Can the use of folk remedies increase the risk of infection?
In some communities, there are remedies that use pureed aquatic vegetables (coriander, watercress) and raw water to treat diseases. Internal medicine can be at risk of infection from raw vegetables/drinks, which can cause SLGL. In addition, some people who have used undercooked animal liver products (pork, beef, lamb liver) to support the treatment of liver and gallbladder diseases are also at high risk of infection.
In particular, these situations often produce the clinical picture or Halzoun syndrome due to ingestion of undercooked infected beef livers containing metacercariae cysts. Fasciola spp. Adherence to the posterior wall of the pharyngeal mucosa causing allergic pharyngitis and persistent dry cough was first described in 1905 in Lebanon. This situation makes it easy for clinicians to misdiagnose with respiratory and ENT diseases.
Interestingly, ingestion of infected raw livers by dogs that feed on the feces of infected cows and sheep helps spread the disease in water supplies, but has also been rarely reported in humans.
Does climate change affect the increase in fascioliasis?
Recent studies show that species F. hepatica Development depends greatly on climatic conditions, the possibility of detecting diseases in humans will be high if the investigation is carried out in high altitude areas. Lymnaea sp. have increased resistance to low temperatures, in winter they grow little or not at all, high temperatures and dryness also hinder their growth and affect the chance of infection.
Cyst development is prolonged at low temperatures if humidity is adequate, but they are susceptible to disease and desiccation at temperatures above 250C. On the other hand, high humidity and long rainy season will cause high infection in animals and from there humans will also be highly infected during the rainy season. Besides, Temperature and rainfall are related to parasitic infections. Fasciola sp. and infection is seasonal.
In Europe, the incidence of SLGL is higher in summer and autumn than in winter; in North Africa, the peak of acute cases occurs in August. Because aquatic plants play a role in the transmission cycle, infection also depends on their growing season, for example, watercress larvae usually develop from September of the previous year to April of the following year, but the highest incidence is still in September‐October of each year..
In addition, the ecological conditions favorable for human infection with SLGL also need to be considered. Field and laboratory studies show that SLGL has the ability to spread very widely, related to the ecological niche advantage of the snail host as well as the adaptation of the species. Fasciola spp. Different environmental types are only suitable for some disease‐carrying snail species or some atypical habitats representing ecological regions are associated with unusual disease distribution on Jesis Island of Corsica or Ly Son Island (Quang Ngai) and Phu Quoc Island (Kien Giang) of Vietnam (Mas Coma et al., 1999; Huynh Hong Quang et al., 2007).
The presence of ALS at altitudes of 3500‐4200m above sea level in the Andes highlands of South America or Da Lat, Vietnam is also worth noting. This means that not only can snails and worms survive in such high altitudes, but they can also develop appropriate methods so that the infection rate is higher than possible (Huynh Hong Quang et al., 2016). Therefore, it is necessary to have replicated studies to explain this issue in the future and we should also pay attention to favorable conditions to develop a plan to prevent ALS at each stage.
In Vietnam, up to now, almost 63/63 provinces and cities have patients with giant liver fluke, the disease occurs year‐round, regardless of whether the patient lives at the highest altitude (Lang Son) or the lowest (Western provinces) compared to sea level, or in any climate condition, the hottest (Nghe An) or coldest (Lang Son), there are cases recorded and treated.
Was human‐to‐human transmission established by adaptation?
Previously, humans were considered to be only incidental hosts and ruminants/herbivores were the definitive hosts. However, recent studies have shown that humans play an important role in the transmission of LF, at least in the highly endemic areas of South America, especially in the Andes‐Bolivian highlands.
In 2013, the World Health Organization (WHO, 2013 ‐Fact sheet) also mentioned human‐to‐human transmission (WHO, 2013). However, to achieve this, all essential characteristics must be met, including a sufficiently high and sustained human prevalence over time under appropriate conditions, and eggs laid in human feces must be proven to be viable and resistant to conditions when entering the human body.
The intensity of SLGL infection in humans and adaptation to complete the cycle?
‐Previously, analysis of human cases showed that the number of eggs detected was quite low in areas where the disease was less endemic in humans and where the disease was more prevalent in livestock. In the 1990s, this rate was higher and the egg density was higher (up to 440 eggs per gram of feces), but such cases were rare. In particular, in the study in Bolivia, the number of eggs found was much higher in humans in endemic areas, ranging from 24‐5,064 eggs/gram of feces, with an average of 474‐1,001 eggs/gram of feces, while in Porto, Portugal, the average number of eggs was 233 eggs/gram of feces, with a range of 25‐2,100;
‐Notably, although the prevalence and fecal egg intensity in children (75%, 24‐4440 eggs/g of feces) were higher than in adults (41.7%, 144‐864 eggs/g of feces) in highly endemic areas through global surveys, this may be explained by the fact that in highly endemic areas, adults either retain a quantity of juvenile worms or may be newly infected because they live in areas with a high risk of infection, so new infections often occur and the reason is that humans are accidental hosts so it is very difficult for the worms to live long enough to lay mature eggs;
‐Through many epidemiological investigations in the Central Highlands, Vietnam as well as clinical practice in laboratory diagnosis of SLGL cases, the number and rate of found eggs as well as the intensity of eggs/gram of stool detected were very low (< 5%), which may be due to many reasons such as experience in making stool specimens, lack of coordination of multiple techniques, careful identification of egg morphology, or the species of worm living in the human body does not survive to the egg‐laying stage, or the release of eggs into the environment in batches while the test is not continuous on a case;
‐Recently, at the Quy Nhon Malaria‐Parasitology‐CT Institute, a pilot study was conducted to evaluate the effectiveness of TCBZ at a dose of 20 mg/kg as recommended by the World Health Organization (WHO, 2018) and the Ministry of Health (2020). Stool tests were conducted to find Fasciola spp. eggs in all cases diagnosed with Fasciola spp., and the results showed that the detection rate of Fasciola spp. eggs was up to 8‐10% (n = 130 patients). This again shows that the flukes may gradually adapt to the human body and complete the cycle to the egg‐laying stage, so the chance of detecting fluke eggs may increase.
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