The morphology and life-history of Trypanosoma (Herpetosoma) microti of the field-vole, Microtus agrestis

Trypanosomiasis: An emerging disease in Alpine swift (Tachymarptis melba) nestlings in Switzerland?

Alpine swifts (Tachymarptis melba) are sub-Saharan migratory birds, which, in Switzerland, nest in colonies that have been continuously monitored for over 40 years. In the summer of 2022, despite favourable environmental conditions, an unexpectedly high number of sudden mortalities (30-80%) occurred in 20 to 45-day-old nestlings from several nesting sites, of which 3 were monitored in detail. Nestlings submitted for post-mortem analysis (n = 5) were in good body condition but exhibited extensive subcutaneous haematomas (n = 5), myocardial petechiae (n = 2) and stunted growth of primary feathers (n = 1). In all birds, 4-5 μm large, amastigote-like protozoans were identified in skeletal and cardiac muscle sections. These tissues tested positive in a PCR targeting the 18S-rRNA gene of Trypanosoma spp. Amplified sequences showed 99.63% identity with sequences of Trypanosoma corvi (JN006854 and AY461665) and Trypanosoma sp. (AJ620557, JN006841). 72 blood smears of 45-day-old nestlings from two colonies were assessed, of which 20 contained trypomastigote forms, some with high parasitaemia (highest average of 56.4 in 10 high power fields, 400x magnification). Trypomastigote morphometrics (n = 36; mean total length = 30.0 μm; length of free flagellum = 5.8 μm) were consistent with those of T. bouffardi. These findings suggest that an avian trypanosomiasis causing mass nestling mortality could be an emerging disease in Swiss Alpine swift populations.

Evidence for a role of the host-specific flea (Paraceras melis) in the transmission of Trypanosoma (Megatrypanum) pestanai to the European badger

We investigated the epidemiology of Trypanosoma pestanai infection in European badgers (Meles meles) from Wytham Woods (Oxfordshire, UK) to determine prevalence rates and to identify the arthropod vector responsible for transmission. A total of 245 badger blood samples was collected during September and November 2009 and examined by PCR using primers derived from the 18S rRNA of T. pestanai. The parasite was detected in blood from 31% of individuals tested. T. pestanai was isolated from primary cultures of Wytham badger peripheral blood mononuclear cells and propagated continually in vitro. This population was compared with cultures of two geographically distinct isolates of the parasite by amplified fragment length polymorphism (AFLP) and PCR analysis of 18S rDNA and ITS1 sequences. High levels of genotypic polymorphism were observed between the isolates. PCR analysis of badger fleas (Paraceras melis) collected from infected individuals at Wytham indicated the presence of T. pestanai and this was confirmed by examination of dissected specimens. Wet smears and Giemsa-stained preparations from dissected fleas revealed large numbers of trypanosome-like forms in the hindgut, some of which were undergoing binary fission. We conclude that P. melis is the primary vector of T. pestanai in European badgers.

A role for vector-independent transmission in rodent trypanosome infection?

Within host-pathogen systems where vector-borne transmission is the primary route of infection, little or no attention has been paid to the relative importance of secondary or alternative routes of transmission. Here, by contrast, we report the results from a controlled longitudinal field-scale experiment in which the prevalence of fleas (Siphonaptera) was manipulated and the occurrence and distribution of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in a natural field vole (Microtus agrestis) population was monitored over a 2-year period. A non-systemic insecticide was applied to individual voles within two treatment grids and the prevalences of fleas and of T. microti were monitored on these and on two control grids. Blood samples were taken from all voles and PCR-based methods used to determine infection status. Insecticidal treatment was highly effective at reducing overall flea prevalence and recaptured animals (treated ca. 4 weeks previously) were very rarely infested (ca. 3%, compared with 50-70+% normally). On the other hand, the probability of trypanosome infection was reduced in treated animals on experimental grids to only around one-third of that normally observed. This suggests that direct, as opposed to flea-borne, transmission may not only occur, it may also be of epidemiological importance. The possibility that the importance of such transmission routes may have been underestimated in 'vector-borne' infections more generally is discussed.

Trypanosomes, fleas and field voles: ecological dynamics of a host-vector--parasite interaction

To investigate the prevalence of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in its field vole (Microtus agrestis) host, we monitored over a 2-year period a range of intrinsic and extrinsic parameters pertaining to host demographics, infection status and vector (flea) prevalence. Generalized Linear Mixed Modelling was used to analyse patterns of both flea and trypanosome occurrence. Overall, males of all sizes and ages were more likely to be infested with fleas than their female counterparts. Flea prevalence also showed direct density dependence during the winter, but patterns of density dependence varied amongst body mass (age) classes during the summer. Trypanosome prevalence did not vary between the sexes but was positively related to past flea prevalence with a lag of 3 months, with the highest levels occurring during the autumn season. A convex age-prevalence distribution was observed, suggesting that individuals develop a degree of immunity to trypanosome infection with age and exposure. An interaction between age and whether the individual was new or recaptured suggested that infected animals are less likely to become territory holders than their uninfected counterparts.

Characterization of SSU and LSU rRNA genes of three Trypanosoma (Herpetosoma) grosi isolates maintained in Mongolian jirds

Trypanosoma (Herpetosoma) grosi, which naturally parasitizes Apodemus spp., can experimentally infect Mongolian jirds (Meriones unguiculatus). Three isolates from A. agrarius, A. peninsulae, and A. speciosus (named SESUJI, HANTO, and AKHA isolates, respectively) of different geographical origin (AKHA from Japan, and the others from Vladivostok), exhibited different durations of parasitaemia in laboratory jirds (2 weeks for HANTO, and 3 weeks for the others). To assess the genetic background of these T. grosi isolates, their small (SSU) and large subunit (LSU) ribosomal RNA genes (rDNA) were sequenced along with those of 2 other Herpetosoma species from squirrels. The SSU rDNA sequences of these 3 species along with available sequences of 3 other Herpetosoma trypanosomes (T. lewisi, T. musculi and T. microti) seemed to reflect well the phylogenetic relationship of their hosts. Three isolates of T. grosi exhibited base changes at 2-6 positions of 2019-base 18S rDNA, at 5-29 positions of 1817/1818-base 28Salpha rDNA, or 1-5 positions of 1557-1559-base 28Sbeta rDNA, and none was separated from the other 2 isolates by rDNA nucleotide sequences. Since base changes of Herpetosoma trypanosomes at the level of inter- and intra-species might occur frequently in specified rDNA regions, the molecular analysis on these regions of rodent trypanosomes could help species/strain differentiation and systematic revision of Herpetosoma trypanosome species, which must be more abundant than presently known.

Oral transmission of trypanosomes of the subgenus Herpetosoma from small mammals

The rodents Microtus agrestis, Clethrionomys glareolus, Apodemus sylvaticus and white BK rats were given either a single intraperitoneal (i.p.) injection, an intragastric (i.g.) inoculation or an oral (p.o.) inoculation of the culture forms, including metacyclic trypomastigotes, of Trypanosoma microti, T. evotomys, T. grosi and T. lewisi, respectively. Similar levels of parasitaemia were produced by each of the three routes of infection, although the prepatent period was 3-5 days shorter in the case of the i.p.-injected animals. The oral inoculation of blood from mice infected with T. musculi into uninfected mice (outbred) and from rats infected with T. lewisi into uninfected BK rats produced parasitaemia after 6-8 days. This is the first report of the oral and i.g. transmission of T. microti, T. evotomys and T. grosi into their specific homologous hosts.

Studies on cross-immunity in Herpetosoma trypanosomes of Microtus, Clethrionomys and Apodemus

Laboratory-bred rodents of three species were inoculated with heterologous Herpetosoma trypanosome species as follows: Microtus agrestis with Trypanosoma evotomys or T. grosi, Apodemus sylvaticus with T. evotomys or T. microti and Clethrionomys glareolus with T. grosi or T. microti. The three rodent species were subsequently challenged with their natural trypanosome parasite, i.e. T. microti for M. agrestis, T. grosi for A. sylvaticus and T. evotomys for C. glareolus. The parasitaemias and courses of infection that developed were followed. All challenged animals showed some degree of cross-immunity; not all became infected, and those that did had lower levels of parasitaemia and shorter patent periods than control animals. No C. glareolus previously inoculated with T. microti developed T. evotomys infections on challenge, and an infection was observed in just one of ten M. agrestis inoculated first with T. evotomys and later with T. microti.

Trypanosoma (Herpetosoma) rangeli Tejera, 1920: influence of host weight, size of inoculum, and route of infection upon experimental parasitemia

To study the influence of host age, inoculum size, and route of infection on Trypanosoma (Herpetosoma) rangeli, 12 lots of 6.0 g albino mice (NMRI strain) were infected up. with from 25x10¹ to 25x10(6) trypomastigotes/gram body weight harvested from LIT medium. The lower inocula produced low but persistent parasitemias, while the higher inocula produced high levels of parasitemia that fell quickly, suggesting the mobilization of resistance mechanisms. In other experiments, i.p. inoculation produced higher parasitemias than s.c. inoculation, and 6.0 g mice had higher parasitemias than 16.0 or 26.0 g mice. Thus, a standard methodology would seem to be necessary in the study of the various strains and/or species that may make up the T. rangeli complex.

Trypanosoma musculi: influence of uric acid on in vitro formation of metacyclic trypomastigotes

Uric acid is the most important constituent in the urine of insects. Infective metacyclic forms of the stercorarian trypanosomes are produced in the rectum of their insect vector and are thus in contact with uric acid. Using a culture system which permitted the growth of the insect stages of Trypanosoma musculi, we studied the influence of uric acid on the metacyclogenesis of this parasite. When added to the culture, uric acid enhanced the production of metacyclic forms. Furthermore, it rendered these trypanosomes highly infective by the oral route. It is suggested that uric acid may play an important role on the metacyclogenesis of T. musculi.

Isoenzyme characterization of trypanosomes of the subgenus Herpetosoma

Isoenzyme analysis was used to characterize 6 species of trypanosomes of the subgenus Herpetosoma using 13 different enzyme systems. The species studied were Trypanosoma lewisi, T. musculi, T. grosi, T. microti, T. evotomys and T. nabiasi which cannot be distinguished on morphological grounds. Extracts for thin-layer starch-gel electrophoresis were prepared from cultures of insect forms in either Schneider's Drosophila or Grace's insect tissue culture media with foetal calf serum or a nutrient agar medium. Extracts of T. lewisi and T. musculi bloodstream forms were also run for comparison. All parasites gave distinct patterns which enabled them to be differentiated on one or more enzyme systems. Two types of computer analysis were used to group the parasites; using these techniques the murine parasites T. lewisi, T. musculi and T. grosi fell into one broad group, and T. microti and T. evotomys of microtine rodents formed another. These findings are in accord with earlier observations on the behavioural characteristics of these parasites in their mammalian host and their vector (fleas). The clear differences observed provide the basis for the application of other biochemical and immunological techniques for differentiation within this subgenus of trypanosomes.

In vitro cultivation of Herpetosoma trypanosomes in insect cell tissue culture media

The cultivation of Herpetosoma trypanosomes in insect tissue culture media supplemented with foetal calf serum is described. Trypanosoma lewisi and T. musculi, which can be grown in blood agar media, were compared with four other species of Herpetosoma trypanosomes, T. microti, T. evotomys, T. grosi and T. nabiasi, in their growth in Schneider's Drosophila medium, Grace's, Mitsuhashi-Maramorosch, RPMI 1640, TCM 199 and nutrient blood agar media. Schneider's Drosophila and Grace's media supplemented with 20% foetal calf serum proved the most suitable media for growth of all parasites except T. nabiasi from rabbits which was not successfully established. Primary cultures were passaged after approximately 3 weeks and were maintained to continuously produce metacyclic trypomastigotes which produced less virulent infections although they maintained their infectivity to their respective hosts. The growth patterns in culture and morphology of the parasites are described.

In vitro production of metacyclic forms of Trypanosoma musculi and their infectivity in CBA mice

Bloodstream forms of Trypanosoma musculi, cultured in Schneider's drosophila medium at room temperature, multiply and differentiate through a series of developmental stages into infective metacyclic trypomastigotes in 10 days. Oral inoculation with these culture forms into CBA mice produced a parasitemia similar to that produced by intraperitoneal infection with bloodstream forms except for a three-day longer prepatent period. Attempts to induce parasitemia with bloodstream forms given orally were unsuccessful.

Reproduction, structure and host specificity of Trypanosoma (Herpetosoms) tamiasi sp. n. from the eastern chipmunk, Tamias striatus

Trypanosoma (Herpetosoma) tamiasi sp. n. is described from blood and organs of the eastern chipmunk, Tamias striatus, and the least chipmunk, Eutamias minimus. In experimentally infected Tamias striatus and E. minimus, Trypanosoma tamiasi reproduced by equal binary fission in the trypo-, sphaero-, epi-, or amastigote form, mainly in lymphoid organs. Trypomastigotes developed from amastigotes through epimastigotes, or from sphaeromastigotes, mainly in the same organs. The mean lengths of body and flagellum of trypomastigotes increased linearly until the organisms reached a maximum length of similar to 37-39 mum. The distance between the nucleus and kinetoplast increased to a mean total length of similar to 33 mum, and thereafter remained constant. Parasitemias of up to 2.5 times 10-7 trypanosomes/ml were produced in Tamias striatus by inoculation with bloodstream, culture, or flea gut forms of Trypanosoma tamiasi; natural parasitemias in Tamias striatus peaked at up to 2.1 times 10-7 trypanosomes/ml. One E. minimus and 2 Spermophilus tridecemlineatus developed parasitemias of more than 1 times 10-6 trypanosomes/ml after inoculation of bloodstream forms of Trypanosoma tamiasi; other experimentally inoculated rodents, including mice, rats, and Spermophilus richardsonii, proved refractory. In chipmunk fleas, Megabothris acerbus, Megabothris quirini, and Tamiophila grandis, bloodstream forms of Trypanosoma tamiasi developed to metacyclic forms in 4-9 days; in rat fleas, Xenopsylla cheopis and Nosopsyllus fasciatus, they survived with little development for up to 2 days, and in kissing bugs, Rhodnius prolixus, up to 10 days. Apparently, the speciation of this trypanosome involved adaptation to certain species of both fleas and rodents.

Taxonomy of trypanosomes (Protozoa: Trypanosomatidae) of Spermophilus spp. (Rodentia: Sciuridae)

(1)Spermophilus columbianus, S. franklinii, S. lateralis tescorum, S. richardsonii, S. tridecemlineatusands. undulatus plesius(ground squirrels) were collected from Alberta and Yukon Territory (S. u. plesiusonly), Canada. Trypanosome infections were detected in all butS. l. tescorum. (2) All six species of squirrels were experimentally inoculated with trypanosomes from naturally infectedS. columbianus, S. franklinii, S. richardsoniiandS. tridecemlineatus. The strains fromS. columbianus, S. richardsoniiandS. tridecemlineatusproduced infections in some or all of the other host species, whereas the strain fromS. frankliniidid not. (3) Natural transmission of trypanosomes has not been demonstrated, but it seems likely that fleas act as vectors. (4) Intensities and durations of experimental infections were variable and depended upon the trypanosome strain, host species and individual. Infections were non-pathogenic. (5) Previously infected ground squirrels could not be reinfected with the same or a different trypanosome strain and immunity appeared to be lifelong. (6) Size comparisons among and within trypanosome strains from naturally and experimentally infected ground squirrels revealed that the strains fromS. frankliniiandS. tridecemlineatuswere similar to one another, but different from the other three trypanosome strains (those fromS. columbianus, S. richardsoniiandS. undulatus). (7) It is suggested that there is only one species of trypanosome,Trypanosoma otospermophili, in the genusSpermophilusin North America and that differences in size and types of infection are due to host-induced variations (i.e. they are plastoxenodemes).T. spermophili(present in EurasianSpermophilusspp.) might be synonymous withT. otospermophili.