Pathophysiology of the Rhesus Macaque Model for Inhalational Brucellosis

Abstract

The objective of this study was to characterize the rhesus macaque (RM) as a model for inhalational brucellosis in support of the U.S. Food and Drug Administration's (FDA) Animal Rule. The pathophysiology of chronic Brucella melitensis aerosol infection was monitored in two phases that each occurred over an 8-week time period; dose escalation (8 RMs; targeted doses of 5.0E؉03, 5.0E؉04, or 5.0E؉05 CFU/animal or the unchallenged control) and natural history (12 RMs; targeted dose of 2.50E؉05 CFU/ animal or the unchallenged control). RMs given an aerosol challenge with B. melitensis developed undulating fevers (6/6 phase I; 8/9 phase II), positive enriched blood cultures (5/10; phase II), and bacterial burdens in tissues starting 14 to 21 days postchallenge (6/6 phase I; 10/10 phase II). In addition, 80% (8/10; phase II) of infected RMs seroconverted 14 to 21 days postchallenge. RMs developed elevations in certain liver enzymes and had an increased inflammatory response by 3 weeks postchallenge as shown by increases in C-reactive protein (6/8) and neopterin (4/8), which correlated with the onset of a fever. As early as 14 days postchallenge, positive liver biopsy specimens were detected (2/8), and ultrasound imaging showed the development of splenomegaly. Finally, histopathologic examination found lesions attributed to Brucella infection in the liver, kidney, lung, and/or spleen of all animals. The disease progression observed with the RMs in this study is analogous to human brucellosis pathophysiology. Thus, the results from this study support the use of the RM as an animal model for inhalational brucellosis to evaluate the efficacy of novel vaccines and therapeutics against B. melitensis. Brucella is a Gram-negative coccobacillus that includes certain species that can cause disease in animals and humans. Brucella melitensis, one of the major species of Brucella, is an etiologic agent for brucellosis. This highly infectious pathogen can infect animals and humans, and it is considered to be one of the most severe human pathogens in the Brucella genus (25). Humans are usually infected following contact with infected animals or ingestion of contaminated milk, milk products, and meat. In addition, brucellosis is one of the most common laboratory-acquired infections, as well as the most common zoonosis (11). While B. melitensis is not typically considered a lethal pathogen in humans (less than 5% fatality rate), it can cause significant disease. Human brucellosis presents as a prolonged febrile illness with flu-like symptoms, such as night sweats, headache, depression, and arthritis. Chronic illness can lead to meningitis and endocarditis. In addition, relapses can occur, even with antibiotic treatment (13). Notably, humans can remain asymptomatic for weeks, months, or even years while infected with this pathogen (3).Brucella species are considered potential biological warfare agents due to their high infectivity, ability to debilitate infected people, and the persistent nature of human disease. In addition, Brucella i...

The Pathophysiology of Inhalational Brucellosis in Balb/c Mice

“…Overall, there were minimal changes in the hematology parameters for all the aerosol challenged Balb/c mice, which is similar to observations for the non-human primate (NHP) inhalational brucellosis model20 and human brucellosis patients420. Mild leucopenia with relative lymphocytosis, along with mild anemia and thrombocytopenia has been observed in human brucellosis patients21.…”

“…The lack of physical changes and unremarkable hematology results for the aerosol and IN challenged mice is consistent with human brucellosis patients, in which constitutive symptoms were observed in only 26% of 100 studied human brucellosis cases, and hematology results were indistinct for the majority of these patients22122232425. In addition, the mouse model is consistent with the NHP inhalational brucellosis model2026, in which abnormal clinical observations were rarely noted and the clinical hematology results only involved minimal changes to anemia-related parameters20. Endocarditis was observed for 8% (14/186) of challenged mice, which is consistent with this rare complication being observed in human brucellosis patients24.…”

“…Unlike the vast majority of human brucellosis patients and the NHP inhalational brucellosis model, the aerosol- and IN-challenged mice did not exhibit a fever at any point during the post-challenge period2021. The lack of a fever in mice infected with brucellosis has been noted previously by Silva et al18.…”

Particle size and pathogenicity in the respiratory tract

“…Bacterial pathogens such as Francisella tularensis , Burkholderia pseudomallei , Brucella suis , and Yersinia pestis proliferate within the alveolar spaces or alveolar macrophages causing an influx of neutrophils that contribute to a massive cytokine storm resulting in edema and pneumonic consolidation characteristic of primary pneumonia. Eventually tissue destruction leads to dissemination to visceral organs, septic shock and death 69 - 72 , 75 , 76 , 79 - 82 77 …”

Medical Countermeasures for Biothreat Agents: Need for Inhalation Challenge Models

“…Brucella species are considered potential biothreat agents due to their high infectivity, the persistent nature of human disease, and its easy dissemination by aerosols to cause disease. Rhesus macaque (RM) has been demonstrated as an animal model for inhalational brucellosis to evaluate the efficacy of novel vaccines against B. melitensis [7].…”