Differential diagnosis of human lymphatic filariasis using PCR-RFLP

Diagnosis of human nematode infections

Many hundreds of millions of people throughout the world are infected by nematodes found in the intestine or tissues with a high prevalence in developing countries. Despite their frequency and morbidity, these infections, which may affect migrants and travelers, remain difficult to diagnosis even in developed countries. This is primarily due to the variety of clinical signs often associated with a lack of highly sensitive and specific diagnostic tools. Parasitological diagnosis is often difficult to achieve and can neither be applied during the pre-patent period nor for parasitic impasses. Serological diagnosis is frequently hampered by a lack of specificity due to cross-reaction with others helminthes. Molecular biology methods still require optimization. The diagnostic approach applied by a clinician of a suspected nematode infection is based on a vast set of data including patient history and way of life, clinical examination, non-specific biological tests and, when available, specific diagnostic tests.

Inter and intra-specific diversity of parasites that cause lymphatic filariasis

Lymphatic filariasis is caused by three closely related nematode parasites: Wuchereria bancrofti, Brugia malayi and Brugia timori. These species have many ecological variants that differ in several aspects of their biology such as mosquito vector species, host range, periodicity, and morphology. Although the genome of B. malayi (the first genome sequenced from a parasitic nematode) has been available for more than five years, very little is known about genetic variability among the lymphatic dwelling filariae. The genetic diversity among these worms is not only interesting from a biological perspective, but it may have important practical implications for the Global Program to Eliminate Lymphatic Filariasis, as the parasites may respond differently to diagnostic tests and/or medical interventions. Therefore, better information on their genetic variability is urgently needed. With improved methods for nucleic acid extraction and recent advances in sequencing chemistry and instrumentation, this gap can be filled relatively inexpensively. Improved information on filarial genetic diversity may increase the chances of success for lymphatic filariasis elimination programs.

Development of loop-mediated isothermal amplification method for detecting Wuchereria bancrofti DNA in human blood and vector mosquitoes

We have developed loop-mediated isothermal amplification (LAMP) method to detect Wuchereria bancrofti DNA. The sensitivity and specificity of LAMP method were equivalent to those of PCR method which detects SspI repeat sequence in W. bancrofti genomic DNA: both methods detected one thousandth of W. bancrofti DNA from one microfilaria (Mf), and did not cross-react with DNAs of Brugia malayi, B. pahangi, Dirofilaria immitis, human and Culex quinquefasciatus. We also examined the sensitivity of LAMP using the mimic samples of patient's blood or blood-fed mosquitoes containing one W. bancrofti Mf per sample. The LAMP method was able to detect W. bancrofti DNA in 1000 μl of blood or in a pool of 60 mosquitoes, indicating its usefulness in detecting/monitoring W. bancrofti infection in humans and vector mosquitoes in endemic areas.

Filariasis: diagnosis and treatment

Filariasis is an infectious disease of the lymphatics and subcutaneous tissues caused by nematodes or filariae. Carried by mosquito vectors, this disease causes millions of people to suffer from lymphedema and elephantiasis, characteristics of filariasis infection. This disease can be diagnosed through the identification of microfilariae in blood or skin samples, antigen detection, radiographic imaging, or polymerase chain reaction. Mass drug administration by the World Health Organization has helped to diminish the incidence of filariasis. However, continued research on new drugs and vaccinations will be needed to control and reduce the microfilarial levels in the human population.

The development and evaluation of a single step multiplex PCR method for simultaneous detection of Brugia malayi and Wuchereria bancrofti

A single step novel multiplex polymerase chain reaction (PCR) has been developed for simultaneous detection of human filarial parasites, Brugia malayi and Wuchereria bancrofti, from blood samples and mosquitoes. The primers used were novel and have been tested with the parasite DNA amplifying 188bp (BM) and 129bp (WB) DNA fragments, specific to B. malayi and W. bancrofti, respectively, in a single reaction. The specificity of the PCR product was confirmed by DNA sequencing and slot blot hybridization assay. The test was found highly sensitive for both B. malayi and W. bancrofti by detecting the parasitaemia up to the level of one microfilaria per reaction. The assay was further evaluated on 98 blood samples and 144 mosquito samples collected from filarial endemic areas. The PCR was found to be more efficient in comparison to microscopy by detecting 8% and 5% more filarial parasites in field-collected blood and mosquito samples, respectively. This novel PCR that offers scope for simultaneous detection of both the parasites may be used as a diagnostic tool for the detection of filariasis in population and can be adopted for rapid surveillance and monitoring of mosquitoes for use in the effective control of filariasis.

Random amplified polymorphic DNA (RAPD) for differentiation between Thai and Myanmar strains of Wuchereria bancrofti

BACKGROUND

Lymphatic filariasis (LF) is a mosquito-borne disease caused by mosquito-transmitted filarial nematodes, including Wuchereria bancrofti and Brugia malayi. The Lymphatic Filariasis Elimination Program in Thailand has reduced the prevalence of nocturnally subperiodic W. bancrofti (Thai strain), mainly transmitted by the Ochlerotatus (Aedes) niveus group in Thailand to 0.57/100,000 population. However, it is estimated that more than one million Myanmar migrants with high prevalence of bancroftian filariasis have settled in the large urban cities of Thailand. These infected migrants carry the nocturnally periodic W. bancrofti (Myanmar strain) which has Culex quinquefasciatus as the main mosquito vector. Although transmissions of the Myanmar strain of W. bancrofti by the Thai Cx. quinquefasciatus has never been reported, previous study showed that Cx. quinquefasciatus could nurture the Myanmar strain of W. bancrofti to the infective stage. Thus, the potential now exists for a re-emergence of bancroftian filariasis in Thailand. The present study was undertaken in an attempt to differentiate between the Thai and Myanmar strains of W. bancrofti.

METHODS

The microfilarial periodicity of Thai and the Myanmar strains of W. bancrofti were determined. Comparative morphology and morphometry of microfilariae and a study of random amplified polymorphic DNA (RAPD) was performed. The Nei's genetic distance was calculated, and a phylogenetic tree was constructed using the Unweighted Pair Group Method with Arithmetic mean (UPGMA).

RESULTS

The Thai strain of W. bancrofti was nocturnally subperiodic, and the Myanmar strain of W. bancrofti was nocturnally periodic. The body length, cephalic space length, and cephalic space width of the Thai strain of W. bancrofti were significantly larger than those of the Myanmar strain of W. bancrofti (p < 0.05). However, an overlapping mean of these parameters made it impractical for field application. RAPD-PCR profiles showed specific bands characteristic for the Myanmar strain of W. bancrofti. The phylogenetic tree indicated two genetically distinct clusters of the Thai and Myanmar strains of W. bancrofti.

DISCUSSION

This study was the first report on the genetic polymorphism of the Thai and Myanmar strains of W. bancrofti. Differentiation between the Thai and Myanmar strains of W. bancrofti could not rely on morphological criteria alone. However, RAPD profiles revealed a significant diversity between the two strains. The RAPD-PCR technique was suitable for differentiating Thai and Myanmar strains of W. bancrofti. The RAPD marker could be used for epidemiological assessment of the Myanmar strains of W. bancrofti in Thailand.

Molecular characterization of Thelazia lacrymalis (Nematoda, Spirurida) affecting equids: a tool for vector identification

Equine thelaziosis caused by the eyeworm Thelazia lacrymalis is a parasitic disease transmitted by muscid flies. Although equine thelaziosis is known to have worldwide distribution, information on the epidemiology and presence of the intermediate hosts of T. lacrymalis is lacking. In the present work, a PCR-RFLP based assay on the first and/or second internal transcribed spacer (ITS1 and ITS2) of ribosomal DNA was developed for the detection of T. lacrymalis DNA in its putative vector(s). The sensitivity of the technique was also assessed. The restriction patterns obtained readily differentiated T. lacrymalis from four species of Musca (Diptera, Muscidae) (i.e. Musca autumnalis, Musca domestica, Musca larvipara and Musca osiris), which are potential vectors of equine eyeworms. The molecular assay presented herein is a useful tool to identify the intermediate host(s) of T. lacrymalis in natural conditions and to study its/their ecology and epidemiology.