Sathaporn Jittapalapong

Trypanosoma evansi and Surra: A Review and Perspectives on Transmission, Epidemiology and Control, Impact, and Zoonotic Aspects

This paper reviews the transmission modes of Trypanosoma evansi. Its worldwide distribution is attributed to mechanical transmission. While the role of tabanids is clear, we raise questions on the relative role of Haematobia sp. and the possible role of Stomoxys sp. in delayed transmission. A review of the available trypanocidal drugs and their efficacy in various host species is useful for understanding how they interact in disease epidemiology, which is complex. Although there are similarities with other mechanically transmitted trypanosomes, T. evansi has a more complex epidemiology due to the diversity of its hosts and vectors. The impact of clinical and subclinical disease is difficult to establish. A model was developed for buffaloes in the Philippines, which could be transferred to other places and livestock systems. Since Trypanosoma evansi was reported in humans, further research is required to investigate its zoonotic potential. Surra remains a potentially emerging disease that is a threat to Australia, Spain, and France. A number of questions about the disease have yet to be resolved. This brief review of the basic knowledge of T. evansi suggests that there is renewed interest in the parasite, which is spreading and has a major economic impact.

Host surveys, ixodid tick biology and transmission scenarios as related to the tick-borne pathogen, Ehrlichia canis

The ehrlichioses have been subject to increasing interest from veterinary and public health perspectives, but experimental studies of these diseases and their etiologic agents can be challenging. Ehrlichia canis, the primary etiologic agent of canine monocytic ehrlichiosis, is relatively well characterized and offers unique advantages and opportunities to study interactions between a monocytotropic pathogen and both its vertebrate and invertebrate hosts. Historically, advances in tick-borne disease control strategies have typically followed explication of tick-pathogen-vertebrate interactions, thus it is reasonable to expect novel, more sustainable approaches to control of these diseases as the transmission of their associated infections are investigated at the molecular through ecological levels. Better understanding of the interactions between E. canis and its canine and tick hosts would also elucidate similar interactions for other Ehrlichia species as well as the potential roles of canine sentinels, reservoirs and models of tick-borne zoonoses. This article summarizes natural exposure studies and experimental investigations of E. canis in the context of what is understood about biological vectors of tick-borne Anaplasmataceae.

Molecular and serological prevalence of Babesia bovis and Babesia bigemina in water buffaloes in the north region of Brazil

Bovine babesiosis is a tick-borne disease caused mainly by Babesia bovis and Babesia bigemina, which are associated to considerable economic losses in cattle herds worldwide. Approximately 60% of buffalo herds in South America are located in Northern Brazil. Little is known about the impact of babesiosis on buffalo herds in Brazil. The present work aimed to verify the occurrence of B. bovis and B. bigemina in 542 water buffaloes in the state of Pará, Northern Brazil, using molecular and serological techniques. The percentage of seropositive animals for B. bovis and B. bigemina was 41.2% and 19.0%, respectively, by ELISA. B. bovis and B. bigemina DNA were detected in 15 and 16% of sampled buffaloes, respectively. A high correlation (Kappa index of 0.9) between serological and molecular tests suggests that the combination of the utilized techniques in the present study is suitable for babesiosis diagnosis in an endemic unstable area. Significantly difference of positivity for serological and molecular assays was verified to localities and reproductive status of sampled animals, but not between buffalo breeds. The immune status of sampled buffaloes associated to the circulation of babesiosis agents in sampled population suggests that the studied area is at risk to clinical babesiosis outbreaks. Furthermore, this study demonstrated that this region can be classified as endemically unstable.

Detection of Hepatozoon canis in stray dogs and cats in Bangkok, Thailand

Abstract:  A rapidly increasing stray animal population in Bangkok has caused concern regarding transmission of vector‐borne and zoonotic diseases. The purpose of this study was to determine if stray animals in Bangkok are a potential reservoir of Hepatozoon, a genus of tick‐borne parasites that has received little attention in Thailand. Blood samples were collected from stray companion animals near monasteries in 42 Bangkok metropolitan districts. Both dogs and cats were sampled from 26 districts, dogs alone from 4 districts and cats alone from 12 districts. Samples were collected from a total of 308 dogs and 300 cats. Light microscopy and an 18 S rRNA gene‐based PCR assay were used to test these samples for evidence of Hepatozoon infection. Gamonts were observed in blood smears for 2.6% of dogs and 0.7% of cats by microscopy. The PCR assay detected Hepatozoon in buffy coats from 11.4% of dogs and 32.3% of cats tested. The prevalence of infection was the same between male and female dogs or cats, and PCR‐positive dogs and cats were found in 36.6% and 36.8% of the districts surveyed, respectively. There was an association between the percentages of PCR‐positive dogs and cats in districts where both host species were sampled. Sequences of representative amplicons were closest to those reported for H. canis. These results represent the first molecular confirmation that H. canis is indigenous to Thailand. The unexpectedly high prevalence of Hepatozoon among stray cats indicates that their role in the epizootiology of hepatozoonosis should be investigated.

Epidemiology of leptospira transmitted by rodents in southeast Asia.

Background Leptospirosis is the most common bacterial zoonoses and has been identified as an important emerging global public health problem in Southeast Asia. Rodents are important reservoirs for human leptospirosis, but epidemiological data is lacking. Methodology/Principal Findings We sampled rodents living in different habitats from seven localities distributed across Southeast Asia (Thailand, Lao PDR and Cambodia), between 2009 to 2010. Human isolates were also obtained from localities close to where rodents were sampled. The prevalence of Leptospira infection was assessed by real-time PCR using DNA extracted from rodent kidneys, targeting the lipL32 gene. Sequencing rrs and secY genes, and Multi Locus Variable-number Tandem Repeat (VNTR) analyses were performed on DNA extracted from rat kidneys for Leptospira isolates molecular typing. Four species were detected in rodents, L. borgpetersenii (56% of positive samples), L. interrogans (36%), L. kirschneri (3%) and L. weilli (2%), which were identical to human isolates. Mean prevalence in rodents was approximately 7%, and largely varied across localities and habitats, but not between rodent species. The two most abundant Leptospira species displayed different habitat requirements: L. interrogans was linked to humid habitats (rice fields and forests) while L. borgpetersenii was abundant in both humid and dry habitats (non-floodable lands). Conclusion/Significance L. interrogans and L. borgpetersenii species are widely distributed amongst rodent populations, and strain typing confirmed rodents as reservoirs for human leptospirosis. Differences in habitat requirements for L. interrogans and L. borgpetersenii supported differential transmission modes. In Southeast Asia, human infection risk is not only restricted to activities taking place in wetlands and rice fields as is commonly accepted, but should also include tasks such as forestry work, as well as the hunting and preparation of rodents for consumption, which deserve more attention in future epidemiological studies.

Infectious Diseases and Their Outbreaks in Asia-Pacific: Biodiversity and Its Regulation Loss Matter

Despite increasing control measures, numerous parasitic and infectious diseases are emerging, re-emerging or causing recurrent outbreaks particularly in Asia and the Pacific region, a hot spot of both infectious disease emergence and biodiversity at risk. We investigate how biodiversity affects the distribution of infectious diseases and their outbreaks in this region, taking into account socio-economics (population size, GDP, public health expenditure), geography (latitude and nation size), climate (precipitation, temperature) and biodiversity (bird and mammal species richness, forest cover, mammal and bird species at threat). We show, among countries, that the overall richness of infectious diseases is positively correlated with the richness of birds and mammals, but the number of zoonotic disease outbreaks is positively correlated with the number of threatened mammal and bird species and the number of vector-borne disease outbreaks is negatively correlated with forest cover. These results suggest that, among countries, biodiversity is a source of pathogens, but also that the loss of biodiversity or its regulation, as measured by forest cover or threatened species, seems to be associated with an increase in zoonotic and vector-borne disease outbreaks.

Detection of Ehrlichia canis in Canine Carrier Blood and in Individual Experimentally Infected Ticks with a p30-Based PCR Assay

ABSTRACT Detection of vector-borne pathogens is necessary for investigation of their association with vertebrate and invertebrate hosts. The ability to detect Ehrlichia spp. within individual experimentally infected ticks would be valuable for studies to evaluate the relative competence of different vector species and transmission scenarios. The purpose of this study was to develop a sensitive PCR assay based on oligonucleotide sequences from the unique Ehrlichia canis gene, p30, to facilitate studies that require monitoring this pathogen in canine and tick hosts during experimental transmission. Homologous sequences for Ehrlichia chaffeensis p28 were compared to sequences of primers derived from a sequence conserved among E. canis isolates. Criteria for primer selection included annealing scores, identity of the primers to homologous E. chaffeensis sequences, and the availability of similarly optimal primers that were nested within the target template sequence. The p30-based assay was at least 100-fold more sensitive than a previously reported nested 16S ribosomal DNA (rDNA)-based assay and did not amplify the 200-bp target amplicon from E. chaffeensis, the human granulocytic ehrlichiosis agent, or Ehrlichia muris DNA. The assay was used to detect E. canis in canine carrier blood and in experimentally infected Rhipicephalus sanguineus ticks. Optimized procedures for preparing tissues from these hosts for PCR assay are described. Our results indicated that this p30-based PCR assay will be useful for experimental investigations, that it has potential as a routine test, and that this approach to PCR assay design may be applicable to other pathogens that occur at low levels in affected hosts.

Tabanids: Neglected subjects of research, but important vectors of disease agents!

Tabanids are nuisance pests for people and livestock because of their painful and irritating bite, persistent biting behavior, and blood ingestion. About 4400 tabanid species have been described; they are seasonally present in all kinds of landscapes, latitudes, and altitudes. High populations have a significant economic impact on outdoor activities, tourism, and livestock production. Tabanids are also vectors of animal disease agents, including viruses, bacteria and parasites. However, tabanids have received little attention in comparison with other hematophagous Diptera. Here, we highlight the many direct and indirect impacts of tabanids and provide a brief summary of tabanid morphology, biology, and life cycle. Impacts include pathogen transmission, parasite transportation (Dermatobia hominis), biological transmission (Loa loa), and mechanical transmission of viruses, such as equine infectious anemia virus, protozoa, such as Trypanosoma evansi and Besnotia besnoiti, and bacteria, such as Bacillus anthracis and Anaplasma marginale. We discuss parameters of mechanical transmission and its mathematical modeling. Control methods for tabanid populations are also summarized; these include trapping, the use of insecticides, repellents, and livestock protection. Lastly recommendations are provided for the direction of future research.

Recent Discoveries of New Hantaviruses Widen Their Range and Question Their Origins

Hantaviruses belong to the Bunyaviridae family. While usually hosted by wild mammals, they are potentially pathogenic for humans, and several serologically distinct groups associated with different syndromes have been identified. Yet, investigations have mostly been conducted where human infections by hantaviruses constitute a real and well‐identified public health problem, i.e., the holarctic and neotropical areas. Some hantaviruses have also been described from a Suncus murinus in India and a Bandicota indica in Thailand. In addition, recent investigations in Cambodia revealed new Hantavirus types. More recently, two new Hantavirus species were described: Sangassou from a Hylomyscus simus, and Tanganya from a Crocidura theresae, both from Africa (Guinea), thus strongly questioning the current views about geographic range, evolution, and epidemiology of hantaviruses. In such a framework, we have conducted a survey of Hantavirus diversity in Southeast Asia which allows us to isolate the Thailand virus and address questions about the taxonomy of their rodent hosts. Here we present a molecular analysis of representatives of all currently known Hantavirus species, thus allowing the comparison between the newly described ones with a large range sample of rodent hantaviruses. Our results clearly point to the presence of a particular lineage of hantaviruses in Southeast Asia. It also strongly suggests that new viruses, additional mammalian hosts and different related syndromes in humans are likely to be discovered in the near future, particularly in Southeast Asia and in Africa, where Muridae rodents are highly diversified. Furthermore, additional work is also urgently needed to investigate the hantaviruses associated with Crociduridae and Soricidae.

Antibody-ELISA for Trypanosoma evansi: Application in a serological survey of dairy cattle, Thailand, and validation of a locally produced antigen

Trypanosoma evansi is generally considered a mild pathogen in bovines. However, in Asia, acute and chronic signs have been observed in cattle, with high levels of parasitaemia, abortion and death. Investigations in Asian cattle are needed to better understand this epidemiological situation. To generate comparable data at a regional level, development and standardization of an antibody-enzyme linked immunosorbent assay for T. evansi (ELISA/T. evansi) was initiated and applied in an epidemiological survey carried out in dairy cattle in Thailand. A batch of 1979 samples was collected from dairy farms located throughout the countrys four regions. Soluble T. evansi antigens initially produced in France were also produced in Thailand for comparison and technology transfer. Screening of 500 samples allowed us to identify reference samples and to determine the cut-off value of the ELISA. Seropositive animals - some of them confirmed by PCR - were found in the four regions, in 12 out of 13 provinces, in 22 out of 31 districts, in 56 farms out of 222 (25%, 95%CI+/-6%) and in 163 animals out of 1979 (8.2, 95%CI+/-1.2%). Estimated seroprevalence in 35 farms ranged between 1% and 30%, and in 21 farms it was >30%. Approximately 25% of survey cattle were exposed to the infection, in various situations. A sub-sample of 160 sera was tested on both antigens. Wilcoxons (Z=1.24; p=0.22) and McNemarss tests (CHI2=3.55; p=0.09) did not show any significant differences, showing that the locally produced antigen is suitable for further evaluation in the surrounding countries. Use of this standardized serological method will broaden knowledge of the prevalence and impact of the disease at the regional level in South-East Asia. Further validation of this ELISA will be necessary in other host species such as buffalo, horse and pig.