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| SHORT RESEARCH COMMUNICATION |
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| Year : 2020 | Volume
: 57
| Issue : 2 | Page : 187-188 |
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Human Rickettsia felis infection in India
Siraj A Khan1, Trishna Bora1, Allen L Richards2
1 Medical Entomology, Arbovirology and Rickettsial Disease Division, ICMR-Regional Medical Research Centre, Northeast Region Assam, India
2 Rickettsial Disease Research Unit, Naval Medical Research Center, 503 Robert Grant Avenue, Silver Spring, Maryland, USA
| Date of Submission | 21-Feb-2019 |
| Date of Acceptance | 25-Sep-2019 |
| Date of Web Publication | 14-Jul-2021 |
Correspondence Address:
Dr Siraj A Khan
ICMR- Regional Medical Research Centre, Northeast Region Dibrugarh, Assam
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0972-9062.310873
Keywords: Felis; human infection; Northeast India; Rickettsia
How to cite this article:
Khan SA, Bora T, Richards AL. Human Rickettsia felis infection in India. J Vector Borne Dis 2020;57:187-8 |
Rickettsia felis, a flea-borne spotted fever group rickettsioses, is an important cause of febrile illness in Asia. More than 20 countries have reported R. felis in the cat flea Ctenocephalides felis, which is the primary vector for this rickettsia[1]. R. felis has also been detected in ticks, mites and more recently in mosquitoes, suggesting additional arthropod’s potential role in transmitting the disease[1],[2]. There are scarce reports of human infection with R. felis in India. However, during the past few years, rickettsial diseases have been a rising concern of public health threat throughout India. Among these, scrub typhus (ST) has drawn nationwide attention due to its prevalence and distribution, followed by spotted fever group rickettsioses (SFGR) and murine typhus[3]. Herein, we document the first human case of R. felis infection in the hilly state of Nagaland, Northeast India.
Following the re-emergence of ST in Nagaland (26.1584° N, 94.5624° E) bordering Myanmar; there had been an increasing number of ST cases detected in this state[4]. This led to an epidemiological survey conducted during 2013 in a ST endemic village of Porba in the Phek district of Nagaland. Porba has roughly a population of 2800 individuals. During the survey, blood samples were randomly collected from 317 residents. Serum samples were screened for IgG antibodies against all three rickettsial sero-groups viz., ST, SFGR and typhus group rickettsiae (TGR) using group specific ELISA assays previously described[5]. Serology results demonstrated the highest prevalence of seropositives against ST at 35.6% (113/317) followed by a low prevalence of antibodies against SFGR at 2.2% (7/317) and no detection of TGR. The SFGR sero-positive samples, of which five were from males and two from females were further subjected to rickettsia specific PCR for subsequent gene amplification. DNA was extracted from blood samples using Qiagen blood mini kit as per manufacturers’ instruction (Qiagen, Hilden, Germany). PCR amplification was targeted for detection of Rickettsia specific 17 kDa antigen gene, citrate synthetase (gltA), outer membrane protein A (ompA) and outer membrane protein B (ompB)[6]. Amplicons were observed for the 17 kDa gene 434bp fragment for only one of the 7 samples. The blood sample was obtained from a 65 year old asymptomatic male living in Middle Khel (Mid segment of Porba village). Sequence analysis of the 17 kDa gene (GenBank Accession no: KM365086) performed by MEGA version 7.0 (Pennsylvania State University, PA, USA) revealed 100% similarity with R. felis. Closest homology was observed with R. felis strains prevalent in Mexico, Japan and California, Texas and South Carolina, USA [Figure 1]. Other genes were not amplified. On interviewing the person, he could not recall any prolonged fever in the past months or bite of insects. However, it was observed that homes in his locality had quite a number of domestic pets (especially dogs and cats) and in almost every household. | Figure 1: Dendrogram representing the sequence. Evolutionary history was inferred using Maximum Likelihood method based on the Kimura 2-parameter model.
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Worldwide, very few human R. felis infections have been reported, out of which 12 cases have been identified in Asia[7]. There have been quite a number of reports of R. felis infection in asymptomatic subjects in Sub-Saharan Africa[1], which led to the suspicion of humans possibly being a reservoir for R. felis[8]. However, its detection in an asymptomatic host does not give a true picture of the pathogenic potential of R. felis in causing human disease. The recent detection of R. felis in Aedes albopictus mosquito (which is a potential vector of dengue and chi-kungunya) warrants attention and further studies in this direction[2]. Every year, a large number of dengue and chi-kungunya cases occur in India, including Northeast (NE) states. Aedes albopictus is a well-established vector for these diseases in the NE states[9],[10]. Given the abundance of Aedes spp., there is every possibility of advantageous niche for enhancing R. felis transmission, beside its primary ones. Thus, there is an immediate need for understanding the transmission dynamics of rickettsial diseases in India and especially identifying potential vectors/reservoir host. It is important to look for R. felis infection in patients with fever of unidentified origin. However, the non-specific disease presentation and lack of appropriate diagnostic remains a major obstacle in actual case identification. An expanded survey by epidemiologists needs to focus on generating information in terms of the disease epidemiology to understand the complex paradigm of R. felis transmission in India. Most importantly, awareness among clinicians about R. felis existence in India is paramount.
Ethical statement
Written consent was obtained from the study participants. This study was approved by the institutional ethics committee of the Regional Medical Research Centre, Dibrugarh, Assam, India.
| References | |  |
| 1. | Parola P. Rickettsia felis: From a rare disease in the USA to a common cause of fever in sub-Saharan Africa. Clin Microbiol Infect 2011; 17(7): 996–1000.  |
| 2. | Socolovschi C, Pages F, Raoult D. Rickettsia felis in Aedes albopictus mosquitoes, Libreville, Gabon. Emerg Infect Dis 2012; 18(10): 1687–9. |
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| 4. | Khan SA, Dutta P, Khan AM, Topno R, Borah J, Chowdhury P, et al. Re-emergence of scrub typhus in northeast India. Int J Infect Dis 2012; 16(12): e889–90. |
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| 6. | Jiang J, Blair PJ, Felices V, Moron C, Cespedes M, Anaya E, et al. Phylogenetic analysis of a novel molecular isolate of spotted fever group Rickettsiae from northern Peru: Candidatus Rickettsia andeanae. Ann N Y Acad Sci 2005; 1063: 337–42. |
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| 8. | Mediannikov O, Socolovschi C, Eduoard S, Fenollar F, Mouffok N, Bassene H, et al. Common epidemiology of Rickettsia felis infection and malaria, Africa. Emerg Infect Dis 2013; 19(11): 1775–83. |
| 9. | Dutta P, Khan SA, Khan AM, Sharma CK, Mahanta J. Survey of mosquito species in Nagaland, a hilly state of north east region of India. J Environ Biol 2010; 31(5): 781–5. |
| 10. | Dutta P, Khan SA, Khan AM, Sharma CK, Mahanta J. Entomological observations on dengue vector mosquitoes following a suspected outbreak of dengue in certain parts of Nagaland with a note on their susceptibility to insecticides. J Environ Biol 2004; 25(2): 209–12. |
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