MyMedR

Efficacy of three pyrethroids against Leptotrombidium fletcheri (Acari: Trombiculidae) infected and noninfected with scrub typhus

Ho TM, Ismail S

J Med Entomol, 1991 Nov;28(6):776-9.

PMID: 1770512

Toxicities of three pyrethroids, d-phenothrin, decamethrin, and permethrin, were evaluated in the laboratory against Leptotrombidium fletcheri (Womersley & Heaslip). The susceptibilities between populations of the species infected and noninfected with scrub typhus were investigated. The three pesticides exhibited different toxicities to the chiggers. D- phenothrin was the most toxic, followed by decamethrin, then permethrin. There were no significant differences between susceptibilities of the infected and noninfected populations. Log-probit regression lines indicated that the species was most sensitive to increasing concentrations of d-phenothrin and least sensitive to permethrin. The results show that the three pesticides are potential candidates for chemical control of L. fletcheri. It may be possible in the future to conduct similar bioassays only with the noninfected population, thus reducing risk of infection to workers conducting the bioassays. Similarly, there may not be a need to separate field-collected chiggers into the two populations before performing the bioassays.

Fulltext A preliminary survey of Aedes aegypti in Selangor, Peninsular Malaysia

Ho TM, Vythilingam I

Med J Malaysia, 1980 Jun;34(4):409-14.

PMID: 7219273

A preliminary survey of Aedes aegypti was carried out in 6 areas in the state of Selangor, Malaysia. The densities of Ae. aegypti and Ae. albopictus in the areas were discussed. Results indicated that the distribution of larval habitats varied with the housing type. The most ommon indoor larval habitat in urban areas is the bathroom tank. In both urban and rural areas, outdoor preference is for the earthenware jars. Anttraps have decreased in importance as larvae breeding habitats. The accuracy of house searches can be increased by increasing the number of larvae examined per container to 5 or more. Further study is required to determine whether the findings of this survey is peculiar to the areas surveyed or is representative of the whole country, and whether there is a seasonal fluctuation in the types of preferred larval habitats.

Fulltext Effect of a commercial air ionizer on dust mites Dermatophagoides pteronyssinus and Dermatophagoides farinae (Acari: Pyroglyphidae) in the laboratory

Abidin SZ, Ho TM

Asian Pac J Trop Biomed, 2012 Feb;2(2):156-8.

PMID: 23569888 DOI: 10.1016/S2221-1691(11)60212-8

To investigate the short and long term efficacy of a commercial air ionizer in killing Dermatophagoides pteronyssinus (D. pteronyssinus) and Dermatophagoides farinae (D. farinae) mites.

Effects of microwave radiation on house dust mites, Dermatophagoides pteronyssinus and Dermatophagoides farinae (Astigmata: Pyroglyphidae)

Ernieenor FC, Ho TM

Southeast Asian J. Trop. Med. Public Health, 2010 Nov;41(6):1335-41.

PMID: 21329308

Dermatophagoides pteronyssinus and Dermatophagoides farinae mites are commonly found in house dust, and are important sources of allergens affecting humans. Various approaches to killing the mites have been examined. This study investigated the mortalities of adult mites exposed to 2,450 MHz microwave radiation produced by 3 ovens at various exposure times and power settings. The ovens all had 3 power settings. The average maximum water temperatures generated at high, medium and low power settings were 99.4 +/- 0.2, 84.1 +/- 0.4 and 44.8 +/- 0.9 degrees C, respectively. At high and medium settings, there was 100.0% mortality in both species when exposed for 300 seconds. The mean mortality rates at low power were 10.8 +/- 0.7% for D. pteronyssinus and 9.7 +/- 2.6% for D. farinae. When mites were exposed in the presence of culture media, the mortality rates decreased with increasing weight of media. The mean mortality with the largest amount of media tested at high power setting was 61.4%.

Residual activity of benzyl benzoate against Dermatophagoides pteronyssinus (Acari: Pyroglyphidae)

Suhaili ZA, Ho TM

Southeast Asian J. Trop. Med. Public Health, 2008 May;39(3):507-10.

PMID: 18564691

The residual effect of a commercial spray containing 2.0% benzyl benzoate against Dermatophagoides pteronyssinus was evaluated in the laboratory. Filter papers treated with benzyl benzoate were dried for 2 hours and placed in Petri dishes. Adult mites were then added and mortality was assessed following 24 hour contact and at succeeding 4 weeks intervals up to week 28 post-treatment using the same treated filter papers. There was 100% mortality at 24 hours post-treatment, declining progressively to 71% by week 28. Probit analysis estimated a median lethal time (LT50) of 59 weeks.

Fulltext Laboratory evaluation of propoxur and fenvalerate against infected and noninfected Leptotrombidium fletcheri (Acari: Trombiculidae)

Ho TM, Fauziah MK

Southeast Asian J. Trop. Med. Public Health, 1993 Sep;24(3):570-2.

PMID: 8160070

Fulltext Laboratory evaluation of two commercial repellants against Leptotrombidium fletcheri (Acari: Trombiculidae)

Ho TM, Fauziah MK

Southeast Asian J. Trop. Med. Public Health, 1993 Mar;24(1):165-9.

PMID: 8362291

Two commercial repellants were evaluated in the laboratory against Leptotrombidium fletcheri chiggers. The active ingredient in one was DEET and in the other was citrus oil. Excito-toxicity effect was studied and it was determined by the time ("escape time") chiggers took to move off filter papers treated with the repellants. All chiggers exposed on filter papers treated with DEET died and did not move off the treated papers. None of the chiggers that were placed on papers treated with citrus oil were killed. Escape times on papers treated with a 2-sec spray of citrus oil were longer than those for the 4- and 8-sec sprays. The weights of citrus oil deposited increased with increasing spray times. Electron microscopy showed that the repellants had no effect on the texture of the filter papers. It was concluded that the spray containing DEET was more effective; however, both repellants should be further evaluated under field conditions for protection against chigger bites.

Fulltext Acariasis on pet Burmese python, Python molurus bivittatus in Malaysia

Mariana A, Vellayan S, Halimaton I, Ho TM

Asian Pac J Trop Med, 2011 Mar;4(3):227-8.

PMID: 21771459 DOI: 10.1016/S1995-7645(11)60075-8

OBJECTIVE: To identify the acari present on pet Burmese pythons in Malaysia and to determine whether there is any potential public health risk related to handling of the snakes.

METHODS: Two sub-adult Burmese pythons kept as pets for a period of about 6 to 7 months by different owners, were brought to an exotic animal practice for treatment. On a complete medical examination, some ticks and mites (acari) were detected beneath the dorsal and ventral scales along body length of the snakes. Ticks were directly identified and mites were mounted prior to identification.

RESULTS: A total of 12 ticks represented by 3 males, 2 females and 7 nymphal stages of Rhipicephalus sanguineus (R. sanguineus) were extracted from the first python while the other one was with 25 female Ophionyssus natricis (O. natricis) mesostigmatid mites. Only adult female mites were found. These mites are common ectoparasites of Burmese pythons.

CONCLUSIONS: Both the acarine species found on the Burmese pythons are known vectors of pathogens. This is the first record that R. sanguineus has been reported from a pet Burmese python in Malaysia.

Fulltext House dust mite fauna in the Klang Valley, Malaysia

Mariana A, Ho TM, Sofian-Azirun M, Wong AL

Southeast Asian J. Trop. Med. Public Health, 2000 Dec;31(4):712-21.

PMID: 11414418

Allergy to house dust mites (HDM) is an important cause of asthma and rhinitis in Malaysia. This study was carried out to evaluate the dust mite fauna in the Klang Valley. Dust samples were collected from 20 houses from March 1994 to February 1995. Thirty-three dust samples from mattresses were examined monthly for the occurrence of HDM. A total of 22 species in 9 families of HDM was identified. The most common and densely populated species was Blomia tropicalis with an average density of 8,934 mites/g of dust. Dermatophagoides pteronyssinus was the next in abundance, followed by Malayoglyphus intermedius. All houses surveyed were found to be infested with HDM and every house had at least 6 species of HDM. B. tropicalis and D. pteronyssinus were found in all mattresses. HDM in the Klang Valley were found to be highly prevalent and present in high densities. In this study, counts of D. pteronyssinus was found to exceed the proposed exposure threshold of 500 mites/g dust, for triggering acute asthma. Although counts of B. tropicalis exceeded D. pteronyssinus, no conclusion could be made because there is currently no exposure threshold for triggering acute asthma, for this species. Monthly distribution of B. tropicalis and D. pteronyssinus showed 2 peaks and 4 peaks, respectively. The major peak for D. pteronysinus was in January 1995 whereas for B. tropicalis, the major peak was more variable and occurred between November 1994 to January 1995. Both the species showed minor peak in April 1994.

Prevalence of allergy to some inhalants among rhinitis patients in Malaysia

Ho TM, Murad S, Kesavapillai R, Singaram SP

Asian Pac J Allergy Immunol, 1995 Jun;13(1):11-6.

PMID: 7488338

This study was conducted to determine the seasonal prevalence of allergies to house dust, D. pteronyssinus, D. farinae, cat fur, dog hair, mixed moulds, mixed grass pollens and American cockroach. A total of 314 patients with clinically suspected allergic rhinitis was examined by prick test using commercial preparations of the above allergens. Total serum IgE of the patients was determined by a Sandwich ELISA. Ninety-six percent of the patients tested positive to more than one allergen. Most were positive to a combination of 4 allergens. More than 70% of the patients were positive to house dust, D. pteronyssinus, D. farinae and cat fur. Analysis indicates that for an individual who tests positive for house dust, there is a very high risk of the person being allergic to the dust mites and cat fur too. Most of the allergens had 2 peak period of high positive PT rates; mixed moulds and mixed grass pollens had 3 peaks. There was significant positive correlation between the monthly positive PT rates against mixed moulds and mixed grass pollens with maximum daily mean temperature and mean temperature at 14.00 hours.

Fulltext Serological findings of Coxiella burnetii infection among patients with fevers in a health centre in Sarawak, Malaysia

Tay ST, Ho TM, Rohani MY

Southeast Asian J. Trop. Med. Public Health, 1998 Mar;29(1):94-5.

PMID: 9740277

Laboratory evaluation of five pesticides for control of Leptotrombidium fletcheri (Acari: Trombiculidae)

Ho TM, Fauziah MK, Saleh I

Southeast Asian J. Trop. Med. Public Health, 1992 Mar;23(1):125-7.

PMID: 1523464

Five pesticides were evaluated against laboratory colonies of Leptotrombidium fletcheri (Womersly and Heaslip) by the Pasteur pipet technique. The pesticides were dieldrin (LC50 = 3.6 ppm, LC99 = 18.2 ppm), bromopropylate (LC50 = 9.2 ppm, LC99 = 239.6 ppm), dicofol (LC50 = 27.8 ppm, LC99 = 118.1 ppm), fenthion (LC50 = 15.4 ppm, LC99 = 29.7 ppm), and malathion (LC50 = 84.7 ppm, LC99 = 313.9 ppm). Dieldrin was the most toxic. Dicofol was recommended for further evaluation in field trials.

Evaluation of the MAST CLA allergy system for diagnosis of allergies to house dust mites and cats

Ho TM, DeBruynne J, Ahamad M, Darussamin H

Asian Pac J Allergy Immunol, 1997 Sep;15(3):123-6.

PMID: 9438543

The MAST CLA system was evaluated against skin prick test (SPT) for diagnosis of allergies to house dust mites (Dermatophagoides pteronyssinus, Dermatophagoides farinae) and cats. Forty three asthmatic children were examined by SPT and MAST CLA. Chi-square analysis indicated significant association between SPT and MAST CLA results for the house dust mites but not for cats. The sensitivities of MAST CLA for house dust mites and cats were 100 and 25% respectively; specificities were all less than 50%. The efficiency of MAST CLA for detection of allergy to the house dust mites was 88% and 44% for cats. A significant linear correlation was found between SPT wheal size and MAST CLA grade for D. farinae but not for D. pteronyssinus and cats. It is concluded that the MAST CLA allergy system can be used to supplement SPT for diagnosis of allergies to house dust mites but not to cats.

Fulltext Life-cycle, longevity and fecundity of Blomia tropicalis (Acari: Glycyphagidae) in a tropical laboratory

Mariana A, Ho TM, Heah SK

Southeast Asian J. Trop. Med. Public Health, 1996 Jun;27(2):392-5.

PMID: 9280009

In the present study on the life-cycle of Blomia tropicalis, freshly laid eggs were observed until they developed into adults; the development periods between stages were recorded. The eggs took an average of 22.9 +/- 6.4 days to develop to adults. For longevity experiments, newly emerged adults were kept at 25 degrees C and observed until they died. There was no significant difference in longevities of the different sexes (p = 0.053). Production of eggs by mated females were monitored until egg production stopped and the female died. Mated females and males survived an average of 32.2 +/- 15.4 and 30.9 +/- 17.7 days respectively. The difference in longevity of the mated females, and males was not significant (p = 0.747). Longevity of the mated females was found to be significantly (p < 0.05) shorter than unmated females.

Fulltext Use of hemolymph test for detection of rickettsiae in Malaysian ticks

Tay ST, Ho TM, Rohani MY

Southeast Asian J. Trop. Med. Public Health, 1996 Sep;27(3):642-4.

PMID: 9185285

Fulltext Development of ELISA for diagnosis of allergy to Dermatophagoides farinae

Ho TM, Radha K, Shahnaz M, Singaram SP

Med J Malaysia, 1993 Sep;48(3):308-12.

PMID: 8183144

An indirect enzyme linked immunosorbent assay (ELISA) was developed for the diagnosis of allergy to a house dust mite, Dermatophagoides farinae. The efficacy of the ELISA was then evaluated against a prick test using a commercial allergen. Eighty five suspected allergic rhinitis patients from the Otorhinolaryngology Department, Kuala Lumpur General Hospital, were tested with the ELISA and prick test. Prick test and ELISA results were positive in 84.7% and 80.0% of the patients respectively. The ELISA was found to have 87.5% sensitivity, 61.5% specificity, 92.6% positive predictive value, 47.1% negative predictive value, 7.4% false positive and 52.9% false negative. There was total agreement between the prick test and ELISA for prick test grades of 3+ and 4+. It is concluded that the ELISA is a useful assay for detection of individuals who are highly sensitive to D. farinae.

Development of an enzyme-linked immunosorbent assay for detection of IgE antibodies specific to Dermatophagoides pteronyssinus

Ho TM, Yit YH, Husain M

Asian Pac J Allergy Immunol, 1988 Dec;6(2):103-6.

PMID: 3146256

Allergy to Dermatophagoides pteronyssinus was determined in 61 rhinitis patients using prick test (PT), enzyme-immunoassay (EIA) and enzyme-linked immunosorbent assay (ELISA). A total of 43 patients tested positive with PT. Forty six patients were positive when tested with EIA and ELISA. With PT as standard test, EIA was found to have 83.7% sensitivity and 44.4% specificity; ELISA had 81.4% sensitivity and 38.9% specificity. There was a linear relationship between absorbance values obtained by EIA and ELISA. The performance time was 8 hours, 24 hours and 30 minutes for ELISA, EIA and PT respectively. The cost per test for ELISA, EIA and PT was US$ 0.20, US$ 5.20 and US$ 0.14 respectively. It was concluded that ELISA was more cost-effective than EIA should be used to supplement PT for a more complete diagnosis of allergy.

Fulltext The first graduates in 1910

Cheah JS, Ho TM, Ng BY

Ann Acad Med Singap, 2005 Jul;34(6):19C-24C.

PMID: 16010376

The Medical School in Singapore was founded on 3 July 1905 and named the Straits and Federated Malay States Government Medical School. There were 23 students in the first enrollment; 16 students attended the full course, while 7 attended a 2-year course for hospital assistants. The pioneer group of 7 that graduated in May 1910 (the Magnificent Seven) consisted of Drs Chen Su Lan, Edwin Williborod deCruz, and John Gnanapragasam from Singapore; Drs Willie Carnegie and Mark W Chill from Penang; Dr SR Krishnan from Seramban and Dr John Scott Lee from Ipoh. In December 1910, a further 6 students graduated. Of this first batch of 13 graduates in 1910, we describe the careers of 6; no records exist of the remaining 7.

Fulltext Scanning electron micrographs of medically important dust mite, Suidasia pontifica (Acari: Astigmata: Saproglyphidae) in Malaysia

Ahamad M, Louis SR, Hamid Z, Ho TM

Trop Biomed, 2011 Aug;28(2):275-82.

PMID: 22041746

Scanning electron microscope (SEM) images of dust mites, Suidasia pontifica, is presented to provide an improved visualization of the taxonomic characters of these mites. Suidasia pontifica can easily be identified by its scale-like cuticle, presence of external vertical setae (ve), longer external scapular setae (sce) compared to internal scapular setae (sci) and 3 ventral spines on apex of tarsus I. The differences in morphology of male and female S. pontifica are also discussed.

Fulltext Serological screening of Tick-borne encephalitis (TBE) among Malaysian encephalitis patients

Thayan R, Khairullah NS, Ho TM

Trop Biomed, 2004 Dec;21(2):153-6.

PMID: 16493408

Tick-borne encephalitis (TBE) is a viral infection of the central nervous system and is caused by tick bites, usually after travel to rural or forested areas. The disease is prevalent in Scandinavia, Western Europe, Central Europe and the former Soviet Union and East Asia including Japan. In Malaysia, so far there are no reported cases of TBE. In the present time, many illnesses have been attributed to traveling to other parts of the world. Thus it is important to carry out TBE prevalence study to determine whether the virus is present among Malaysian population. Samples (sera and CSF) from patients admitted to major MOH hospitals in Peninsular Malaysia and Sabah with a clinical diagnosis of encephalitis but is IgM negative for JE, were tested for TBEV IgM ELISA and TBEV IgG ELISA (DRG, Germany). Out of the 600 samples screened for TBEV IgG, all were non-reactive. In addition, out of the 100 samples screened for TBEV IgM, all the samples were also non-reactive. Our results indicate that currently TBE is not present in the Malaysian population. Among the reasons for this could be lack of the infection agent, absence of the suitable vector or subjects selected for the study did not fit the criteria of possible exposure to TBE infections. Hence we recommend that for any future study, the selection of subjects should include those who returned from tick-infested forested areas.

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