomatous inflammation–follicular (TF) provide contradictory estimates of the magnitude of the public health threat from trachoma in the Solomon Islands. Improved characterisation of the biology of trachoma in the region may support policy makers as they decide what interventions are required. Here, age-specific profiles of anti-Pgp3 antibodies and conjunctival scarring were examined to determine whether there is evidence of ongoing transmission and pathology from ocular Chlamydia trachomatis (Ct) infection. Methods: A total of 1511 individuals aged ≥1 year were enrolled from randomly selected households in 13 villages in which >10% of children aged 1–9 years had TF prior to a single round of azithromycin mass drug administration undertaken six months previously. Blood was collected to be screened for antibodies to the Ct antigen Pgp3. Tarsal conjunctival photographs were collected for analysis of scarring severity. Results: Anti-Pgp3 seropositivity was 18% in 1–9 year olds, sharply increasing around the age of sexual debut to reach 69% in those over 25 years. Anti-Pgp3 seropositivity did not increase significantly between the ages of 1–9 years and was not associated with TF (p=0.581) or scarring in children (p=0.472). Conjunctival scars were visible in 13.1% of photographs. Mild (p<0.0001) but not severe (p=0.149) scars increased in prevalence with age. Conclusions: Neither conjunctival scars nor lymphoid follicles were associated with antibodies to Ct, suggesting that they are unlikely to be a direct result of ocular Ct infection . Clinical signs of trachoma were prevalent in this population but were not indicative of the underlying rates of Ct infection. The current World Health Organization guidelines for trachoma elimination indicated that this population should receive intervention with mass distribution of antibiotics, but the data presented here suggest that this may not have been appropriate.

Trachoma, Anti-Pgp3 Serology, and Ocular Chlamydia trachomatis Infection in Papua New Guinea

“…This pattern in PNG closely resembles that seen in the Solomon Islands and Vanuatu, where the prevalence of TF is high in children, but TT is rarely seen in adults [ 7 , 8 ]. In the Solomon Islands and Vanuatu, the prevalence of ocular CT infection in children with TF was 3.9% and 1.8%, respectively [ 11 , 28 ], and anti-Pgp3 seroprevalence did not increase with age [ 12 ]. By contrast, the prevalence of ocular CT infection on Kiritimati Island in Kiribati is 24% among children; there, anti-Pgp3 seroprevalence among 1- to 9-year-olds exceeds 50% [ 29 ].…”

“…Conjunctival swabs were collected from children with TF using previously described methods [ 12 ]. As usual in studies of ocular CT infection [ 19–22 ], to contain study costs, a maximum of 1 eye was swabbed per person; where an individual’s eye was swabbed, we swabbed the right eye.…”

“…Dried blood spots were collected as described previously [ 12 ]. Specimens were refrigerated within 1 day, frozen within 1 week, and then shipped at ambient temperatures to the PNG-IMR laboratory.…”

“…In the Solomon Islands and Vanuatu, nucleic acid amplification–based testing for ocular Chlamydia trachomatis (CT) infection has demonstrated that the prevalence of infection is much lower than in districts outside of Melanesia with similar TF prevalence [ 11 ]. This finding is complemented by serological data suggesting that ocular CT transmission is low [ 12 ]. These data suggest that TF in Melanesian countries may not be entirely due to CT.…”

No Serological Evidence of Trachoma or Yaws Among Residents of Registered Camps and Makeshift Settlements in Cox’s Bazar, Bangladesh

“…Seroprevalence of anti-C. trachomatis antibodies typically increases with age among 1to 9-year-olds in areas with ongoing transmission [10][11][12] but remain relatively flat, with low seroconversion rates, 13 in the absence of transmission [14][15][16] and in settings where the presence of TF does not correlate with ocular C. trachomatis infection. 17,18 Serologic testing is standard for yaws diagnosis: the T. pallidum particle agglutination (TPPA) assay reflects a history of T. pallidum infection, whereas nontreponemal tests such as rapid plasmin reagin (RPR) detect antibodies against host molecules released in response to infection, giving an indication of current or recent exposure. These tests together are diagnostic for active yaws or syphilis (caused by T. pallidum sp.…”