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Relative Abundance of a Vector of Scrub Typhus, Leptotrombidium Sialkotense, in Southern Yunnan Province, China

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Relative Abundance of a Vector of Scrub Typhus, Leptotrombidium Sialkotense, in Southern Yunnan Province, China ISSN (Print) 0023-4001 ISSN (Online) 1738-0006 Korean J Parasitol Vol. 58, No. 2: 153-159, April 2020 ▣ ORIGINAL ARTICLE https://doi.org/10.3347/kjp.2020.58.2.153 Relative Abundance of a Vector of Scrub Typhus, Leptotrombidium sialkotense, in Southern Yunnan Province, China 1,2 1,2,3, 1 2 2 2 2 Yan Lv , Xian-Guo Guo *, Dao-Chao Jin , Wen-Yu Song , Rong Fan , Cheng-Fu Zhao , Zhi-Wei Zhang , Ke-Yu Mao2, Yun-Ji Zou2, Zhi-Hua Yang2 1Institute of Entomology, Guizhou University, and the Provincial Key Laboratory for Agricultural Pest Management in Mountainous Region, Guiyang 550025, China; 2Vector Laboratory, Institute of Pathogens and Vectors, Yunnan Provincial Key Laboratory for Zoonosis Control and Prevention, Dali University, Dali, Yunnan Province 671000, China; 3Yunnan Provincial Key Laboratory of Entomological Biopharmaceutical Research and Development, Dali University, Dali, Yunnan Province 671000, China Abstract: The chigger mite Leptotrombidium sialkotense is one of the 6 main vectors of scrub typhus in China. Before present study, L. sialkotense was found in some parts of Hunan province, China with a narrow geographical distribution. During field investigation 2016-2017, we found L. sialkotense in Jingha, southern Yunnan, China. Of 15 small mammal host species, L. sialkotense were collected from 6 species of the hosts. Rattus brunneusculus was a dominant host of L. sialko- tense, from which 98.3% of the mites were collected. The chigger mite showed a relatively high infestation prevalence (PM = 11.7%) and mean abundance (MA= 0.5) in comparison with the rest 5 host species. These results reveal a certain host specificity of L. sialkotense to a rat R. brunneusculus. The mite L. sialkotense showed an aggregated distribution on the host (P< 0.05). A positive correlation observed between L. sialkotense and the body length of hosts. There was a posi- tive interspecific association between L. sialkotense and 2 other dominant vectors, L. deliense and L. scutellare. Key words: Leptotrombidium sialkotense, chigger mite, vector, scrub typhu, host selection, rodent INTRODUCTION south [8-10]. Located in the southwest of China, Yunnan prov- ince is one of main foci of scrub typhus in China, with the dis- Chigger mites refer to 2 taxonomic families (Trombiculidae tribution of the disease in all the 16 prefectures and munici- and Leeuwenhoekiidae), and they belong to Acariformes, Aca- palities of the province. Of total 129 counties in 16 prefectures ri, Arachnida under Arthropoda [1-3]. There are more than and municipalities of Yunnan province, 118 counties have the 3,700 species of chigger mites widely distributed in the world cases of scrub typhus reported [10,11]. As an independent spe- and more than 400 species found in China [3-5]. The larvae of cies of chigger mites, Leptotrombidium sialkotense is one of the 6 chigger mites (chiggers) are the exclusive vector of scrub ty- main vectors of scrub typhus in China, and it plays an impor- phus (tsutsugamushi disease) and they are the only ectopara- tant role in the transmission of the disease [1,12]. Vercammen- sitic and disease-transmitting stage in their complex life cycle Grandjean and Langston [2] first named Leptotrombidium (Lep- [6,7]. The taxonomic identification of chigger mites has long totrombidium) imphalum sialkotense in 1976. After that some been based on the morphology of the larvae. Rodents and Chinese scholars described a new species of chigger mite, Lep- some other small mammals are the most important hosts of totrombidium (Leptotrombidium) jishoum in 1988 [13], which the larvae (chiggers). Scrub typhus transmitted by chiggers is was afterwards proved to be the synonymous species of L. (L.) widely distributed in many parts of China, especially in the imphalum sialkotense and was finally revised to Leptotrombidium sialkotense [14]. Leptotrombidium sialkotense was first found in Received 5 December 2019, revised 20 February 2020, accepted 24 February 2020. Jishou of Hunan province in 1988. Before this study, Chinese • Corresponding author ([email protected]) * scientists generally thought that L. sialkotense was an endemic © 2020, Korean Society for Parasitology and Tropical Medicine species of chigger mite in some parts of China with a very nar- This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0) row geographical distribution and it was mainly confined to which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Jishou, Guzhang and Baojing in Hunan province. During the 153 154 Korean J Parasitol Vol. 58, No. 2: 153-159, April 2020 investigation on chigger mite distribution in Yunnan province, tense mite was chosen as the target for the further statistical we found L. sialkotense at Jingha village, Jinghong county of Xi- analyses in this paper. shuangbanna Dai Autonomous prefecture in southern Yun- nan, where is far from the original distribution areas of L. si- Infestation calculation alkotense. The distribution of L. sialkotense at Jingha village is The constituent ratio (Cr), prevalence (PM), mean abun- the first report of the mite in the whole Yunnan province, dance (MA), and mean intensity (MI) were used to calculate which is of academic significance. the infestation of L. sialkotense on its hosts, rodents and some other small mammals [1,19-21]. MATERIALS AND METHODS N H M M C i 100% ； P m 100% ； MA ； MI r N M H H H Field investigation m From a field investigation from April 2016 to March 2017, SpatialNi and patternN are the analysis individuals of chigger mite species i and all With the combination of a random deviation test (F test), Iwao's regression equation was Leptotrombidium sialkotense was found at a localized area, Jing- the mite species; M, Hm, and H the individuals of L. sialkotense, used to analyze the spatial distribution pattern of L. sialkotense on 6 hosts [22-24]. The ha village in Jinghong county of Xishuangbanna Dai Autono- infestedformulasN hosts are asand follows: all the hostsH [1,19-21]. M M C i 100% ； P m 100% ； MA ； MI Mr* M (Iwao’sM linear regression) mous prefecture in southern Yunnan, southwest China. Jingha N H H H m N N H N M M village is near the coast of the Lancang river (a river from the Spatial 1 patterni 2 analysis； m ；2 2 ； Cr [N100 2% PM1 M 100 %1 MAM ] MI N H i i H H northwest to the south in Yunnan province), and located at SpatialWith2 the pattern combination analysisi 11 of a random ideviation test (F test),m F N With the combination1 of* a random deviation2 test (F test), Iwao's regression equation was 21˚50′ north latitude and 100˚52′ east longitude with an alti- Iwaoused's toregression analyze theequation spatialM i wasdistribution usedM ito analyzepattern of the L. spatial sialkotense dis- on 6 hosts [22-24]. The Spatial patternN analysis2 i1 tude of 500-700 m [15]. The village is a rubber planting area tribution formulas With the pattern are combination as follows:of L. sialkotense of a random on deviation6 hosts [22-24]. test (F test),The forIwao's- regression equation was with lots of rubber woodlands dotted with some banana mulasusedM* toare analyze as follows:M (Iwao’sthe spatial linear distribution regression) pattern of L. sialkotense on 6 hosts [22-24]. The N N formulas1 are as follows: 2 2 fields, farmlands, bush areas and broad-leaved forests. N[Ni 2 2 1 MH 1 M ] M M MC* Mi M100 (Iwao’s% ； P linear i mregression)100% ； MAi ； MI r 2 ij Mi11 2 i F j 1N N N H N H H 1 i 22 2 m M i 2 ; M1 i * M i * 1 [N 2 1 Mi 1 M i ] Ni Mi M i M i Collection of chigger mites and their hosts 2 N 2 i1 i 11i FSpatial pattern analysisN In field survey, the mousetraps were set to capture the host 1 * 2 With the combinationM i of a random M i deviation test (F test), Iwao's regression equation was Statistical analysisN 2 on ecological niche animals (rodents and some other small mammals) in evening Basedused to on analyze the constituent thei1 spatial ratio, distribution Levins' niche pattern breadth of L.was sialkotense adopted to on evaluate 6 hosts the [22-24]. host- The specificityformulasN i [16,21,25].are as follows: and checked in the next morning. Each captured host was put M 1 ij 2 M* j 1 M (Iwao’s linear i regression) into a separate cloth bag and brought to the laboratory where B N Mi i Si ; M i * M i 1 2 N N 1 Ni 2 M i 2 2 S MPihij 2 the host was anaesthetized with ether. Each anaesthetized host [N 2 1 M i 1 M i ] jh11 i 2 i11 i M i ; M i * M i 1 was carefully examined and chiggers were collected mainly InF IwaoN’s regression,N M andM M* are the mean and mean Statisticali analysis1 on ecological* i niche 2 Some other statistical analysesM M from the both auricles and external auditory canals of each crowding Based on of the the constituent mites (L. ratio,sialkotensei Levins'); αi niche and breadthβ the intercept was adopted to evaluate the host- Mann-WhitneyN U-tests2 i1 were used to detect the difference in the individuals of L. sialkotense host, where chiggers often attached. All the collected chiggers andStatisticalspecificity regression [16,21,25].analysis coefficient. on ecological In F test, nicheMij, and Ni are the individ- among different genders and ages of hosts. The correlation between the number of L.
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