Journal Article

Characterization of the rhesus macaque (Macaca mulatta) scrub typhus model: Susceptibility to intradermal challenge with the human pathogen Orientia tsutsugamushi Karp

Im-erbsin, Rawiwan, Jones, James W., Sunyakumthorn, Piyanate, Dunachie, Susanna J., Lombardini, Eric D., Day, Nicholas P. J., Jenjaroen, Kemajittra, Mason, Carl J., Somponpun, Suwit J., Blacksell, Stuart D., Richards, Allen L., Paris, Daniel H., Anantatat, Tippawan, Burke, Robin L.

2018

Overview

Scrub typhus is an important endemic disease in tropical Asia caused by Orientia tsutsugamushi for which no effective broadly protective vaccine is available. The successful evaluation of vaccine candidates requires well-characterized animal models and a better understanding of the immune response against O. tsutsugamushi. While many animal species have been used to study host immunity and vaccine responses in scrub typhus, only limited data exists in non-human primate (NHP) models. In this study we evaluated a NHP scrub typhus disease model based on intradermal inoculation of O. tsutsugamushi Karp strain in rhesus macaques (n = 7). After an intradermal inoculation with 106 murine LD50 of O. tsutsugamushi at the anterior thigh (n = 4) or mock inoculum (n = 3), a series of time course investigations involving hematological, biochemical, molecular and immunological assays were performed, until day 28, when tissues were collected for pathology and immunohistochemistry. In all NHPs with O. tsutsugamushi inoculation, but not with mock inoculation, the development of a classic eschar with central necrosis, regional lymphadenopathy, and elevation of body temperature was observed on days 7-21 post inoculation (pi); bacteremia was detected by qPCR on days 6-18 pi; and alteration of liver enzyme function and increase of white blood cells on day 14 pi. Immune assays demonstrated raised serum levels of soluble cell adhesion molecules, anti-O. tsutsugamushi-specific antibody responses (IgM and IgG) and pathogen-specific cell-mediated immune responses in inoculated macaques. The qPCR assays detected O. tsutsugamushi in eschar, spleen, draining and non-draining lymph nodes, and immuno-double staining demonstrated intracellular O. tsutsugamushi in antigen presenting cells of eschars and lymph nodes. These data show the potential of using rhesus macaques as a scrub typhus model, for evaluation of correlates of protection in both natural and vaccine induced immunity, and support the evaluation of future vaccine candidates against scrub typhus.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Animal models / Animal species / Animals / Antigen-presenting cells / Antigens / Armed forces / Assaying / Bacteremia / Bacteria / Biology and life sciences / Blood cells / Body temperature / Cell adhesion / Cell adhesion & migration / Cell adhesion molecules / Cell Adhesion Molecules - blood / Defence mechanisms / Disease / Disease control / Disease Models, Animal / Drainage / Endemic species / Evaluation / Funding / Genetic aspects / Health care / Hematology / Humans / Immune response / Immune response (cell-mediated) / Immune system / Immunity / Immunity, Cellular / Immunoglobulin G / Immunoglobulin M / Immunohistochemistry / Immunology / Infections / Injections, Intradermal / Inoculation / Inoculum / Laboratory animals / Leukocytes / Liver / Liver - enzymology / Liver - microbiology / Liver - pathology / Lymph / Lymph nodes / Lymphadenopathy / Lymphadenopathy - microbiology / Lymphatic system / Macaca mulatta / Macaca mulatta - microbiology / Medicine and Health Sciences / Molecules / Mortality causes / Necrosis / Orientia tsutsugamushi / Orientia tsutsugamushi - genetics / Orientia tsutsugamushi - immunology / Orientia tsutsugamushi - pathogenicity / Pathogens / Pathology / Physiological aspects / Polymerase chain reaction / Preventive medicine / Real-Time Polymerase Chain Reaction / Regional development / Research and Analysis Methods / Rhesus monkey / Scrub typhus / Scrub Typhus - immunology / Scrub Typhus - microbiology / Serum / Serum levels / Spleen / Spleen - immunology / Spleen - microbiology / Spleen - pathology / Strain / Supervision / Thigh / Tissue / Toxicity tests / Tropical climate / Tropical diseases / Typhus / Vaccines / Veterinary medicine / White blood cells