Translational Model of Zika Virus Disease in Baboons

Abstract

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus with devastating outcomes seen recently in the Americas due to the association of maternal ZIKV infection with fetal microcephaly and other fetal malformations not previously associated with flavivirus infections. Here, we have developed the olive baboon (Papio anubis) as a nonhuman primate (NHP) translational model for the study of ZIKV pathogenesis and associated disease outcomes to contrast and compare with humans and other major NHPs, such as macaques. Following subcutaneous inoculation of adult male and nonpregnant female baboons, viremia was detected at 3 and 4 days postinfection (dpi) with the concordant presentation of a visible rash and conjunctivitis, similar to human ZIKV infection. Furthermore, virus was detected in the mucosa and cerebrospinal fluid. A robust ZIKV-specific IgM and IgG antibody response was also observed in all the animals. These data show striking similarity between humans and the olive baboon following infection with ZIKV, suggesting our model is a suitable translational NHP model to study ZIKV pathogenesis and potential therapeutics.IMPORTANCE ZIKV was first identified in 1947 in a sentinel rhesus monkey in Uganda and subsequently spread to Southeast Asia. Until 2007, only a small number of cases were reported, and ZIKV infection was relatively minor until the South Pacific and Brazilian outbreaks, where more severe outcomes were reported. Here, we present the baboon as a nonhuman primate model for contrast and comparison with other published animal models of ZIKV, such as the mouse and macaque species. Baboons breed year round and are not currently a primary nonhuman primate species used in biomedical research, making them more readily available for studies other than human immunodeficiency virus studies, which many macaque species are designated for. This, taken together with the similarities baboons have with humans, such as immunology, reproduction, genetics, and size, makes the baboon an attractive NHP model for ZIKV studies in comparison to other nonhuman primates.

Keywords: West Nile virus; ZIKV; Zika virus; baboon; flavivirus; nonhuman primate.

FIG 1

Timeline of ZIKV infection and sample collection from male and female olive baboons. Adult nonpregnant female and male baboons (n = 3) were infected subcutaneously with ZIKV at 10⁴ FFU and 10⁶ FFU, respectively. For the female study, blood and saliva were collected at 0, 2, 4, 8, 14, 21, and 43 dpi. Urine was collected at 0, 2, 4, 6, 10, 14, 21, and 43 dpi and CSF at 0, 2, 8, 14, 21, and 43 dpi. For the male study, blood was collected at 0, 3, 4, 5, 6, 7, 11, 13, 20, 27, 34, and 41 dpi. Urine and saliva were collected at 0, 4, 6, 11, 13, 20, 27, 34, and 41 dpi and CSF at 4, 6, 11, 13, 20, 34, and 41 dpi. Necropsies were performed at 43 dpi for the female study and 41 dpi for the male study.

FIG 2

Whole-blood platelet counts from male and female baboons. CBCs were performed on EDTA-anticoagulated whole blood for female (A) and male (B) baboons. Platelet counts per milliliter of whole blood are shown for the specified time points postinfection with ZIKV.

FIG 3

ZIKV loads in blood, mucosal fluids, and CSF from infected male and female baboons. ZIKV RNA was extracted from specimens collected from each animal at the indicated days postinfection and quantitated by one-step qRT-PCR in whole blood, saliva, CSF, and urine from females (A, C, E, and G) and males (B, D, F, and H).

FIG 4

ZIKV loads in tissues collected at necropsy. ZIKV RNA was extracted from flash-frozen tissue samples collected at necropsy on day 41 postinfection and quantitated by one-step qRT-PCR. LT, left; RT, right; Sem. Ves., seminal vesicle; Ing. LN, inguinal lymph node; Mes LN, mesenteric lymph node.

FIG 5

Anti-ZIKV IgM and IgG and anti-WNV IgG responses in male and female baboon sera. Sera from infected baboons were tested by ELISA for antibodies (Abs) directed against ZIKV infection. IgM (A) and IgG (C) antibodies in female sera and IgM (B) and IgG (D) antibodies in male sera were tested at the indicated days postinfection. Male (F) and female (E) sera from ZIKV-infected baboons were also tested by ELISA for the presence of IgG antibodies against WNV. Female F2 and male M3 tested positive for WNV infection. The dashed lines represent the assay cutoff controls for IgM and IgG detection in the samples.

FIG 6

Cytokines and growth factor expression in baboon sera following ZIKV infection. Cytokine and growth factor expression for the female (A) and male (B) baboons were determined during the acute (bars A) and convalescent/latent (bars L) phases post-ZIKV infection. A paired t test was used to test for differences between preinfection (day 0) plasma cytokine concentrations and peak plasma cytokine concentrations obtained in the acute phase (≤10 dpi) and the convalescent phase (≥14 dpi) for each baboon, since individual starting concentrations were highly variable between animals, as was the day of the peak plasma cytokine response. All the data are presented as means and standard errors of the mean (SEM). The numbers above the bars are P values; bars without the numbers have P values of >0.1.

FIG 7

ELISPOT assay for detecting ZIKV antigen-specific IFN-γ-producing cells. Aliquots of PBMCs from ZIKV-infected baboons were stimulated with either ZIKV envelope protein, ZIKV NS1 protein, or PHA as a positive control. The total number of SFCs in duplicate wells was determined for each sample and adjusted to that for negative-control medium-only background wells.