Auxiliary Hosts Research Articles

A systematic review of the parasites (Plathelminthes: Cestoda) of the domestic goose (Anser anser dom.)

In many countries, poultry (including Anser anser dom.) play an important role in meeting population needs for meet. One of the factors that affect directly the meat quality and the industrial products obtained from domestic waterfowl are helminths, which cause diseases in their hosts. Helminthological research of the helminth fauna of domestic geese has been carried out in many countries, including Azerbaijan. Nevertherless, there is no general survey or species list of the world fauna of the domestic goose helminths. Tapeworms (Class: Cestoda) also parasitize the geese, causing them serious harm. Taking into account the relevance of the topic, we set the task to determine and systematize the species composition of tapeworms parasitizing the domestic goose (A. anser dom.) with the use of extensive literature data and our personal material. The species list is arranged in alphabetical order, families, genera and species of cestodes follow the nomenclature and classification by Khalil et al. (1994) and Olson et al. (2001), with updates by Kuchta et al. (2008) and Caira et al. (2014). We also took into account the classification adopted from the database of Fauna Europaea. Each species is provided with the following data: scientific name, author and year of description, synonyms, final, intermediate and auxiliary hosts, habitat in the bird body, collecting localities, geographic distribution, prevalence (PI) and intensity (II) of infection, and literature sources. An analysis of the worldwide literature and our personal data has established that 147 helminth species (Trematoda – 64 species, Cestoda – 33, Nematoda – 46, Acanthocephala – 4) are hitherto known from the domestic goose. The 33 tapeworm species of this list belong to five families (Dilepididae – 1 species, Hymenolepididae – 27, Mesocestoididae – 1, Paruterinidae – 1, and Diphyllobothriidae – 3). In Azerbaijan, 11 cestod species were found in the domestic goose. Six of them (Diorchis inflata, Drepanidotaenia lanceolata, D. przewalskii, Fimbriaria fasciolaris, Tschertkovilepis setigera, Ligula intestinalis) were registered in the course of our helminthological studies. The cestodes D. inflata and L. intestinalis were recorded in domestic geese in Azerbaijan for the first time. Five helminth species (Dilepis undula, Drepanidotaenia lanceolata, Ligula interrupta, L. intestinalis, Schistocephalus solidus) parasitize both birds and mammals (D. lanceolata in humans). Of these, two species (D. lanceolata and L. intestinalis) were found in Azerbaijan.

A systematic review of tapeworms (Plathelminthes, Cestoda) of domestic ducks (Anas platyrhynchos dom.)

Tapeworms of domestic ducks (Anas platyrhynchos dom.) causing helminthiasis and serious damage to the hosts, cause economic damage in the poultry industry. Helminthological research devoted to the study of the parasite fauna, including tapeworms of domestic ducks, has been carried out in many countries. But there is no review information on the study of the helminth fauna of domestic ducks. We take our own materials and literature data and summarise the information on cestode parasites of Anas platyrhynchos dom., which have been recorded in the world until 2020. Each species is provided with the following data: scientific name, authority and year, intermediate and auxiliary hosts, habitat in the host body, collecting localities and geographic distribution, prevalence and intensity of infection and literature sources. Based on our own research and analysis of literature data, it was revealed that hitherto there are 419 species of helminths (Trematoda – 213, Cestoda – 89, Nematoda – 79, Acanthocephala – 11) recorded parasitising domestic ducks. The tapeworms found in Azerbaijan belong to four families (Dilepididae – 3, Hymenolepididae – 68, Davaineidae – 13, Diphyllobothriidae – 5). In Azerbaijan, 11 out of 89 species of helminths have been found in domestic ducks. Six of them were also noted in the course of our helminthological studies. The cestoda Diorchis inflata was recorded the first time in domestic ducks in Azerbaijan. Most species of cestodes were found in the north-eastern regions of Azerbaijan (Shabran – 11 species, Khachmaz – 6 species) and the southern region (Astara – 4 species). All of these areas are located on the shores of the Caspian Sea and are located on the annual migration route of wild birds involved in the spread of cestodes, which are considered biohelminths. Six species (Drepanidotaenia lanceolata, Hymenolepis apodemi, Hymenolepis diminuta, Ligula interrupta, Ligula intestinalis, Schistocephalus solidus) of cestodes parasitize both birds and mammals (D. lanceolata, H. diminuta in humans).

Reproductive performance in generalist haematophagous ectoparasites: maternal environment, rearing conditions or both?

We tested whether and how the maternal environment (i.e. host species exploited by a mother), rearing conditions (i.e. host species exploited by her offspring) or both (i.e. matches and mismatches in host species exploited by a mother and her offspring) affect reproductive performance in the offspring. We experimentally manipulated maternal and rearing environments in two generalist fleas (Xenopsylla conformis and Xenopsylla ramesis) implementing a factorial cross-rearing design. Mothers exploited either the principal host (PH) or auxiliary hosts that were either closely (CAH) or distantly related (DAH) to the PH. After six generations of infesting a given host species, we cross-reared fleas within and between host species. These fleas reproduced and we measured their reproductive performance both quantitatively (i.e. egg number) and qualitatively (i.e. egg size, development time, body size of the next generation). We found that identity of the host a flea was reared on (=actual host) had the strongest effect on its performance. Individuals reared on the PH performed considerably better than those reared on either auxiliary host. Moreover, fleas reared on a CAH performed better than those reared on a DAH. Actual host identity also had a stronger effect on reproductive performance in X. ramesis than in X. conformis. Nevertheless, there was no difference in performance between match and mismatch maternal and actual host identities. We conclude that rearing environment has the strongest effect on fitness in generalist parasites. Moreover, phylogenetic distance between an auxiliary host and the PH determines the level of suitability of the former.

Chemical control of polyphagous pests on their auxiliary hosts can minimize insecticide resistance: A case study of Spodoptera exigua Hübner (Lepidoptera: Noctuidae) in cotton agroecosystem

Use of insecticides for agricultural pest management have significant environmental impacts. Using integrated approaches to minimize the frequency of insecticide application by incorporating cultural control tactics can keep environmental hazards to the minimum. The alternate hosts of polyphagous pests have significant role in population development and success of chemical control. Spodoptera exigua Hübner is a polyphagous insect pest of frequently cultivated crops (castor, cauliflower, okra and spinach) in cotton agroecosystem of Pakistan. Since the timeline of cultivation of these crops coincide and the field are often adjoining, S. exigua therefore keeps on migrating from one crop to the other both in winter and summer. Such shifting has a significant effect on the susceptibility of the larvae against the commonly used insecticides. To reveal these effects, toxicity of chlorpyrifos and cypermethrin were tested against the larvae fed on their natal hosts, then shifted to their auxiliary hosts and finally upon their reversal to the natal host. Results have demonstrated that resistance of S. exigua decreased significantly when the populations are cultured on a single host in the laboratory. Field population collected from castor crop demonstrated the highest decrease in resistance ratios against chlorpyrifos and cypermethrin (i.e., 210- and 403-folds, respectively) compared to its field population. Moreover, alternation of generations among cotton and alternate crops, in general, decreased the resistance against chlorpyrifos and cypermethrin. But when these populations return to cotton again, their resistance has been found to be increased significantly. A similar but more obvious change in resistance ratio is observed when the pest population from cotton hosts is fed on spinach (a host available in the later developmental stages of cotton) and vice versa upon their return to cotton. Hence it is suggested that for effective management of S. exigua a continual routine of pest control on available alternate hosts, especially castor and spinach should be administered at critical stages of cotton crop development, i.e. early seedling stage and the late fruiting stage.

Variation in Telial Formation of <i>Puccinia striiformis</i> in the United States

Puccinia striiformis, the causal agent of stripe rust in wheat, barley, and various wild grasses, produces urediniospores and teliospores on these primary or auxiliary hosts. Telial formation, which stops producing infectious urediniospores, is affected by various host and environmental conditions. However, it is not clear if variation exists among different isolates in the United States. To determine the differences in the pathogen population, 1423 isolates collected in the United States from 2013 to 2016 were tested for telial formation in the seedling stage at a diurnal temperature profile of 4°C - 20°C. The percentages of telial formation varied greatly among the isolates. Of the 1423 isolates, 62.97% produced telia with the percentages of telial formation ranging from 1% to 95% under the test conditions. The formation of telia was significantly affected by the year and the month when the isolates were collected. The epidemiological regions or states, host plants (wheat, barley, and grasses), and races of the isolates did not significantly affect telial formation. However, significant effects on telial formation were observed by interactions between year and region, year and race, month and region and among year, month, and region, as well as between year and month. The results showed that telial formation is a complex trait under the genetic control of the pathogen isolates for adaptation to different environments. Further studies are needed to identify genes involved in the formation of telia and the relationship of telial formation to the survival, aggressiveness, fitness, and evolution of the pathogen.

The fauna and perspective of rodentia ectoparasites in Iran relying on their roles within public health and veterinary characteristics.

Historically, rodents-ectoparasites are responsible for many diseases in human and domestic animal communities because they are well-adapted to the environment and nutritional resources. In addition, ectoparasites can affect the reproductive rates, ecological fitness and the dispersal pattern of their hosts. Data was compiled through all publications relating to ectoparasites fauna from Iranian rodents. Host specificity, rodent-parasites interaction, geographical distribution, ecological trends as well as the medical or veterinary importance of ectoparasites are considered in this review. Also, results compared with other equal global findings. According to the obtained information, the genus Hyalomma considered being the major vector of Crimean-Congo hemorrhagic fever. Sistan-Balouchistan, Isfahan, Fars and Khuzestan are endemic provinces of this disease in Iran. Ixodes ticks (especially Hyalomma spp.) commonly existed throughout the months but had high activity in spring and late autumn seasons. Muridae as the most diversified rodent family was more reiterated exploited host by all parasites in this knowledge. Tatera indica confirmed as a positive host for Francisella tularensis by serological test but the definitive reservoir is still unclear in Iran. Meriones persicus as a nocturnal jird has been permanently presented in semi-desert areas except Dasht-e Kavir desert. This rodent was the frequent host for Pulicid fleas followed by Mus musculus and Cricetulus migratorius (Cricetidae). Rattus norvegicus was specialized host for Polyplax spinulosa (spiny rat louse). Pulex irritans from Pulicidae was spread in particularly west of Iran which known as an endemic focus of plague. Mites were high diversity than other taxa. The domestic vertebrates (sheep, goat and cattle) were primitive hosts and rodents were discovered as auxiliary hosts for ticks in Iran apparently. The available data suggested that lice had a type of model of host specificity due to their morphological traits. Meanwhile, Alborz and Zagros mountains ranges provided the specialized habitats for animals which have been surrounded by northern and western regions. Perhaps these mountainous areas can prevent gene flow between local mammalian populations. Notably, the genealogy of parasite genome can orient toward the evolutionary process into speciation point. In general, more researches are needed to decipher the whole sights of host-parasite association and the role of ectoparasites within zoonosis diseases.

Switching among natal and auxiliary hosts increases vulnerability of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) to insecticides.

The role of insecticidal application and host plant resistance in managing Spodoptera exigua has been well documented, but the effect of different host plants, on which the pest cycles its population in the field, has seldom been investigated. Therefore, we have studied the vulnerability of S. exigua against commonly used insecticides (cypermethrin, chlorpyrifos, lufenuron, and emamectin benzoate) with different mode of actions when it switches its generations from natal to auxiliary hosts and vice versa. Different field populations being established on different host plants including castor, cauliflower, cotton, okra, and spinach were collected and reared in the laboratory before insecticidal bioassays. The role of larval diet and host plant switching on their response to tolerate applied insecticides was studied using leaf‐dip bioassay methods. Host switching demonstrated a significant role in altering the vulnerability of S. exigua populations to tested insecticides. Spodoptera exigua sourced from castor, when switched host to okra and spinach, exhibited 50% higher mortality when treated with emamectin benzoate. This trend in mortality was consistent upon complete host switch cycle (natal—auxiliary—natal host). However, the highest increase (92%) in vulnerability was recorded when the larvae were shifted to spinach from cotton. In general, chlorpyrifos and lufenuron had highest efficacies in terms of larval mortality. The findings of present studies provide insights to a better understanding the behavior of polyphagous pests and the role of different host plants in altering the susceptibility of these pests against applied insecticides. Ultimately the results warrant that due consideration should be given to cropping patterns and time of host switching by pest population during planning and executing chemical control.

The influence of Angiostrongylus cantonensis (Nematoda, Metastrongylidae) infection on the aerobic metabolism of Biomphalaria straminea and Biomphalaria tenagophila (Mollusca, Gastropoda)

Angiostrongylus cantonensis is considered the main agent responsible for human eosinophilic meningoencephalitis. This parasite has low specificity for mollusk hosts and it can also use aquatic snails as auxiliary hosts. Studies based on the metabolic profile of Biomphalaria spp. infected by A. cantonensis have been conducted to observe parasite-host interactions. In the present study, the glucose content in the hemolymph and glycogen content in the digestive gland and cephalopedal mass of Biomphalaria tenagophila and Biomphalaria straminea experimentally infected by A. cantonensis were evaluated, along with the activity of LDH. The snails were dissected from 6 to 21days after infection to collect the hemolymph and separate the tissues. Decreases of 96% and 6.4% in the glucose content triggered a transition from aerobic to anaerobic metabolism in the two infected snail species, B. straminea and B. tenagophila, respectively. That finding was confirmed by high-performance liquid chromatography. These results indicate that when infected, these snails are able to change their metabolic profile, suggesting a strategy to maintain their homeostatic balance.

Energy expenditure for egg production in arthropod ectoparasites: the effect of host species

We studied the energy cost of egg production in two flea species (Parapulex chephrenis and Xenopsylla ramesis) feeding on principal (Acomys cahirinus and Meriones crassus, respectively) and auxiliary (M. crassus and A. cahirinus, respectively) rodent hosts. We predicted that fleas feeding on principal as compared with auxiliary hosts will (a) expend less energy for egg production; (b) produce larger eggs and (c) live longer after oviposition. Both fleas produced more eggs and spent less energy per egg when exploiting principal hosts. Parapulex chephrenis produced larger eggs after exploiting auxiliary hosts, while the opposite was true for X. ramesis. After oviposition, P. chephrenis fed on the auxiliary hosts survived for a shorter time than those fed on the principal hosts, while in X. ramesis the survival time did not differ among hosts. Our results suggested that one of the proximate causes for lower reproductive performance and subsequent lower abundance of fleas on auxiliary hosts is the higher energy cost of egg production. However, in some species, lower offspring number may be compensated to some extent by their size, although this compensation may also compromise their future reproduction via decreased survival. In addition, the reproductive strategy of exploitation of low profitable (i.e. auxiliary) hosts may differ between flea species.

Ectoparasite fitness in auxiliary hosts: phylogenetic distance from a principal host matters

We studied reproductive performance in two flea species (Parapulex chephrenis and Xenopsylla ramesis) exploiting either a principal or one of eight auxiliary host species. We predicted that fleas would produce more eggs and adult offspring when exploiting (i) a principal host than an auxiliary host and (ii) an auxiliary host phylogenetically close to a principal host than an auxiliary host phylogenetically distant from a principal host. In both flea species, egg production per female after one feeding and production of new imago after a timed period of an uninterrupted stay on a host differed significantly between host species. In general, egg and/or new imago production in fleas feeding on an auxiliary host was lower than in fleas feeding on the principal host, except for the auxiliary host that was the closest relative of the principal host. When all auxiliary host species were considered, we did not find any significant relationship between either egg or new imago production in fleas exploiting an auxiliary host and phylogenetic distance between this host and the principal host. However, when the analyses were restricted to auxiliary hosts belonging to the same family as the principal host (Muridae), new imago production (for P.chephrenis) or both egg and new imago production (for X.ramesis) in an auxiliary host decreased significantly with an increase in phylogenetic distance between the auxiliary and principal host. Our results demonstrated that a parasite achieves higher fitness in auxiliary hosts that are either the most closely related to or the most distant from its principal host. This may affect host associations of a parasite invading new areas.

기생충의 보조숙주로서의 한국산 연체동물 감염 실태: 기후변화에서 병원체 전파의 영향에 대한 고찰

본 연구는 한국산 연체동물의 감염 병원체의 실태와 한반도 기후변화에 따른 질병의 변화를 예측하기 위해 연구 보고된 문헌을 고찰하였다. 야생동물은 인체에 기생하는 인수공통전염병 기생충에 대한 중간숙주, 보유숙주 및 연체숙주로 제공되고 있다. 흡충류는 연체동물의 흔한 기생충이며 거의 모든 흡충류는 그들의 생활사에서 1차숙주로서 패류에 감염되며, 대부분은 또 다른 숙주를 포함하는 복잡한 생활사를 가지고 있다. 지금까지 기생충의 생태학에 대한 보조숙주로서의 중요성은 논의된 바 없다. 최근에 기후변화의 관점에서 많은 기생성 질병이 역학적 관심이 증가되고 있다. 한국산 연체동물을 대상으로 연구 보고된 문헌을 중심으로 기생성 병원체를 가진 종들을 조사 한 결과 전체 21종의 패류가 매개 기생체를 가지며, 이들 패류 21종이 가지고 있는 병원체는 모두 39종류로 확인되었다. 이 중 담수패류가 15종 그리고 해산패류에서 6종으로 나타났다. 담수패류 중 다슬기과의 다슬기 (Semisulcospira livertina) 에서 페흡충, 요코가와흡충, 가시입이형흡충 등 가장 많은 11종류의 기생성 병원체를 가지는 것으로 조사되었고, 쇠우렁이 (Parafossarulus manchouricus) 에서는 간흡충, 동양배반흡충, 메기장흡충, 오리오목흡충, 일본극구흡충 등 11종류, 다슬기류 (Semisulcospira sp.) 에서는 폐흡충, 요코가와흡충, 가시입이형흡충 등 10종류, 염주알다슬기(Koreanomelania globus) 에서는 메기소식흡충 등 7종류, 바지락 (Tapes philippinarum) 에서는 Cercariae tapidis 등 3 종류 그리고 나머지 패류에서 1-2 종류의 기생성 병원체를 보유하는 것으로 나타났다. 특히 앞으로 홍수나 가뭄과 같은 극심한 기후변화가 일어난다면 담수패류는 기생성 매개자로서의 매우 중요한 역할을 할 것으로 예측되었다. To determine the status of Korean molluscs infection and relation with climate change of Korean peninsula, references were reviewed. Wild animals serve as intermediate, reservoirs and paratenic hosts to zoonotic parasites of human beings. Trematode are common parasites of molluscs and almost all trematodes infect mollusks as the first host in the life cycle, and most have a complex life cycle involving other hosts. The significance of auxiliary hosts to the ecology of the parasite has not been proper discussion. There is increasing concern as to the impact of climate change on the epidermiology of many parasitic diseases. A total of 21 species for snail transmitted parasites from Korean molluscs has been reviewed. Among them, 15 species was aquatic mollusks and 6 species for marine mollusks. Maximum infections belonged to Semisulcospira livertina had 11 kind of parasite pathogenic organisms, including Paragonimus westermani, Metagonimus yokogawai, Centrocestus armatus, Notocotylus magniovatus, Centrocestus formosanus, incerte cercaria, nipponensis cercaria, Yoshidae cercaria, cristata cercaria, innominatum cercaria and Metagonimus sp. And 11 in Parafossarulus manchouricus including Clonorchis sinensis, Asymphylodora japonica, Cyathocotyle orientalis, Exorchis oviformis, Notocotylus attenuatus, Echinochasmus japonicus, Loxogenes liberum, Cercariae of Loxogenes liberum Type I, Cercariae of Loxogenes liberum Type II, Furcocercus cercariae (Family Sanguincolidae) and Cercaria of Mucobucaris, 10 in Semisulcospira sp. including Paragonimus westermani, Metagonimus yokogawai, Centrocestus armatus, Echinochasmus redioduplicatus, Notocotylus magniovatus, Cercaria incerte, Cercaria nipponensis, Cercaria yoshidae, paludinarum cercaria and Metagonimus sp., 7 in Koreanomelania globus including Pseudexorchis major, Cercaria of parapleurolophocercous type, Metagonimus sp. (A & B), Cercaria nipponensis, Cercaria inserta and Cercaria yoshidae. Also, Tapes philippinarum have 3 pathogenic organisms including Cercariae tapidis, Cercariae furcocercus and Parvatrema sp. In particular, under climatic extremes such as floods and drought, aquatic molluscs may play a more prominent role in parasite transmission in the future.

Digesting blood of an auxiliary host in fleas: effect of phylogenetic distance from a principal host

Fleas are haematophagous ectoparasites that exhibit varying degrees of host specificity. Flea abundance is highest on principal hosts and lower on auxiliary hosts but may vary greatly among auxiliary hosts. We investigated the feeding and energy expenditure for digestion in two flea species Parapulex chephrenis and Xenopsylla ramesis on a principal host (Acomys cahirinus and Meriones crassus, respectively) and eight auxiliary host species. We predicted that fleas would perform better - that is (i) a higher proportion of fleas would take a blood meal, (ii) fleas would take larger blood meals and (iii) fleas would spend less energy on digestion - if they fed on (i) a principal host compared with an auxiliary host and (ii) an auxiliary host phylogenetically close to a principal host compared with an auxiliary host phylogenetically distant from a principal host. Energy costs of digestion were estimated using CO(2) emission and represented energy cost during the first stage of blood digestion. Contrary to our predictions, fleas did not always perform better on a principal than on an auxiliary host or on auxiliary hosts phylogenetically closer to the principal host than on auxiliary hosts phylogenetically distant from a principal host. Variation in flea feeding performance may result from the interplay of several factors including co-occurrence between hosts and susceptibility of a host to flea attacks, the species-specific level of immunocompetence of a host and the level of host specificity of a flea. This study describes the first investigation into the metabolic expenditure of parasitism and its relationship to phylogenetic relationships amongst hosts.

Feeding performance of fleas on different host species: is phylogenetic distance between hosts important?

We asked if and how feeding performance of fleas on an auxiliary host is affected by the phylogenetic distance between this host and the principal host of a flea. We investigated the feeding of 2 flea species, Parapulex chephrenis and Xenopsylla ramesis, on a principal (Acomys cahirinus and Meriones crassus, respectively) and 8 auxiliary host species. We predicted that fleas would perform better (higher proportion of fleas would feed and take larger bloodmeals) on (a) a principal rather than an auxiliary host and (b) auxiliary hosts phylogenetically closer to a principal host. Although feeding performance of fleas differed among different hosts, we found that: (1) fleas did not always perform better on a principal host than on an auxiliary host; and (2) flea performance on an auxiliary host was not negatively correlated with phylogenetic distance of this host from the principal host. In some cases, fleas fed better on hosts that were phylogenetically distant from their principal host. We concluded that variation in flea feeding performance among host species results from interplay between (a) inherent species-specific host defence abilities, (b) inherent species-specific flea abilities to withstand host defences and (c) evolutionary tightness of association between a particular host species and a particular flea species.

Aquatic molluscs as auxiliary hosts for terrestrial nematode parasites: implications for pathogen transmission in a changing climate

Nematodes are common parasites of molluscs but are often overlooked. Both metastrongyloid and rhabditoid species dominate the fauna within land snail and slug populations. Nevertheless, a key characteristic of many laboratory studies is the ability of these terrestrial nematodes to utilize aquatic molluscs as auxiliary hosts. The significance of this to the ecology of the parasite has never been evaluated. There is increasing concern as to the impact of climate change on the epidemiology of many parasitic diseases. In particular, it has been suggested that host switching may increase under the pressure of extreme climatic conditions. It is therefore timely to assess the role that aquatic molluscs may play in transmitting terrestrial nematodes, which include species of medical and veterinary importance such as Angiostrongylus cantonensis, A. vasorum, and Muellerius capillaris. The present review assesses the mechanisms of terrestrial nematode transmission through aquatic molluscs focusing on metastrongyloid and rhabditoid species, the importance of variable susceptibility of molluscan hosts, field studies on natural occurrence within aquatic habitats, and the impact of extreme climatic events (floods and droughts) that may increase in frequency under climate change.

Relative infection levels and taxonomic distances among the host species used by a parasite: insights into parasite specialization

Parasites often exploit more than one host species at any stage in their life-cycle, but the extent to which these host species are used varies greatly. Parasites typically achieve their highest prevalence, intensity and/or abundance in one host species (the principal host), whereas infection levels in auxiliary hosts range from relatively high to very low. The present study examines what influences the distribution of parasite individuals among their different host species, using metazoan parasites that use freshwater fish as their definitive or only host. Specifically, I test the hypothesis that differences in relative infection levels by a parasite among its auxiliary hosts are proportional to the taxonomic distance between the respective auxiliary hosts and the parasite's principal host. Taxonomic distance among hosts is a surrogate measure of their similarity in terms of ecology, physiology and immunology. Using data on 29 parasite species and 6 fish communities, for a total of 47 parasite-locality combinations, it was found that taxonomic distance between the auxiliary hosts and the principal host had no real influence on infection levels in auxiliary hosts, measured as either prevalence, intensity or abundance. The analysis revealed differences in the degree of specialization among major groups of parasites: in terms of abundance or intensity, auxiliary hosts were less important for cestodes than for nematodes and copepods. The lack of an effect of taxonomic distance may indicate that ecological similarity among host species, arising from convergence and not from relatedness, is more important than host phylogeny or taxonomy. Although the results are based on a limited number of parasite taxa, they suggest that parasites may be opportunistic in their colonization of new hosts, and not severely constrained by evolutionary baggage.

Relationships between parasite abundance and the taxonomic distance among a parasite's host species: an example with fleas parasitic on small mammals

Opportunistic parasite species, capable of exploiting several different host species, do not achieve the same abundance on all these hosts. Parasites achieve maximum abundance on their principal host species, and lower abundances on their auxiliary host species. Taxonomic relatedness between the principal and auxiliary host species may determine what abundance a parasite can achieve on its auxiliary hosts, as relatedness should reflect similarities among host species in ecological, physiological and/or immunological characters. We tested this hypothesis with fleas (Siphonaptera) parasitic on small Holarctic mammals. We determined whether the abundance of a flea in its auxiliary hosts decreases with increasing taxonomic distance of these hosts from the principal host. Using data on 106 flea species from 23 regions, for a total of 194 flea–locality combinations, we found consistent support for this relationship, both within and across regions, and even after controlling for the potentially confounding effect of flea phylogeny. These results are most likely explained by a decrease in the efficiency of the parasite's evasive mechanisms against the host's behavioural and immune defences with increasing taxonomic distance from the principal host. Our findings suggest that host switching over evolutionary time may be severely constrained by the coupling of parasite success with the relatedness between new hosts and the original host.

The output of first stage larvae by cats infested with Aelurostrongylus abstrusus.

Aelurostrongylus abstrusus, the lungworm of the cat, has a world wide distribution and has been reported from countries as far apart as America, Great Britain and Palestine. It has a complex life cycle insofar as a molluscan intermediate host is essential and it is possible that auxiliary hosts also play an important part. In Britain, the incidence of active infestation of cats with the parasite has been recorded as 19·4% (Lewis, 1927) and 6·6% (Hamilton, 1966) but the latter author found that, generally, the clinical disease produced by the parasite was of a mild nature. It is known that the average patent period of the infestation in the cat is 8–13 weeks and it seems likely that, in that time, a considerable number of first stage larvae would be evacuated. Information on that point is not available and the object of the following experiment was to ascertain the number of larvae produced by cats during the course of a typical infestation.

Studies on Anafilaroides rostratus Gerichter, 1949 in Cats: II. The Life Cycle

The first stage larva of Anafilaroides rostratus develops, after penetration into the foot of certain molluscs, Laevicaulis alte Fer. Mariella dussumieri Gray, Achatina fulica (Fer.) and Helix aspersa Müller. Two moults occur in the foot of these molluscs in 20–56 days depending on the temperature. After each moult the cuticle is shed. The details of development are described. The infective larvae are found in the foot of these molluscs. Natural infection was found in L. alte.Mice and chickens can act as auxiliary hosts. Probably rats, other rodents and birds can also act in the same capacity.The study of the development of the parasite in the cats is not complete. On ingestion the infective larvae penetrate the stomach wall and reach the lung where the third and the fourth moults occur. Exact times of the occurrence of the moults have not been definitely established. All moults are however completed by the 46th day; from then until the 58th day, immature helminths are found in the lungs. Fully gravid females are found on the 74th day, and larvae are first seen on the 78th day. The worms continue to produce larvae for more than 255 days after maturity. The duration of the life of the adult is probably considerably longer than one year.