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Published on: May 24, 2011
Pathological Responses in Asian House Shrews (Suncus murinus) to the Naturally Acquired Orientia tsutsugamushi
Tharani Balasubramanian1, Uma Sambath1, Ranjana Devi Radja2
1Department of Veterinary Pathology, Rajiv Gandhi Institute of Veterinary Education and Research, Kurumbapet, Puducherry 605009, India.
Abstract:
Scrub typhus is a re-emerging disease caused by Orientia tsutsugamushi, transmitted by mites belonging to the family Trombiculidae. Humans and rodents acquire the infection by the bite of larval mites/chiggers. Suncus murinus, the Asian house shrew, has been reported to harbor the vector mites and has been naturally infected with O. tsutsugamushi. The present study aimed to localize and record O. tsutsugamushi in the tissues and the host response in shrews naturally infected with O. tsutsugamushi. Sheehan's modified May-Grunwald Giemsa staining was carried out in 365 tissues from 87 animals, and rickettsiae were documented in 87 tissues from 20 animals. Immunohistochemical (IHC) staining, using polyclonal antibodies raised against selected epitopes of the 56-kDa antigen, was carried out, and 81/87 tissue sections were tested positive for O. tsutsugamushi. By IHC, in addition to the endothelium, the pathogen was also demonstrated by IHC in cardiomyocytes, the bronchiolar epithelium, stroma of the lungs, hepatocytes, the bile duct epithelium, the epithelium and goblet cells of intestine, the tubular epithelium of the kidney, and splenic macrophages. Furthermore, the pathogen was confirmed by real-time PCR using blood (n = 20) and tissues (n = 81) of the IHC-positive animals. None of the blood samples and only 22 out of 81 IHC-positive tissues were tested positive by PCR. By nucleotide sequencing of the 56-kDa gene, Gilliam and Karp strains were found circulating among these animals. Although these bacterial strains are highly virulent and cause a wide range of pathological alterations, hence exploring their adaptive mechanisms of survival in shrews will be of significance. Given that the pathogen localizes in various organs following a transient bacteremia, we recommend the inclusion of tissues from the heart, lung, intestine, and kidney of reservoir animals, in addition to blood samples, for future molecular surveillance of scrub typhus.
Insights
Scrub typhus, caused by Orientia tsutsugamushi, was found in various shrew tissues, not just blood. This highlights the importance of tissue samples for accurate molecular surveillance of this re-emerging disease.
Area of Science:
- Veterinary Pathology
- Infectious Diseases
- Molecular Epidemiology
Background:
- Scrub typhus is a re-emerging zoonotic disease caused by Orientia tsutsugamushi.
- Asian house shrews (Suncus murinus) are known reservoirs for vector mites and O. tsutsugamushi.
- Understanding pathogen distribution in reservoir hosts is crucial for disease control.
Purpose of the Study:
- To localize Orientia tsutsugamushi within the tissues of naturally infected shrews.
- To characterize the host response to O. tsutsugamushi infection in Suncus murinus.
- To evaluate diagnostic methods for scrub typhus surveillance in reservoir animals.
Main Methods:
- Histopathological examination using Sheehan's modified May-Grunwald Giemsa staining on 365 shrew tissues.
- Immunohistochemical (IHC) staining with antibodies against the 56-kDa antigen of O. tsutsugamushi.
- Real-time PCR and nucleotide sequencing of the 56-kDa gene from blood and tissue samples.
Main Results:
- O. tsutsugamushi was detected in 20 out of 87 infected shrews via Giemsa staining.
- IHC confirmed O. tsutsugamushi in 81/87 tissue sections, localizing it in endothelium, cardiomyocytes, lung, liver, intestine, kidney, and spleen.
- Real-time PCR detected O. tsutsugamushi in only 22/81 IHC-positive tissues, and none of the blood samples; Gilliam and Karp strains were identified.
Conclusions:
- Orientia tsutsugamushi disseminates to multiple organs in shrews, beyond transient bacteremia.
- IHC is more sensitive than PCR for detecting O. tsutsugamushi in infected shrew tissues.
- Tissue samples from heart, lung, intestine, and kidney are recommended for future molecular surveillance of scrub typhus in reservoir hosts.
