Preplanned Studies: Distribution of Triatomines, the Vector of Chagas Disease — Southern China, 2016−2018

Triatomines, also known as kissing bugs, are widespread vectors for Chagas disease that affects 6–8 million people worldwide (1). Although two species of triatomines were recorded in China thirty years ago, there has been little research on them. Due to the increasing risk of the global spread of Chagas disease, triatomines have become a potential public health threat (2) and have begun being monitored in southern China. Social media tools including WeChat and QQ were used to allow local people to report cases after being educated on triatomines. All the samples and data were sent to the National Institute of Parasitic Diseases (NIPD) of China CDC and were reviewed by experts. Triatoma rubrofasciata (T. rubrofasciata) and a novel species of triatomine in 170 habitats in 30 cities in southern China were recorded in this investigation and 99.42% (1,035/1,041) of them were detected around human residences. Since triatomines have been found throughout southern China, continuous surveillance is crucial for public health.

The data of this study was collected from July 2016 to December 2018. First, a questionnaire and promotional literature were displayed to the county-level CDC staff and village doctors to determine the presence of triatomines in suspected distribution areas in 54 cities and 309 counties (counties are subdivisions of prefecture-level cities) in the provincial-level administrative divisions (PLADs) of Guangxi, Guangdong, Hainan, Fujian, and Yunnan. Second, social media tools including WeChat and QQ were used to publicize and popularize information on triatomines and allow locals to collect and report triatomine samples. Local staff were then trained to identify the species of the samples and to ensure consistent quality. Information including time, location, developmental stage, and sex of the samples was recorded. Light traps and Noireau traps were used to collect triatomines in the field (3-4). Finally, all samples and data were sent to the NIPD of China CDC for further verification and aggregation. The morphological identification of the triatomines that was conducted referred to Xiao et al. (1981) and Lent et al. (1979) (5-6).

A total of 1,042 triatomines, 81.96% (854/1,042) of which were adults and 18.04% (188/1,042) were nymphs, were captured from 170 different sites in 67 counties in 30 cities. Among them, 1,041 triatomines were identified as T. rubrofasciata ((Figure 1A, 1B) based on morphology and were captured from 169 different sites distributed in 66 counties of 29 cities in the PLADs of Guangxi, Guangdong, Hainan, and Fujian. This result was far beyond historical records of T. rubrofasciata from 15 different sites in 13 counties of 11 cities before 2016 in museums and the literature (Figure 2A, 2B).

Figure 1. 

Morphology views of the triatomines captured in China. (A) Dorsal view of the female specimen for T. rubrofasciata captured in Shunde District, Foshan City, Guangdong Province; (B) Ventral view of the female specimen for T. rubrofasciata captured in Shunde District, Foshan City, Guangdong Province; (C) Dorsal view of female specimen for the novel species of Triatoma sp. captured in Dali Prefecture, Yunnan Province; (D) Ventral view of female specimen for the novel species of Triatoma sp. captured in Dali Prefecture, Yunnan Province.

Figure 2. 

A comparison of the distribution data for T. rubrofasciata in southern China between (A) historical records and (B) current records.

A female specimen (Figure 1C, 1D) was captured in Dali Prefecture, Yunnan Province, which was different from the other recorded triatomines in both on morphology and molecular data. This triatomine was different from T. rubrofasciata and T. sinica (5), which are often recorded in China, and had the following main morphological differences: 1) darker color, no obviously orange-red or orange-yellow markings; 2) first antennal segment not exceeding tip of head; 3) smaller and shorter synthlipsis; 4) the scutellum was rough and wrinkled, the top of it was slightly upwarping with oblique uplift in the center of both sides (Figure 1C, 1D). The 16S ribosomal RNA (16S rRNA) gene, the cytochrome b gene, and the 28S ribosomal RNA with the highest similarities to T. rubrofasciata in GenBank showed only 93.08%, 77.16%, and 91.55% similarity, respectively. Sequences obtained from 16S rRNA of the Dali species were submitted to GenBank under the accession number MN200191 and the phylogenetic trees were constructed by the 16S rRNA gene of triatomines using the neighbor-joining method by MEGA (Molecular Evolutionary Genetics Analysis Version 6.0. Tamura K, Stecher G, Peterson D, Filipski A, and Kumar S, 2013). The result showed that this triatomine belonged to Triatominae and in the same clade of T. rubrofasciata (Figure 3). Based on the morphological and molecular data, the result showed that this could be a novel species of triatomine.

Figure 3. 

Phylogenetic tree showing the relationships between the Dali triatomine (MN200191) and other Triatominae species.

Among these T. rubrofasciata samples, 305 triatomines were captured from 54 different sites in 29 counties of 13 cities in Guangxi, 280 from 97 different sites in 27 counties of 9 cities in Guangdong, 419 from 11 different sites in 4 counties of 4 cities in Hainan, and 37 from 7 different sites in 6 counties in 3 cities in Fujian. On average, about 6.16 triatomine bugs were collected at each site. Among them, 43.80% (456/1,041) were female, 38.14% (397/1,041) were male, and 18.06% (188/1,041) were nymphs. Meanwhile, 99.42% (1,035/1,041) of the specimens were collected inside human housing and animal housing (which were around human housing), among which 60.90% (634/1,041) were collected inside human housing. Only 0.58% (6/1041) were collected in the environment surrounding human housing, and 74.92% (780/1,041) were captured in July and August with 94.81% (987/1,041) of the total being captured from May to October. It should be noted that triatomines infestations were found in all months except January in Hainan Province.