Infectious diseases, including parasitic infestations, are important health problems in both animals and humans (1–4), which cause economic losses and severe illness (5–10). Parasites are capable of causing acute, chronic, and debilitating types of diseases, leading to production losses in animals (11–15), and many pieces of research have shown the positive role of alternative/complementary medicine in treating parasitic diseases. Echinococcosis is a neglected silent cyclozoonotic parasitic disease caused by the metacestode stages of the genus Echinococcus belonging to the family Taeniidae, affecting a wide spectrum of animal species, including livestock and wildlife, and it also has zoonotic implications (16–19). The genus Echinococcus contains at least nine valid species with different strains and genotypes, namely E. granulosus, E. multilocularis, E. vogeli, E. oligarthra, E. canadensis, E. equinus, E. felidis, E. shiquicus, and E. ortleppi, which are important ones (20, 21).

Echinococcosis is included in the World Health Organization's (WHO) list of neglected tropical diseases. This disease is widespread in its distribution and persists in a variety of environmental conditions in temperate, circumpolar, tropical, and sub-tropical regions (Figure 1). The parasite survives well in arid climatic conditions and subpolar oceanic environmental conditions. Eurasia, Australia, Africa, and South America have a very high disease prevalence, and 50 million people are infected with the disease worldwide (22, 23). Cystic echinococcosis (CE) encompasses a wide geographical area from the eastern parts of Asia to northern America and from the upper northern hemisphere to the southern countries of the African continent (24, 25).

Variable-sized cysts comprise the metacestode stages of E. granulosus, which are filled with a transparent liquid. The presence of this clear liquid led to the coining of the term “hydatids.” A number of scientists and physicians, including Hippocrates, Galen, Aretaeus, Wolckerus, and Bonet, described the different features of hydatids in their timelines. Some researchers described them as an accumulation of serum and mucus in between the laminar cell layers. Francesco Redi first provided evidence of hydatids' metacestode nature and reported that cysticerci could move like animals (26). Jacob Hartman, a professor of medicine at the University of Königsberg/Germany, confirmed the animal-like nature of cysticerci, describing it as a small, spherical structure with a metacestode bladder. Edward Tyson, a professor at Oxford, also found the motility of the hydatids of Cysticercus tenuicollis to be like that of living creatures. Simon Pallas in the Netherlands described hydatids as a distinct group of bladder worms with small bodies on the inner walls of hydatids. Later, Ephraim Goeze discovered tapeworm scoleces in these small bodies called brood capsules. In 1801, Karl Rudolphi introduced the word Echinococcus to the world of science (27).

In the mid-nineteenth century, two different forms of echinococcosis were identified: cystic echinococcosis (CE) and alveolar echinococcosis (AE). There remained a heated debate over the aetiological agents responsible for the causation of CE and AE. Two schools of thought emerged, one with “unicasts,” believing that both forms occur due to the same species of Echinococcus, and the other with “dualists,” claiming that two different species are responsible for causing two different forms of the disease. However, the understanding of the dualist school of thought was supported by Professor Adolf Possely. Clear experimental proof supporting the concepts of a dualist school of thought was provided in 1928 by Posselt in his work “Der Alveolarechinokokkus und seine Chirurgie” (alveolar echinococcus and its surgery). He provided plausible arguments that two different species cause CE and AE, as their morphology, anatomy, and clinical signs clearly differ from each other (28).

Echinococcosis is a neglected tropical disease of public health concern and has serious economic implications. Out of nine known species of Echinococcus, E. granulosus and E. multilocularis pose significant threats to human and animal health in addition to substantial economic losses (29). Treatment costs, production losses, and mortality in infected animals and aberrant human hosts are economic and social calamities caused by this infection. The cosmopolitan distribution of these ailments has led to losses of USD 3 billion annually (30). It has been reported that echinococcosis has led to annual economic losses of USD 212.35 million in India, USD 232.3 million in Iran, and USD 7.708 million in Turkey (31). Followed by Fasciola hepatica, CE is the most important cause of condemnation of livestock viscera. It has been estimated that in Chile, CE leads to economic losses amounting to USD 14.35 million per year (32). Echinococcosis causes substantial economic losses in Pakistan. Losses due to the disease have been estimated at USD 276.20 per 100 infected goats and sheep and USD 165.72 per 100 infected large ruminants and camels. There are losses in terms of quantity and quality of milk, wool, and meat, retarded growth, decreased fertility, and carcass condemnation (33).

Echinococcus species enjoy two different host species: the intermediate host and the definitive host. The definitive hosts of this cestode are the carnivores, especially the dogs that carry this parasite in their small intestines. Both wild and domesticated ruminants, camels, and humans serve as intermediate hosts of different Echinococcus species (23, 34, 35). The life cycles of different species of Echinococcus are depicted in Figure 2. All of the species enjoy a heteroxenic life cycle. The size of adult worms varies from 2 to 11 mm, with 2–7 proglottid segments. Scolex has two rows of rostellar hooks. Each proglottid has a single genital opening, and the mature segment is called the penultimate segment. After fertilization, eggs are fully developed in the uterus and released into the environment along with dog feces. Contaminated water or vegetation ingested by the intermediate host leads to the release of oncospheres from embryonated eggs that penetrate the intestinal wall and spread to various body tissues through circulation. Cyst formation primarily occurs in the lungs and liver, and such infected tissue, when eaten by the canids, releases protoscoleces. They develop into mature worms, completing the life cycle (36–39).

The dynamics of the completion of the life cycle of the Echinococcus species are well supported by the presence of dogs. Home slaughtering practices and feeding the dogs with hydatid cysts facilitate the completion of the parasite's life cycle. Younger children have a great affection for pets, including dogs. Children of such an age are likely at greater risk of suffering from echinococcosis. Regions with widespread grassland are best suited for grazing sheep, goats, and cattle. The pastoral dogs and the nomadic lifestyle play a role in the completion of the synanthropic life cycle of E. granulosus (40). Lack of alertness about the life cycle, poor hygiene, open slaughtering practices, close involvement of ruminants and dogs, and improper disposal of condemned carcasses/offal support the spread of echinococcosis (33). In South Asian countries like Pakistan and India, the slaughtering of food animals is carried out either in an open environment or in slaughterhouses that are easy for dogs to access. Such access by the dogs and ingestion of the offal leads to the completion of the Echinococcus life cycle (18). A general overview of risk factors for E. granulosus infection in dogs and humans is described in Figures 3, 4.

The burden of human echinococcosis can be expressed in disability-adjusted life years (DALYs), which are used to express the burden of human cases of CE and AE. The annual global burden of AE is approximately 18,200 cases, which leads to almost 666,000 DALYs (41). With regard to CE, the annual global burden amounts to 188,000 new cases every year and leads to 184,000 DALYs (42).

Echinococcosis can appear in four different forms: cystic echinococcosis (CE), alveolar echinococcosis (AE), polycystic echinococcosis (PE), and unicystic echinococcosis (UE), caused by E. granulosus, E. multilocularis, E. vogeli, and E. oligarthra, respectively. All of the species share the same common definitive hosts, which are the canids, except E. oligarthra, which has members of the family Felidae as the definitive host (43). Definitive hosts harbor adult worms in the small intestine and release the embryonated eggs of the parasite in the environment with feces. Echinococcus granulosus and E. multilocularis enjoy a wide range of intermediate hosts, including bovines, which harbor the larval stages of the parasite in their visceral organs after ingestion of the embryonated eggs (44, 45). Humans and monkeys serve as aberrant hosts for all species, and diseases may progress from asymptomatic to severe clinical diseases, which can eventually cause death (27, 46). The disease pattern of echinococcosis is usually asymptomatic in livestock, and the diagnosis is generally made on necropsy findings in the abattoir; however, it has serious implications regarding the condemnation of the carcasses. In human CE, clinical signs include asthenia, weight loss, epigastric pain, hepatomegaly, and cholestatic jaundice (47). It may become a fatal disease when the cysts rupture and their fluid contents and protoscoleces are drained into the peritoneal cavity, leading to anaphylactic shock (48).

Sequencing of mitochondrial cytochrome-c oxidase and NADH-dehydrogenase genes has revealed at least 10 genotypes (G1-G10) of CE (49). Echinococcus granulosus sensu lato species complex is a major veterinary and medical concern causing cystic echinococcosis (CE) in the target species across the globe. Genotyping results have indicated that E. granulosus sensu stricto (G1 common sheep strain, G2 Tasmania sheep strain, and G3 buffalo strain), E. equinus (G4 horse strain), E. ortleppi (G5 cattle strain), and E. canadensis (G6 camel strain, G7 pig strain, G8 cervid strain, G9 human strain, and G10 Fennoscandian cervid strain) are the members of this species complex (50–53). Most of the cysts are formed in the liver (70%) and the lungs (20%), while up to 10% are found in other body tissues like the brain, kidneys, marrow cavities of the bones, and ocular orbits. The chances of the formation of cysts in the central nervous system are only 1–2% of the total E. granulosus infections (54, 55). Apart from economic concerns, hydatidosis is a major public health issue as the hydatid cysts grow as unilocular fluid-filled bladders in the internal organs like the lungs and liver of humans (56).

There are a number of diagnostic techniques for echinococcosis, including ultrasonography, serological tests, e.g., enzyme-linked immunosorbent assay, immunoelectrophoresis, immunoblotting, indirect fluorescence antibody test (IFAT), and latex agglutination test (LAT), (57) and molecular methods, e.g., loop-mediated isothermal amplification (LAMP)-based techniques, and polymerase chain reaction (PCR). Each of these has its own advantages and limitations (58, 59).

For the diagnosis of Echinococcus infection, post-mortem analysis of the small intestine and arecoline purgation are reliable tools. Intestinal scraping, fecal sedimentation, and fecal centrifugal flotation methods have high sensitivity and are good indicators of worm burden in the host intestine. The morphology of the eggs of E. granulosus, E. multilocularis, and Taenia species resembles each other, suggesting that methods are not very sensitive and specific (60). The coproantigenic ELISA has also been another tool, as it can detect the E. granulosus antigen both in patent and prepatent stages. The sensitivity of this ELISA is higher for animals with a high infection burden. Another diagnostic tool to access the infection is PCR, which has high specificity and sensitivity (61). Cerebral hydatidosis is a rare form of echinococcosis and accounts for only 2% of total cases. The incidence of this form is higher in children because of frequent contact with pet dogs. However, adults can also get the infection. It is important to distinguish neurohydatidosis from other intracranial cysts when making a diagnosis. In this peculiar form, serological testing is usually not useful as far as diagnostic tools are concerned. The only reliable diagnostic technique is MRI to assess the size of the hydatid cyst and devise a plan to excise it (62) surgically.

Various techniques have been developed over the past 30 years to identify Echinococcus variants. However, several molecular techniques have been used in the past, such as PCR-RAPD (random amplification of polymorphic DNA), PCR-RFLP (restriction fragment length polymorphism), a Southern Blot approach, DNA fingerprinting, and dideoxy fingerprinting. PCR is the preferred method for parasite identification, molecular epidemiology research, and confirmation purposes (63).

Nested PCR and multiplex PCR are frequently used for the differential detection of different Echinococcus species. PCRs that are followed by sequencing help detect variations within species and genotypes (64). While sequencing is a time-consuming and skill-intensive method, it is also the most accurate method for identifying the species of Echinococcus and finding genetic variation.

Recently, approaches like loop-mediated isothermal amplification (LAMP) that are low-cost and simple to use have been created and tested (65). Due to the fact that DNA may be amplified using a straightforward water bath without the use of complicated instruments, LAMP is an ideal technology to utilize in low-resource settings where alveolar and cystic echinococcosis are common. However, because of its high sensitivity, this system can be tricked into giving false positives.

Contemporary methods using single-locus or multilocus microsatellite analysis have been developed to explore the genetic diversity, the population structure of parasites, and the geographic relatedness of Echinococcus species (66, 67).

For the identification of parasitic diseases, real-time PCR (qPCR) has a number of advantages over traditional PCR, including improved sensitivity and specificity, a shorter reaction time, and quantitative estimation of the amount of DNA in the sample (68, 69).

Researchers have long been interested in finding ways to break the life cycle of the Echinococcus species in order to decrease the spread of illness in both animals and people. Using anthelmintics and creating awareness among the masses about slaughter hygiene is one of the most important strategies to reduce the prevalence of echinococcosis. Limited treatment regimens are available for curing patients suffering from echinococcosis, and the focus is on giving benzimidazoles that have only parastiostatic activity. Oral administration over a long time has also led to the development of resistance to varying degrees in the metacestode stages of Echinococcus (47). Amphotericin-B, nitazoxanide, and isoflavones have also been reported to possess anti-Echinococcus activity, but the efficacy of these chemotherapeutic agents is not much higher (70). Imatinib, an anticancer agent, has been found highly effective in killing protoscoleces and metacestodes in vitro at a concentration of 25 μM. This drug was evaluated after keenly investigating the signaling pathways of Echinococcus (71). Pharmacotherapy poses different threats because of drug residues in milk and meat, which can lead to health issues for the end consumer. In addition, low dosage or frequent administration of anthelmintics leads to parasite drug resistance (36). Despite these limitations and drawbacks, vaccination remains a suitable and long-term solution against Echinococcus infection. Vaccine development is a crucial phase, and attention must be paid to developing multifunctional vaccines considering the circulating serotypes and genotypes of E. granulosus (72). Identifying the strain is key to implementing control strategies to curtail disease transmission. Echinococcus spp. continue to be a global problem despite our extensive knowledge of the organism, its control techniques, vaccine research, and clinical case management (73).

Eradication of this notorious infection has been a challenge for both developed and developing countries (74). However, the community's involvement in controlling the incidence of the disease is of high value. Zhang et al. proposed a number of strategies to decrease the number of future cases. Promotion and awareness seminars about the epidemiology of the disease, inspection of animal offal at the slaughterhouses, proper disposal, and condemnation of carcasses with cysts, monthly deworming of dogs with praziquantel, and ultrasonography of suspected patients and their treatment are important to highlight here (75). Killing stray dogs to prevent the shedding of embryonated eggs in the environment is another prevention strategy that was adopted in the past. A complete ban on home-slaughtering practices and rodent control programs must be institutionalized, as E. multilocularis targets rodents as its intermediate host (76). One alternative is to hire a Hydatid Disease Control Officer (HDCO), whose responsibilities would include registering dogs, dosing them monthly with dewormers, and educating the public about echinococcosis control programs (75).

The field of molecular epidemiology (ME) has altered our understanding of the spread of infectious diseases. This area of epidemiology provides the tools that can characterize the etiological agents of infectious illnesses. Furthermore, molecular epidemiology is useful for surveillance tasks, particularly when investigating emerging diseases. Molecular epidemiology is becoming increasingly important in the context of disease emergence and conservation for both human and domestic animal health, as well as for infectious agents in wildlife (111).

The parasite cestode Echinococcus is the cause of echinococcosis, which has two types—cystic and alveolar—and affects people worldwide. When investigating the epidemiology of infectious diseases, it is crucial to comprehend their etiology. It is important to understand how different host species are involved in the transmission of echinococcosis because this has been a problem in many endemic regions. This is even more important when various Echinococcus species, “strains,” or genotypes are present. Molecular epidemiology has been extremely helpful in understanding the wide genetic and phenotypic variability exhibited between the species present within the Echinococcus genus (112, 113).

Formally identifying a species requires effective communication, which is essential when the targeted species have public health significance and necessitate coordinated control measures. Regarding Echinococcus, there have long been taxonomic and nomenclatural ambiguities, especially at the species level. This occurred due to the lack of significant morphological features and the frequent overriding of the importance of host occurrence by taxonomic considerations (111). Echinococcus transmission ecology in areas with a variety of affected host species has been a topic of study for some time. Fortunately, there is widespread agreement that ten species of Echinococcus should be recognized based on morphological, genetic, and ecological factors. Molecular approaches usually confirm original taxonomic assumptions and, more importantly, the validity of certain morphological traits. They have also been instrumental in resolving taxonomic issues.

The taxonomy of Echinococcus has mostly been elucidated due to molecular science. As a result, a useful and educational lexicon for use in epidemiological studies has been created. We must now have the resources available to carry out epidemiological studies. These are useful in clarifying life cycles and transmission patterns in endemic areas, as previously discussed. This will be especially important in regions with several transmission cycles and the potential for mixed infections. Molecular techniques will increasingly inform and direct public health initiatives regarding clinical treatment. Those diagnosed with echinococcosis whose Echinococcus species of infection is unclear or who may have infections from many Echinococcus species are most likely to benefit. The discovery of genotypic variation within a species and its relationship with virulence foreshadows the creation of markers for clinical use.

Conceptualization: MA and AA. Data curation and writing—original draft preparation: MA. Reviewing and editing: AA. Both authors contributed to the article and approved the submitted version.