This study presents the first reported instance of hepatic echinococcosis in an individual with no travel or residency history in an endemic area. Additionally, this is the first laboratory-confirmed case of its genotype in Guangdong. Consequently, it is critical to determine the time and location of infection, identify the source, and, most importantly, understand the transmission pattern.
Following infection, individuals typically remain asymptomatic for extended periods, attributable to the slow growth of cysts, particularly in the liver where growth rates vary from 1 mm to 5 mm in diameter annually (8). The cyst examined in this instance measured approximately 25 mm and exhibited signs of partial calcification, suggesting that the infection may have occurred between 2 to 3 years ago, or possibly earlier. Epidemiological investigations revealed that during this period, the patient resided primarily in Wuhan, Zhuhai, and Nanxiong cities. The likelihood of encountering the infection source in Wuhan and Zhuhai was notably low. Dogs are recognized as a critical reservoir host for echinococcosis, and in Nanxiong, the patient had increased contact with dogs, thus raising the probability of infection. Consequently, it appears more plausible that the infection was contracted in Nanxiong.
Livestock serve as significant intermediate hosts for Echinococcus granulosus. Recent surveys indicate that while the infection rate of Echinococcus in livestock within endemic regions of China has considerably declined, sheep and cattle remain the predominant intermediate hosts. For genotype G7, domestic pigs are the most common intermediate hosts (9), though instances in goats and wildlife have also been reported (3). In Nanxiong, a substantial number of cattle and a smaller number of sheep are annually imported from endemic areas. This movement of livestock poses a risk of introducing pathogens into Guangdong, potentially leading to localized transmission cycles.
Echinococcus species have a global distribution, found in Asia, Europe, North America, Oceania, and some African countries. The primary endemic areas in Northwest China include Xinjiang, Xizang, Qinghai, Gansu, Ningxia, Sichuan, and Inner Mongolia PLADs (4). Currently, of the 9 recognized genotypes of Echinococcus effective in human infection, genotypes G1, G6, and G7 are predominant, comprising 88.4%, 7.34%, and 3.7% of human infections respectively (5). Although the G7 genotype is less commonly observed in humans and animals globally compared to G1, in certain countries like Poland and Austria, it accounts for 100% (30/30) and 92.0% (23/25) of human hydatid cyst cases, respectively (6). Hence, the pathogenicity of E. granulosus genotypes appears to be influenced by geographic factors. The G7 genotype, also known as the “pig strain”, primarily uses pigs as its intermediate hosts, though cattle, goats, sheep, and wild bears can also fulfill this role (6). The broad distribution of the G7 genotype indicates its adaptability and suggests the potential establishment of a cycle involving this genotype in Guangdong.
In 2011, Jin et al. identified the G7 genotype of Echinococcus intermedius in goats from Qinghai Province. By 2014, Zhang et al. detected this genotype in four out of ten human liver cysts in Heilongjiang Province, marking the first documented instance of human infection with the G7 genotype of Echinococcus granulosus in China (6). The current study reveals that cases of echinococcosis of unknown origin in Zhuhai City, Guangdong Province, are attributable to the G7 genotype of E. granulosus. This represents the first report of such infections in Guangdong Province, and the third instance in China. Similar to isolated cases, such as the G7 genotype in Heilongjiang Province (6) and the G5 genotype in Guangxi and Guizhou PLADs (10), the recent case also emerged in a region not typically endemic for echinococcosis. These findings emphasize the urgent need for enhanced echinococcosis prevention and control measures in regions not traditionally affected by the disease, particularly through stringent quarantine and management of potential intermediate hosts such as pigs, cattle, and sheep.
Based on the findings, we propose two potential transmission patterns for echinococcosis in Guangdong. The first is an input pattern, wherein pathogens are introduced into the area through the importation of livestock. Dogs contract the infection by consuming the organs of these infected animals, subsequently transmitting the disease to humans through contact. The second pattern is local, characterized by a consistent, albeit low-level, cycle of echinococcosis among local fauna, with infrequent human transmission. It is imperative to enhance quarantine measures to fully elucidate these transmission dynamics.