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Biomedical subjects

T M Ho

Publications and source records attributed to T M Ho.

At least 37 records · Page 2Linked to original sources
PubMed1995

Prevalence of allergy to some inhalants among rhinitis patients in Malaysia.

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.

Allergens↗
PubMed1995

Seasonal prevalence of air-borne pollen and spores in Kuala Lumpur, Malaysia.

Aerosampling using Rotorod samplers was conducted in the Institute for Medical Research, Kuala Lumpur, Malaysia, from December 1991 to November 1993. Samples were collected twice a week between 10.00 hours to 12.00 hours. Rods were stained and examined microscopically. A total of 8 and 20 types of pollens and mold spores were collected, respectively. More mold spores were collected than pollens. Grass pollen constituted more than 40 percent of total pollen counts. Gramineae pollen counts peaked in March and September. The most abundant mold spore was Cladosporium followed by Rust, Nigrospora, Curvularia and Smut. Cladosporium counts peaked in February and August. Rust counts peaked in June and December whereas counts for Nigrospora peaked in February and October. Highest counts of Smut were recorded in March and October. Curvularia counts peaked in January, June and September.

Allergens↗
PubMed1994

Detection and characterization of Rickettsia tsutsugamushi (Rickettsiales: Rickettsiaceae) in infected Leptotrombidium (Leptotrombidium) fletcheri chiggers (Acari: Trombiculidae) with the polymerase chain reaction.

We developed a method for detecting and characterizing the DNA of Rickettsia tsutsugamushi in chiggers (larval trombiculid mites) by polymerase chain reaction (PCR). Three procedures for extracting DNA from frozen chiggers were compared by evaluating the yield of PCR amplicand obtained with nine oligonucleotide primer pairs derived from the rickettsial 22 kD, 47 kD, groESL, 56 kD, and 110 kD antigen genes. Although extracts and primer pairs differed in amplification efficiency, R. tsutsugamushi DNA was successfully detected in extracts of colonized infected Leptotrombidium (Leptotrombidium) fletcheri (Wormersley & Heaslip) chiggers and in uninfected chigger extracts seeded with known amounts of Karp-strain rickettsiae. The 22 kD gene restriction fragment length polymorphisms (RFLP) observed in PCR amplicands from five rickettsial isolates obtained from the infected chigger colony over a 26-yr period were identical to those of PCR amplicands derived directly from infected chiggers taken from the same colony. This suggests that stable transmission of R. tsutsugamushi occurs in mites (62 generations), and isolates encompass the full genetic heterogeneity found in the chigger. PCR/RFLP analysis is an important new tool for investigating the complex epidemiology of scrub typhus rickettsiae in their mite vectors.

Animals↗
PubMed1993

Development of ELISA for diagnosis of allergy to Dermatophagoides farinae.

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.

Animals↗
PubMed1993

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

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.

Animals↗
PubMed1992

Development and evaluation of dot-immunobinding assay for detection of scrub typhus infection in Leptotrombidium fletcheri (Acari: Trombiculidae).

A dot-immunobinding assay (DIBA) was compared with a direct fluorescent antibody technique (DFAT) for the detection of Rickettsia tsutsugamushi infection in Leptotrombidium fletcheri (Womersley & Heaslip). Laboratory colonies of infected and noninfected chiggers were examined. The relative proportions of positive, negative, and indeterminate results were significantly different between DIBA and DFAT for infected but not for noninfected chiggers. DIBA was more sensitive and had a better negative predictive value and a lower false negative percentage than DFAT. It was concluded that DIBA is a suitable alternative to DFAT for detecting scrub typhus infection in chiggers.

Animals↗
PubMed1992

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

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.

Animals↗
PubMed1991

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

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.

Animals↗
PubMed1990

Phoretic association between Macrocheles muscaedomesticae (Acari: Macrochelidae) and flies inhabiting poultry manure in Peninsular Malaysia.

The phoretic association between Macrocheles muscaedomesticae and flies that inhabited poultry manure in a poultry farm in Sungai Buloh, Selangor, Malaysia was studied. The effects of temperature, relative humidity and fly abundance on phoretic rates also were investigated. The most abundant fly species found was Musca domestica; Musca sorbens, Chrysomyia megacephala and Ophyra chalcogaster were present in relatively large numbers. Representatives of ten families of mites were found on collected Mu. domestica. The most common mite was Ma. muscaedomesticae (Macrochelidae), found on all four species of flies mentioned above. The highest infestation (2.0%) occurred on O. chalcogaster but Mu. domestica had the highest average number infested (5.7). The ventral part of the housefly's abdomen was the most common site of mite attachment. Usually only one mite was found attached per fly. The highest phoretic rate recorded was 64.4 Ma. muscaedomesticae per 1000 Mu. domestica. There was no correlation between phoretic rates and Ma. muscaedomesticae abundance, nor was relative humidity a factor. However, a positive correlation was recorded in this host species between phoretic rates and temperature.

Animals↗
PubMed1988

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

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.

Animals↗