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Biomedical subjects

F Frandsen

Publications and source records attributed to F Frandsen.

At least 73 records · Page 4Linked to original sources
PubMed1980

The influence of environmental conditions and parasite-intermediate host-related factors on the transmission of Echinostoma liei.

Moderate freezing, desiccation, and pH levels of 5 and 6 killed the Echinostoma liei egg immediately or after only partial development, and increasing salinity levels above 3.79 0/00 and temperatures of 33 degrees C and 35 degrees C reduced the developmental potential. Temperatures of 6 degrees C and 8 degrees C and maintenance of eggs in mouse faeces arrested the development of the egg, and increasing temperatures decreaseds the time of development from 40 days at 18 degrees C to nine days at 35 degrees C. Maintenance of unembryonated eggs for 14 weeks in faeces at 12 degrees C and 22 degrees C and for 20 weeks in filtered pond water at 4 degrees C allowed a subsequent normal development, while embryonated eggs maintained at 4 degrees C only retained an unchanged hatchability for three weeks. A miracidium/snail density of 10:10 in 18 litres of water gave rise to an average level of parasitisation of 21%. Increasing miracidium/snail densities gave rise to increasing levels of parasitisation but to a level less than expected. The first intermediate host spectrum of E. liei was shown to be restricted to the genus Biomphalaria, but species variability in susceptibility within the genus and differences in survival of infected susceptible species was also demonstrated to exist. B. glabrata (Puerto Rico and St. Lucia), B. alexandrina (Qalyub), and B. pfeifferi (Malumfashi) were found to be susceptible, while B. camerunensis (Kinshasa) was almost refractory. Increasing size of B. glabrata (Puerto Rico) resulted in increasing daily cercarial production, but resistance to infection with increasing snail size was also demonstrated to exist. E. liei cercarial infectivity to the second intermediate host snail and the subsequent metacercarial infectivity to the mouse was found to be independent of the species of the first intermediate host and of the age of the infection in B. glabrata (Puerto Rico) for up to at least 6 1/2 weeks after the end of the prepatent period. No obvious peak in cercarial shedding fom the host snail occurred during the day. Five species of the genus Bulinus and Physa acuta (Egypt) were found to be highly susceptible as second intermediate host snails, whereas three species of the genus Biomphalaria, Planorbarius corneus (Rabat), Lymnaea natalensis (Egypt), and Helisoma duryi (Florida) all had a lower degree of susceptibility. On the other hand, E. liei metacercarial infectivity to the mouse was independent of the species and size of the second intermediate host snail. Also, the infectivity of metacercariae encysted on snail mucus, in snails harbouring patient redial infections, and in clean second intermediate host snails was comparable. Metacercarial infectivity remained unchanged for at least 12 and 18 weeks, respectively, when encysted in living B. glabrata (Puerto Rico) or when maintained in freshwater at 4 degrees C. Metacercariae in dead decaying B...

Animals↗
PubMed1980

Homologous and heterologous resistance in Echinostoma revolutum infections in mice.

Homologous and heterologous resistance in Echinostoma revolutum infections was studied in mice. A high level of homologous resistance was demonstrated in mice harbouring a 13-day-old primary E. revolutum infection with 9--10 and 11--15 worms, corresponding to a 70.0 and 66.7% reduction in the size of the established worm burden as compared with that of the challenge control group. A 14- and 20-day-old primary infection with 3--4 worms induced a level of resistance of 61.7 and 81.8% respectively, while higher worm levels of 9--10 and 11--15 induced almost complete resistance corresponding to a 95.1--100% reduction in the size of the established worm burden. Complete resistance was also demonstrated in mice challenged 8 days after elimination of a 20-day-old primary infection with 11--15 worms by anthelmintic treatment. A primary 43-day-old Schistosoma mansoni infection induced a 73.1% reduction in the size of the established E. revolutum challenge infection while infections of an age of 79 and 99 days conferred complete resistance to heterologous challenge with E. revolutum. Primary pre-patent S. mansoni infections and a patent S. bovis infection of an age of 56 days did not induce any resistance to challenge with E. revolutum. A primary 14- and 21-day-old infection of E. revolutum did not stimulate any significant level of resistance to heterologous challenge with S. mansoni.

Animals↗
PubMed1979

Discussion of the relationships between Schistosoma and their intermediate hosts, assessment of the degree of host-parasite compatibility and evaluation of schistosome taxonomy.

Studies of the spectrum of the intermediate hosts of schistosomes and the relationships between parasites and intermediate host snails have been carried out with each researcher using different methods. A comparison between compatibility studies has therefore been impossible. The following three basic problems in these kind of studies are discussed in this paper: (1) the standardization of experimental materials such as schistosomes, intermediate and final hosts, (2) the methods involved in the experiments, and (3) the sort of data which must be collected. Standardized methods and materials are described in this paper. The relationships between the genus Schistosoma and the intermediate host snails belonging to the two genera Biomphalaria and Bulinus, and the mechanisms behind the process resulting in various degrees of compatibility between the two involved organisms are reviewed and discussed. Why certain combinations of schistosomes and snails result in the production of cercariae and others do not is still unknown, but there is now some indication of a camouflage behaviour during the intramolluscan stages, e.g., the larvae in the snails cover themselves with snail material and are not recognized as foreign objects. The same mechanism has already been found in the schistosomules in the final host. Much of the confusion in the discussion of the relationships between schistosomes and intermediate hosts is the result of a lack of an objective way to describe and assess the compatibility between the two. Based on a series of experiments with S. haematobium, S. intercalatum, S. bovis, S. mansoni, and several species of possible intermediate hosts, the following index for estimating the degree of compatibility is proposed: the total cercarial production from 100 exposed snails (TCP/100 exposed snails). Seven classes have been suggested: the first one (Class 0) with a TCP/100 exposed snails of zero, is called 'refractory'; the next one (Class I) called 'not very compatible' has a TCP /100 exposed snails between 1 and 10,000; the last group (Class IV) called 'extremely compatible' produced more than 500,001 per 100 exposed snails during the entire lifespan. The ability to use a spectrum of intermediate hosts and the compatibility in the taxonomy of schistosomes is discussed. The results for the different species of schistosomes indicated that each species consists of strains with 'hybrid populations' in between.

Animals↗
PubMed1979

Further studies on the compatibility between s. intercalatum from cameroun and zaïre and species of bulinus.

The results from the infection experiments with Schistosoma intercalatum from Cameroun and from Zaïre and the intermediate hosts, belonging to B. forskalii and B. globosus, could be divided into groups according to the degree of compatibility with the schistosomes. This was indicated by the total cercariae production per 100 exposed snails (TCP/100 exp. snails). B. forskalii from Kinshasa, Zaïre were the snails which were most compatible with S. intercalatum from Cameroun, and B. globosus populations tested were refractory. The TCP/100 exposed snails was about 300,000 for the populations of B. forskalii from Kinshasa compared with the low production for B. forskalii from Cameroun of 125,000. B. wrighti from South Arabia produced 155,000 cercariae per 100 exposed snails. B. cernicus from Mauritius could be separated into two types according to the compatibility with S. intercalatum from Cameroun, the TCP/100 exposed snails was 31,000 and 267,000, respectively. B. globosus from Kinshasa, Zaïre, was very compatible with S. intercalatum from Zaïre and the TCP/100 exposed snails was very high, and 300,000. An albino strain of B. globosus from Rhodesia was the most compatible snail having a TCP/100 exposed snails of 2.4 million cercariae. Other strains of B. globosus from Cameroun and Togo were refractory and less susceptible. It was also possible to infect B. africanus and the two tested populations from Kenya and Tanzania, producing 15,000 and 179,000 cercariae per 100 exposed snails, respectively.

Africa↗
PubMed1979

A comparison of the characteristics of two strains of Schistosoma intercalatum Fisher, 1934 in mice.

Schistosoma intercalatum from Cameroon and Zaire each have their specific snail intermediate host. Hybridization experiments between S. intercalatum from Cameroon and Zaire have resulted in viable miracidia for only two generations. If the two strains are of the same species, cross breeding should be possible for several generations. This paper presents a comparison of the characteristics of the two strains of S. intercalatum in experimental infections in mice. Worm return, male-female worm ratio, growth rate, number of testes in male adult worms are compared. The quantitative distribution of eggs in the tissues of the mice is recorded. A comparison of the size and shape of the parasite eggs is described as are the changes in the weight of the liver and spleen of the infected mice. It is considered that the differences observed between the two strains of S. intercalatum do not necessitate a division of the two strains into two separate species.

Animals↗
PubMed1979

Studies of the relationships between Schistosoma and their intermediate hosts. II. The genus Bulinus and Schistosoma haematobium from Sudan, Zaire and Zambia.

The relationship between Schistosoma haematobium from Sudan, Zaire and Zambia and various species and strains of Bulinus, has been investigated. The main emphasis was placed on evaluating the total cercarial production per 100 exposed snails as an index of the compatibility between snail and schistosome. The observations confirmed the results of previous compatibility studies which showed that there were two groups of S. haematobium, truncatus-borne from Sudan and Zaire, and africanus-borne, from Zambia. They also revealed that this division was not absolute, as some overlapping occurred. However, if the cercarial production was taken as an indication of compatibility, instead of the infection rate, there was a more definite division between the two groups. The observation that there is a truncatus-borne strain of S. haematobium present in Zaire extends the area where there is a mixture of truncatus- and africanus-borne strains farther southwards.

Adult↗
PubMed1979

Studies of the relationship between Schistosoma and their intermediate hosts. III. The genus Biomphalaria and Schistosoma mansoni from Egypt, Kenya, Sudan, Uganda, West Indies (St. Lucia) and Zaire (two different strains: Katanga and Kinshasa).

The compatibility between strains of Schistosoma mansoni from Egypt, Kenya, Sudan, Uganda, the West Indies, and Zaire (two strains which came from Katanga and from Kinshasa), and various species and strains of Biomphalaria, i.e. Biomphalaria pfeifferi, B. alexandrina, B. glabrata and B. camerunensis was investigated. Data as mortality, rate of infection of the surviving snails, duration of infection, cercarial production per day per positive snail, etc., were observed. The main emphasis was placed on determining the total cercarial production per 100 exposed snails for each snail population. It was possible to infect all the tested populations of B pfeifferi with the various strains of S. mansoni, but the observation as e.g. TCP/100 exposed snails varied greatly according to the population of snail and the strain of S. mansoni. The results for the remaining species of Biomphalaria varied greatly, depending on the combination, e.g. B. alexandrina was only susceptible to the local S. mansoni from Egypt. The highest TCP/100 exposed snails was more than 1 million for the strains of S. mansoni from Egypt, Kenya and the West Indies in B. alexandrina, B. pfeifferi and B. glabrata, respectively. The next group, with a TCP/100 exposed snails on 7--800 000 consists of S. mansoni from Sudan, Uganda and Zaire (Katanga) all in B. pfeifferi. The last tested strain of S. mansoni, Zaire (Kinshasa) yielded a cercarial production on 500 000 per 100 exposed snails in B. pfeifferi and B. camerunensis. The shortest prepatent period, 19 days, was observed for S. mansoni from Kinshasa, Zaire, in B. camerunensis, and the longest prepatent period, 25 days, was found for strains from Egypt and from the West Indies in B. alexandrina and B. glabrata, respectively. In general, a very long duration of infection, lasting up to 200 days, was observed.

Animals↗
PubMed1979

Studies of the relationships between Schistosoma and their intermediate hosts. IV. The genus Bulinus and Schistosoma bovis from Morocco.

Schistosoma bovis from Morocco was used in infection experiments with several populations of Bulinus truncatus. The snails from Libya, Malawi, Morocco and Senegal were very compatible with the schistosome since the infection rates were approximately 90%, the mortality was low, and a very high production of cercariae, approximately 1.2 million per 100 exposed snails, was observed. Only a very few B. truncatus (2n = 36) from Rhodesia became infected. B. permembranaceus and B. forskalii were refractory.

Animals↗
PubMed1979

A review of helisoma duryi in biological control.

Biological control of schistosomiasis by means of introduction of the north American planorbid snail, Helisoma duryi, as a competitor of the intermediate host snails has been proposed. The systematics of the genus Helisoma and the geographic distribution of the different species is described. Papers dealing with laboratory experiments or field observations on the competition between H. duryi and different intermediate host snails have been reviewed. The status of H. duryi as intermediate host of trematodes has been evaluated by searching the literature for all the trematode species that are recorded from the genus Helisoma. The list does not include trematodes of medical or veterinary importance and despite many attempts it has not been possible to infect H. duryi with Schistosoma mansoni and S. haematobium. Finally this paper makes a few comments on the experiments that should be performed in the laboratory, under semifield conditions and and field conditions before H. duryi should be actively dispersed in Africa. The aspects to be considered include the nature of the competitive interactions, the relation between H. duryi and different medical and veterinary important trematodes and the effect of H. duryi on the biotope.

Animals↗
PubMed1978

Hybridization between different strains of Schistosoma intercalatum Fisher, 1934 from Cameroun and Zaïre.

The offspring from hybridization experiments between Schistosoma intercalatum, Cameroun (intermediate host Bulinus forskalii) and S. intercalatum, Zaïre (intermediate host B. globosus) was investigated. Reciprocal crosses between the two forms were performed. F1- and F2-miracidia developed in both parental intermediate hosts. The minimum prepatent period was 24 days at 26 degrees C, an average of the prepatent periods for the two parental strains. The total cercariae production per 100 exposed snails decreased sharply from 121 000 for the parental strain from Cameroun in B. forskalii to 21 000 and 5000 from the F1- and F2-generations, respectively. The figures for S. intercalatum, Zaïre in B. globosus were 270 000, 134 000 and 3000, respectively. F1- and F2-generations were from the cross between males from Cameroun and females from Zaïre. The viablility of the four cross-breeding experiments carried out (two with each combinations of the parental strains) were low. It was only possible to obtain F2-cercariae. No miracidia were hatched from eggs produced by the F2-gerneation.

Animals↗