Ecological studies on the intermediate host snails and the relevance to schistosomiasis control

A detailed knoledge of distribution patterns schistosome intermediate hsts and their populations dynamics and factors affecting these patterns will provide useful information about the possibilities and desirability of conducting snail control measures in various transmission situations. On the basis of various case studies the association between the occurence of human water contacts and the presence of schistosome intermediate hosts or infections in the intermediate hosts is illustrated. Other parameters affecting snail distribution patterns and density fluctuations are discussed. It is concluded that ecological studies on the intermediate host are extremely relevant, either to optimally apply existing control measures or to develop alternative measures of snail control, such as ecological or biological control.

Métodos de diagnóstico malacológico

Specific identification of the snail vectors: (a) shell features; (b) animal features (genital organs); (c) biochemical techniques (electrophoresis). The snail infection rates: (a) exposure to light and cercarial identification; (b) snail crushing and identification or the larval forms in the tissues.

Human B19 parvovirus infetion: an example of multiple pathogenic effects determined by differences in host susceptibility

B19 infection offers some general lessons about human viruses and their possible effects on the human host, as follows: (1) Ubiquitous apparently benign viruses may have severe effects on a compromissed host. The virus may be invariable but the host can have diverse susceptibilities. (2) B19 and some other human viruses (through for none is the evidence so clear as for B19) have narrowly targetted effects. The host cell of B19 is a specialised progenitor of mature red cells: impairment of the function of this cell by B19 may cause profound anaemia. (3) The 'normal'host response to B19 may also cause disease, though this is slef limiting. (4) The effects of malfunction of the virus'target cell are exacerbated when the immune response is impaired by congenital or acquired immunodeficiency, immunosupressive therapy or, in the case of the fetus, developmental immaturity that allows the virus to persist.

Biomphalaria occidentalis paraense, 1981 in the state of Minas Gerais, Brazil

A population of Biomphalaria occidentalis was found for the first time in the State of Minas Gerais. It was probavly introduced into the Várzea das Flores dam, in the municipality of Contagem, the area o0f study, during fish stocking in 1985. There is possibility of "competitive exclusion"between that species and B. glabrata, previously the only Biomphalaria found in the region. The present geographical distribution of B. occidentalis in Brazil is listed.

On the safe of pesticides in controlling the terrestrial mollusc pests

The preferred food items of the slugs Laevicaulis alte and the snails Achatina fulica were used to prepare 'poison baits'by injecting the pesticides 'Rogor'and 'Nuvan'to kill these mollusc pests. The 'poison baits'prepared with Thrichosanthes dioica and Lycopersicum esculentum were accepted by 100% individuals of both the species irrespective of the pesticides used. In all cases the slug and the snail individuals died within a considerable length of time following consuption of the bait. The importance of using 'poison bait'lies not only with the sure success in killing the pests but also with the 'safe use'of toxic materials in order to avoid environmental hazards.

Introduction and spreading of Biomphalaria straminea (Dunker, 1848) (Mollusca: Pulmonata: Planorbidae) in Guadeloupe, French West Indies

The finding in 1985 of a well-established population of Biomphalaria straminea in a pond in Grande Terre of Guadeloupe constitutes a new species record for the freshwater molluscan fauna of that island. The following years a rapid extension of the species was documented on Grande Terre and Marie Galante. However, it was never found in the neighboring island of Basse Terre. The invasion of the whole hydrographic system of this island by Melanoides tuberculata during the last decade and the current presence of well-established and dense populations of this snail may explain the failure of the colonization by B. straminea.

Inflammatory cutaneous reaction induced by the lectin of Dioclea grandiflora (Mart. )

The lectin from Dioclea grandiflora (Mart.) that selectively binds glucose and mannose, when subcutaneously injected in mouse induces an inflammatory cutaneous reaction whose histological analysis reveals an hemorrhagic ulceration with exudative reaction accompanied by an influx of polymorphonuclear leukocytes and giant cells. The presence of lymphocytes and plasma cells in the lesion was insignificant. In order to characterize the in vivo action of inflammatory factors generated by this lesion, distinct lines of mice were used: high and low antibody responder mice; the genetically selected mice to the acute phase of inflammatory reaction; lines of mice deficient in C5, a protein of the complement system. It is shown that the lectin of D. grandiflora acts as an inflammatory agent probably promoting exocytosis and release of mediators.

Ovipositional substrates used by Calyptrate Diptera in Tijuca forest, Rio de Janeiro

Twenty seven species of calyptrate muscoids were reared from a forested area of Rio de Janeiro (Tijuca Forest). Substrates for obtaining flies were beef liver, fish, mouse, frog, shrimp, snail carcasses, human faeces, banana and papaya fruits. The most frequent species found were: Fannia sp. (subgroup pusio) (49.9% on shrimp). Hemilucilia flavifacies (95.0% on liver). Phaenicia eximia (49.4% on mouse), Synthesiomyia nudiseta ( 100.0% on fish), Ophyra aenescens (100.0% on shrimp), Oxyvinia excisa (100.0% on faeces), Euboettecheria collusor (52.4% on faeces) and Pattonella intermutans (61.0% on frog).

Degree of host-parasite compatibility between Schistosoma mansoni and their intermediate molluscan hosts in Brazil

The compatibility of Biomphalaria tenagophila, B. straminea and B. glabrata from Minas Gerais with different strains of Schistosoma mansoni was evaluated using the method of Frandsen (1979b) in standardized experiments. One hundred and fifty of each species of snail were individually exposed in the laboratory to 50 miracidia of S. mansoni lines LE, SJ and AL. The cercariae from the infected snails were counted and used to calculate TCP/100 indices, which were compared with those of Frandsen (1979b). For B. tenagophila the TCP/100 indices varied from 37,996 to 74,266 (class II and III). The snail was poorly compatible with LE (class II) and compatible with SJ and AL (class III). For B. straminea the indices varied from 9,484 to 20,508. The snail was not very compatible with SJ (class I) and poorly compatible with LE and AL (class II). For B. glabrata the indices varied from 588,828 to 1,039,065. The snails was extremely compatible (class VI) with the three lines of S. mansoni. These results confirm the epidemiological importance of B. glabrata in Brazil followed by B. tenagophila and B. straminea.

Control of schistosomiasis transmission

Despite the success of control programmes, schistosomiasis is still a serious public health problem in the world. More than 70 countries where 200 million individuals are evaluated to be infected of a total 600 million at risk. Though there have been important local success in the control of transmission, globally the infection has increased. Economic constrains in developing countries, environmental changes associated with migration and water resources development have been blocking the progress. The main objective of schistosomiasis control is to achieve reduction of disease due to schistosomiasis. We discussed the control measures like: health education, diagnosis and chemotherapy, safe water supplies, sanitation and snail control. We emphasized the need to give priority to school-age children and the importance of integrating the measures of control into locally available systems of health care. The control of schistosomiasis is directly related to the capacity of the preventive health services of an endemic country. The strategy of control requires long-term commitment from the international to the local level.

Schistosomiasis control in China

After three decades' efforts, schistosomiasis japonica were controlled in one-third (4/12) of endemic provinces and 68.2 (259/380) of endemic counties throughout the country. The remaining 121 endemic counties are located primarily in the lake and mountainous regions. The epidemiological and ecological features of the lake and mountainous areas are different from the other endemic areas. The major schistosomiasis control efforts in China can be characterized as follows: (1) Application of centralized leadership and management, since schistosomiasis control is a task not only of the Ministry of Public Health, but also of all local governments in the endemic areas; (2) Integration of actions taken by various departments or bureaus, such as agriculture, water conservation and public health; (3) Promotion of mass participation; (4) Organization of strong professional teams; (5) Raising sufficient funds. Strategies on schistosomiasis control applied in different areas are divided into three levels: (1) In the areas where the schistosomiasis has been successfully controlled, surveillance must be maintained and immediate action should be taken where new infections occur and/or vector snails are found, so that control can be reestablished quickly; (2) In the areas where schistosomiasis has been partially controlled, any residents and/or live-stock infected should be examined and treated promptly with due care, and environment modifying and/or mollusciding must be used to eliminate the remaining snails; (3) In the areas where transmission has not been controlled, the main strategy is to control morbidity. Mass or selective chemotherapy with praziquental should be applied to both infected persosns and the live-stock, and environment modification for the snail-ridden areas should be taken but should be coordinated with agriculture where possible. Advance cases must be treated; and epidemics of Katayama fever prevented; water supply and sanitation shoud be improved and health education emphasized. Annual mass or selective chemotherapy with praziquental both reduces the prevalence rate and decreases the intensity of the infection for inhabitants and live-stock. As a consequence of the therapy a low prevalence rate can be obtained in a short time. The length of such arrangement period can be decided in accordance with the prevalence of the infection before the drug program is begun. Therefore,a maintenance phase is urgently needed. As China's ecomony expands and people's living standard rises, schistosomiasis will be controlled more effectively and successfully.

Schistosomiasis control in a primary health care system

The successful implementation of a Primary Health Care System (PHC) in any country depends primarily on the ability to adapt its concepts and principles to the country's culture and development stage. Thus, the PHC system should reflect a balanced interaction between available resources, such as health manpower capabilities, and the nature and magnitude of the health problems. In addition, PHC should be viewed as the inlet to a multi-level pyramidal health system which caters to both community and individual needs in a balanced way. The adage that Ministries of Health should "work with and for the people" in health development, is especially true in the area of PHC, and hence, the health policy should aim to integrate health services in community development and involve people in its planning, implementation and evaluation.

Schistosomiasis in a low prevalence area: incomplete urbanization increasing risk of infection in Paracambi, RJ, Brazil

The risk of schistosomiais infection and heavy infection in the locality of Sabugo was evaluated in relation to housing in areas with different urbanization development and to residential supply with snail-infested water. Critical sanitary conditions were found in areas of incomplete urbanization, where healthy water supply sources were scarce, and draining of sewage, without previous treatment, was made directly to the water-bodies used for domestic and leisure activities, despite being Biomphalaria tenagophila snail breeding-places. Stool examinations (Kato-Katz and Lutz methods) showed prevalence of 2.9%, mean intensity of 79 eggs per gram of stool and 47% of positive cases presenting intense infection. The use of snail-contaminated water for domestic purposes was considered a risk factor for infection. It is concluded that incomplete urbanization would facilitate transmission, probably enhancing the intensity of infection and that a low prevalence could hide a highly focal transmission. The relevance of these facts upon the efficiency of epidemiologic study methods and disease control planning are then discussed.

Eurytrema coelomaticum: influence of the infection on the reproduction and nucleic acids contents in the albumen gland and ovotestis of Bradybaena similaris

The number of eggs laid per snail in Bradybaena similaris and the nucleic acids (DNA and RNA) in the albumen gland and ovotestis were quantified in snails infected with sporocysts of the digenetic trematode Eurytrema coelomaticum. The total number of eggs laid per mollusc was reduced by 96.32% at the end of the larval development. The DNA concentration increased by 700% and the RNA concentration was reduced by 8,38% by the time when the daughter sporocysts of E. coelomaticum were released from B. similaris. The relation between these values and the inhibition of the reproduction observed in infected molluscs is discussed.

Thirty new loci for age at menarche identified by a meta-analysis of genome-wide association studies.

To identify loci for age at menarche, we performed a meta-analysis of 32 genome-wide association studies in 87,802 women of European descent, with replication in up to 14,731 women. In addition to the known loci at LIN28B (P = 5.4 × 10⁻⁶⁰) and 9q31.2 (P = 2.2 × 10⁻³³), we identified 30 new menarche loci (all P < 5 × 10⁻⁸) and found suggestive evidence for a further 10 loci (P < 1.9 × 10⁻⁶). The new loci included four previously associated with body mass index (in or near FTO, SEC16B, TRA2B and TMEM18), three in or near other genes implicated in energy homeostasis (BSX, CRTC1 and MCHR2) and three in or near genes implicated in hormonal regulation (INHBA, PCSK2 and RXRG). Ingenuity and gene-set enrichment pathway analyses identified coenzyme A and fatty acid biosynthesis as biological processes related to menarche timing.