Hydatidosis in Sardinia: review and recommendations

Does the trained immune system play an important role in the extreme longevity that is seen in the Sardinian blue zone?

Villages in the island of Sardinia in the Mediterranean that display exceptional longevity are clustered within a defined mountainous region. Because of their unique location we hypothesize that these villages had a unique infectious disease exposure relevant to the observed successful longevity. These highland villages had a significant exposure to malaria in the first half of the 20th century after which malaria was eliminated due to vector control mechanisms. In addition, there is likely a high incidence of Helicobacter pylori infections among shepherds in Sardinia, the primary occupation of many living in the LBZ, as well as helminth infections among children. This suggests that individuals living in the LBZ had a unique infectious disease exposure. Specifically, we hypothesize that the continued high exposure of residents in the LBZ to these infectious agents prior to the 1950s lead to the generation of a uniquely trained (or imprinted) immune system. Once some of these diseases were eliminated in the latter half of the century, individuals within the LBZ were equipped with a trained immune system that was uniquely capable of not only responding effectively to common infections but also responding in a manner that maximized maintaining tissue health. In addition, there are lifestyle factors that also favor such a trained immune system. This hypothesis may help explain the slow progression of chronic immune mediated diseases as well as other chronic non-transmissible age-related diseases seen in the Sardinian LBZ and serve as a template for future studies that support or refute this hypothesis.

Echinococcosis/hydatidosis: a severe threat in Mediterranean countries

Echinococcosis/hydatidosis is one of the most important parasitic zoonotic diseases in the world. Both cystic hydatidosis (CE) caused by Echinococcus granulosus and alveolar echinococcosis (AE) caused by E. multilocularis have been reported in several countries of the Mediterranean region (MR). E. granulosus has always been present in the MR and is the most common species. This parasite depends on the dog-sheep cycle and is actively transmitted in all pastoral regions where sheep, cattle and camelids predominate. E. multilocularis occurs only sporadically in limited areas of France, Serbia and Montenegro, Turkey, Tunisia and Morocco. However recent evidence indicates that it is spreading into other regions of the Mediterranean. Due to the lack of well-documented data, and to the fact that CE is not a notifiable disease in the majority of M countries, the precise incidence and prevalence of CE in humans and animals are not known. Published data suggests that prevalence is rather high in North Africa, Turkey, Greece, and in several regions of Italy and Spain. CE is an increasing public health and socio-economic concern due to the considerable morbidity rates that give rise to high economic losses both in the public health sector and in the livestock industry. Hospitalisation for human CE lasts from 2 weeks to more than 1 month in case of surgery. A number of factors contribute to the increase of prevalence and to the spreading of CE in the MR. These include the diversity of livestock production systems (predominantly extensive, traditional animal husbandry), small, ill-equipped and unsupervised slaughter-houses, illegal and family slaughtering, low public awareness of hydatid diseases, and the high population of stray dogs. Cyprus is the only country where an eradication programme has been successfully implemented. There have been, however, important developments in the last decade in CE epidemiology, in the diagnosis of canine infection, in strain characterisation and in immune strategies against CE in animals. This scientific progress, together with effective health education programmes, will likely improve control programmes and reduce the time required to achieve significant decreases in prevalence or eradication.

Control of cystic echinococcosis/hydatidosis: 1863-2002

Echinococcosis/hydatidosis, caused by Echinococcus granulosus, is a chronic and debilitating zoonotic larval cestode infection in humans, which is principally transmitted between dogs and domestic livestock, particularly sheep. Human hydatid disease occurs in almost all pastoral communities and rangeland areas of the underdeveloped and developed world. Control programmes against hydatidosis have been implemented in several endemic countries, states, provinces, districts or regions to reduce or eliminate cystic echinococcosis (CE) as a public health problem. This review assesses the impact of 13 of the hydatid control programmes implemented, since the first was introduced in Iceland in 1863. Five island-based control programmes (Iceland, New Zealand, Tasmania, Falklands and Cyprus) resulted, over various intervention periods (from <15 to >50 years), in successful control of transmission as evidenced by major reduction in incidence rates of human CE, and prevalence levels in sheep and dogs. By 2002, two countries, Iceland and New Zealand, and one island-state, Tasmania, had already declared that hydatid disease had been eliminated from their territories. Other hydatid programmes implemented in South America (Argentina, Chile, Uruguay), in Europe (mid-Wales, Sardinia) and in East Africa (northwest Kenya), showed varying degrees of success, but some were considered as having failed. Reasons for the eventual success of certain hydatid control programmes and the problems encountered in others are analysed and discussed, and recommendations for likely optimal approaches considered. The application of new control tools, including use of a hydatid vaccine, are also considered.

Causality or coincidence: may the slow disappearance of helminths be responsible for the imbalances in immune control mechanisms?

Intestinal infection continues to be a problem worldwide and helminths, which currently infect billions of individuals, are primary culprits. The major burden of disease falls on the populations of developing countries, given that over the last four to five decades helminth infections are disappearing in industrialized societies. In developing countries, a major source of immunomodulatory signals in post-natal life are parasites, particularly helminths, which, unlike most bacteria and viruses, selectively stimulate Th2 function. Helminths and their eggs are probably the most potent stimulators of mucosal Th2 responses. Responses elicited by worms can modulate immune reactions to other parasites, bacterial, viral infections and several unrelated diseases. Bacterial and protozoal infections may also protect against atopy and asthma, through the induction of the Th1 regulatory responses. Today, people in developed countries often live in ultra-hygienic environments, avoiding exposure to viruses, bacteria, ectoparasites and endoparasites, particularly helminths. Perhaps failure to acquire worms and experience mucosal Th2 conditioning predisposes to unrelated diseases. In contrast to this hypothesis it has also been suggested that Th2 responses can make the host more susceptible to other important diseases and to contribute to the spread of them.

Dot immunobinding assay as a new diagnostic test for human hydatid disease

Bovine and human hydatid antigens collected from hepatic cysts and characterized by SDS-PAGE immunoblotting show similar patterns. The bovine hydatid antigen has been used to develop a simple and fast in vitro diagnostic assay for human hydatidosis. This method, named HA-DIA (hydatid antigen dot immunobinding assay), consists of incubation of a serum sample with a textile colloidal dye (pink) and a nitrocellulose stick to which the hydatid antigen has been bound. The presence of parasite-specific antibodies leads to dyeing of the stick reactive area, and a coloured spot appears. HA-DIA sensitivity and specificity have been studied in comparison with RAST-IgE and ELISA-IgG by testing 17 sera of patients with hydatid disease and 36 control sera from patients affected with other parasitic and non-parasitic diseases. HA-DIA showed positive results in all the patients' sera and in none of the control sera. Correlation with ELISA--IgG and RAST-IgE was significant. HA-DIA has been demonstrated to be of good predictive value, allowing a speedy diagnosis of hydatid disease. In view of its simplicity, not requiring any laboratory instruments, it is particularly suitable for large-scale field screening.

Cloning and characterisation of an immunodominant major surface antigen of Echinococcus multilocularis

A lambda gt11 cDNA expression library from mRNA of Echinococcus multilocularis protoscolices has been constructed in Escherichia coli Y1090. Immunoscreening with pooled sera obtained from patients suffering from E. multilocularis disease revealed 5 reactive clones. By partial DNA sequence comparison all clones proved to encode the same gene. The complete cDNA sequence of the clone pEM10 with the largest insert of 2.2 kb was determined and an open reading frame of 1.7 kb could be described. The derived amino acid sequence shares 42.6% identity with human microvillar cytovillin found in the membranes of placenta and carcinoma tissues. The coding region of the cDNA of pEM10 was amplified by polymerase chain reaction (PCR) and cloned in frame into expression vector pGEX-3X. Immunoblot analysis revealed the expression of a recombinant antigen of 65 kDa and a protein with the same molecular weight was also found in the lysate of E. multilocularis protoscolices. In contrast, the protein was absent from hydatid fluid or larvae of Echinococcus granulosus. By means of immunofluorescence studies this immunodominant antigen could be located in the germinal layer of brood capsules and in the tegument of E. multilocularis protoscolices. The fusion protein was purified and used for diagnostic purposes in immunoblot. The diagnostic value of this antigen is discussed.

Epidemiology of hydatid disease in Sardinia: a study of fertility of cysts in sheep

Hydatidosis, caused by Echinococcus granulosus, is a cyclozoonotic disease of economic significance in Sardinia. The life-cycle involves stray and sheep dogs as definitive hosts and sheep, pigs, goats and cattle as intermediate hosts. The most important intermediate host is sheep, due to home slaughtering with ready access of the viscera to dogs. This survey was undertaken in 1987 to ascertain the epidemiological significance of sheep in maintaining the life-cycle. A total of 700 (91.3%) of 767 sheep harboured hydatid cysts. The frequency distribution of the number of hydatid cysts was over-dispersed. Of 497 infected sheep, 7.6% had fertile cysts, 75.7% sterile cysts and 16.7% fertile + sterile cysts.

Epidemiology of hydatidosis/echinococcosis in Ouarzazate, the pre-Saharian region of Morocco

In the Ouarzazate province of Southern Morocco, 1085 cattle and 358 sheep were examined for hydatid cysts. The prevalence was 44.6% (range 8.3-83.4%) in cattle and 5.3% (range 1.3-28.6%) in sheep. The prevalence increased with the age of the animals. The lung was the predominant site of infection, followed by the liver. In cattle, 14.2% of hydatid cysts were fertile and 16.4% had degenerative changes. The mean loss per head of cattle slaughtered was about 1 kg of liver and 900 g of lungs in the urban abattoirs. In monetary terms at the current price of 1980, this meant a loss of U.S. +4.5 at urban and +1.6 at rural abattoirs. The mean prevalence of infection in 61 stray dogs was 50.8%, with a mean worm burden of 413. The urban dogs had a lower infection rate (42.9%) than the rural dogs (61.5%). There were 130 dogs per 1000 inhabitants. The human population was ignorant of the life-cycle of Echinococcus granulosus and was not aware of risk of infection through dogs. Dogs become infected at abattoirs, at home slaughter and in the field by consuming dead carcasses. The maintenance and transmission of E. granulosus in animals and man is related to social, religious and cultural factors.