Overview
An investigation was initiated following an encounter with a triatomine bug by a couple from the United States during their stay in Lisbon, Portugal, in August of last year. The incident prompted a multi-institutional effort to identify the specimen and determine its geographical origin. The bug was subsequently identified as a third-stage nymph of *Triatoma rubrofasciata*, a species known for its involvement in Chagas disease transmission, though primarily in specific endemic regions.
Research Context
Triatomine bugs, often referred to as 'kissing bugs', are known vectors for the parasite *Trypanosoma cruzi*, the causative agent of Chagas disease. This disease is endemic in regions such as Latin America, but the presence of triatomine bugs can occasionally be reported in non-endemic areas, typically through accidental importation. The presented case is noteworthy due to the species identified and its unusual presence in Europe, prompting an examination of its journey and potential implications for public health understanding.
Approach
Upon notification of the incident, the couple returned to the U.S. and submitted the preserved insect specimen for analysis. The diagnostic process involved two primary stages:
- Morphological Identification: Researchers at the Centers for Disease Control and Prevention (CDC) Division of Parasitic Diseases and Malaria in Atlanta, Georgia, initially examined the bug using morphological characteristics.
- Molecular Identification and Geographic Origin Determination: Following the initial identification, further molecular analysis was conducted. This involved extracting DNA from the specimen. The DNA was then amplified via Polymerase Chain Reaction (PCR) targeting specific genes: the mitochondrial cytochrome oxidase I (COI) gene and the nuclear 18S ribosomal RNA gene. The amplified sequences were compared against existing genetic databases, specifically GenBank, to confirm the species identification and infer its probable geographic origin.
The couple also underwent blood tests for *Trypanosoma cruzi* antibodies at the CDC to ascertain whether any transmission had occurred, given the bug's potential as a vector.
Findings
- Species Identification: Morphological and molecular analyses conclusively identified the specimen as a third-stage nymph of *Triatoma rubrofasciata*. This species is part of the Triatominae subfamily, which encompasses approximately 150 species globally.
- Geographic Origin: Genetic sequencing of the COI gene revealed a 99.8% match with *T. rubrofasciata* sequences originating from Thailand found in the GenBank database. This strong genetic correlation suggested a likely origin of Southeast Asia, specifically Thailand, for the specimen found in Lisbon.
- Lack of Parasite Transmission: Blood tests conducted on both individuals for *Trypanosoma cruzi* antibodies returned negative results, indicating no evidence of infection with the Chagas disease parasite.
- Patient Symptoms: The female traveler experienced a bite on her lower eyelid, which resulted in significant swelling and required medical attention.
Why This Matters
The case represents an atypical instance of intercontinental triatomine bug displacement, specifically for *T. rubrofasciata* from Southeast Asia to Europe. While the individuals did not contract Chagas disease, the incident highlights the potential for unexpected encounters with vector insects in non-endemic regions due to international travel and globalized movement. This scenario underscores the importance of continued vigilance and diagnostic capabilities for identifying unusual vector introductions, even if disease transmission is not a primary outcome in a given instance.
Key Limitations Mentioned by Researchers
The research publication noted the difficulty in precisely determining the exact route the bug took to reach Lisbon. While the genetic evidence strongly points to a Southeast Asian origin, the specific mechanism or pathway of its transport from Thailand to the luxury hotel in Portugal remains unconfirmed.