Establishment of the Black-Tailed Prairie Dog (Cynomys ludovicianus) as a Novel Animal Model for Comparing Smallpox Vaccines Administered Preexposure in both High- and Low-Dose Monkeypox Virus Challenges

Abstract

The 2003 monkeypox virus (MPXV) outbreak and subsequent laboratory studies demonstrated that the black-tailed prairie dog is susceptible to MPXV infection and that the ensuing rash illness is similar to human systemic orthopoxvirus (OPXV) infection, including a 7-to 9-day incubation period and, likely, in some cases a respiratory route of infection; these features distinguish this model from others. The need for safe and efficacious vaccines for OPVX in areas where it is endemic or epidemic is important to protect an increasingly OPXV-naïve population. In this study, we tested current and investigational smallpox vaccines for safety, induction of anti-OPXV antibodies, and protection against mortality and morbidity in two MPXV challenges. Although smallpox has been eradicated (5), orthopoxviruses (OPXVs), such as variola virus (VARV) (6, 32), monkeypox virus (MPXV) (3, 10, 57), vaccinia virus (VACV) (4, 76), and others (53,68,77), are a continuing public health concern (61, 67). Due to cellular and humoral protective effects (7,15,16,46,73), the traditional live VACV-based smallpox vaccines provide cross-protection against multiple OPXV threats (48). Unfortunately, the cessation of routine vaccination (37) has left much of the global population fully susceptible to OPXV infections (34), and the adverse effects of first-and secondgeneration vaccines (78) coupled with increases in the global immunocompromised population (59) underline the need for continued development and testing of safer smallpox vaccines (30).Testing of smallpox vaccines requires the development of relevant animal models. Current smallpox vaccine testing animal models include ectromelia virus (ECTV) infection of mice (75), VACV infection of mice (63), rabbitpox virus (RPXV) and VACV infection of rabbits (1, 18), VARV and MPXV infection of nonhuman primates (NHP) (13,19,21,25,26,31), and others (65, 74). Limitations of current models include abbreviated disease incubation periods and/or differences from human systemic orthopoxvirus disease presentation and progression The validation of alternative animal models for smallpox vaccine testing is an ongoing effort (2, 19, 39).The MPXV outbreak in the United States in 2003 (3) identified a potential alternative model as it established that MPXV can be transmitted to black-tailed prairie dogs (Cynomys ludovicianus) (42). Investigations of the MPXV outbreak and epidemiological, immunological, and pathological studies of prairie dogs infected with MPXV (8,12,27,28,35,38,43,57,58,64,69,74,80) determined that this rodent species can manifest MPXV infection similar to human systemic OPXV disease. This disease model shares a respiratory route of infection, similar disease incubation period, and similar rash illness (20,29,38,42,80) with human MPXV and VARV infections, thus making it a potentially useful small animal model for testing vaccines and therapeutics (29,70). A particular strength of this model is its 7-to 9-day incubation period, which is more similar to that seen in human disease than many other a...

Humoral Immunity to Smallpox Vaccines and Monkeypox Virus Challenge: Proteomic Assessment and Clinical Correlations

“…Monkeypox virus infection of prairie dogs produces disease that is highly similar to that in humans after systemic OPV infection, and protection from disease occurs when animals are vaccinated prior to challenge with monkeypox virus (24,25). Additionally, since vaccination in humans produces an antibody response correlated with protection, a highly similar response in prairie dogs would further support their use as a surrogate animal model of OPV vaccination.…”

“…In Dryvax revaccination cases, only a modest increase in the number of recognized targets has been seen (40). We also recently showed that disease severity, as judged by weight loss, lesion count, and nasal involvement, was significantly limited upon challenge after vaccination, particularly after Dryvax or Acam2000 vaccination (25). Although the limited number of immunodominant antigens after vaccination may have been expected to continue dominating the profile, along with the addition of a few novel targets that may have been recognized during vaccination but failed to generate a detectable antibody response, the large increase here suggests that differences in virus pathogenicities or life cycles affect immune recognition.…”

“…The animals ranged between 9 and 12 months of age during vaccination and challenge. Sera from a series of studies described previously (25) were utilized and are summarized in Table 1. The animals in study 1 (n ϭ 9 animals) were divided into 2 groups of 3 animals each and inoculated with Dryvax or Acam2000 with 2 ϫ 10 5 PFU of vaccine via multiple puncture (m.p.).…”

“…ELISA. A modified version of an enzyme-linked immunosorbent assay (ELISA) was used for analysis of prairie dog anti-OPV (25). Briefly, microtiter plates (Immulon II; Dynatech) were coated with crude VACV or BSC-40 cell lysate by overnight incubation and subsequently inactivated, blocked, and washed prior to incubation with dilutions of prairie dog sera and then ImmunoPure A/G-horseradish peroxidase (HRP) conjugate (Pierce).…”

“…)-infection model, including a protracted asymptomatic incubation phase similar to that of human smallpox (24). Further refinement of the model allowed testing of vaccine efficacy using 1st-, 2nd-, and 3rd-generation smallpox vaccines (25).…”