Identification and characterization of the causative triatomine bugs of anaphylactic shock in Zhanjiang, China

Abstract

Background: Two health concerns primarily related to triatomine bugs are transmission of Trypanosoma cruzi through infective feces, and allergic reactions induced by triatomine bites. In the Southwestern United States, reduviid bugs bites commonly cause insect allergy. In South China, four cases of anaphylactic shock have been reported after this bite exposure. To further classify the species of these bugs and confirm the sensitization of the triatomine saliva, we caught triatomine bugs from the region where the bites occurred and performed phylogenetic and immunohistochemical (IHC) analysis.

Methods: Triatomine bugs were collected in Donghai Island of Zhanjiang City in South China. The genomic DNA was extracted from three legs of the bugs. The fragments of mitochondrial 16S rRNA, cytochrome c oxidase subunit I (COI) gene and nuclear ribosomal 18S and 28S rRNA genes were obtained by PCR and sequenced. A phylogenetic tree was constructed based on the sequence of 16S rRNA gene using a maximum likelihood method with MEGA 7.0 software. Trypanosomal specific fragments and vertebrate COI genes were amplified from the fecal DNA to detect the infection of trypanosomes and analyze the blood feeding patterns, respectively. Paraffin-embedded sections were then prepared from adult triatomines and sent for IHC staining.

Results: We collected two adult triatomine bugs in Donghai Island. Morphological and molecular analyses indicated that the triatomines were Triatoma rubrofasciata. No fragments of T. cruzi or other trypanosomes were detected from the fecal DNA. Mitochondrial gene segments of Homo sapiens and Mus musculus were successfully amplified. The allergens which induced specific IgE antibodies in human serum were localized in the triatomine saliva by IHC assay.

Conclusions: The two triatomine bugs from Donghai Island were T. rubrofasciata. They had bitten humans and mice. Their saliva should contain the allergens related to the allergic symptoms and even anaphylactic shock of exposed residents. Great consideration should be given to this triatomine bugs due to their considerable distribution and potential threat to public health in South China.

Keywords: Anaphylactic shock; Chagas disease; Triatoma rubrofasciata; Trypanosoma cruzi.

Fig. 1

The location of Hewujing Village on Donghai Island of South China

Fig. 2

The house where we collected the two adult triatomine bugs

Fig. 3

a and b Dorsal and ventral views of the female T. rubrofasciata; c and d Dorsal and ventral views of the male T. rubrofasciata. I: Orange-red margin along the outer edge of the abdomen which extended horizontally between segments; II: Orange-red margin along the side of the pronotum; III: The genital region of the female adult bug was strongly projecting posteriad; IV: The first segment surpassed the apex of its head; V: Eyes at the sides of a long and cone-shaped head; VI: Ocelli; VII: Anterior angles produced into short spines of a reddish yellow color; VIII: The stout proboscis hinged beneath the thorax, covered with short hairs which were progressively longer towards tip

Fig. 4

Phylogenetic tree inferred by mitochondrial 16S rRNA genes. The Maximum Likelihood method with the Tamura-Nei mode was used

Fig. 5

Immunolocalization of salivary allergens of the triatomine bug. The bugs were fixed, embedded, and sectioned as described in Materials and Methods. a The serum (1:20) of healthy people as control antibody; b The serum (1:20) of the allergic patient as primary antibody. HRP labeled secondary antibody (goat anti-human IgE antibody) localizes allergens in the luminal contents of the salivary glands (I and II) and the cytoplasm of epithelium (III and IV) (original magnification, × 400)