Genetic diversity of Trypanosoma evansi in buffalo based on internal transcribed spacer (ITS) regions

Assessment of genetic diversity of Trypanosoma evansi in the domestic animal populations through ITS-1 gene sequence analysis

Trypanosoma evansi infects domestic animals, causing a debilitating and occasionally fatal disease. The disease leads to significant economic losses to farmers and poses a substantial impediment to the growth of livestock production in developing nations, including India. Considering the challenges associated with managing this infection, there is an urgent need to enhance our understanding of the molecular and genetic diversity of T. evansi. Therefore, this study was planned to analyze the genetic diversity of T. evansi using available internal transcribed spacer-1 (ITS-1) gene sequences from India and compare them with sequences from around the globe. Blood samples used in this study were collected from naturally infected animals including dogs, cattle, and buffaloes in the Indian state of Madhya Pradesh. Using the ITS-1 gene, we amplified a 540 base pairs (bp) segment using polymerase chain reaction (PCR), sequenced it, and identified intra-specific variations. Phylogenetic analysis of 90 sequences, including 27 from India, revealed three distinct clusters with high bootstrap support values. A haplotype network analysis identified 34 haplotypes, with H7 being the most prevalent, indicating a complex evolutionary history involving multiple countries. The genetic analysis of the Indian population revealed distinct characteristics. Despite low nucleotide diversity, there was high haplotype diversity in comparison to other populations. Tajima's D, Fu and Li's D, and Fu and Li's F exhibited non-significant negative values, indicating potential stability. Additionally, the slightly positive values in Fu's Fs, Raggedness (r), and Ramos-Onsins and Rozas (R2) statistics suggested a lack of recent significant selective pressures or population expansions. Furthermore, the presence of genetic differentiation and gene flow among T. evansi populations highlighted ongoing evolutionary processes. These findings collectively depicted a complex genetic landscape, suggesting both stability and ongoing evolutionary dynamics within the Indian population of T. evansi. The findings of this study are important for understanding the evolutionary history and population dynamics of T. evansi, and they may help us develop effective control strategies.

Molecular prevalence, associated risk factors and genetic characterization of Trypanosoma evansi in camels

Surra is a major infectious disease of camels being caused by Trypanosoma evansi (T. evansi) in developing countries, including Egypt. However, the identification of changes in the T. evansi prevalence in Egypt is important. In this study, the prevalence of T. evansi and its associated risk factors as well as the genetic characterization of the parasite were estimated. Blood samples were collected from 163 camels from two governorates in Lower Egypt. PCR targeting RoTat 1.2VSG was used for the detection of T. evansi and internal transcribed spacer 1 (ITS-1) was used for sequencing analysis and genetic characterization. Overall prevalence was 19.6% using RoTat 1.2VSG. The risk of the infection in females was 4 times higher than in males (P = 0.0004, OR = 4; 95% CI = 0.79-8.96) and in camels with a history of clinical signs it was 2.3 times higher than camels without clinical signs (P = 0.04, OR = 2.3, 95% CI = 1.035-5.15). Analysis of the ITS-1 sequences of four T. evansi isolates showed little heterogeneity compared to similar sequences in the database. Sequence and phylogenetic analysis, based on the ITS-1 region, confirmed the presence of two distinct genotypes of T. evansi in Egyptian camels with more than 99% similarity with T. evansi isolates from different countries across the ITS-1 region and were closely related to Filipino and Chinese isolates. The results of the study can be used for the observation and prevention of disease and updating the epidemiological data.

Silent Trypanosoma evansi infection in humans from India revealed by serological and molecular surveys, and characterized by variable surface glycoprotein gene sequences

BACKGROUND

The importance of emerging atypical human trypanosomosis is gaining momentum due to increasing detection and its possible impact on human health. A cross sectional study of atypical human trypanosomosis due to Trypanosoma evansi was carried out in Kolkata and Canning area of West Bengal state of India where previously a death was reported.

METHODS

In this study blood and serum samples from 173 individuals were collected during August to December 2014. To check the presence of antibodies against T. evansi, card agglutination test and for the presence of T. evansi specific DNA, PCR were conducted.

RESULTS

T. evansi infection was identified in 5.2% (9/173) human blood samples by CATT serological test (Card agglutination test for trypanosomosis). PCR targeting VSG gene sequences suggested active T. evansi infection in 2.89% (5/173). VSG gene sequences herein determined for five isolates from human cases shared high similarity (89.4-100%). Phylogenetic inference clustered the human isolates with other isolates from different host species from India and other countries, forming a clade exclusive of Indian isolates (84.0 to 100% sequence similarity).

CONCLUSION

First report of symptomless human T. evansi infection detected by combined serological and PCR assays. First phylogenetic analysis of VSG gene sequences including human isolates of T. evansi in which Indian isolates of T. evansi from human and other hosts clustered in a single clade.

Molecular characterization of Trypanosoma evansi, T. vivax and T. congolense in camels (Camelus dromedarius) of KSA

Background

Trypanosoma evansi is the leading infectious Trypanosoma spp. in camels (Camelus dromedarius) present in the Kingdom of Saudi Arabia (KSA) that could lead to extensive economic losses. The present study was aimed to assess the prevalence rate of T. evansi in Taif governorate, Makkah province, KSA using parasitological and molecular evaluations, and analyze their genetic relationship targeting internal transcribed spacer 1 (ITS1) and variable surface glycoprotein (VSG) genes. For evaluation, we have used 102 blood samples of camels obtained from three different regions in Taif.

Results

Results show a considerable prevalence rate of trypanosomosis 2/102 (2.0%) according to Giemsa-stained buffy coat smear, and 16/102 (15.7%) according to touchdown PCR. T. evansi (n = 10/102, 9.8%) was the main infectious species found in camels then T. vivax (n = 3/102, 2.9%). Mixed infections were detected in three camels with T. evansi, T. vivax, and T. congolense (n = 3/102, 2.9%). Regarding gender, the results indicate that female camels (11/66, 16.7%) show higher prevalence of Trypanosoma than males (5/36, 13.9%). Sequencing and phylogenetic analyses of ITS1 and VSG showed their relationships with T. evansi in other hosts from different countries.

Conclusions

In our peer knowledge, it is the first time to report a research-based prevalence of trypanosomosis in the camels of Taif governorate, Makkah province, KSA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03148-0.

Molecular detection of Trypanosoma evansi in dogs from India and Southeast Asia

Trypanosoma evansi, the causative agent of surra, is a hemoflagellate protozoan mechanically transmitted by hematophagous flies, mainly in tropical and subtropical regions. This protozoan affects several mammalian hosts, including dogs, which are highly susceptible to the infection. To investigate the occurrence of T. evansi in dogs, a total of 672 DNA samples from India (n = 228), Indonesia (n = 57), Malaysia (n = 45), the Philippines (n = 103), Thailand (n = 120), and Vietnam (n = 119) were screened by using species-specific conventional PCR. Of the tested dogs, 10 (1.5%) scored positive to T. evansi. In particular, positive samples were detected in canine blood samples collected from India (n = 4; 1.8%), Indonesia (n = 4; 7%), and Malaysia (n = 2; 4.4%). All tested samples from the Philippines, Thailand and Vietnam were negative. Nucleotide sequence analysis revealed a high variation (i.e. from 0.4% to 6.2%) among the RoTat 1.2 variant surface glycoprotein (vsg) gene. Although the number of sequences included in this analysis is relatively small, this nucleotide variation may indicate the divergence of T. evansi RoTat 1.2 vsg gene among different strains. The high incidence of T. evansi previously reported in cattle and buffaloes in India and Southeast Asia suggests that these animals are the main source of infection to dogs.

Molecular Identification of Trypanosoma evansi Isolated from Arabian Camels (Camelus dromedarius) in Riyadh and Al-Qassim, Saudi Arabia

We analyzed the blood from 400 one-humped camels, Camelus dromedarius (C. dromedarius), in Riyadh and Al-Qassim, Saudi Arabia to determine if they were infected with the parasite Trypanosoma spp. Polymerase chain reaction (PCR) targeting the internal transcribed spacer 1 (ITS1) gene was used to detect the prevalence of Trypanosoma spp. in the camels. Trypanosoma evansi (T. evansi) was detected in 79 of 200 camels in Riyadh, an infection rate of 39.5%, and in 92 of 200 camels in Al-Qassim, an infection rate of 46%. Sequence and phylogenetic analyses revealed that the isolated T. evansi was closely related to the T. evansi that was detected in C. dromedarius in Egypt and the T. evansi strain B15.1 18S ribosomal RNA gene identified from buffalo in Thailand. A BLAST search revealed that the sequences are also similar to those of T. evansi from beef cattle in Thailand and to T. brucei B8/18 18S ribosomal RNA from pigs in Nigeria.

New Haplotypes of Trypanosoma evansi Identified in Dromedary Camels from Algeria

PURPOSE

Surra is a zoonotic disease caused by Trypanosoma evansi (Trypanozoon), a salivary trypanosome native to Africa which affects a wide range of mammals worldwide and causes mortality and significant economic loss. The present study was devoted to the molecular characterization of T. evansi derived from naturally infected dromedary camels in Algeria.

METHODS

A total of 148 blood samples were collected from mixed age camels living in one of four geographic regions (Ouargla, El Oued, Biskra and Ghardaia) of Algeria. Samples underwent PCR amplification and sequencing of the internal transcribed spacer 1 (ITS1) complete sequence.

RESULTS

DNA of Trypanosoma spp. was found in 19 camels (12.84%). Trypanosoma spp. molecular positivity was not affected by sex (p = 0.50), age (p = 0.08), or geographic location (p = 0.12). Based on multiple sequence alignment of the obtained DNA sequences with representative T. evansi ITS1 sequences available globally, the Algerian sequences were grouped within four different haplotypes including two which were original.

CONCLUSION

Results of this study provide preliminary data on which future studies of genetic diversity and molecular epidemiology of T. evansi can be based.

Genetic and parasitological identification of Trypanosoma evansi infecting cattle in South Sulawesi, Indonesia

Background and Aim:

Sulawesi is an Indonesian island located within the Wallacea region that contains a distinctive mix of Asian and Australasian species. This distinctiveness extends to parasites, including Trypanosoma evansi, the cause of surra. Surra has non-specific clinical signs such as anemia, anorexia, weight loss, drop in milk production, and reproductive disorders which cause economic losses. Due to the trade of livestock, surra has spread in Indonesia from one island to another. The aim of this study was to investigate the trypanosomes infecting cattle in South Sulawesi, using internal transcribed spacer (ITS2) ribosomal DNA (rDNA) sequencing.

Materials and Methods:

A total of 100 whole blood samples were collected from cattle in Makassar, South Sulawesi Province, Indonesia. All samples were tested using conventional parasitological methods (CPT), namely, thin blood smear, buffy coat smears, and polymerase chain reaction (PCR) testing. Positive PCR results were sequenced and phylogenetically analyzed.

Results:

Only one of the 100 samples was found to be positive with microscopic observation; however, PCR analysis revealed that 3% (3/100) of samples were positive. Sequencing identified the positive samples as T. evansi, China isolate (KU552344), with a homology of 99%. Two out of three sequences showed variations in ITS2 region.

Conclusion:

Based on CPT and molecular analysis, T. evansi isolates from infected cattle in South Sulawesi demonstrate genetic diversity of ITS2 sequences.

Molecular characterization and phylogenetic analysis of Trypanosoma evansi from Northern India based on 18S ribosomal gene

Six Trypanosoma evansi isolates were collected from ponies (PH1 and PK6), camel (CB2), donkeys (DJ3 and DH4) and cattle (CK5) from different States of Northern India (Haryana, Rajasthan, Uttar Pradesh and Gujarat) for molecular characterization based on 18S rRNA gene. The 18S rRNA gene (2251 bp) of different isolates was amplified, cloned and custom sequenced separately. Based on sequence and phylogenetic analysis of all six isolates, collected from different hosts as well as geographical areas, were having high identity among Indian T. evansi strains (99.7%) and with other strains of T. evansi (99.2%) distributed worldwide. There is less genetic diversity among different salivarian strains of T. evansi except few nucleotide changes at significant locations in one Indian isolate of camel origin (CB2). All Indian T. evansi isolates were grouped in salivarian clade with high bootstrap values and remained far away from stercorarian clade having 88-90% nucleotide identity. The study will be helpful in understanding the evolutionary relationship, molecular epidemiology and variation in disease pathogenesis among different T. evansi strains. Further, more studies are required on large number of isolates collected from diverse host and geographical areas to reaffirm the present finding.

Trypanosoma vivax is the second leading cause of camel trypanosomosis in Sudan after Trypanosoma evansi

BACKGROUND

This study was conducted in response to recurring reports from eastern Sudan of camel trypanosomosis that can no longer be treated by currently available trypanocidal drugs. One hundred and eighty-nine blood samples were obtained from camels in different herds and local markets in the western part of Sudan, and a cross-sectional study was carried out between December 2015 and February 2016 to identify the causative agents and possible circulating genotypes.

RESULTS

The prevalence of trypanosomes detected using the conventional parasitological techniques of Giemsa-stained blood smears, wet blood smears and the microhematocrit centrifugation technique (MHCT) was 7% (13/189), 11% (21/189) and 19% (36/189), respectively. However, a multi-species KIN-PCR targeting the ITS region revealed that the prevalence of Trypanosoma evansi was 37% (70/189), while that of T. vivax was 25% (47/189). Consequently, we used a T. evansi-specific PCR (RoTat1.2 VSG gene) to analyse the KIN-PCR-positive samples and a T. vivax-specific PCR (Cathepsin L-like gene) to analyse all of the samples. The prevalence of T. evansi was 59% (41/70), while the prevalence of T. vivax was 31% (59/189). Mixed infections were detected in 18% (34/189) of the samples. These results were further confirmed by sequencing and a phylogenetic analysis of the complete internal transcribed spacer (ITS) region of T. evansi and the TviCatL gene of T. vivax.

CONCLUSION

We conclude that T. vivax was newly introduced to the camel population and that T. evansi is no longer the single cause of camel trypanosomosis in Sudan. The presence of T. vivax in camels detected in this study is a challenge in the choice of diagnostic approaches, particularly serology, and PCRs. However, an analysis of drug resistance should be performed, and the genotypic variation should be verified. To our knowledge, this is the first molecular study on T. vivax and mixed-infection with T. vivax and T. evansi in Sudanese camels.

Molecular characterization of internal transcribed spacer 1 (ITS 1) region of different Trypanosoma evansi isolates of India

Six Trypanosoma evansi isolates collected from ponies (PH1 and PK6), camel (CB2), donkeys (DJ3 and DH4) and cattle (CK5) from Haryana, Rajasthan, Uttar Pradesh and Gujarat states of India were used for molecular characterization of internal transcribed spacer 1 (ITS 1). The DNA was isolated from purified trypanosomes of these six isolates after propagation in mice model. ITS1-PCR of purified parasite DNA yielded an amplification product approximately 540 bp in size. Nucleotide sequence of ITS1 gene of CB2 isolate had 530 bp while CK5, DH4, DJ3, and PH1 isolates had 532 bp, whereas, PK6 isolates had 533 bp size. Blast data of the Indian isolates revealed 99 % homology with other available sequences of T. evansi. Multiple alignment of nucleotide sequence of ITS1 gene variants from Indian T. evansi isolates with selected homologous sequences from GenBank revealed that nucleotide substitution mostly occurred at the position of 101-103, 218-223, 243-244, 301-396 and 470-480. The isolates PH1, CK5, DH4 and DJ3 were found more associated with T. evansi isolates from the Philippines, Thailand, Iran, Egypt and China, whereas, PK6 and CB2 isolates were related to each other and were phylogenetically distant from rest of the Indian isolates used in this study. Based on the ITS1 rDNA sequence, the Neighbour-Joining consensus tree indicated clear evidence of existence of genetic diversity among T. evansi isolates from India.

Phylogeny of Trypanosoma brucei and Trypanosoma evansi in naturally infected cattle in Nigeria by analysis of repetitive and ribosomal DNA sequences

In continuing efforts to better understand the genetics of bovine trypanosomosis, we assessed genetic diversity of Trypanosoma brucei and Trypanosoma evansi in naturally infected Nigerian cattle using repetitive DNA and internal transcribed spacer 1 of rDNA sequences and compared these sequences to species from other countries. The length of repetitive DNA sequences in both species ranged from 161 to 244 bp and 239 to 240 bp for T. brucei and T. evansi, respectively, while the ITS1 rDNA sequences length range from 299 to 364 bp. The mean GC content of ITS1 rDNA sequences was 33.57 %, and that of repetitive sequences were 39.9 and 31.1 % for T. brucei and T. evansi, respectively. Result from sequence alignment revealed both T. brucei and T. evansi repetitive DNA sequences to be more polymorphic than ITS1 rDNA sequences, with moderate points of deletion and insertions. T. brucei separated into two clades when subjected to phylogenetic analysis. T. evansi repetitive DNA sequences clustered tightly within the T. brucei clade while the ITS1 rDNA sequences of T. brucei were clearly separated from T. theileri and T. vivax individually used as outgroups. This study suggest that ITS1 rDNA sequences may not be suitable for phylogenetic differentiation of the Trypanozoon group and also suggest that T. evansi may be a phenotypic variant of T. brucei which may have potential implications in designing prevention and therapeutic strategies.

Microsatellite typing and population structuring of Trypanosoma evansi in Mindanao, Philippines

Trypanosoma evansi, a blood-borne protozoan parasite with an extensive geographical range is the causative agent of the livestock disease known as surra. A total of 140 out of 179 T. evansi isolates collected between 2006 and 2007 from 44 villages (comprising of 16 reported surra outbreaks) in 3 provinces (Agusan del Sur (ADS), Surigao del Sur (SDS) and Agusan del Norte (ADN)) in Mindanao, Philippines were each successfully genotyped using a suite of 7 polymorphic microsatellites. The study identified 16 multi locus genotypes (MLG) within the T. evansi isolates and evidence of the spread of surra outbreaks from one village to another, most likely due to the movement of infected animals. Genotyping provided evidence of population sub-structuring with 3 populations (I, II and III (only 1 isolate)) identified. The most abundant population was II, which was the predominant population in ADS and SDS (p=0.022). In addition, buffalo mortality was statistically higher in outbreak areas associated with isolates from population I (13.6%) than with isolates from population II (6.9%) (p=0.047). The present study has highlighted the utility of microsatellite loci to improve understanding of the epidemiology of T. evansi and in tracking surra outbreaks.

The internal transcribed spacer 1 (ITS-1), a controversial marker for the genetic diversity of Trypanosoma evansi

Seven Trypanosoma evansi isolates from China and a Trypanosoma congolense sp. gifted from Kenya were characterized genetically by the internal transcribed spacer 1 (ITS-1) of nuclear ribosomal DNA (rDNA). The ITS-1 rDNA with the length of 338-342 bp was amplified by polymerase chain reaction (PCR) and sequenced from individual isolates of T. evansi. Although sequence variation between T. evansi isolates from China only was 0.3-3.8%, the constructed phylogenetic tree based on the ITS-1 rDNA sequence by the method of neighbor-joining and maximum parsimony revealed the genetic diversity among T. evansi isolates from China. For T. congolense sp., the most phylogenetically related species was T. congolense IL1180. Although the sequence variation ranged 0.8-14.5% between T. congolense isolates, the phylogenetic tree can not reflected the genetic diversity among T. congolense isolates perhaps because of the fewer number of isolates and sequences. The data could be applicable for the survey of parasite dynamics, epidemiological studies as well as prevention and control of the disease.

Population genetics of Trypanosoma evansi from camel in the Sudan

Genetic variation of microsatellite loci is a widely used method for the analysis of population genetic structure of microorganisms. We have investigated genetic variation at 15 microsatellite loci of T. evansi isolated from camels in Sudan and Kenya to evaluate the genetic information partitioned within and between individuals and between sites. We detected a strong signal of isolation by distance across the area sampled. The results also indicate that either, and as expected, T. evansi is purely clonal and structured in small units at very local scales and that there are numerous allelic dropouts in the data, or that this species often sexually recombines without the need of the “normal” definitive host, the tsetse fly or as the recurrent immigration from sexually recombined T. brucei brucei. Though the first hypothesis is the most likely, discriminating between these two incompatible hypotheses will require further studies at much localized scales.

Trypanosomiasis due to Trypanosoma evansi is a widely distributed disease of livestock, affecting especially camelids and equines and is transmitted by biting flies. The disease is of great concern to many developing countries such as Sudan, where its large camel population estimated at over 4.6 million heads is at risk. It is generally believed that T. evansi has evolved when camels infected with T. brucei moved to tsetse-free areas, but only a few studies have been carried out to elucidate the genetic make-up of T. evansi. Therefore, in the current study, 15 microsatellite markers from non-coding loci on 38 isolates of T. evansi originating from different locations in Sudan were analyzed. Three reference strains from Sudan and Kenya were additionally analyzed and compared to the recent isolates. The results of this study revealed a highly significant isolation by distance pattern with rather small neighborhood sizes. It also suggested that T. evansi is either purely clonal with numerous problems of allelic dropouts or that it often sexually recombines without the need of the definitive host, the tsetse fly, or as the result of recurrent immigration from sexually recombined T. brucei brucei mutants.

Molecular epidemiology of camel trypanosomiasis based on ITS1 rDNA and RoTat 1.2 VSG gene in the Sudan

Background

Internal transcribed spacer one (ITS1) of the ribosomal DNA is known to be a suitable target for PCR-based detection of trypanosomes. The analysis of this region provides a multi-species-specific diagnosis by a single PCR. Using ITS1 primer-based PCR, a cross sectional study was carried out in the period from September to November 2009 on samples collected from 687 camels from geographically distinct zones in the Sudan to detect all possible African trypanosomes, which can infect camels.

Results

The results showed that all PCR-positive camels were infected with a single parasite species; Trypanosoma evansi. The highest prevalence, 57.1% (117/205), was observed in the Butana plains of mid-Eastern Sudan and the lowest, 6.0% (4/67), was in the Umshadeeda eastern part of White Nile State. In another experiment, the RoTat 1.2 gene encoding the variable surface glycoprotein (VSG) of T. evansi was analyzed for its presence or absence by a polymerase chain reaction (PCR) using T. evansi species-specific primers. The study showed that the RoTat 1.2 VSG gene was absent in thirteen out of thirty T. evansi-positive samples.

Conclusions

It is concluded that camel trypanosomiasis in Sudan is apparently caused by a single parasite species T. evansi and there were no other typanosomes species detected. In addition, the disease is highly prevalent in the country, which strengthens the need to change control policies and institute measures that help prevent the spread of the parasite. To our knowledge, this is the first molecular diagnosis report, which gives a picture of camel trypanosomiasis covering large geographical areas in Sudan.

Molecular identification and phylogenetic analysis of Trypanosoma evansi from dromedary camels (Camelus dromedarius) in Egypt, a pilot study

Animal trypanosomiasis is one of the major constraints of livestock industry in developing countries. In the present study, prevalence of Trypanosome evansi was assessed in the blood of dromedary camels (Camelus dromedarius) brought to Al Bassatein abattoir, Cairo, Egypt, by mouse inoculation test out of 84 tested camels, 4 animals (4.7%) were infected. Molecular analysis was achieved by PCR amplification and sequence analysis of part of ribosomal RNA gene including 18S, ITS1, 5.8S and ITS2 regions. Despite the conserved nature of 18S region, ITS region showed obvious heterogeneity compared to analogous sequences in database. Analysis of transferrin receptor encoding gene (ESAG6) showed variable repertoire in the studied isolates, which may indicate to a novel structure of T. evansi population from Egypt and/or a difference in host range. Furthermore, analysis of variable surface glycoprotein RoTat 1.2 gene marker revealed some heterogeneity at this gene locus. To our knowledge, this is the first molecular analysis of T. evansi in Egypt.

Genetic diversity of Trypanosoma evansi in beef cattle based on internal transcribed spacer region

This study was focused on genetic diversity of Trypanosoma evansi which is a widely distributed haemoflagellate of veterinary importance that infects a variety of larger mammals including horses, mules, camels, buffalo, cattle and deer. The genetic diversity of T. evansi of beef cattle LAM19 was accomplished by using phylogenetic analysis based on internal transcribed spacer region (ITS). Blood sample was collected from a naturally infected beef cattle LAM 19 and parasitemia was raised by mouse inoculation. The parasites were collected and isolated by using DE 52 DEAE cellulose anion exchange column prior to DNA extraction. Upon PCR amplification of ITS region, the product of 1300bp in size was obtained. The ITS nucleotide sequences were analyzed and revealed that it could demonstrate the genetic diversity of T. evansi of beef cattle LAM19. Based on the ITS tree, beef cattle LAM 19 T. evansi were categorized into two main groups where the genetic diversity occurred within Group 1. The data could be applicable for the survey of parasite dynamics, epidemiological studies as well as prevention and control of the disease.