Over the past decades, various free-living animals (hosts) and their parasites have invaded recipient areas in which they had not previously occurred, thus gaining the status of aliens or exotics. In general this happened to a low extent for hundreds of years. With variable frequency, invasions have been followed by the dispersal and establishment of non-indigenous species, whether host or parasite. In the literature thus far, colonizations by both hosts and parasites have not been treated and reviewed together, although both are usually interwoven in various ways. As to those factors permitting invasive success and colonization strength, various hypotheses have been put forward depending on the scientific background of respective authors and on the conspicuousness of certain invasions. Researchers who have tried to analyse characteristic developmental patterns, the speed of dispersal or the degree of genetic divergence in populations of alien species have come to different conclusions. Among parasitologists, the applied aspects of parasite invasions, such as the negative effects on economically important hosts, have long been at the centre of interest. In this contribution, invasions by hosts as well as parasites are considered comparatively, revealing many similarities and a few differences. Two helminths, the liver fluke, Fasciola hepatica, of cattle and sheep and the swimbladder nematode, Anguillicola crassus, of eels are shown to be useful as model parasites for the study of animal invasions and environmental global change. Introductions of F. hepatica have been associated with imports of cattle or other grazing animals. In various target areas, susceptible lymnaeid snails serving as intermediate hosts were either naturally present and/or were introduced from the donor continent of the parasite (Europe) and/or from other regions which were not within the original range of the parasite, partly reflecting progressive stages of a global biota change. In several introduced areas, F. hepatica co-occurs with native or exotic populations of the congeneric F. gigantica, with thus far unknown implications. Over the fluke's extended range, in addition to domestic stock animals, wild native or naturalized mammals can also serve as final hosts. Indigenous and displaced populations of F. hepatica, however, have not yet been studied comparatively from an evolutionary perspective. A. crassus, from the Far East, has invaded three continents, without the previous naturalization of its natural host Anguilla japonica, by switching to the respective indigenous eel species. Local entomostrac crustaceans serve as susceptible intermediate hosts. The novel final hosts turned out to be naive in respect to the introduced nematode with far reaching consequences for the parasite's morphology (size), abundance and pathogenicity. Comparative infection experiments with Japanese and European eels yielded many differences in the hosts' immune defence, mirroring coevolution versus an abrupt host switch associated with the introduction of the helminth. In other associations of native hosts and invasive parasites, the elevated pathogenicity of the parasite seems to result from other deficiencies such as a lack of anti-parasitic behaviour of the naive host compared to the donor host which displays distinct behavioural patterns, keeping the abundance of the parasite low. From the small amount of available literature, it can be concluded that the adaptation of certain populations of the novel host to the alien parasite takes several decades to a century or more. Summarizing all we know about hosts and parasites as aliens, tentative patterns and principles can be figured out, but individual case studies teach us that generalizations should be avoided.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022149X06000199

Hosts and parasites as aliens.

BACKGROUND: The role of iatrogenic transmission within the HIV/AIDS pandemic remains contentious. Estimates of the risk of HIV transmission from injections and blood transfusions are required to inform appropriate prevention policy. OBJECTIVES: Systematic review and meta-analysis of the literature on HIV-1 infectivity for parenteral transmission and blood transfusion. REVIEW METHODS: All identified studies with relevant transmission probability estimates up to May 2005 were included. STATISTICAL METHODS: When appropriate, summary estimates for accidental percutaneous and blood product exposures were derived. RESULTS: Infectivity estimates following a needlestick exposure ranged from 0.00 to 2.38% [weighted mean, 0.23%; 95% confidence interval (CI), 0.00-0.46%; n = 21]. Three estimates of infectivity per intravenous drug injection ranged from 0.63 to 2.4% (median, 0.8%); a summary estimate could not be calculated. The quality of the only estimate of infectivity per contaminated medical injection (1.9-6.9%) was assessed. Instead we propose a range of 0.24-0.65%. Infectivity estimates for confirmed contaminated blood transfusions range from 88.3 to 100.0% (weighted mean, 92.5%; 95% CI, 89.0-96.1%; n = 6). CONCLUSIONS: Infectivity estimates for infected blood transfusions are larger than for other modes of HIV transmission. Few studies on transmission risk per contaminated injection were found. However, transmission risk per needlestick injury, where needles are more likely to be rinsed or disinfected between recipients (especially for medical injections), may be representative of non-intravenous medical injections and lower than the risk from intravenous injections, which are likely to be deeper and to involve more fluids. Further work is needed to better estimate transmission probability related to contaminated injections and its likely contribution to overall HIV transmission.

Risk of hiv-1 transmission for parenteral exposure and blood transfusion: a systematic review and meta-analysis

Apple snails (Ampullariidae) are among the largest and most ecologically important freshwater snails. The introduction of multiple species has reinvigorated the field and spurred a burgeoning body of research since the early 1990s, particularly regarding two species introduced to Asian wetlands and elsewhere, where they have become serious agricultural pests. This review places these recent advances in the context of previous work, across diverse fields ranging from phylogenetics and biogeography through ecology and developmental biology, and the more applied areas of environmental health and human disease. The review does not deal with the role of ampullariids as pests, nor their control and management, as this has been substantially reviewed elsewhere. Despite this large and diverse body of research, significant gaps in knowledge of these important snails remain, particularly in a comparative framework. The great majority of the work to date concerns a single species, Pomacea canaliculata, which we see as having the potential to become a model organism in a wide range of fields. However, additional comparative data are essential for understanding this diverse and potentially informative group. With the rapid advances in genomic technologies, many questions, seemingly intractable two decades ago, can be addressed, and ampullariids will provide valuable insights to our understanding across diverse fields in integrative biology.

/pdf/insights-from-an-integrated-view-of-the-biology-of-apple-3tajznzpe0.pdf

Insights from an Integrated View of the Biology of Apple Snails (Caenogastropoda: Ampullariidae)

At least 14 species of apple snail (Ampullariidae) have been released to water bodies outside their native ranges; however, less than half of these species have become widespread or caused appreciable impacts. We review evidence for the impact of apple snails on natural and managed wetlands focusing on those studies that have elucidated impact mechanisms. Significant changes in wetland ecosystems have been noted in regions where the snails are established: Two species in particular (Pomacea canaliculata and Pomacea maculata) have become major pests of aquatic crops, including rice, and caused enormous increases in molluscicide use. Invasive apple snails have also altered macrophyte community structure in natural and managed wetlands through selective herbivory and certain apple snail species can potentially shift the balance of freshwater ecosystems from clear water (macrophyte dominated) to turbid (plankton dominated) states by depleting densities of native aquatic plants. Furthermore, the introductions of some apple snail species have altered benthic community structure either directly, through predation, or indirectly, through exploitation competition or as a result of management actions. To date much of the evidence for these impacts has been based on correlations, with few manipulative field or mesocosm experiments. Greater attention to impact monitoring is required, and, for Asia in particular, a landscape approach to impact management that includes both natural and managed-rice wetlands is recommended.

Impact of invasive apple snails on the functioning and services of natural and managed wetlands

Macroinvertebrate communities as bioindicators of water quality in conventional and organic irrigated rice fields in Guanacaste, Costa Rica

Several species of snails, including Pomacea haustrum, Marisa cornuarietis and Helisoma duryi, have been identified as probable competitors and/or predators of planorbid intermediate hosts of Schistosoma. During the last few years, studies carried out in the Caribbean region have shown reductions and even disappearances of populations of Biomphalaria glabrata and B. straminea in breeding places where the snail Melanoides tuberculata was introduced. Observations made over a period of 10 years in two lakes close to Belo Horizonte, MG, showed that there were marked reductions in autochthonous populations of B. glabrata and B. straminea after the arrival of M. tuberculata, both Biomphalaria species disappearing completely after eight years.

http://www.scielo.br/pdf/mioc/v96s0/23x.pdf

Possible competitive displacement of planorbids by Melanoides tuberculata in Minas Gerais, Brazil

A malacological survey to detect foci of transmission of schistosomiasis and other parasitic diseases was undertaken into water-courses from 13 municipalities of microregion of Belo Horizonte, MG, Brazil. From 1990 to 1996, 22,066 snails were collected. From those, 378 (1.7%) were found infected by trematodes: Biomphalaria glabrata (7,920), infected by Schistosoma mansoni (1.9%), Echinostomatidae (1.2%), Strigeidae (0.6%), Cercaria minense (0.1%) and Derogenidae (-0.1%); B. straminea (4,093) infected by Strigeidae (0.6%), Echinostomatidae (0.2%), Clinostomatidae (-0.1%) and two unidentified cercariae; B. tenagophila (1,338), infected by Strigeidae (0.1%) and Physa marmorata (1,776) by Echinostomatidae (1.6%). The snails Biomphalaria peregrina, B. occidentalis, B. schrammi, Drepanotrema depressissimum, D. lucidum, D. cimex, Physa cubensis, Lymnaea columella, Melania tuberculata, Idiopyrgus souleyetianus, Pomacea sp, Anodontites sp and Ancylidae were found noninfected. Snails from 9 municipalities were infected by S. mansoni and from 11 by other trematodes.

/pdf/lymnic-snails-from-the-microregion-of-belo-horizonte-minas-45gu3smmq6.pdf

[Lymnic snails from the microregion of Belo Horizonte, Minas Gerais, Brazil with an emphasis on parasite disease vectors]

Published and unpublished observations on geographical distribution of Biomphalaria snails in the State of Minas Gerais, Brazil, were compiled. This work is aimed at knowing the present occurrence of Biomphalaria species in this region, and at contributing to the elaboration of the planorbid chart of Minas Gerais. In malacological surveys, performed by several researchers, the presence of seven species of this genus was recorded. Those planorbids were found in 12 mesoregions, in 283 (33.1%) municipalities out of 853 with the following distribution: B. glabrata (185 municipalities), B. straminea (125), B. tenagophila (58), B. peregrina (57), B. schrammi (26), B. intermedia (20) and B. occidentalis (2). B. glabrata and B. tenagophila are found naturally infected by Schistosoma mansoni in Minas Gerais. In 24 municipalities the three snail hosts of S. mansoni in Brazil, B. glabrata, B. tenagophila and B. straminea, are present.

/pdf/geographical-distribution-of-biomphalaria-snails-in-the-4lx7cj2vj0.pdf

Geographical distribution of Biomphalaria snails in the State of Minas Gerais, Brazil

Descreve-se a atual distribuicao dos planorbideos hospedeiros intermediarios do Schistosoma mansoni no Lago da Pampulha, Belo Horizonte, MG (Brasil) e a rapida dispersao de Biomphalaria tenagophila por todo o perimetro lacustre Relata-se o primeiro encontro de B tenagophila naturalmente infectada por S mansoni, naquela colecao hidrica Discute-se, a importância epidemiologica destas observacoes e a possibilidade da B tenagophila vir a substituir a primitiva populacao de B glabrata no Lago da Pampulha

/pdf/situacao-atual-da-esquistossomose-mansoni-no-lago-da-3ck4d8ez6m.pdf

Situação atual da esquistossomose mansoni no Lago da Pampulha, Belo Horizonte, MG, Brasil

/pdf/unusual-histological-findings-in-biomphalaria-glabrata-with-4fh3d4gqwc.pdf

Carlos Tito Guimarães

Papers

Possible competitive displacement of planorbids by Melanoides tuberculata in Minas Gerais, Brazil

[Lymnic snails from the microregion of Belo Horizonte, Minas Gerais, Brazil with an emphasis on parasite disease vectors]

Geographical distribution of Biomphalaria snails in the State of Minas Gerais, Brazil

Situação atual da esquistossomose mansoni no Lago da Pampulha, Belo Horizonte, MG, Brasil

Unusual histological findings in Biomphalaria glabrata with high degree of resistance to Schistosoma mansoni miracidia