Prior to the work of Cable and Hopp (J. Parasit. 40(6): 674.680, 1954) Neoechinorhynchus emydis (L e i d y, 1851) was the only recognized species of Acanthocephala in North American turtles. To date, a total of five species have been described. Of these, two species (Neoechinorbynchus pseudemydis Cable and Hopp, 1954, and N. emyditoides Fisher, 1960) were recovered from six of 12 Louisiana turtles (Pseudemys scripta elegans (Wied)) examined by Fisher (J. Parasit. 46(2): 257-266, 1960). He (1960) also found N. chrysemydis Cable and Hopp, 1954 in Pseudemys scripta subsp. The data pt .sented are results of studies conducted between the spring of 1965 and the summer of 1966. Seventynine turtles (48 female and 31 males) encompassing seven species (47 Pseudemys scripta elegans (Wied), three P. floridana hoyi (Holbrook), eight Chelydra serpentina serpentina (L.), eight Kinosternon subrubrum hippocrepis Gray, seven Terrapene carolina carolina (L.), five T. c. triunguis (Agassiz) and one Trionyx muticus (LeSueur) collected from Baton Rouge and vicinity were examined. This investigation revealed the presence of three species of Acanthocephala (Neoechinorhynchus pseudemydis, N. emyditoides, and N. chrysemydis) in Louisiana turtles and confirms Fisher’s (1960) work. Of the seven species of turtles examined, only P. s. e!egans (25 16 females and 9 males) and P. floridana hoyi (2 females) were positive with infection. Three of the 25 P. s. e!egans had mixed infection comprising three species of Neoechinorhynchus while seven had two species respectively. P. f!oridana hoyi represents a host record for N. chrysemydis;

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Myiasis in man and animals in the old world

Available data in the literature pertaining to the life-history characteristics of all known species of mammalian schistosomes have been gathered, and correlations between such variables as length of pre-patent period, adult worm size, rate of progeny production and progeny size have been explored. Accommodation of the schistosome life-cycle to the constraints imposed by certain host characteristics such as life-expectancy and size is discussed. Of the 23 known species of mammalian schistosomes, 20 species apparently rely to a major extent on relatively large-bodied and long-lived mammals such as primates, ungulates and proboscideans for their transmission. Only 1 species, Schistosomatium douthitti, is exclusively dependent on rodents for its transmission. S. douthitti attains maturity within its definitive host faster than any other mammalian schistosome, and is the only species known to be capable of producing viable eggs by facultative parthenogenesis. For all species of mammalian schistosomes, adult worm size, as estimated by female length, is positively correlated with the number of uterine eggs contained within the female (r = 0·682). For the 7 species for which data exist, rate of egg production/worm pair/day is positively correlated with uterine egg counts (r = 0·873) and inversely correlated with egg length (r = −0·787) and miracidium length (r = −0·953). Length of the pre-patent period is positively correlated with egg length (r = 0·503). With respect to the molluscan host, the number of cercariae produced by snails is positively correlated with the shell size of the snail (r = 0·657). For the 5 species for which data exist, the rate of egg production is inversely correlated with shell size of the intermediate host (r = −0·955) and the common logarithm of the number of cercariae produced (r = −0·893). Comparisons between species suggest that exceptionally low rates of cercariae production in the intermediate host may be compensated for by rapid rates of egg production in the definitive host, implying a degree of integration in the schistosome life-cycle not previously appreciated. Most species of mammalian schistosomes have long-lived definitive hosts, and snail hosts capable of producing many cercariae; compensatory relationships are therefore less obvious in such species. Additional quantitative data on all aspects of schistosome life-histories, particularly rate and duration of egg production, are needed to confirm or refute the relationships discussed above.

A comparative study of the life-histories of mammalian schistosomes.

Experimental concurrent infection with two or more parasite species in mammalian host models may result in heterologous antagonistic and synergistic interactions ranging in magnitude from reduced/enhanced growth and fecundity to blockage/enhancement of establishment/expulsion. With some exceptions only, there is a reasonable correlation between the levels of interaction monitored by parasitological and by clinico-pathological parameters. Heterologous antagonistic interactions mediated by functional and specific immunological cross-reactivity occur between closely related parasite species exhibiting a marked immunobiological similarity. In contrast, antagonistic interactions between antigenetically more remote species of helminths, protozoan-induced resistance to helminth infection and helminth-induced suppression of concurrent protozoan infection generally appear mediated by immunologically non-specific factors like macrophage activation and inflammatory reactions. Synergistic heterologous interactions between helminths, helminth-induced enhancement of concurrent protozoan infection and interference with the development and maintenance of resistance to helminth infection in response to concurrent protozoan infection are generally thought to be mediated by non-specific parasite-induced immunosuppression. Concurrent experimental infection is very complex. There are problems and limitations in extrapolating from experimental studies on concurrent infection in laboratory animals to natural polyparasitism. This fact, coupled with the complex influence of ecological factors on the pattern and frequency of concurrent natural infection means that major consequences of natural concurrent parasite infection have not been definitively demonstrated. Appropriately planned and controlled field studies and further laboratory experiments on primate and domestic animal models are imperative for elucidation of the importance of heterologous interactions in concurrent parasite infection for the disease pattern in man and domestic stock. Experimental studies hitherto conducted on concurrent parasite infection pointing to natural heterologous interactions may be a valuable starting point for further studies.

Heterologous antagonistic and synergistic interactions between helminths and between helminths and protozoans in concurrent experimental infection of mammalian hosts.

Summary

The phylogeny of Oestridae was analysed at the generic level using 118 characters from all developmental stages and including morphology, ontogeny, physiology and behaviour. Four major clades were given subfamilial rank with the phylogenetic relationship (Cuterebrinae (Gasterophilinae (Hypodermatinae + Oestrinae))). The subdermal parasites of the African elephant, Neocuterebra squamosa Grunberg and Ruttenia loxodontis Rodhain, had their most probable affiliation subordinate to the clade of stomach parasites, although their exact position needs further investigation. Genus Ochotonia Grunin, which is known from a single third-instar larva only, was the probable sister group of all other Hypodermatinae. Twenty-five oestrid genera were recognised as valid and those containing more than one species were defined through lists of autapomorphies. Cuterebra Clark was proposed as a senior synonym of Alouattamyia Townsend, Andinocuterebra Guimaraes, Pseudogametes Bischof and Rogenhofera Brauer. The clade of hypodermatine ungulate parasites (Hypoderma Latreille +Pallasiomyia Rubtzov +Pavlovskiata Grunin +Przhevalskiana Grunin +Strobiloestrus Brauer) remained largely unresolved, and genus Przhevalskiana emerged without defining characters.

Phylogeny of Oestridae (Insecta: Diptera)

Publisher Summary This chapter provides an updated and comprehensive review on the main features of cattle schistosomiasis. The adult worms are obligate parasites of the blood vascular system of vertebrates. They live in the perivesical, nasal or mesenteric, and hepatic veins of the host where they feed on blood and produce nonoperculated eggs with a characteristic terminal or lateral spine. As many as 10 different species of schistosomes have been reported to naturally infect cattle. The geographical distribution of schistosome species infecting cattle is mainly determined by the distribution of their respective intermediate host snails. It is noted that most infections in endemic areas occur at a subclinical level. However, it has been established that high rates of prevalence of subclinical infections cause significant losses due to long-term effects on animal growth and productivity and increased susceptibility to other parasitic or bacterial disease. Despite this, schistosomes of veterinary concern have received relatively little attention. In addition, suitable drugs are not available for mass treatment in domestic stock and are unlikely to be developed in the near future. However, recent progress in identifying potentially protective parasite antigens has opened new perspectives in the control strategy against schistosomiasis.

Schistosomiasis in cattle.

Summary Natural infections of Schistosoma margrebowiei were found in Bulinus forskali group snails (B. forskali and B. scalaris) at Lochinvar National Park, Zambia. This is the first record of a natural snail host for this species. The most abundant host in the Park for S. margrebowiei and S. leiperi is the lechwe (Kobus leche). Examination of a small sample of lechwe revealed that animals less than one year old had pure infections of S. margrebowiei and those over five years old had S. leiperi only. It is suggested that these findings are related to the different habitats occupied by the snail hosts for the two parasites and the annual movements of the lechwe herds in response to the local flood cycle. The possibility of some cross-immunity between S. leiperi and S. margrebowiei is discussed.

Observations on the life-cycle of Schistosoma margrebowiei and its possible interactions with S. leiperi in Zambia

A note on the life-cycles of some amphistome flukes in Zambia

Summary Eggs and first instar larvae of Strobiloestrus vanzyli Zumpt are described for the first time and it is suggested that there is a subdermal migration of the larvae from the site of oviposition on the hosts' hairs to the site of encystment and warble formation. Intrastadial morphological changes are reported for all larval instars and the descriptions of second and third stage larvae are enlarged. Wild caught adults and those reared from larvae extracted from lechwe antelope (Kobus leche) are compared with the published descriptions of Strobiloestrus species and with other specimens of this genus. The diagnostic features within the genus are discussed and it is concluded that S. vanzyli may not be a separate species from S. erikssoni. Strobiloestrus is considered in relation to other Oestridae, Hypodermatinae and Hypodermatini and it is suggested that this genus forms a distinctive group within the Hypodermatini but has some features in common with the Oestrinae.

Immature stages and affinities of the southern lechwe warblefly, Strobiloestrus vanzyli Zumpt (Diptera: Oestridae)

Summary A migratory population of wildebeest (Connochaetes taurinus) in Liuwa Plain National Park in the Western Province of Zambia was sampled for nasal bots (Diptera: Oestridae: Oestrinae) during 1975–78. Infestations from 32 antelope included Gedoelstia spp. (two species), Oestrus aureoargentatus and O. variolosus. A total of 1913 second and third instar larvae was recorded from the sinuses and nasal septa with individual parasite loads varying from 4 to 144 bots. No obvious pathogenicity was attributable to these oestrids, all four species of which were judged to be multivoltine in this habitat. The significance of this voltinism in relation to the migratory course of the wildebeest is discussed together with a consideration of parasite densities and the potential threat of myiasis to domestic livestock in the area.

G.W. Howard

Papers

Observations on the life-cycle of Schistosoma margrebowiei and its possible interactions with S. leiperi in Zambia

A note on the life-cycles of some amphistome flukes in Zambia

Immature stages and affinities of the southern lechwe warblefly, Strobiloestrus vanzyli Zumpt (Diptera: Oestridae)

Nasal botflies of migrating wildebeest from western Zambia