Rattus Tanezumi Research Articles

Molecular Surveillance for Vector-Borne Bacteria in Rodents and Tree Shrews of Peninsular Malaysia Oil Palm Plantations

Many human clinical cases attributed to vector-borne pathogens are underreported in Malaysia, especially in rural localities where healthcare infrastructures are lacking. Here, 217 small mammals, consisting of rodents and tree shrews, were trapped in oil palm plantations in the Peninsular Malaysia states of Johor and Perak. Species identification was performed using morphological and DNA barcoding analyses, and 203 small mammals were included in the detection of selected vector-borne bacteria. The DNA extracted from the spleens was examined for Orientia tsutsugamushi, Borrelia spp., Bartonella spp. and Rickettsia spp. using established PCR assays. The small mammals collected in this study included Rattus tanezumi R3 mitotype (n = 113), Rattus argentiventer (n = 24), Rattus tiomanicus (n = 22), Rattus exulans (n = 17), Rattus tanezumi sensu stricto (n = 1) and Tupaia glis (n = 40). Orientia tsutsugamushi, Borrelia spp. and Bartonella phoceensis were detected in the small mammals with the respective detection rates of 12.3%, 5.9% and 4.9%. Rickettsia spp., however, was not detected. This study encountered the presence of both Lyme disease and relapsing fever-related borreliae in small mammals collected from the oil palm plantation study sites. All three microorganisms (Orientia tsutsugamushi, Borrelia spp. and Bartonella phoceensis) were detected in the R. tanezumi R3 mitotype, suggesting that the species is a competent host for multiple microorganisms. Further investigations are warranted to elucidate the relationships between the ectoparasites, the small mammals and the respective pathogens.

Epidemiology of Human Leptospirosis in Bantul District, Yogyakarta Province, Indonesia

Bantul District has the highest number of leptospirosis cases in Yogyakarta Province. Transmission of leptospirosis occurs primarily through exposure to water and soil contaminated with the urine of infected animals. This study aims to describe the epidemiological characteristics of leptospirosis in Bantul District, Yogyakarta. This is cross-sectional research. Leptospirosis cases were collected from active and passive detections. Selected positive cases underwent home visits for interviews about epidemiological data. Rat surveys were carried out to find out the existing rat species and successful traps in the study area. The most leptospirosis cases were found at Kasihan public health center. There were 74 suspect cases, 4 probable cases, and 15 cases positively confirmed. The cases increased from January to April and from November - December. Cases in males were more related to his work as a farmer. Fever, headache and muscle aches are the most common symptoms felt by leptospirosis sufferers. The most caught rats was Rattus tanezumi. Leptospirosis epidemiological information can be used as a basis or reference for Bantul District Health Office in prevention and control of leptospirosis in priority areas

Tissue cysts and serological detection toxoplasmosis among wild rats from Surabaya, East Java, Indonesia.

The protozoan Toxoplasma gondii is the source of zoonosis toxoplasmosis and causes public health problems throughout the world. Environmental contamination by oocysts excreted by cats as definitive hosts affects the spread of this disease. Wild rats as rodents can be used as an indicator of environmental contamination by oocysts, considering that rats have a habit of living in dirty environments and can be infected by oocysts from the environment. This study aims to detect toxoplasmosis from tissue cysts and serological tests in wild rats as an indicator of environmental contamination in Surabaya. A total of 100 wild rats collected from Surabaya were collected in five areas (West, East, Central, North, and South of Surabaya) obtained from three trapping locations: housing, dense settlements, and markets. All samples were examined microscopically for parasitological tests through the brain tissue samples, and the serum was examined using the toxoplasma modified agglutination test to detect the presence of IgG and Immunoglobulin M (IgM). This research used 100 wild rat samples, 77 Rattus tanezumi and 33 Rattus norvegicus, with evidence of 31% in serology and active infection with 19% tissue cyst. The results showed that the seroprevalence of T. gondii in wild rats was 31% (30% for IgG and 1% for IgM). Tissue cysts in the rat brain samples tested were 19% (19/100). The IgG prevalence rate in female rats was 25% (8/32), while for males, it was 32.3% (22/68). The highest seropositive IgG from densely populated settlements was 50%, markets were 25.8%, and housing was 12.1%. The highest seropositive IgM from densely populated settlements was 2.8%. Population density and the presence of cats are factors supporting the high seropositive rate at the trapping location. This study revealed that there has been toxoplasmosis contamination in Surabaya with evidence of 31% in serology and active infection with 19% tissue cyst. It is necessary for controlling with surveillance in cats to prevent transmission in humans.

Species diversity, abundance, and movement of small mammals in the dry evergreen forest at Khao Yai National Park, Thailand

Abstract. Chanachai Y, Nathalang A, Duengkae P, Sukmasuang R. 2022. Species diversity, abundance, and movement of small mammals in the dry evergreen forest at Khao Yai National Park, Thailand. Biodiversitas 23: 5892-5901. Small mammals play an integral role in the forest ecosystem. This research was conducted on The Mo Singto Forest Dynamics Plot, Khao Yai National Park. Trapping of small mammals was carried out in June-September 2019 and from January-April 2020 based on a total of 64 Tomahawk for small mammal live traps were systematically placed in an 8×8 grid of 20 m intervals, ripe bananas and palm oil as bait was used. Trap cages were opened for 3 consecutive months per season in each study period covering a total study period of 1 year. The result showed that a total of 4015 individuals from 9 species, 9 genera, 4 families and 3 orders were captured with a sampling effort of 32,555 trap nights. The most common species were Red Spiny Rat (Maxomys surifer), followed by Northern Tree Shrew (Tupaia belangeri), Long-tailed Giant Rat (Leopoldamys sabanus), Indochinese Ground Squirrel (Menetes berdmorei), Asian House Rat (Rattus tanezumi), Indomalayan Niviventer (Niviventer fulvescens), Savile's Bandicoot Rat (Bandicota savilei), (Tamiops mcclellandii), and Short-tailed Gymnure (Hylomys suillus) respectively. Considering the number of small mammals caught, Maxomys surifer was the most abundant, accounting for 61.69% of all mammals caught. The sex ratio was found to somewhat favor females in both seasons. This study indicated that the small mammal diversity was high in the primary dry evergreen forest. These results have important implications not only for conservation but are also useful for further investigation if there is any disturbance or change in the area or any potential disasters that may occur in the future.

Comparative phylogeography of two commensal rat species (Rattus tanezumi and Rattus norvegicus) in China: Insights from mitochondrial DNA, microsatellite, and 2b-RAD data.

Rattus norvegicus and Rattus tanezumi are dominant species of Chinese house rats, but the colonization and demographic history of two species in China have not been thoroughly explored. Phylogenetic analyses with mitochondrial DNA including 486 individuals from 31 localities revealed that R. norvegicus is widely distributed in China, R. tanezumi is mainly distributed in southern China with currently invading northward; northeast China was the natal region of R. norvegicus, while the spread of R. tanezumi in China most likely started from the southeast coast. A total of 123 individuals from 18 localities were subjected to 2b‐RAD analyses. In neighbor‐joining tree, individuals of R. tanezumi grouped into geographic‐specific branches, and populations from southeast coast were ancestral groups, which confirmed the colonization route from southeast coast to central and western China. However, individuals of R. norvegicus were generally grouped into two clusters instead of geographic‐specific branches. One cluster comprised inland populations, and another cluster included both southeast coast and inland populations, which indicated that spread history of R. norvegicus in China was complex; in addition to on‐land colonization, shipping transportation also have played great roles. ADMIXTURE and principal component analyses provided further supports for the colonization history. Demographic analyses revealed that climate changes at ~40,000 to 18,000 years ago and ~4000 years ago had led to population declines of both species; the R. norvegicus declined rapidly while the population of R. tanezumi continuously expanded since ~1500 years ago, indicating the importance of interspecies' competition in their population size changes. Our study provided a valuable framework for further investigation on phylogeography of two species in China.

Molecular Identification and Genetic Variation of Rattus Species From Oil Palm Plantations of Malaysia Based on Mitochondrial Cytochrome Oxidase Subunit I (COI) Gene Sequences.

Rats (Rattus species) are the most notorious vertebrate pests in Malaysian oil palm plantations. Although many studies have been conducted on Asian rats, little attention has been paid to their species composition and phylogenetic relationships in oil palm plantations in Peninsular Malaysia. We determined the mitochondrial cytochrome oxidase subunit I (COI) gene sequence (708 bp) for 216 individual rats collected from five oil palm plantations in Peninsular Malaysia. Phylogenetic analysis in conjunction with comparison with sequences from the nucleotide sequence database revealed five distinct lineages in the Malaysian oil plantations: Rattus tiomanicus, Rattus argentiventer, Rattus exulans, Rattus tanezumi, and a taxon corresponding to the Malayan house rat, which was most frequently observed (∼50%). The last taxon has traditionally been classified as a synonym of Rattus rattus (Rattus rattus diardii) or Rattus tanezumi, but our phylogenetic analysis placed it as an independent lineage, which is not particularly closely related to R. rattus or R. tanezumi, and which we refer to as Rattus diardii. The construction of the network showed that there is considerable genetic variation within the lineages of R. diardii and R tiomanicus, suggesting that these two species are native to the Malay Peninsula.

Optimizing the capture of neophobic rice field rats in lowland Asian rice ecosystems

BACKGROUNDTrapping is a key method for monitoring small mammals and is also one of a number of methods recommended under an ecologically‐based rodent management program to control rodent pest populations. Live‐traps are widely used globally for studying small mammal populations. In Asia where rodents are major pests of rice, single capture traps typically provide low trap success. We compared the trap success between two types of live‐traps in rice fields in Indonesia and the Philippines.RESULTSMultiple‐capture traps (MCTs) in conjunction with a linear trap barrier were significantly more effective in catching rodent pest species than single‐capture traps (SCTs) in Indonesia and the Philippines. In Indonesia, MCTs captured more individuals with a mean (±SE) percent trap success rate of (15.54 ± 4.29) compared to SCTs (3.88 ± 1.58). In the Philippines, MCTs captured more species of rodents and had a significantly higher recapture rate (1.96 ± 0.79), than SCTs (0.58 ± 0.32).CONCLUSIONMultiple‐capture traps with a linear trap‐barrier were more effective for capturing Rattus argentiventer and Rattus tanezumi in rice field ecosystems compared to single‐capture traps. MCTs captured more species of rodent pests in the Philippines and recaptured more individuals of each species. These results indicate that rodent populations can be more effectively monitored and controlled by using a multi‐capture trap with barrier system than the use of single capture traps on their own. This is the first time these two trap types have been compared for use in rice ecosystems in Asia. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Preferensi Tikus terhadap Beberapa Jenis Umpan yang Berbeda di Kawasan Pemukiman

This study aims to determine the preferences of rats for different types of feed in the residential area of ​​RT 6 and RT 8, Kandang Limun Village, Muara Bangkahulu District, Bengkulu City. The method used was random sampling with 20 clip-type mouse traps and four different types of feed baits distributed randomly around the residential areas of RT 6 and RT 8 in Kandang Limun Village. The rat collection was carried out in five replications and the number was counted, identified and preserved. Rat morphometry data were analyzed quantitatively and described descriptively. The results showed that there were two types of rats with a total of 13 individuals collected, namely Rattus tanezumi (12 individuals) and Suncus murinus (1 individual). The level of preference of rats for salted fish is 6%, sweet potato and corn is 3%, while cassava is the least preferred feed (1%). In conclusion, two species of rats were found in the residential area of ​​RT 6 and RT 8, Kandang Limun Village. The rats prefer salted fish bait than sweet potato, corn and cassava. 
 Keywords: Settlement, Preference, Rat, Bait

First Record of Lineage IV of Rattus tanezumi (Rodentia: Muridae) from the southern Ryukyus, Japan

Based on mitochondrial cytochrome b gene sequences, we report representatives of the Lineage IV of Rattus tanezumi (Rodentia: Muridae) from Miyakojima, Taramajima, and Yonagunijima Islands in the southern Ryukyus as the first record of the lineage from Japan. The new record of Lineage IV provides an addition to the mammal fauna of Japan essentially at the species level. Accordingly, the genus Rattus in Japan consists of five species: R. rattus, Lineage II of R. tanezumi, Lineage IV of R. tanezumi, R. norvegicus, and R. exulans. The Miyakojima–Taramajima and Yonagunijima samples of the Lineage IV had discernible genetic differences, suggesting different origins. From Miyakojima Island and Kojima Island (an islet close to Miyakojima Island). We also found Lineage II of R. tanezumi, indicating that the two lineages coexist on Miyakojima Island. Morphological comparisons of these Lineage IV and Lineage II specimens suggest a greater molar length in Lineage IV than in Lineage II, and differences in the foramen magnum shape. Future detailed studies on genetic structures, morphological characteristics, and distribution of Lineage IV and Lineage II rats in the southern Ryukyus are needed to clarify their evolutionary history.

Epidemiological Evidence for Fecal-Oral Transmission of Murine Kobuvirus.

BackgroundMurine Kobuvirus (MuKV) is a novel picornavirus of the genus Kobuvirus, and was first identified in the feces of murine rodents in the USA in 2011. There is limited information on the transmission route of MuKV. Thus, we conducted a study to investigate virus detection rates in fecal, serum, throat, and lung tissue samples from murine rodents.ResultsA total of 413 fecal samples, 385 lung samples, 269 throat swab samples, and 183 serum samples were collected from 413 murine rodents (Rattus norvegicus, Rattus tanezumi, and Rattus rattus) captured in urban Shenzhen. Kobuviruses were detected via RT-PCR. Only fecal samples were positive, with prevalence rates of 34.9% in Rattus norvegicus and 29.4% in Rattus tanezumi. Phylogenetic analysis based on partial 3D and complete VP1 sequence regions indicated that all of the MuKV sequences obtained belonged to Aichivirus A, and were genetically closely related to other MuKVs reported in China, Hungary, and the USA. Twenty-eight full-length MuKV sequences were acquired. Phylogenetic analysis of two sequences randomly selected from the two species (SZ59 and SZ171) indicated that they shared very high nucleotide and amino acid identity with one another (94.0 and 99.3%, respectively), and comparison with human Kobuvirus revealed amino acid identity values of ~80%. Additionally, a sewage-derived sequence shared high similarity with the rat-derived sequences identified in this study, with respective nucleotide and amino acid identity values from 86.5 and 90.7% to 87.2 and 91.1%.ConclusionThe results of the current study provide evidence that murine Kobuvirus is transmitted via the fecal-oral route.

Fat Analysis of House Rat (Rattus tanezumi) in Meatball Using Gas Chromatography-mass Spectrometry (GC-MS) Combined with Principal Component Analysis

Counterfeit food products are starting to become a new problem around the people of Indonesia. Problems that are getting special attention especially the concern of contamination of food products by non-halal meat. This research aim was to analyze the fatty acids contained in house rat. The method that used was GC-MS method combined with Principle Component Analysis (PCA). Method of extraction grease was using oven at 90ºC - 100ºC for approximately one hour. After that, the derivatization process changed the fat into a methyl esters that easily evaporated. The derivatization process were using NaOCH3 and BF3. Methyl Esther compounds were injected into the chromatography instrument system GC-MS. GC-MS analysis results shows that the composition of fatty acid compounds from house rat fat with SI values > 90. Composition of fatty acids of house rat fats include: Myristate (0,19±0,03)%, Palmitoleat (2,40±0,29)%, Methyl Palmitate (27,65±0,32)%, oleate (45,81±3,25)%, and Stearate (4,65±0,28)%. Total content of house rat fatty acids was as high as 48.21% of unsaturated fatty acid and 31.49% of saturated fatty acids. The GC-MS method combined with PCA can post the fat of house rat. House rat fatty acids based on PCA's chemetrics demonstrate the resemblance of chemical physical properties with chicken fatty acids.

Predicting the potential distribution of a previously undetected cryptic invasive synanthropic Asian house rat (Rattus tanezumi) in South Africa

Abstract Three species of Rattus, Norway rat (R. norvergicus), black rat (R. rattus) and Asian house rat (R. tanezumi) are currently known to occur in South Africa. The latter two species are cryptic and form part of the Rattus rattus species complex. Historically, R. norvegicus has been reported to occur along the coast and in urban centres, R. rattus is widespread in most urban areas, except in the drier areas, while R. tanezumi was only recorded to occur in the country (and Africa) ca. 15 years ago, and its distribution remains unknown. The aim of this study was to predict the potential distribution of R. tanezumi in South Africa and assess how it overlaps with that of R. norvegicus and R. rattus using species distribution modelling. Rattus tanezumi was predicted to mainly occur in most inland urban areas and along the coast. The distribution of R. rattus was as expected, in contrast, the predicted range of R. norvegicus was not restricted to the coast but also included inland urban areas. All three species showed broad potential distributional ranges that overlapped extensively indicating that their establishment and spread may be influenced by similar factors such as proximity to urban areas and a wet and moderate climate. These results allow insights into assessing their risk of establishment and for formulating appropriate intervention strategies for their management and control.

Molecular evidence of rat bocavirus among rodents in Peninsular Malaysia.

Rat bocavirus (RBoV) and rodent bocavirus (RoBoV) have previously been detected in Rattus norvegicus; however, these viruses have not been reported in rodent populations in Malaysia. We investigated the presence of RBoV and RoBoV in archived rodent specimens. DNA barcoding of the rodent cytochrome c oxidase gene identified five different species: Rattus tanezumi R3 mitotype, Rattus tiomanicus, Rattus exulans, Rattus argentiventer, and Rattus tanezumi sensu stricto. Three spleens were positive for RBoV (1.84%; 3/163), but no RoBoV was detected. Phylogenetic analyzes of the partial non-structural protein 1 gene grouped Malaysian RBoV strains with RBoV strains from China. Further studies among rats from different geographical locations are warranted for this relatively new virus.

Occurrence and Habitat Use of Non-native Small Mammals in Upland Urban-Forest Environment in Northern Philippines

In the Philippines, few researches have been conducted about small mammals in urban areas at high elevation, where forests remain and non-native pest species can proliferate. Previous studies in Baguio City, Benguet Province reported three non-native species. This study extended these prior surveys by sampling in 13 localities, employing standard trapping method to document the distribution of species in an urban-forest setting. In 4,711 trap nights, 94 individuals were captured, consisting of four non-native species: Rattus exulans, Rattus tanezumi, Mus musculus, and Suncus murinus. Analysis of occurrence and relative abundance of species showed that small mammal distribution varied among the habitats, and appeared that variation may have been related to differences in vegetation structure or a habitat’s disturbance level. Rattus tanezumi was the most widespread, being especially common in backyard farms and in the public market. Suncus murinus was also widespread but less abundant than R. tanezumi. Rattus exulans was uncommon and restricted to certain area of a given habitat, particularly preferring weed-dominated areas. These suggest that non-native species are common and widespread in urban-forest setting but with apparent habitat preferences. The non-detection of native species is notable, suggesting that thorough studies can be done in the future.

Molecular Detection of Bartonella Species in Rodents Residing in Urban and Suburban Areas of Central Thailand.

Bartonella spp. are Gram-negative zoonotic bacteria transmitted to humans via various blood-sucking arthropods. Rodents have been identified as reservoir hosts of several zoonotic pathogens, including Bartonella spp. In Thailand, studies of Bartonella spp. in rodents from urban areas are limited; thus, a study in this area is necessary. The objectives of this study were to detect Bartonella spp. in rodents in Thailand and to compare the species’ distribution across different areas. In total, 70 blood samples from rodents in urban and suburban areas were tested for Bartonella spp. using a conventional polymerase chain reaction that targeted the citrate synthase (gltA) gene. All Bartonella-positive sequences were analyzed using polymorphism in order to build a phylogenetic tree. Approximately 38% of the rodents studied contained Bartonella DNA. Both Rattus exulans (Pacific rat) and R. tanezumi (Asian house rat) contained Bartonella spp. Four species of Bartonella were detected in blood samples: B. tribocorum, B. phoceensis, B. grahamii, and B. rattimassiliensis. In addition, eight Pacific rats contained the B. kosoyi–B. tribocorum complex. Bartonella phoceensis and B. tribocorum–B. kosoyi complexes were found in a specific habitat (p < 0.05). Interestingly, only seven haplotypes were identified in the sequences analyzed, and only haplotype A was found in both rodent species. Finally, a monitoring program for zoonotic Bartonella infection, especially the B. kosoyi–B. tribocorum complex, B. phoceensis, B. grahamii, and B. rattimassiliensis should be established, especially in high-risk areas.

Detection and Genetic Characterization of Seoul Virus in Liver Tissue Samples From Rattus norvegicus and Rattus tanezumi in Urban Areas of Southern China.

Rodents are important hosts of hantaviruses, and lungs and kidneys are known to be the preferred organs of these viruses. Recently, hantaviruses were detected in liver samples from wild rodents in Hungary and the United States, and feeder rats in the Netherlands. However, few studies have detected hantaviruses in the liver of rats from China. In this study, hantaviruses were investigated in liver samples from R. norvegicus and R. tanezumi trapped in urban areas of southern China. A total of 461 R. norvegicus and 64 R. tanezumi were trapped. Using a pan-hantavirus PCR method, hantaviruses were detected in liver, lung, and serum samples from these animals. About 7.43% of liver samples were positive for Seoul virus (SEOV). The detection rate of SEOV in liver samples from R. norvegicus (8.24%) was higher than that from R. tanezumi (1.56%), suggesting the predominant role of R. norvegicus in the transmission of SEOV in urban areas of China. Three R. norvegicus had SEOV RNA in their liver samples but not in their lung samples, suggesting that the liver might be one of the targeted organs of SEOV. The first full SEOV protein-coding sequences (CDS) of the S and M segments, and partial CDS of the L segment from R. tanezumi were amplified. Several full and partial CDS of the S, M, and L segments from R. norvegicus were also obtained. The SEOV sequences obtained from different animals were highly similar, suggesting the cross-species transmission potential of SEOV between R. norvegicus and R. tanezumi.

Effectiveness of snap traps on capturing rodent and small mammals in rural area of two provinces (Yogyakarta and West Java) in Indonesia

The study was conducted to determine the effectiveness of snap traps on capturing the rodents and small mammals in two provinces (Yogyakarta and West Java). A small rural area surrounded by large scale ricecrops which indicate rodent damage seasonally was selected as the study site. The trappings were executed during the period of November 2018 – August 2020. Consecutive trappings were performed in two regions using snap traps baited with fresh salty fish and roasted coconut. Around 40-65 traps were set in West Java study sites and 60-65 traps in Yogyakarta for every single trap night, respectively. We checked the captured animals in the early morning and collected them for identification and sexing. In the late afternoon we continued with cleaning of the traps and put in the new same type of bait. A total of 517 animals were obtained with the proportion of the two sexes was almost the same (45.45% males:54.40% females). Based on the physical characteristics, those captured animals were three rodent species (Rattus argentiventer, Rattus tanezumi, Bandicota indica) and one species of insectivore (Suncus murinus). Regarding trapping rate of success, Yogyakarta denoted average values (21.38% in the first trapping and 26.04% from the second trapping) compared to West Java which was only accounted for half of them (11.31% and 11.24% from the first and second trapping, respectively). The heterogeneous habitat configuration probably allowed this situation to occur in Yogyakarta. Moreover, rodent control activities in West Java were implemented more intensively compared to Yogyakarta.

Genomic analysis unveils mechanisms of northward invasion and signatures of plateau adaptation in the Asian house rat

The Asian house rat (AHR), Rattus tanezumi, has recently invaded the northern half of China. The AHR is a highly adaptive rat species that has also successfully conquered the Qinghai-Tibet Plateau (QTP) and replaced the brown rat (BR), R. norvegicus, at the edge of the QTP. Here, we assembled a draft genome of the AHR and explored the mechanisms of its northward invasion and the genetic basis underlying plateau adaptation in this species. Population genomic analyses revealed that the northwardly invasive AHRs consisted of two independent and genetically distinct populations which might result from multiple independent primary invasion events. One invasive population exhibited reduced genetic diversity and distinct population structure compared with its source population, while the other displayed preserved genetic polymorphisms and little genetic differentiation from its source population. Genes involved in G-protein coupled receptors and carbohydrate metabolism may contribute to the local adaptation of northern AHRs. In particular, RTN4 was identified as a key gene for AHRs in the QTP that favours adaptation to high-altitude hypoxia. Coincidently, the physiological performance and transcriptome profiles of hypoxia-exposed rats both showed better hypoxia adaptation in AHRs than in BRs that failed to colonize the heart of the QTP, which may have facilitated the replacement of the BR population by the invading AHRs at the edge of the QTP. This study provides profound insights into the multiple origins of the northwardly invasive AHR and the great tolerance to hypoxia in this species.

Orientia tsutsugamushi dynamics in vectors and hosts: ecology and risk factors for foci of scrub typhus transmission in northern Thailand

BackgroundScrub typhus is an important neglected vector-borne zoonotic disease across the Asia–Pacific region, with an expanding known distribution. The disease ecology is poorly understood, despite the large global burden of disease. The key determinants of high-risk areas of transmission to humans are unknown.MethodsSmall mammals and chiggers were collected over an 18-month period at three sites of differing ecological profiles with high scrub typhus transmission in Chiang Rai Province, northern Thailand. Field samples were identified and tested for Orientia tsutsugamushi by real-time PCR. The rates and dynamics of infection were recorded, and positive and negative individuals were mapped over time at the scale of single villages. Ecological analyses were performed to describe the species richness, community structure and interactions between infected and uninfected species and habitats. Generalised linear modelling (GLM) was applied to examine these interactions.ResultsThe site with the highest rates of human infection was associated with the highest number of infected chigger pools (41%), individual chiggers (16%), proportion of the known vector species Leptotrombidium deliense (71%) and chigger index (151). Chigger species diversity was lowest (Shannon diversity index H′: 1.77) and rodent density appeared to be high. There were no consistent discrete foci of infection identified at any of the study sites. The small mammals Rattus tanezumi and Bandicota indica and the chiggers L. deliense and Walchia kritochaeta emerged as central nodes in the network analysis. In the GLM, the end of the dry season, and to a lesser extent the end of the wet season, was associated with O. tsutsugamushi-infected small mammals and chiggers. A clear positive association was seen between O. tsutsugamushi-positive chigger pools and the combination of O. tsutsugamushi-positive chigger pools and O. tsutsugamushi-positive small mammals with lowland habitats.ConclusionsThese findings begin to reveal some of the factors that may determine high-risk foci of scrub typhus at a fine local scale. Understanding these factors may allow practical public health interventions to reduce disease risk. Further studies are needed in areas with diverse ecology.Graphical abstract

Commensal Rodent Habitat Expansion Enhances Arthropod Disease Vectors on a Tropical Volcanic Island.

On volcanic islands, the release of animals from predators and competitors can lead to increased body size and population density as well as the expanded habitat use of introduced animals relative to their mainland counterparts. Such alterations might facilitate the spread of diseases on islands when these exotic animals also carry pathogenic agents; however, this has rarely been investigated. The commensal Asian house rat (Rattus tanezumi) is confined to human residential surroundings in mainland Taiwan but can be observed in the forests of nearby Orchid Island, which is a tropical volcanic island. Orchid Island is also a hot spot for scrub typhus, a lethal febrile disease transmitted by larval trombiculid mites (chiggers) that are infected primarily with the rickettsia Orientia tsutsugamushi (OT). We predicted an increase in chigger abundance when rodents (the primary host of chiggers) invade forests from human settlements since soils are largely absent in the latter habitat but necessary for the survival of nymphal and adult mites. A trimonthly rodent survey at 10 sites in three habitats (human residential, grassland, and forest) found only R. tanezumi and showed more R. tanezumi and chiggers in forests than in human residential sites. There was a positive association between rodent and chigger abundance, as well as between rodent body weight and chigger load. Lastly, >95% of chiggers were Leptotrombidium deliense and their OT infection rates were similar among all habitats. Our study demonstrated potentially elevated risks of scrub typhus when this commensal rat species is allowed to invade natural habitats on islands. Additionally, while the success of invasive species can be ascribed to their parasites being left behind, island invaders might instead obtain more parasites if the parasite requires only a single host (e.g., trombiculid mite), is a host generalist (e.g., L. deliense), and is transferred from unsuitable to suitable habitats (i.e., human settlements on the mainland to forests on an island).