Intratracheal Inoculation with Brucella melitensis in the Pregnant Guinea Pig Is an Improved Model for Reproductive Pathogenesis and Vaccine Studies

Abstract

Reproductive failure is the hallmark of brucellosis in animals. An uncommon but important complication in pregnant women who become acutely infected with Brucella melitensis is spontaneous pregnancy loss or vertical transmission to the fetus. Unfortunately, the mechanism behind reproductive failure is still obscure, partially due to the lack of a proper study model. Recently, it was demonstrated that intratracheal inoculation (IT) of non-pregnant guinea pigs would replicate features of clinical disease in humans. To determine if IT would induce reproductive disease, guinea pigs were infected at mid-gestation and monitored them daily for fever and abortions. Fever developed between day 14 to 18 post-inoculation and by 3-weeks post-inoculation, 75% of pregnant guinea pigs experienced stillbirths or spontaneous abortions mimicking natural disease. Next, to investigate the guinea pig as a model for evaluating vaccine efficacy during pregnancy, non-pregnant guinea pigs were vaccinated with S19, 16MΔvjbR + Quil-A, or 100 μl PBS + Quil-A. Guinea pigs were bred and vaccinated guinea pigs were challenged at mid-gestation with B. melitensis IT and monitored for fever and abortions. Vaccination with both vaccines prevented fever and protected against abortion. Together, this study indicates that pregnant guinea pigs are an appropriate animal model to study reproductive disease and offer an improved model to evaluate the ability of vaccine candidates to protect against a serious manifestation of disease.

Intratracheal inoculation results in Brucella-associated reproductive disease in male mouse and guinea pig models of infection

“…), 100% of the guinea pigs had colonization of the spleen, liver, and lung (Figure 1B). Colonization of male guinea pigs is similar to that seen in non-pregnant and pregnant female guinea pigs when dosed with 10 7 IT, where colonization of the spleen, liver, and lung occurs in 91.6% of the animals during the peracute stage of infection and 100% by the acute stage (Hensel et al, 2019(Hensel et al, , 2020. When the kinetics of colonization in guinea pigs was explored, colonization of the liver (p < 0.01), spleen (p < 0.05), and lung (p < 0.05) was significantly increased at 4-weeks compared to 8-weeks p.i.…”

“…For this study, intratracheal inoculation was utilized as it mimics a natural transmission route, and IT intratracheal inoculation with 10 7 16 M has been shown to reliably produce reproductive disease in female guinea pigs (Hensel et al, 2019(Hensel et al, , 2020. Although a dose of 10-100 CFU reportedly results in clinical symptoms in humans, occupational exposures such as handling aborted placentas or unknown microbial cultures on an open bench could result in a much higher aerosolized dose (Pappas et al, 2003(Pappas et al, , 2006.…”

“…In order to deliver a targeted aerosol dose, an intratracheal route of inoculation using the PennCentury MicroSprayer™ was applied. This device has previously been used to inoculate guinea pigs and mice and generates a particle size that produces lower airway disease (Hensel et al, 2019(Hensel et al, , 2020. The benefit of intratracheal inoculation includes delivering a small particle size that is evenly distributed to the lower airways, and this route allows for a known infectious dose since it does not depend on the individual animal's respiratory physiology such as respiratory rate and depth.…”

“…The benefit of intratracheal inoculation includes delivering a small particle size that is evenly distributed to the lower airways, and this route allows for a known infectious dose since it does not depend on the individual animal’s respiratory physiology such as respiratory rate and depth. Dose titration and kinetics of this route of inoculation for B. melitensis were previously characterized in female guinea pigs, which resulted in colonization and pathologic changes in the uterus and placenta ( Gregory et al, 2019 ; Hensel et al, 2019 , 2020 ). Therefore, the objective of this study was to first characterize the kinetics of B. melitensis 16 M infection with an emphasis on impact to the male reproductive tract following intratracheal inoculation in two of the most commonly used animal models, C57Bl/6 mice and Hartley guinea pigs.…”

Comparative Review of Brucellosis in Small Domestic Ruminants

“…In favor of this, the promoting role of erythritol on B. melitensis expression on virulence genes, such as the Type IV secretion system VirB and flagellar proteins was also more recently demonstrated ( 58 ). However, there is increasing evidence that B. melitensis infect placenta and produce abortion in hosts such as humans ( 59 , 60 ), mice and guinea pigs ( 61 , 62 ), where erythritol is not a major component of the placenta. A clue to this mystery might have been recently deciphered by Barbier et al, who assigned a crucial role to the host polyol pathway enzyme aldose reductase, which catalyzes the synthesis of several alternative carbon (C) sources (including erythritol) for Brucella availability ( 63 ).…”