Emergence of zoonotic Brugia pahangi parasite in Thailand

Investigating the impact of climate and seasonality on mosquito (Diptera: Culicidae) vector populations in the connecting areas of the Tenasserim range forests in Thailand

Mosquito-borne diseases pose a significant public health challenge globally. Our study focused on the seasonal diversity of mosquito species in the connecting areas of the Tenasserim (also known as Tanaosri) range forests in Thailand. Additionally, we employed the geometric morphometric technique to assess variations in wing size and shape among five predominant mosquito species. Throughout the study period, we collected a total of 9,522 mosquitoes, encompassing 42 species across eight genera. In these connecting areas of forests, the Simpson index and Shannon species diversity index were recorded at 0.86 and 2.36, respectively, indicating a high level of mosquito diversity. Our analysis using the Analysis of Similarities (ANOSIM) test showed significant seasonal differences in mosquito communities, with an R-value of 0.30 (p < 0.05) in the lower connecting areas and 0.37 (p < 0.05) in the upper connecting areas. Additionally, canonical correspondence analyses showed that the abundance of each mosquito species is influenced by various climate factors. Phenotypic analyses of wing size and shape have deepened our understanding of local adaptation and the seasonal pressures impacting these vectors. Notably, most species exhibited larger wing sizes in the dry season compared to other seasons. Additionally, seasonal assessments of wing shape in five predominant mosquito species revealed significant differences across seasonal populations (p < 0.05). Ongoing monitoring of these populations is crucial to enhancing our understanding of the seasonal effects on mosquito abundance and physiological adaptations. These insights are essential for developing more effective strategies to manage mosquito-borne diseases.

In vivo mosquito repellency effect of citronella (Cymbopogon nardus (L.) Rendle) essential oil bath bomb formulation in dogs

Background and Aim

Mosquitoes carry numerous diseases of medical and veterinary significance. While citronella essential oil is safe as a mosquito repellent, extensive research does not document its ability to deter mosquitoes from animals. This study assessed the citronella essential oil bath bomb's ability to repel Culex quinquefasciatus mosquitoes in dogs.

Materials and Methods

Citronella essential oil's chemical composition was analyzed using gas chromatography-mass spectrometry (GC-MS). Through freeze-thaw testing, a bath bomb formulation containing 6% w/w citronella essential oil was assessed for its physical and chemical stability. Thirty-two healthy client-owned mixed-breed dogs were employed to test the mosquito-repellency effects of citronella essential oil (treatment group) and olive oil (control group) bath bomb formulations. Bath bombs were tested for irritation effects on animal skin for 15-day post-application.

Results

Thirty-six compounds were identified through GC-MS, with citronellal (23.38%), δ-cadinene (12.25%), and geraniol (9.09%) being the most prevalent constituents. The bath bomb maintained its original physical properties after undergoing six freeze-thawing cycles and retained over 90% of its citronella essential oil. About 100%, 69.28%, and 65.58% mosquito repellency were displayed by the citronella essential oil bath bomb at 3 h, 6 h, and 8 h, respectively. None of the test animals exhibited skin irritation during the study.

Conclusion

The citronella bath bomb effectively repelled C. quinquefasciatus in dogs without irritating their skin. The formulation's physical and chemical stability is demonstrated by the results of freeze-thaw stability testing. Further studies should be conducted to evaluate the repelling activity against other mosquito species.

Ocular Brugia pahangi Filariasis Complicated by Severe Macular Damage in Thailand: Case Report and Literature Review

Extralymphatic filariasis caused by filaria of zoonotic origins has been frequently reported in Thailand over recent years. Here, we report the first case of ocular filariasis in a 7.5-year-old Thai boy who initially presented with progressive conjunctival redness and blurred vision in his right eye. A small, slender, coiled worm was found and surgically removed from the right anterior chamber. Histopathological examination illustrated predominant eosinophilic inflammation surrounding the parasite, which showed smooth and thin cuticle, prominent lateral chords, flat and broad muscle cells, one intestine, and two reproductive tubes with unsegmented ova, typically characteristic of a female adult Brugia filarial nematode. The parasite was also molecularly identified as B. pahangi, based on mitochondrial cytochrome c oxidase subunit I sequence analysis. The patient was then empirically prescribed albendazole, systemic prednisolone, and topical methylprednisolone. Unfortunately, his vision did not recover after 2 months due to severe maculopathy, most likely resulting from parasitic infestation and subsequent vitreous inflammation. To the best of our knowledge, this is the first case of ocular infestation by B. pahangi with visual complications that occurred outside a filariasis-endemic area of Thailand. Furthermore, this report provides clinical data on preceding cases of B. pahangi filariasis formally reported in southeast Asian countries, including Thailand and Malaysia, which facilitate a better understanding of the epidemiology of this sporadic zoonotic infection for effective disease elimination.

Five years of post-validation surveillance of lymphatic filariasis in Thailand

BACKGROUND

The World Health Organization (WHO) validated Thailand in 2017 as having eliminated lymphatic filariasis (LF) as a public health problem with recommendations for continued surveillance. This article describes measures and progress made in Thailand with post-validation surveillance (PVS) of LF from 2018 until 2022.

METHODS

The implementation unit (IU) is a sub-village in 11 former LF endemic provinces. Human blood surveys are targeted in 10% of IUs each year. In Wuchereria bancrofti areas, filaria antigen test strips (FTS) are used, and in Brugia malayi areas, antibody test kits (Filaria DIAG RAPID) are used. Positive cases are confirmed by thick blood film (TBF) and polymerase chain reaction (PCR). Vector surveys for mosquito species identification and dissection for microfilaria (Mf)/filarial larvae are done in 1% of IUs where human blood surveys are conducted. Human blood surveys using FTS are conducted among migrants in five provinces. Surveillance of cats is done in areas that previously recorded > 1.0% Mf rate among cats. Morbidity management and disability prevention (MMDP) are done every 2 years in LF-endemic areas where chronic disease patients reside.

RESULTS

From 2018 to 2022, in a total of 357 IUs in 11 provinces, human blood surveys were conducted in 145 IUs (41%) with an average population coverage of 81%. A total of 22,468 FTS and 27,741 FilariaDIAG RAPID were performed. 27 cases were detected: 3 cases of W. bancrofti in Kanchanaburi province and 24 cases of B. malayi in Narathiwat province. 4 cases of W. bancrofti were detected in two provinces through routine public health surveillance. Vector surveys in 47 IUs detected B. malayi Mf filarial larvae only in Narathiwat province. Chronic LF patients reduced from 114 in 2017 to 76 in 2022. Surveys among 7633 unregistered migrants yielded 12 cases of W. bancrofti. Mf rate among cats in Narathiwat province declined from 1.9% in 2018 to 0.7% in 2022. MMDP assessments revealed gaps in healthcare provider's management of chronic cases due to staff turnover.

CONCLUSIONS

In 2022, after 5 years of PVS, Thailand re-surveyed 41% of its previously endemic IUs and demonstrated ongoing transmission in only one province of Narathiwat, where Mf prevalence is below the WHO provisional transmission threshold of 1%. This study highlights the importance of continued disease surveillance measures and vigilance among health care providers in LF receptive areas.