Risk of infection with arboviruses in a healthy population in Pakistan based on seroprevalence

Abstract

Infectious diseases caused by arboviruses are a public health concern in Pakistan. However, studies on data prevalence and threats posed by arboviruses are limited. This study investigated the seroprevalence of arboviruses in a healthy population in Pakistan, including severe fever with thrombocytopenia syndrome virus (SFTSV), Crimean-Congo hemorrhagic fever virus (CCHFV), Tamdy virus (TAMV), and Karshi virus (KSIV) based on a newly established luciferase immunoprecipitation system (LIPS) assays, and Zika virus (ZIKV) by enzyme-linked immunosorbent assays (ELISA). Neutralizing activities against these arboviruses were further examined from the antibody positive samples. The results showed that the seroprevalence of SFTSV, CCHFV, TAMV, KSIV, and ZIKV was 17.37%, 7.58%, 4.41%, 1.10%, and 6.48%, respectively, and neutralizing to SFTSV (1.79%), CCHFV (2.62%), and ZIKV (0.69%) were identified, as well as to the SFTSV-related Guertu virus (GTV, 0.83%). Risk factors associated with the incidence of exposure and levels of antibody response were analyzed. Moreover, co-exposure to different arboviruses was demonstrated, as thirty-seven individuals were having antibodies against multiple viruses and thirteen showed neutralizing activity. Males, individuals aged ≤40 years, and outdoor workers had a high risk of exposure to arboviruses. All these results reveal the substantial risks of infection with arboviruses in Pakistan, and indicate the threat from co-exposure to multiple arboviruses. The findings raise the need for further epidemiologic investigation in expanded regions and populations and the necessity to improve health surveillance in Pakistan.

Keywords: Arbovirus; Mosquito-borne virus; Pakistan; Seroprevalence; Tick-borne virus.

Fig. 1

Seroprevalence of severe fever with thrombocytopenia syndrome virus (SFTSV), Crimean-Congo hemorrhagic fever virus (CCHFV), Tamdy virus (TAMV), Karshi virus (KSIV) and Zika virus (ZIKV) among humans in Pakistan. A The levels of antibody response to SFTSV, CCHFV, TAMV, and KSIV were determined by luciferase ​immunoprecipitation ​system (LIPS) assays and were expressed as the fold change of luciferase activity to cut-off values. B Representative immunofluorescence assay (IFA) results of human serum samples having antibody response to CCHFV. Images of three LIPS-negative samples and seven LIPS-positive samples are presented. The samples having neutralization to CCHFV are indicated by red characters. Three samples from Wuhan, China are shown as control, and the positive control was blotted using a polyclonal antibody specific to CCHFV NP. C The levels of antibody response to ZIKV were measured by ELISA and were shown as the OD values.

Fig. 2

Serologic evidence of human co-exposure to multiple arboviruses in Pakistan. Antibody titers to different viruses are shown in columns, and neutralizing activity against viruses is presented in colored circles. Cases with antibody titers to two or three viruses and neutralizing activity against one or two of these viruses are shown in bold. Cases with neutralizing activity against severe fever with thrombocytopenia syndrome virus (SFTSV) and Guertu virus (GTV) are shown in light blue, and those with neutralizing activity against two other viruses are shown in lavender. Cases with antibody response to SFTSV and neutralizing activity against GTV are shown in light green. Antibody titers are expressed as the fold changes in luciferase activity or enzyme-linked immunosorbent assays (ELISA) optical density values compared to cut-off values. Neutralizing titers are expressed as the reciprocal of the highest dilution that prevents viral infection.

Fig. 3

Risk factors for transmission of arboviruses based on seroprevalence and antibody levels. Seroprevalence of different viruses is shown in columns, and antibody responses are shown in box plots with 10–90% percentiles. The titer of the antibody response is indicated by the fold change of luciferase activity by luciferase ​immunoprecipitation ​system (LIPS) or enzyme-linked immunosorbent assays (ELISA) optical density values compared to cut-off values. Statistical significance was set at P ​< ​0.05 for statistical analysis. Individuals with no significant difference are not indicated in the figure. Asterisk indicates statistically significant differences (∗P ​< ​0.05; ∗∗P ​< ​0.01).