Comparison of Three Methods to Extract Plasmodium falciparum DNA from Whole Blood and Dried Blood Spots

This study aimed to compare the effectiveness of three DNA extraction methods: the GF-1 Blood DNA Extraction Kit (GF-1 BD Kit), which employs a spin column along with lysing and washing buffers; the tris-ethylenediaminetetraacetic acid and proteinase K (TE-pK) method, which utilizes a combination of TE buffer and proteinase K for cell lysis; and DNAzol® Direct (DN 131), a single reagent combined with heating for the extraction process. Plasmodium falciparum DNA was extracted from both whole blood and dried blook spots (DBSs), with consideration of DNA concentration, purity, cost, time requirement, and limit of parasite detection (LOD) for each method. The target gene in this study was 18S rRNA, resulting in a 395-bp product using specific primers. In the comparative analysis, the DN 131 method yielded significantly higher DNA quantities from whole blood and DBSs than the GF-1 BD Kit and TE-pK methods. In addition, the DNA purity obtained from whole blood and DBSs using the GF-1 BD Kit significantly exceeded that obtained using the TE-pK and DN 131 methods. For LOD, the whole blood extracted using the DN 131, GF-1 BD Kit, and TE-pK methods revealed 0.012, 0.012, and 1.6 parasites/µL, respectively. In the case of DBSs, the LODs for the DN 131, GF-1 BD Kit, and TE-pK methods were 1.6, 8, and 200 parasites/µL, respectively. The results revealed that the TE-pK method was the most cost-effective, whereas the DN 131 method showed the simplest protocol. These findings offer alternative approaches for extracting Plasmodium DNA that are particularly well-suited for large-scale studies conducted in resource-limited settings.

Formalin-fixed stool improves the performance of the Kato-Katz method

Background and Aim

Parasitic infections are a public health problem worldwide, including in Thailand. An epidemiological survey for helminthiasis based on stool examination uses the Kato-Katz method as recommended by the World Health Organization. Limitations of this method include the need for fresh stool, time requirement, and lack of quality control. The aim of this study was to enhance the efficiency of the Kato-Katz technique using formalin and glycerol solutions and to implement specimen preparation in fieldwork.

Materials and Methods

For the Kato-Katz method, stool samples were divided into formalin-fixed and unfixed groups at various time points and processes. Fresh echinostome eggs were added to each stool group. Incubation with glycerol increased the clearing process. Each group was observed and photographed using a light microscope. Parasite eggs were imaged and compared using the standard Kato-Katz method.

Results

Visualization of echinostome eggs from formalin-fixed stool slides was significantly better than that from unfixed stool slides (p < 0.01). Stool samples fixed for 7 days retained normal echinostome eggs morphology. Incubation with glycerol for 1 h resulted in increased Kato-Katz performance by digesting the stool content and enhancing egg observation. Moreover, the results of the Kato-Katz method using fixed and fixed stool plus glycerol for natural helminth infection showed good quality of Opisthorchis viverrini and Taenia egg visualization and normal morphology with a clear background of slides.

Conclusion

Formalin-fixed stool could be more suitable than fresh stool for the Kato-Katz method.

Comparison of 3 DNA extraction methods for extracting DNA from an adult Culex quinquefasciatus (Diptera: Culicidae)

The aim of this study was to compare 3 DNA extraction methods: the PureLink Genomic DNA kit, DNAzol Direct reagent, and a microwave-based method, for extracting DNA from an adult Culex quinquefasciatus by focusing on the quantity and purity of DNA, cost, and time required. Ten mosquitoes were individually used for DNA extraction by each method. Based on the results obtained, DNA was extracted from each method using specific primers, resulting in a polymerase chain reaction (PCR) product with a length of 274 bp. The DNA quantity extracted using the DNAzol Direct (179.08 ± 3.77 ng/µl) differs significantly from that of the commercial kit (115.98 ± 4.57 ng/µl) and a microwave-based method (119.26 ± 3.06 ng/µl). The absorbance ratio of DNA extracted using the PureLink Genomic DNA kit, the DNAzol Direct, and the microwave-based methods was 1.92 ± 0.02, 1.79 ± 0.01, and 1.87 ± 0.01, respectively. Among the 3 methods evaluated, the microwave-based method is simpler, less expensive, and more time efficient. This is the first evaluation of the microwave-based method for extracting DNA from an adult mosquito. This study provides a useful guide for alternative DNA extraction methods for PCR-based assays, especially in low-resource settings.

Reduction of carcinogens in fermented fish (pla-ra and pla-som) by heating

Background and Aim

The risk factors for cholangiocarcinoma (CCA) are opisthorchiasis and the intake of a combination of nitroso compounds through the consumption of traditionally fermented fish, which is very popular in areas where liver flukes are endemic. The incidence of CCA remains high because this cultural habit of rural people has been altered. Therefore, decreasing nitrate and nitrite concentrations in fermented fish are an alternative approach to reducing the risk of CCA. Thus, this study aimed to reduce nitrate and nitrite concentrations in fermented foods by heating and investigated its effect on CCA development in a hamster model.

Materials and Methods

We used Association of Official Analytical Chemists method 973.31 to measure the nitrate and nitrite concentrations in both fermented fish (pla-ra [PR]) and pickled fish (pla-som [PS]) before and after boiling for 5 and 30 min, respectively. The same samples were fed to Opisthorchis viverrini (OV)-infected or -uninfected hamsters for 3 months. Thereafter, the hamsters' liver and blood were collected for analysis.

Results

The levels of nitrates and nitrites in PS and PR significantly decreased following boiling for 5 and 30 min. The OV-PR and OV-PS groups showed dramatically increased numbers of inflammatory cells, fibrosis surrounding the bile duct, and focal fibrotic areas. However, after boiling the fermented dishes for 5 and 30 min, the extent of inflammatory cell infiltration and intensity of fibrosis in these groups were decreased.

Conclusion

Our findings suggest that boiling reduces nitrate and nitrite toxicity in fermented dishes, as evidenced by reduced hepatic inflammation. However, regardless of heating, kidney tissues are adversely affected when fermented meals are consumed daily.

Efficacy of Dipterocarpus alatus oil combination with Rhinacanthus nasutus leaf and Garcinia mangostana pericarps against canine demodicosis

Background and Aim:

Canine demodicosis is a skin disease that is a major global health problem in dogs. Ivermectin is a drug of choice for treatment, but it may cause toxicity in dogs carrying multidrug resistance mutation-1 gene mutations. Hence, alternative herbal medicines are used instead of the drug, such as Dipterocarpus alatus oil (YN oil), Rhinacanthus nasutus leaf (WC), and Garcinia mangostana pericarps (MG) extracts. This study aimed to determine the efficacy of D. alatus oil, R. nasutus leaf, and G. mangostana pericarp extracts on canine demodicosis in vivo.

Materials and Methods:

Twenty-five mixed-breed dogs with localized demodicosis were examined. Dogs were diagnosed with demodicosis through deep skin scraping and screened with the inclusion criteria. Five dogs of each group were treated in five treatment groups (ivermectin, YN oil, YN oil+WC, YN oil+MG, and YN oil+WC+MG) for 1 month. The individual dogs were clinically evaluated, and the dermatological lesions were monitored daily for 60 days.

Results:

Dermatological lesion improvement was predominantly observed in the group of dogs treated with YN oil+WC. This was evidenced by the disappearance of the hyperpigmentation and lichenification on day 28 post-treatment and alopecia on day 56 post-treatment. Moreover, no allergic or clinical signs were observed during treatment.

Conclusion:

YN oil+WC is an alternative herbal medicine that could be used for the treatment of localized canine demodicosis.

Exposure to dexamethasone modifies transcriptomic responses of free-living stages of Strongyloides stercoralis

Hyperinfection and disseminated infection by the parasitic nematode Strongyloides stercoralis can be induced by iatrogenic administration of steroids and immunosuppression and lead to an elevated risk of mortality. Responses of free-living stages of S. stercoralis to the therapeutic corticosteroid dexamethasone (DXM) were investigated using RNA-seq transcriptomes of DXM-treated female and male worms. A total of 17,950 genes representing the transcriptome of these free-living adult stages were obtained, among which 199 and 263 were differentially expressed between DXM-treated females and DXM-treated males, respectively, compared with controls. According to Gene Ontology analysis, differentially expressed genes from DXM-treated females participate in developmental process, multicellular organismal process, cell differentiation, carbohydrate metabolic process and embryonic morphogenesis. Others are involved in signaling and signal transduction, including cAMP, cGMP-dependent protein kinase pathway, endocrine system, and thyroid hormone pathway, as based on Kyoto Encyclopedia of Genes and Genomes analysis. The novel findings warrant deeper investigation of the influence of DXM on growth and other pathways in this neglected tropical disease pathogen, particularly in a setting of autoimmune and/or allergic disease, which may require the clinical use of steroid-like hormones during latent or covert strongyloidiasis.

Zoonotic Helminthiases in Rodents (Bandicota indica, Bandicota savilei, and Leopoldamys edwardsi) from Vientiane Capital, Lao PDR

Zoonotic helminths of three rodent species, Bandicota indiaca, Bandicota savilei, and Leopoldamys edwardsi, were investigated in Vientiane capital, Lao PDR. A total of 310 rodents were infected with 11 species of helminth parasites. There were 168 (54.2%) of 310 rodents infected with zoonotic helminths. From our results, there are six recorded zoonotic helminth species, and the highest prevalence was exhibited by Raillietina sp. (30.7%), followed by Hymenolepis diminuta (17.7%), Hymenolepis nana (2.6%), Echinostoma ilocanum (1.9%), Echinostoma malayanum (1.3%), and Angiostrongylus cantonensis (1%). This is the first study of zoonotic helminths in L. edwardsi and the first report of H. diminuta, H. nana, E. ilocanum, and E. malayanum in Bandicota indica and B. savilei, and the first demonstration of A. cantonenensis in B. indica in Lao PDR. From our results, these three rodents are potentially important reservoir hosts of zoonotic helminths. Thus, effective control programs should be considered for implementation to prevent the transmission of these zoonoses in this area.

Spirometra species from Asia: Genetic diversity and taxonomic challenges

Despite considerable controversy concerning the taxonomy of species within the genus Spirometra, human sparganosis and spirometrosis mainly in Asia and Europe has long been confidently ascribed to Spirometra erinaceieuropaei. Recently, the mitochondrial genomes of purported "S. erinaceieuropaei", "Spirometra decipiens" and "Spirometra ranarum" from Asia have been determined. However, it has been pointed out that the morphological criteria used for identifying these species are unsuitable and thus these identifications are questionable. In the present study, therefore, Spirometra samples from Asia were re-examined based on mitochondrial cytochrome c oxidase subunit 1 gene sequences and the identification of these species was discussed. Haplotype network and phylogenetic analyses revealed that: i) two distinct Spirometra species, Type I and Type II, are present in Asia and neither of which is close to likely European "S. erinaceieuropaei"; ii) Type I is genetically diverse and widely distributed, however Type II is known so far from Japan and Korea; iii) "S. decipiens" and "S. ranarum" reported from Asia are conspecific with Type I; iv) Type I is probably conspecific with Spirometra mansoni, and Type II may represent an undescribed species.

Current status of Opisthorchis viverrini, minute intestinal fluke and Taenia spp. infections among inhabitants in the Kenethao district of northern Lao PDR

Background

This study reports the prevalence of Ov/minute intestinal fluke (MIF) and Taenia infections among inhabitants of the Kenethao district, northern Lao PDR.

Methods

Fecal samples from 580 inhabitants were examined using the formalin-ethyl acetate concentration technique.

Results

The prevalence of Ov/MIF, Taenia spp. and coinfection was 45.3, 11.9 and 6.1%, respectively. There was no significant difference between males and females for Ov/MIF (p=0.813) and Taenia infection (p=0.759). The prevalence of Ov/MIF was significantly associated with age (p=0.005), but not for Taenia infection (p=0.836). Consumption of raw fish (p=0.001) and raw meat (p=0.046) was significantly associated with parasitic infections.

Conclusions

The results suggest that Ov/MIF and Taenia spp. are highly endemic in this area and there is a need for projects to eliminate these parasites.

Investigation of the in vitro cysticidal activity of miltefosine against Acanthamoeba spp

The present study evaluated the in vitro efficacy of miltefosine against cysts of Acanthamoeba spp. belonging to genotypes T3, T4 and T5. Each genotype was incubated with miltefosine at the concentration of 2.42, 4.84, 9.68, 19.36, 38.72 and 77.44 mM for different periods; 1, 3, 5, 7 d at 37 °C. The viability was assessed by staining with 0.4% trypan blue and culturing on NNA medium at 30 °C for 1 month. The results showed 100% eradication of cyst stage of all concentrations, but exhibited a different degree of activity against different genotypes. The MCC of 38.72 mM could kill genotype T4 and T5 after 1 d of incubation, whereas the killing of T3 needed MCC of 77.44 mM at the same incubation time. Miltefosine showed statistically highly significant difference (P < 0.001) in comparison to non-treated control. Although our finding needs to confirm in animal models, this information may be the guideline for optimizing therapy or considered to combine with the other drugs for effective treatment.

Molecular identification and genetic diversity of Gnathostoma spinigerum larvae in freshwater fishes in southern Lao PDR, Cambodia, and Myanmar

Gnathostomiasis, an emerging food-borne parasitic zoonosis in Asia, is mainly caused by Gnathostoma spinigerum (Nematoda: Gnathostomatidae). Consumption of raw meat or freshwater fishes in endemic areas is the major risk factor. Throughout Southeast Asia, including Thailand, Lao PDR, Cambodia, and Myanmar, freshwater fish are often consumed raw or undercooked. The risk of this practice for gnathostomiasis infection in Lao PDR, Cambodia, and Myanmar has never been evaluated. Here, we identified larvae of Gnathostoma species contaminating freshwater fishes sold at local markets in these three countries. Public health authorities should advise people living in, or travelling to, these areas to avoid eating raw or undercooked freshwater fishes. Identification of larvae was done using molecular methods: DNA was sequenced from Gnathostoma advanced third-stage larvae recovered from snakehead fishes (Channa striata) and freshwater swamp eels (Monopterus albus). Phylogenetic analysis of a portion of the mitochondrial cytochrome c oxidase subunit I gene showed that the G. spinigerum sequences recovered from southern Lao PDR, Cambodia, and Myanmar samples had high similarity to those of G. spinigerum from China. Sequences of the nuclear ribosomal DNA internal transcribed spacer 2 region closely resembled sequences of G. spinigerum from Thailand, Indonesia, the USA, and central Lao PDR. This is the first molecular evidence of G. spinigerum from freshwater fishes in southern Lao PDR, Cambodia, and Myanmar.

Effect of Temperature on the Killing of Opisthorchis viverrini Eggs In Vitro

Contaminated liver fluke egg in the environment has led to the high prevalence of human opisthorchiasis associated with cholangiocarcinoma in Southeast Asia. To find the effective lessening methods of Opisthorchis viverrini eggs in the contaminated environment, we investigated the temperature conditions for killing of these trematode eggs in vitro. Numerous O. viverrini eggs were obtained in the proximal part of uteri of adult worms from experimental hamsters. Mature eggs with miracidium were allocated by experimental groups (2 control: positive and negative and 4 treatment: 50, 60, 70, and 80°C) with 0.85% saline, and treated by the experimental plan. Eggs in each experimental groups were observed under the confocal microscope after stain with Propidium Iodide (PI) to evaluate the effect of temperatures. Eggs in 70 and 80°C groups were all killed after over 10 min heated. Majority of eggs in 60°C (10, 15, and 30 min heated), 70 and 80°C (5 min heated) groups were inactivated. However in 50°C group, below half of eggs were to be killed in all time lapse (10, 15 and 30 min). In order to prevent O. viverrini infection and cholangiocarcinoma, direct treatment of sewage by heating at 70 or 80°C at least 10 min is essential. Therefore, treatment of O. viverrini eggs at a high temperature is a potential method for controlling egg contamination in sewage.

An Alternative Method for Extracting Plasmodium DNA from EDTA Whole Blood for Malaria Diagnosis

Molecular techniques have been introduced for malaria diagnosis because they offer greater sensitivity and specificity than microscopic examinations. Therefore, DNA isolation methods have been developed for easy preparation and cost effectiveness. The present study described a simple protocol for Plasmodium DNA isolation from EDTA-whole blood. This study demonstrated that after heating infected blood samples with Tris–EDTA buffer and proteinase K solution, without isolation and purification steps, the supernatant can be used as a DNA template for amplification by PCR. The sensitivity of the extracted DNA of Plasmodium falciparum and Plasmodium vivax was separately analyzed by both PCR and semi-nested PCR (Sn-PCR). The results revealed that for PCR the limit of detection was 40 parasites/μl for P. falciparum and 35.2 parasites/μl for P. vivax, whereas for Sn-PCR the limit of detection was 1.6 parasites/μl for P. falciparum and 1.4 parasites/μl for P. vivax. This new method was then verified by DNA extraction of whole blood from 11 asymptomatic Myanmar migrant workers and analyzed by Sn-PCR. The results revealed that DNA can be extracted from all samples, and there were 2 positive samples for Plasmodium (P. falciparum and P. vivax). Therefore, the protocol can be an alternative method for DNA extraction in laboratories with limited resources and a lack of trained technicians for malaria diagnosis. In addition, this protocol can be applied for subclinical cases, and this will be helpful for epidemiology and control.

Status and Risk Factors of Strongyloides stercoralis Infection in Rural Communities of Xayaburi Province, Lao PDR

The present study was performed to reveal the current status and risk factors of Strongyloides stercoralis infections in the villages of Kenethao district, Xayaburi Province, Lao PDR. Fecal specimens were collected and examined for S. stercoralis using Koga-agar plate culture technique. Among 516 individuals, the prevalence of S. stercoralis and hookworm infection was 44.2% and 17.1%, respectively. Co-infection was detected in 13.2% of the cases. The prevalence did not significantly differ between males and females (P=0.193). However, the prevalence of S. stercoralis infection increased significantly with age (P=0.041). Of the risk factors examined, both performing farming activities (P=0.001) and walking barefoot when going outside of the house (P=0.003) showed significant correlations with S. stercoralis infections. Our results suggest that S. stercoralis is highly endemic in this area. The National Helminth Control Program of Lao PDR should take actions to control S. stercoralis infection. In addition, provision of health education about the benefits of wearing shoes would be important for reducing infection in the study area. Moreover, the application of high-sensitivity diagnostic approaches is needed to obtain the true impact of S. stercoralis infections in all rural communities in order to provide surveillance activities in Lao PDR.

An eleven-year retrospective hospital-based study of epidemiological data regarding human strongyloidiasis in northeast Thailand

Background

Human strongyloidiasis is a chronic and persistent gastrointestinal disease caused by infection with soil-transmitted helminths of the genus Strongyloides. The aim of this research was to obtain diagnostic prevalence regarding strongyloidiasis in northeast Thailand through a hospital-based study.

Methods

Patients’ demographic data and the results of stool examinations conducted using the formalin ethyl acetate concentration technique were collected from the parasitology laboratory records at Srinagarind Hospital in Khon Kaen, Thailand. The relevant information from years 2004 to 2014 was collected and descriptively analyzed.

Results

Of a total of 22,338 patients, 3889 (17.4%) had stool samples that tested positive for Strongyloides larvae. The highest prevalence was 22.8% (95% CI = 19.6–26.2%) in the year 2004. This percentage progressively decreased, reaching 11.2% (95% CI = 10.2–12.4%) in 2013 and remaining stable at 12.9% (95% CI = 11.8–14.1%) in 2014. Males (2741 cases) had double the positivity rate of females (1148 cases). The prevalence of infection was highest (25.9%; 95% CI = 24.5–27.3%) among patients that were 51–60 years of age.

Conclusions

Areas endemic for strongyloidiasis should be emphasized under the national helminth control program and health education campaigns. Nationwide assessments should also be performed regarding Strongyloides infection, including risk factors, treatment, and prevention. The diagnostic laboratory data presented here identify the geographical focus of disease to be the northeastern region of the country. Further targeted surveillance using more sensitive methods will almost certainly reveal a higher individual disease burden than found in this report.

Identification of antigenic proteins in Strongyloides stercoralis by proteomic analysis

Strongyloides stercoralis is an intestinal helminth that infects people worldwide. Hyperinfection or disseminated human strongyloidiasis can involve vital organs, leading to lethal outcomes. We analyzed immunoproteomics of antigenic spots, derived from S. stercoralis third-stage larvae and reacted with human strongyloidiasis sera, by two-dimensional gel electrophoresis and immunoblotting. Of 26 excised antigenic spots analyzed by liquid chromatography-electrospray ionization-tandem mass spectrometry, 20 proteins were identified. Most proteins were associated with enzymes involved in the metabolic process, energy generation, and oxidation-reduction. The proteins relate to promotion of worm development, cell division, cell signaling and transportation, and regulation of muscular contraction. Identification of antigenic proteins shows promise in helping to discover potential diagnostic protein markers or vaccine candidates for S. stercoralis infection.

In Vitro and In Vivo Inhibitory Effects of α-Mangostin on Cholangiocarcinoma Cells and Allografts

We investigated the anti-cholangiocarcinoma effect of α-mangostin from Garcinia mangostana pericarp extract (GM) in a human cholangiocarcinoma (CCA) cell line and a hamster CCA allograft model. In vitro, human CCA cells were treated with GM at various concentrations and for different time periods; then cell-cycle arrest and apoptosis were evaluated using flow cytometry, and metastatic potential with wound healing assays. In vivo, hamster allografts were treated with GM, gemcitabine (positive control) and a placebo (negative control) for 1 month; tumor weight and volume were then determined. Histopathological features and immunostaining (CK19 and PCNA) characteristics were examined by microscopy. The present study found that α-mangostin could: inhibit CCA cell proliferation by inducing apoptosis through the mitochondrial pathway; induce G1 cell-cycle arrest; and inhibit metastasis. Moreover, α-mangostin could inhibit CCA growth, i.e. reduce tumor mass (weight and size) and alter CCA pathology, as evidenced by reduced positive staining for CK19 and PCNA. The present study thus suggested that α-mangostin is a promising anti-CCA compound whose ready availability in tropical countries might indicate use for prevention and treatment of CCA.

Carcinogenic Liver Fluke and Others Contaminated in Pickled Fish of Northeastern Thailand

Twenty provinces in northeastern Thailand were investigated for fluke metacercariae contamination in pickled fish, or pla-som, during January –June 2016. A total of 129 pickled fish shops were randomly chosen. Samples were digested with acid-pepsin and those found to be infected with metacercariae were fed to hamsters to test for metacercariae infectivity. The results demonstrated that only 20.2% of the pla-som samples were infected with fluke metacercariae (mc), at various levels (1 to 268 mc/kg). All recovered fluke metacercariae were inactive, degenerated and could not develop to adults in the animal model. In conclusion, the fluke mc infection status in pla-som was correlated with the prevalence of fluke infection in this region known for high O.viverrini and cholangiocarcinoma development. Clearly, systematic control of the fluke life cycle is needed. Whether pickling is an effective preventive measure needs further assessment.

Angiostrongylus cantonensis and A. malaysiensis Broadly Overlap in Thailand, Lao PDR, Cambodia and Myanmar: A Molecular Survey of Larvae in Land Snails

Angiostrongylus cantonensis is a zoonotic nematode parasite causing human eosinophilic meningitis (or meningoencephalitis) worldwide. A closely related species, Angiostrongylus malaysiensis, might also be a human pathogen. Larvae were obtained from land snails in Lao PDR, Cambodia, Myanmar and Thailand. We sequenced two nuclear gene regions (nuclear ribosomal ITS2 and SSU rRNA) and a portion of one mitochondrial gene (COI) from these larvae. Angiostrongylus cantonensis and A. malaysiensis were identified. This is the first report of the molecular identification of the two Angiostrongylus species in Lao PDR, Cambodia and Myanmar. The regional distributions of the two species broadly overlap. Phylogenetic relationships were inferred including data from Angiostrongylus species deposited in public databases. All the gene regions we sequenced have potential value in distinguishing between species of Angiostrongylus. The COI gene exhibited the greatest intraspecific variation in the study region (five haplotypes in A. cantonensis and four in A. malaysiensis) and might be suitable for more detailed phylogeographic studies.

Strongyloides stercoralis diagnostic polypeptides for human strongyloidiasis and their proteomic analysis

Human strongyloidiasis is a deleterious gastrointestinal disease mainly caused by Strongyloides stercoralis infection. Strongyloides stercoralis is a soil-transmitted helminthiasis that is distributed around the globe. Although definitive diagnosis is carried out through the detection of parasite objects in human stool samples, the development of reliable immunological assays is an important alternative approach for supportive diagnosis. We characterized the two sensitive and specific bands of S. stercoralis filariform larvae that reacted with human strongyloidiasis sera based on immunoblot analysis. Serum samples obtained from strongyloidiasis patients showed a sensitivity of 90 and 80 % at the approximate molecular mass of 26 and 29-kDa polypeptide bands, respectively. The reactive specificity of the 26-kDa band was 76.5 % while for the 29-kDa band was 92.2 %. Proteomic analysis identified the 26-kDa band protein was 14-3-3 protein zeta, while the 29-kDa band protein was ADP/ATP translocase 4. The results provided a basic framework for further studies regarding the potential of the S. stercoralis recombinant antigen to become a leading to diagnostic tool.

Animal Models for Echinostoma malayanum Infection: Worm Recovery and Some Pathology

Echinostomes are intestinal trematodes that infect a wide range of vertebrate hosts, including humans, in their adult stage and also parasitize numerous invertebrate and cold-blooded vertebrate hosts in their larval stages. The purpose of this study was to compare Echinostoma malayanum parasite growth, including worm recovery, body size of adult worms, eggs per worm, eggs per gram of feces, and pathological changes in the small intestine of experimental animals. In this study, 6-8-week-old male hamsters, rats, mice, and gerbils were infected with echinostome metacercariae and then sacrificed at day 60 post-infection. The small intestine and feces of each infected animal were collected and then processed for analysis. The results showed that worm recovery, eggs per worm, and eggs per gram of feces from all infected hamsters were higher compared with infected rats and mice. However, in infected gerbils, no parasites were observed in the small intestine, and there were no parasite eggs in the feces. The volume of eggs per gram of feces and eggs per worm were related to parasite size. The results of histopathological changes in the small intestine of infected groups showed abnormal villi and goblet cells, as evidenced by short villi and an increase in the number and size of goblet cells compared with the normal control group.

Development and usefulness of an immunochromatographic device to detect antibodies for rapid diagnosis of human gnathostomiasis

Background

Human gnathostomiasis is a serious tropical disease, which is often overlooked. There is an urgent need to improve tools to aid the potential diagnosis of the disease in endemic regions. To overcome this, we produced the immunochromatographic test (ICT) kit for a rapid and simple diagnosis of human gnathostomiasis.

Findings

The recombinant protein (named rGslic18) was applied to ICT kit as the antigen. The diagnostic value of ICT kit was evaluated using serum samples from parasitologically proven and clinically suspected gnathostomiasis patients, healthy volunteers and patients with other parasitic diseases. The ICT kit exhibited quite high sensitivity (93.75 %) and specificity (97.01 %).

Conclusions

The ICT kit is simple, convenient and easy to implement and expected to provide reliable diagnostic results for human gnathostomiasis. It also will be a promising diagnostic tool not only for large-scale epidemiological surveys in endemic or remote areas where diagnostic facilities are poor but also for a rapid clinical diagnosis in the bedside laboratory.

Proteomic analysis identification of antigenic proteins in Gnathostoma spinigerum larvae

Gnathostoma spinigerum is the causative agent of human gnathostomiasis. The advanced third stage larva (AL3) of this nematode can migrate into the subcutaneous tissues, including vital organs, often producing severe pathological effects. This study performed immuno-proteomic analysis of antigenic spots, derived from G. spinigerum advanced third stage larva (GSAL3) and recognized by human gnathostomiasis sera, using two-dimensional (2-DE) gel electrophoresis based-liquid chromatography/tandem mass spectrometry (LC/MS-MS), and followed by the aid of a database search. The crude GSAL3 extract was fractionated using IPG strips (pH 3-11NL) and followed by SDS-PAGE in the second dimension. Each gel was stained with colloidal Coomassie blue or was electro-transferred onto a nitrocellulose membrane and probed with gnathostomiasis human sera by immunoblotting. Individual Coomassie-stained protein spots corresponding to the antigenic spots recognized by immunoblotting were excised and processed using LC/MS-MS. Of the 93 antigenic spots excised, 87 were identified by LC/MS-MS. Twenty-seven protein types were found, the most abundant being Ascaris suum37. Six spots showed good quality spectra, but could not be identified. This appears to be the first attempt to characterize antigenic proteins from GSAL3 using a proteomic approach. Immuno-proteomics shows promise to assist the search for candidate proteins for diagnosis and vaccine/drug design and may provide better understand of the host-parasite relationship in human gnathostomiasis.

Clinical Features, Risk Factors, and Treatments of Microsporidial Epithelial Keratitis

OBJECTIVE

To report the clinical manifestations, risk factors, and treatments of microsporidial epithelial keratitis in Thailand.

METHODS

Twenty eyes of 19 patients were diagnosed and the clinical presentations, risk factors, and management were analyzed.

RESULTS

Of 19 patients, six patients (32%) had no apparent risk factors. Predisposing factors included soil exposure (6/19, 32%), water contamination (6/19, 32%), and eye liner (1/19, 4%). Twelve cases (63%) were detected in the rainy season. All cases presented with disseminated, punctated, elevated, epithelial keratitis. Corneal scrapings with Gram-chromotrope staining were positive in all patients. Moxifloxacin 0.5% eye drops were given and all 16 patients experienced complete resolution. Three recurrent cases were resolved with only topical moxifloxacin without corneal scraping or swabbing.

CONCLUSIONS

Predisposing factors were not found in some patients; thus, corneal scraping with staining should be considered in cases having a high index of suspicion. The incidence is increased during the rainy season; therefore, clinicians should have more awareness during these times. Debridement with topical moxifloxacin eye drops, without any systemic medication, may be an effective treatment. Corneal scraping or swabbing may not be required in recurrences.

Molecular detection and treatment of tick-borne pathogens in domestic dogs in Khon Kaen, northeastern Thailand

We determined the prevalence of tick-borne pathogens in domestic dogs using microscopy and polymerase chain reaction (PCR) techniques. A total of 303 EDTA blood samples were collected from domestic dogs in Khon Kaen Province, Thailand, in May 2013. Microscopic observation of Giemsa-stained smears and molecular diagnosis using conventional PCR were performed. Infected dogs were treated with imidocarb dipropionate, a combination of imidocarb dipropionate and doxycycline, or doxycycline alone. Seventy-one (23.4%) out of 303 dogs were positive for DNA of tick-borne pathogens. Of the 303 animals, 13.2% and 1.3% were positive for a single infection with Babesia spp or Ehrlichia canis, respec- tively using microscopy; whereas 19.5% and 3.0% were positive using the PCR technique. Co-infection with Babesia spp and E. canis was observed in 0.7%, and coinfection with Hepatozoon canis and E. canis in 0.3%. Infected dogs were treated with the assigned drugs, and elimination of the pathogens was demonstrated by microscopy and PCR. The results indicated that while both microscopic and PCR diagnostic techniques were useful for tick-borne pathogen detection, PCR was more effective. Imidocarb dipropionate and doxycycline were found to be effective for treatment of babesiosis and ehrlichiosis, respectively. The present study suggests that the PCR technique has high sensitivity and specificity for Babesia and Ehrlichia diagnosis as well as for detection of Babesia spp, E. canis and H. canis DNA in EDTA blood specimens.

A dot-ELISA test using a Gnathostoma spinigerum recombinant matrix metalloproteinase protein for the serodiagnosis of human gnathostomiasis

Gnathostomiasis caused by Gnathostoma spinigerum, is a hazardous food- borne helminthic zoonosis, and is endemic especially in developing countries in Asia. Definitive diagnosis, relying upon identification of worms from human tissues or body, is rarely accomplished. Consequently, sensitive supporting tools such as serological tests have been used widely. But these methods are time con- suming, need sophisticated equipment and are impractical in some settings. In the present study a dot enzyme-linked immunosorbent assay (dot-ELISA), using C. spin igerum recombinant matrix metalloproteinase protein as the antigen, was developed and assessed using sera of gnathostomiasis and other parasitosis pa- tients as well as healthy controls. The accuracy, sensitivity, specificity, positive and negative predictive values were 97.4%, 100%, 96.1%, 92.9%, and 100%, respectively. The dot-ELISA appears to be a suitable rapid test for diagnostic purpose as well as epidemiological studies.

Evaluation of IgG4 subclass antibody detection by peptide-based ELISA for the diagnosis of human paragonimiasis heterotrema

A synthetic peptide was prepared based on the antigenic region of Paragonimus westermani pre-procathepsin L, and its applicability for immunodiagnosis for human paragonimiasis (due to Paragonimus heterotremus) was tested using an ELISA to detect IgG4 antibodies in the sera of patients. Sera from other helminthiases, tuberculosis, and healthy volunteers were used as the references. This peptide-based assay system gave sensitivity, specificity, accuracy, and positive and negative predictive values of 100%, 94.6%, 96.2%, 100%, and 88.9%, respectively. Cross reactivity was frequently seen against the sera of fascioliasis (75%) and hookworm infections (50%). Since differential diagnosis between paragonimiasis and fascioliasis can be easily done by clinical presentation and fascioliasis serology, this cross reaction is not a serious problem. Sera from patients with other parasitoses (0-25%) rarely responded to this synthetic antigen. This synthetic peptide antigen seems to be useful for development of a standardized diagnostic system for paragonimiasis.

Molecular detection of Ancylostoma duodenale, Ancylostoma ceylanicum, and Necator americanus in humans in northeastern and southern Thailand

The 2 principal species of hookworms infecting humans are Necator americanus and Ancylostoma duodenale. Case studies on zoonotic hookworm infections with Ancylostoma ceylanicum and/or Ancylostoma caninum are known mainly from Asian countries. Of these 2 zoonotic species, only A. ceylanicum can develop to adulthood in humans. In the present study, we report a molecular-based survey of human hookworm infections present in southern and northeastern Thailand. Thirty larval hookworm samples were obtained from fecal agar plate cultures of 10 patients in northeastren Thailand and 20 in southern Thailand. Partial ITS1, 5.8S, and ITS2 regions of the ribosomal DNA genes were amplified using PCR. The amplicons were sequenced, aligned, and compared with other hookworm sequences in GenBank database. The results showed that, in Thailand, N. americanus is more prevalent than Ancylostoma spp. and is found in both study areas. Sporadic cases of A. ceylanicum and A. duodenale infection were seen in northeastern Thailand.

Molecular differentiation of Opisthorchis viverrini and Clonorchis sinensis eggs by multiplex real-time PCR with high resolution melting analysis

Opisthorchis viverrini and Clonorchis sinensis are parasites known to be carcinogenic and causative agents of cholangiocarcinoma in Asia. The standard method for diagnosis for those parasite infections is stool examination to detect parasite eggs. However, the method has low sensitivity, and eggs of O. viverrini and C. sinensis are difficult to distinguish from each other and from those of some other trematodes. Here, we report a multiplex real-time PCR coupled with high resolution melting (HRM) analysis for the differentiation of O. viverrini and C. sinensis eggs in fecal samples. Using 2 pairs of species-specific primers, DNA sequences from a portion of the mitochondrial NADH dehydrogenase subunit 2 (nad 2) gene, were amplified to generate 209 and 165 bp products for O. viverrini and C. sinensis, respectively. The distinct characteristics of HRM patterns were analyzed, and the melting temperatures peaked at 82.4±0.09℃ and 85.9±0.08℃ for O. viverrini and C. sinensis, respectively. This technique was able to detect as few as 1 egg of O. viverrini and 2 eggs of C. sinensis in a 150 mg fecal sample, which is equivalent to 7 and 14 eggs per gram of feces, respectively. The method is species-specific, rapid, simple, and does not require fluorescent probes or post-PCR processing for discrimination of eggs of the 2 species. It offers a new tool for differentiation and detection of Asian liver fluke infections in stool specimens.

A recombinant matrix metalloproteinase protein from Gnathostoma spinigerum for serodiagnosis of neurognathostomiasis

Neurognathostomiasis is a severe form of human gnathostomiasis which can lead to disease and death. Diagnosis of neurognathostomiasis is made presumptively by using clinical manifestations. Immunoblotting, which recognizes antigenic components of molecular mass 21 kDa and 24 kDa in larval extracts of Gnathostoma spinigerum (Gs 21/24), has high sensitivity and specificity for diagnosis of neurognathostomiasis. However, only very small amounts of the Gs 21/24 antigens can be prepared from parasites harvested from natural or experimental animals. To overcome this problem, we recently produced a recombinant matrix metalloproteinase (rMMP) protein from G. spinigerum. In this study, we evaluated this rMMP alongside the Gs 21/24 antigens for serodiagnosis of human neurognathostomiasis. We studied sera from 40 patients from Srinagarind Hospital, Khon Kaen University, Thailand, with clinical criteria consistent with those of neurognathostomiasis, and sera from 30 healthy control adults from Thailand. All sera were tested for specific IgG antibodies against both G. spinigerum crude larval extract and rMMP protein using immunoblot analysis. The sensitivity and specificity for both antigenic preparations were all 100%. These results show that G. spinigerum rMMP protein can be used as an alternative diagnostic antigen, in place of larval extract, for serodiagnosis of neurognathostomiasis.

A cross-sectional study on intestinal parasitic infections in rural communities, northeast Thailand

Despite the existence of effective anthelmintics, parasitic infections remain a major public health problem in Southeast Asia, including Thailand. In rural communities, continuing infection is often reinforced by dietary habits that have a strong cultural basis and by poor personal hygiene and sanitation. This study presents a survey of the prevalence of intestinal parasitic infections among the people in rural Thailand. The community-based cross-sectional study was conducted in villages in Khon Kaen Province, northeastern Thailand, from March to August 2013. A total of 253 stool samples from 102 males and 140 females, aged 2-80 years, were prepared using formalin-ethyl acetate concentration methods and examined using light microscopy. Ninety-four individuals (37.2%) were infected with 1 or more parasite species. Presence of parasitic infection was significantly correlated with gender (P=0.001); nearly half of males in this survey (49.0%) were infected. Older people had a higher prevalence than younger members of the population. The most common parasite found was Opisthorchis viverrini (26.9%), followed by Strongyloides stercoralis (9.5%), Taenia spp. (1.6%), echinostomes (0.4%), and hookworms (0.4%). The prevalence of intestinal protozoa was Blastocystis hominis 1.6%, Entamoeba histolytica 0.8%, Entamoeba coli 0.8%, Balantidium coli 0.4%, Iodamoeba bütschlii 0.4%, and Sarcocystis hominis 0.4%. Co-infections of various helminths and protozoa were present in 15.9% of the people. The present results show that the prevalence of parasitic infections in this region is still high. Proactive education about dietary habits, personal hygiene, and sanitation should be provided to the people in this community to reduce the prevalence of intestinal parasite infections. Moreover, development of policies and programs to control parasites is needed.

Histopathological changes in tissues of Bithynia siamensis goniomphalos incubated in crude extracts of camellia seed and mangosteen pericarp

The present study was performed to observe histopathological changes in tissues of Bithynia siamensis goniomphalos (Gastropoda, Bithyniidae) incubated in crude extract solutions of camellia (Camellia oleifera) seed and mangosteen (Garcinia mangostana) pericarp, and furthermore to estimate the molluscicidal effects of 2 plant substances. Substantial numbers of bithyniid snails were incubated in various concentrations of 2 plant solution for 24 hr. As the positive control, snails incubated in various concentrations of niclosamide, a chemical molluscicide, were used. The histopathological findings were observed in sectioned snail specimens of each experimental and control groups. The results showed that both camellia and mangosteen extracts had molluscicidal effects at 24 hr with 50% lethal concentration (LC50) at concentrations of 0.003 and 0.002 g/ml, respectively, while niclosamide had LC50 at concentrations 0.599 ppm. B. siamensis goniomphalos snail tissues (foot, gill, and digestive system) showed disruption of columnar muscle fibers of the foot, reduction of the length and number of gill cilia, numerous mucous vacuoles, and irregularly shaped of epithelial cells. Irregular apical and calciferous cells, dilatation of the digestive gland tubule, and large hemolymphatic spaces, and irregular apical surfaces, detachment of cilia, and enlargement of lysosomal vacuoles of epidermis were also shown in all groups. By the present study, it is confirmed that 2 plants, camellia and mangosteen, are keeping some substance having molluscicidal effects, and histopathological findings obtained in this study will provide some clues in further studies on their action mechanisms to use them as natural molluscicides.

A combination of praziquantel and the traditional medicinal plant Thunbergia laurifolia on Opisthorchis viverrini infection and cholangiocarcinoma in a hamster model

Cholangiocarcinoma (CCA) associated by Opisthorchis viverrini remains a health problem in Southeast Asia including Thailand. At present, there is still no efficient treatment for CCA. Thunbergia laurifolia is a traditionally used medicinal plant; its aqueous leave extract possesses the antioxidant activity and anti-inflammatory on hamster opisthorchiasis had been reported previously. Here, we demonstrate the combined effects of the T. laurifolia extract plus antihelminthic drug, praziquantel (PZ) on hamsters with opisthorchiasis and hamsters with opisthorchiasis related-cholangiocarcinoma through light microscopic observations of histopathological changes, as well as liver function tests for alanine transaminase (ALT) and alkaline phosphatase, and kidney function tests for blood urea nitrogen and creatinine. Results showed T. laurifolia extract combined with praziquantel reduced inflammatory cell aggregation and inhibiting CCA development, which were correlated to the serum ALT level. These present studies suggest that administration of T. laurifolia after praziquantel treatment clearly improve the hepatobiliary system and could reduce the risk of subsequent CCA development in human.

Application of recombinant Gnathostoma spinigerum matrix metalloproteinase-like protein for serodiagnosis of human gnathostomiasis by immunoblotting

Matrix metalloproteinase (MMPs) is the extracellular zinc-dependent endopeptidase and is secreted for degrading extracellular matrix molecules of host tissues. A cDNA encoding MMP-like protein of Gnathostoma spinigerum larvae was amplified by reverse transcription-polymerase chain reaction, and was cloned into a prokaryotic expression vector, and expressed in Escherichia coli. Total immunoglobulin G class (total IgG) antibody responses to the recombinant MMP-like protein were analyzed by immunoblot diagnosis of human gnathostomiasis. Serum samples from proven and clinically suspected cases of gnathostomiasis, other parasitic diseases patients, and from healthy volunteers were tested. The immunoblotting gave high sensitivity (100%) and specificity (94.7%). Positive and negative predictive values were 85.4% and 100%, respectively. Recombinant MMP-like protein can be used as a diagnostic antigen and potentially replace native parasite antigens to develop a gnathostomiasis diagnostic kit.

Hypoalbuminemia as a predictor of diarrhea caused by blastocystis hominis

Blastocystis hominis is an intestinal protozoan found worldwide, particularly in developing countries, that may cause gastrointestinal symptoms, including diarrhea. We conducted a hospital-based study to identify clinical factors predictive of diarrhea caused by B. hominis. We studied patients with positive stool samples for B. hominis by formalin ethyl acetate concentration technique at Srinagarind Hospital, Khon Kaen University, Khon Kaen, Thailand between 2003 and 2010. Patients were divided into diarrhea and non-diarrhea groups. Diarrhea patients were categorized if the diarrhea was associated with B. hominis only. In total, 81 patients with isolated B. hominis infection were studied. Of those, 17 patients (21%) had diarrhea associated with B. hominis infection. Eight variables were included in the final model predicting diarrhea caused by B. hominis on multiple logistic regression analysis. Only serum albumin level was significantly associated with diarrhea cases in this study with an adjusted OR of 0.162 and a 95% CI of 0.027- 0.957. Hypoalbuminemia is associated with diarrhea associated with blastocystosis.

Viable metacercariae of Opisthorchis viverrini in northeastern Thai cyprinid fish dishes--as part of a rational program for control of O. viverrini-associated cholangiocarcinoma

Among the various types of chronic helminthic infections, only schistosomiasis hematobium, opisthorchiasis, and clonorchiasis in a long-standing inflammation are found to be causative agents of cancer. Opisthorchiasis and Opisthorchis viverrini-associated bile duct cancer are prevalent among the residents in northeastern Thailand, who prefer consuming raw or improperly cooked cyprinid fish. Although numerous studies have reported on the presence of O. viverrini metacercariae in freshwater cyprinid fishes, none of the data has been derived directly from cyprinid fish dishes. Here, we have demonstrated the presence of viable metacercariae in a number of cyprinid fish dishes that are among the favorite foods of northeastern Thais. Traditional salt-fermented and grilled cyprinid fish were found to be safe to consume, but not raw fish salad or cyprinid fish fermented in sticky rice for 69 h. This information could be used as part of a rational and sustainable control program for O. viverrini-associated bile duct cancer.

A simple PCR condition for detection of a single cyst of Acanthamoeba species

Acanthamoeba is a free-living protozoan with a worldwide distribution in a variety of natural and artificial habitats. It has even been found in contact lens solution. Acanthamoeba spp. can cause infections such as granulomatous amoebic encephalitis and amoebic keratitis. Specific and sensitive diagnosis of Acanthamoeba infections can prevent clinical symptoms from worsening. Recently, PCR technique has been used for Acanthamoeba diagnosis. Unfortunately the dormant cyst of Acanthamoeba is resistant to chemical reagents; thus, most extraction of DNA uses a commercial DNA extraction kit for obtaining DNA for further use in polymerase chain reaction (PCR). Therefore in the present study, we improved the ability to diagnose Acanthamoeba using a simplified PCR technique. Interestingly, heating at 94°C for 10 min could release DNA which is amplified with specific primers designed from 16S rRNA. The PCR product is about 180 bp. This technique is a simple and efficient method for detection of Acanthamoeba-even a single cyst-and does not require high-cost reagents or complicated procedures to extract DNA.

Down-regulated expression of HSP70 in correlation with clinicopathology of cholangiocarcinoma

Cholangiocarcinoma is a crucial health problem in northeast Thailand. Although rare, it is a highly fatal disease and the prognosis of CCA patients is very poor. To determine if expression of specific genes is useful for diagnosis and prognosis for CCA. We examined the expression of HSP70, HSP90, RB1, cyclin D1, and HDAC6 in 50 resections of human CCA tissues by quantitative real-time PCR. The expression of HSP70, RB1, and HDAC6 was "dominant down-regulation," while the expression of cyclin D1 and HSP90 was "dominant up-regulation." There were no correlations between RB1, cyclin D1, HSP90, and clinicopathological parameters such as status, histology type, histological grading, stage of CCA, and metastasis. A significant association was found between HDAC6 and CCA staging (p = 0.000), CCA gross type and HSP70 (p = 0.046) as well as RB1 expression (p = 0.046). Patients with down-regulation of HSP70 had significantly poorer prognosis than those in the up-regulation group (p = 0.002). Expression of HSP70 may be useful as a new prognostic marker for CCA.

Gnathostoma spinigerum: molecular cloning, expression and characterization of the cyclophilin protein

In this study, a cDNA encoding cyclophilin (CyP) of Gnathostoma spinigerum was cloned into a prokaryotic expression vector and expressed in Escherichia coli. The predicted molecular mass of the putative protein was 18.6kDa, and the deduced amino acid sequence had 86, 84.8, 81.3 and 77.2% identity with the CyP of Dirofilaria immitis, Brugia malayi, Onchocerca volvulus and Caenorhabditis elegans, respectively. A prediction of linear B-cell epitopes with high hydrophilicity and immunoblotting results indicated that the recombinant CyP has antigenicity to humans. The recombinant CyP protein reacted with human gnathostomiasis sera but not with other parasitosis or healthy control sera, suggesting that it might be useful for the serodiagnosis of human gnathostomiasis.

Evaluation of human IgG class and subclass antibodies to a 24 kDa antigenic component of Gnathostoma spinigerum for the serodiagnosis of gnathostomiasis

The immunoglobulin G class (total IgG) and subclass (IgG1, IgG2, IgG3, and IgG4) antibody responses to the spirurid worm Gnathostoma spinigerum were analyzed by immunoblotting technique for the antibodies' potential use in the serodiagnosis of human gnathostomiasis. Serum samples from patients with proven gnathostomiasis and from clinically suspected cases of gnathostomiasis with migratory swelling were tested. Sera from patients with other parasitic illnesses and from healthy volunteers were also analyzed. The total IgG antibody to an antigenic band of approximately 24 kDa from a somatic extract of G. spinigerum advanced third-stage larvae (GS24) gave the highest sensitivity (91.6%) and 87.8% specificity. Individual IgG subclass detection had a lower sensitivity than the detection of specific total IgG antibody, but IgG4 had a slightly higher specificity (93.9%). However, for cost effectiveness, we suggest that anti GS24 total IgG is sufficient for the routine serodiagnosis of human gnathostomiasis as well as for seroepidemiological studies in developing countries.

A modified filter paper culture technique for screening of Strongyloides stercoralis ivermectin sensitivity in clinical specimens

An in vitro test for the detection of ivermectin sensitivity of Strongyloides stercoralis in human clinical specimens was developed. The test has a simple procedure that combines parasite culture with a drug assay. It is based on the principle of the drug effect on larval development test, combined with a modified coproculture using the filter paper culture technique. This does not require parasite isolation, and drug sensitivity can be shown in relationship to the dose. This test can be applied in field surveys for anthelmintic sensitivity and for appropriate drug rotation strategies when drug resistance occurs.