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Biomedical subjects

Thiravat Hemachudha

Publications and source records attributed to Thiravat Hemachudha.

At least 19 recordsLinked to original sources
PubMed2006

Duplex nested RT-PCR for detection of Nipah virus RNA from urine specimens of bats.

A method for duplex nested RT-PCR (nRT-PCR) with internal control (IC) for the detection of Nipah virus RNA is described. Incorporation of IC RNA distinguished false and true negative results. The extrinsic RNA was added directly to the PCR master mix and co-amplified with virus specific RNA in a duplex reaction to determine the presence of PCR inhibitor. Limit of detection was affected minimally when IC was added. Of 53 pooled urine samples collected from fruit bats (Pteropus lylei), 16 were validated by the presence of IC band on gel electrophoresis. Seven of these were also Nipah virus RNA positive. The remaining 37 samples were considered invalid. Twenty-two urine samples became valid after dilution of 1:5 and re-examined; two were Nipah virus RNA positive. These nine positive results were confirmed by sequencing of heminested PCR products. The result indicated that at least two different Nipah strains circulated in this bat species from Thailand. This method should be useful for surveillance for Nipah virus infection in animals in a country where a biosecurity level (BSL) 4 laboratory is not available. PCR inhibitors were present in a significant number of bat urine samples. The technique described in this study should improve reliability of surveillance statistics.

Animals↗
PubMed2006

A simple method for detection of rabies viral sequences in 16-year old archival brain specimens with one-week fixation in formalin.

Archival formalin-fixed and paraffin-embedded brain tissues are important source for diagnosis and molecular analysis. However, nucleic acids are particularly vulnerable to degradation during tissue processing. The brain cutting process usually is performed after 1 week of brain storage in formalin followed by embedding of each particular neuro-anatomical specimen in paraffin. A simple method of deparaffinization, proteinase K digestion and RNA extraction using the Boom technique to obtain rabies RNA in unbuffered, formalin-fixed and paraffin-embedded brain tissues kept at 30 degrees C for 16 years is described. Reverse transcription-polymerase chain reaction (RT-PCR) can be used to identify rabies viral N gene sequences of 150 bases in length in all patients, but not from every immunohistochemical (IHC)-positive specimen. Direct sequencing of 301bp of N gene was achieved in 4 of 7 patients. Results of sequencing a single sample of 1432 bases of N gene from a 24h processed formalin-fixed and paraffin-embedded rabies infected brain tissue after 1 month storage were in accord with those from frozen specimen analysis. It is strongly suggested that for further molecular analysis, a piece of fresh brain tissue should be saved prior to the brain sectioning process and stored no longer than 24h in formalin before embedding.

Animals↗
PubMed2006

Rabies.

Despite increases in our understanding of rabies pathogenesis, it remains an inevitably fatal disease. Lack of awareness, low level of political commitment to rabies control, and failure to recognize and correlate clinical, laboratory, and neuroimaging features contribute to continuing deaths. Clinical symptomatology, once believed to be unique, may be variable, even in patients associated with lyssaviruses of the same genotype. This article discusses virus transport, the role of virus and host response mechanisms in relation to protean clinical manifestations, and mechanisms responsible for relative intactness of consciousness in human rabies. Differential involvement of the anterior horn cell in furious rabies and the peripheral nerve in paralytic rabies is summarized. Escape mechanisms from host defenses explain why a fatal outcome is unavoidable regardless of therapy. Neuroprotective treatment, using a coma-induction regimen, proves not to be beneficial. Survival of patients with excellent recovery relies on early innate and adaptive immunity plus adequate intensive care support.

Humans↗
PubMed2006

Failure of therapeutic coma and ketamine for therapy of human rabies.

The recent success in treating a human rabies patient in Milwaukee prompted the use of a similar therapeutic approach in a 33-year-old male Thai patient who was admitted in the early stages of furious rabies. He received therapeutic coma with intravenous diazepam and sodium thiopental to maintain an electroencephalographic burst suppression pattern, which was maintained for a period of 46 h, as well as intravenous ketamine (48 mg/kg/day) as a continuous infusion and ribavirin (48 to 128 mg/kg/day) via a nasogastric tube. He never developed rabies virus antibodies and he died on his 8th hospital day. At least three other patients have been treated unsuccessfully with a similar therapeutic approach. Because of the lack of a clear scientific rationale, high associated costs, and potential complications of therapeutic coma, the authors recommend caution in taking this approach for the therapy of rabies outside the setting of a clinical trial. More experimental work is also needed in cell culture systems and in animal models of rabies in order to develop effective therapy for human rabies.

Adult↗
PubMed2005

Complex genetic structure of the rabies virus in Bangkok and its surrounding provinces, Thailand: implications for canine rabies control.

Dog vaccination and population management have been suggested as priorities in attempts at disease control in canine rabies-endemic countries. Budget limitations and the complexity of social, cultural and religious variables have complicated progress in the developing world. In Bangkok, Thailand, an intensive canine vaccination and sterilization programme has been in place since November 2002. Our objective was to determine if the rabies virus could be mapped according to its genetic variations and geographical location on the small localized scale of Bangkok and its surrounding provinces. Phylogenetic characterization of 69 samples from Bangkok and five neighbouring and two remote provinces, by limited sequence analysis of the rabies virus nucleoprotein gene, distinguished six different clades. Rabies viruses of four clades were intermixed in Bangkok and in the surrounding highly populated regions whereas the other two clades were confined to rural and less populated provinces. Such a complex pattern of gene flow, particularly in Bangkok, may affect the outcome of canine control programmes.

Animals↗
PubMed2005

Mechanisms of escape phenomenon of spinal cord and brainstem in human rabies.

BACKGROUND: Rabies virus preferentially involves brainstem, thalamus and spinal cord in human furious and paralytic rabies beginning in the early stage of illness. Nevertheless, rabies patient remains alert until the pre-terminal phase. Weakness of extremities develops only when furious rabies patient becomes comatose; whereas peripheral nerve dysfunction is responsible for weakness in paralytic rabies. METHODS: Evidence of apoptosis and mitochondrial outer membrane permeabilization in brain and spinal cord of 10 rabies patients was examined and these findings were correlated with the presence of rabies virus antigen. RESULTS: Although apoptosis was evident in most of the regions, cytochrome c leakage was relatively absent in spinal cord of nearly all patients despite the abundant presence of rabies virus antigen. Such finding was also noted in brainstem of 5 patients. CONCLUSION: Cell death in human rabies may be delayed in spinal cord and the reticular activating system, such as brainstem, thus explaining absence of weakness due to spinal cord dysfunction and preservation of consciousness.

Adolescent↗
PubMed2005

Pneumomediastinum as initial presentation of paralytic rabies: a case report.

BACKGROUND: Rabies is readily diagnosed when it presents as the classic furious form. Paralytic and atypical forms can pose significant problems in diagnosis. Catastrophic incidents included 7 organ transplant recipients who died of rabies recently in United States and Germany. Although rabies remains top in the lists of differential diagnosis of encephalitis in rabies endemic area, its complication may divert physicians from making a relevant management. We encountered an unusual case of paralytic rabies who presented with spontaneous pneumomediastinum. CASE PRESENTATION: A young male presented with fever and dysphagia. There was a history of fluctuating consciousness and aerophobia but they were absent or could not be demonstrated at the time of admission. He exhibited subcutaneous chest wall emphysema and was found to have pneumomediastinum which resulted in surgical intervention. He developed paralysis followed by seizures during postoperative period. Diagnosis was confirmed by demonstration of rabies RNA in saliva during the preterminal phase and by the autopsy. Over 200 hospital staff subsequently received rabies postexposure prophylaxis. CONCLUSION: Spontaneous pneumomediastinum can be a rare complication of rabies. It may lead clinicians to perform inappropriate treatment, particularly when phobic spasms are not present and agitation is not prominent. High level of awareness of rabies in any patient with confusion albeit subtle or with any obscure neurological presentations such as difficulty swallowing with no identifiable causes must be borne in mind.

Adolescent↗
PubMed2005

Difference in neuropathogenetic mechanisms in human furious and paralytic rabies.

Whereas paralysis is the hallmark for paralytic rabies, the precise pathological basis of paralysis is not known. It is unclear whether weakness results from involvement of anterior horn cells or of motor nerve fibers. There is also no conclusive data on the cause of the neuropathic pain which occurs at the bitten region, although it has been presumed to be related to sensory ganglionopathy. In this study, six laboratory-proven rabies patients (three paralytic and three furious) were assessed clinically and electrophysiologically. Our data suggests that peripheral nerve dysfunction, most likely demyelination, contributes to the weakness in paralytic rabies. In furious rabies, progressive focal denervation, starting at the bitten segment, was evident even in the absence of demonstrable weakness and the electrophysiologic study suggested anterior horn cell dysfunction. In two paralytic and one furious rabies patients who had severe paresthesias as a prodrome, electrophysiologic studies suggested dorsal root ganglionopathy. Postmortem studies in two paralytic and one furious rabies patients, who had local neuropathic pain, showed severe dorsal root ganglionitis. Intense inflammation of the spinal nerve roots was observed more in paralytic rabies patients. Inflammation was mainly noted in the spinal cord segment corresponding to the bite in all cases; however, central chromatolysis of the anterior horn cells could be demonstrated only in furious rabies patient. We conclude that differential sites of neural involvement and possibly different neuropathogenetic mechanisms may explain the clinical diversity in human rabies.

Adult↗
PubMed2005

Transmission dynamics of rabies virus in Thailand: implications for disease control.

BACKGROUND: In Thailand, rabies remains a neglected disease with authorities continuing to rely on human death statistics while ignoring the financial burden resulting from an enormous increase in post-exposure prophylaxis. Past attempts to conduct a mass dog vaccination and sterilization program have been limited to Bangkok city and have not been successful. We have used molecular epidemiology to define geographic localization of rabies virus phylogroups and their pattern of spread in Thailand. METHODS: We analyzed 239 nucleoprotein gene sequences from animal and human brain samples collected from all over Thailand between 1998 and 2002. We then reconstructed a phylogenetic tree correlating these data with geographical information. RESULTS: All sequences formed a monophyletic tree of 2 distinct phylogroups, TH1 and TH2. Three subgroups were identified in the TH1 subgroup and were distributed in the middle region of the country. Eight subgroups of TH2 viruses were identified widely distributed throughout the country overlapping the TH1 territory. There was a correlation between human-dependent transportation routes and the distribution of virus. CONCLUSION: Inter-regional migration paths of the viruses might be correlated with translocation of dogs associated with humans. Interconnecting factors between human socioeconomic and population density might determine the transmission dynamics of virus in a rural-to-urban polarity. The presence of 2 or more rabies virus groups in a location might be indicative of a gene flow, reflecting a translocation of dogs within such region and adjacent areas. Different approaches may be required for rabies control based on the homo- or heterogeneity of the virus. Areas containing homogeneous virus populations should be targeted first. Control of dog movement associated with humans is essential.

Animals↗
PubMed2005

Rabies control in South and Southeast Asia.

We have the knowledge and tools to eliminate the threat of canine rabies but this disease, nevertheless, remains a public health threat in many parts of the world. Lack of motivation by governments, cultural issues and inadequate funding remain barriers. This is amazing since the number of human rabies deaths worldwide is greater than that from polio, meningococcal meningitis, Japanese encephalitis, yellow fever, SARS, bird flue and other scourges that attract more attention. Safe and effective vaccines are now widely available. Reduced dose effective and less expensive post-exposure vaccination regimens have helped eliminate nerve tissue vaccines in Thailand, Philippines and Sri Lanka. India and Pakistan, the major users of dangerous nerve tissue derived Semple type vaccine, are now considering following suite. Immediate wound care and prompt use of a potent vaccine will save a majority of infected persons. Rabies immunoglobulin, injected into and around bite wounds, provides added safety for the severely exposed. The high cost of rabies immunoglobulin and tissue culture vaccines are remaining barriers, but new manufacturers and the use of intradermal vaccination schedules can reduce costs. Ultimately, it is the need to control rabies in dogs that must occupy most of our attention. The tools are available, but attitudes must change before they can be applied. There have been many new developments since publication of the last WHO rabies expert committee report in 1992 (new version in print)] and we will address those that have practical applicability.

Animals↗
PubMed2005

Pathophysiology of human paralytic rabies.

Furious rabies is a well-recognized clinical disorder in humans but the paralytic form is not as easily identified. The mechanisms responsible for the weakness and longer survival periods are not clear. Several hypotheses have been proposed, including rabies virus variants associated with a particular vector, location of wounds, incubation period, influence of prior rabies vaccination, and virus localization in the central nervous system (CNS). However, none of these have been substantiated. Regarding molecular analyses of rabies viruses isolated from both furious and paralytic rabies patients, only minor genetic variations with no specific patterns in glyco- (G), phospho- (P), and nucleoprotein (N) sequences have been identified and arginine 333 in G protein was present in all samples. Regional distribution of rabies virus antigenin rabies patients whose survival periods were 7 days or less and magnetic resonance imaging (MRI) of the CNS indicated brainstem and spinal cord as predilection sites regardless of clinical presentations. There are clinical, electrophysiological, and pathological indications that peripheral nerve dysfunction is responsible for weakness in paralytic rabies whereas in furious rabies, even in the absence of clinical weakness, abundant denervation potentials with normal sensory nerve conduction studies and proximal motor latencies suggest anterior horn cell dysfunction. The lack of cellular immunity to rabies virus antigen accompanied by an absence of cerebrospinal fluid (CSF) rabies neutralizing antibody in most paralytic rabies patients may argue against role of an immune response against rabies virus-positive axons. Aberrant immune responses to peripheral nerve antigen, in particular those mediated by one or more cellular-dependent mechanisms, may be involved as is supported by the absence of putative anti-ganglioside antibodies commonly found in immune-mediated peripheral nerve diseases. Longer survival period in paralytic rabies may possibly be related to currently unidentified mechanism(s) on neuronal gene expression, required for virus transcription/replication and for maintaining neuronal survival.

Animals↗
PubMed2005

Survey for bat lyssaviruses, Thailand.

Surveillance for lyssaviruses was conducted among bat populations in 8 provinces in Thailand. In 2002 and 2003, a total of 932 bats of 11 species were captured and released after serum collection. Lyssavirus infection was determined by conducting virus neutralization assays on bat serum samples. Of collected samples, 538 were either hemolysed or insufficient in volume, which left 394 suitable for analysis. These samples included the following: Pteropus lylei (n = 335), Eonycteris spelaea (n = 45), Hipposideros armiger (n = 13), and Rousettus leschennaulti (n = 1). No serum samples had evidence of neutralizing antibodies when tested against rabies virus. However, 16 samples had detectable neutralizing antibodies against Aravan virus, Khujand virus, Irkut virus, or Australian bat lyssavirus; all were specifically associated with fruit bats P. lylei (n = 15) and E. spelaea (n = 1). These results are consistent with the presence of naturally occurring viruses related to new putative lyssavirus genotypes.

Animals↗
PubMed2005

Bat Nipah virus, Thailand.

Surveillance for Nipah virus (NV) was conducted in Thailand's bat population. Immunoglobulin G antibodies to NV were detected with enzyme immunoassay in 82 of 1,304 bats. NV RNA was found in bat saliva and urine. These data suggest the persistence of NV infection in Thai bats.

Animals↗
PubMed2005

Rabies and dog population control in Thailand: success or failure?

Despite a success in reducing rabies deaths from almost 200 to less than 20 annually, this may not be considered a success. More than 400,000 persons required rabies post-exposure prophylaxis (PEP) in 2003, more than 4 times as many as those in 1991 [93,641 cases in 1991; 183,815 in 1996 and 350,535 in 2001]. The number of samples submitted for testing in rabies diagnostic laboratories has been declining. However, the percent of samples that were confirmed infected with rabies during the 10 year period remained unchanged; within a range of 23 - 30% (MOPH report). Of the 6 million dogs roughly estimated to live in Thailand, there are no reliable data indicating their relative population densities or distribution patterns in various regions throughout the country. However, in a survey conducted by the Bureau of National Statistics and the Bangkok Metropolitan Administration in 1999, it was estimated that approximately 630,000 dogs dwell in Bangkok city (an area of 1 565 sq km). In this survey, approximately 110,000 of the dogs living in Bangkok were considered to be ownerless (stray or feral), whereas the remainder was believed to be owned or were community dogs. Nevertheless, it has not been known how many of the latter group can be accessible or are in compliance with local rabies control regulations. When the dog population statistics collected in 1999 are compared to an earlier survey conducted in 1992, the stray dog population appears to have almost tripled in size in Bangkok over the eight year

Animals↗