Experimental respiratory anthrax infection in the common marmoset (Callithrix jacchus)

Abstract

Inhalational anthrax is a rare but potentially fatal infection in man. The common marmoset (Callithrix jacchus) was evaluated as a small non-human primate (NHP) model of inhalational anthrax infection, as an alternative to larger NHP species. The marmoset was found to be susceptible to inhalational exposure to Bacillus anthracis Ames strain. The pathophysiology of infection following inhalational exposure was similar to that previously reported in the rhesus and cynomolgus macaque and humans. The calculated LD(50) for B. anthracis Ames strain in the marmoset was 1.47 x 10(3) colony-forming units, compared with a published LD(50) of 5.5 x 10(4) spores in the rhesus macaque and 4.13 x 10(3) spores in the cynomolgus macaque. This suggests that the common marmoset is an appropriate alternative NHP and will be used for the evaluation of medical countermeasures against respiratory anthrax infection.

Figure 1

Gram stained spleen section from marmoset taken at necropsy (day 4 post-challenge) infected with 1.0 × 10³ cfu by the aerosol route. Numerous black bacilli were evident. 10× magnification.

Figure 2

Haemotoxylin and eosin stained brain (cerebral cortex) section from marmoset taken at necropsy (day 4 post-challenge) infected with 1.0 × 10³ cfu by the aerosol route. Scattered bacilli are evident by Gram staining within capillaries and leptomeningeal vessels. 20× magnification.

Figure 3

Haemotoxylin and eosin stained liver section from marmoset taken at necropsy (day 4 post-challenge) infected with 1.0 × 10³cfu by the aerosol route. Evidence of fibrinoid necrosis of the hepatic vessel (arrowed) and numerous bacilli and neutrophils are present. 40× magnification.

Figure 4

Gram stained liver section from marmoset taken at necropsy (day 4 post-challenge) infected with 1.0 × 10³ cfu by the aerosol route. Numerous bacilli within sinusoids and vessels were evident. 20× magnification.

Figure 5

Gram stained lung section from marmoset taken at necropsy (day 4 post-challenge) infected with 1.0 × 10³ cfu by the aerosol route. Mild alveolar congestion was evident with numerous bacilli within capillaries. 20× magnification.

Figure 6

(a–d) Splenic grading system (a) Grade 1: normal spleen, (b) Grade 2: cellularly dense red pulp with white pulp lymphoid follicle, (c) Grade 3: less dense red pulp with prominent germinal centre, (d) Grade 4: depleted red pulp replaced with fibrin and bacilli. All at 10× magnification.