The genus Heterakis Dujardin, 1845 is one of the most widely distributed genera of nematode parasites of domestic and wild birds. Geographically and ecologically predominant species include Heterakis gallinarum Schrank, 1788 and Heterakis dispar Schrank, 1790. Prevalence and occurrence of these nematodes in the domestic goose (Anser anser dom.) depend on their biological and morphological specifics which ensure the highest viability, fast growth and maximum fertility in the host. This study presents the abundance and species composition of nematodes of the genus Heterakis in the domestic goose in Ukraine. Comparative study of morphological and metrical characteristics of H. gallinarum and H. dispar adult females and males is presented. Additional morphometric characteristics are proposed for easier identification of the two species. Stages and periods of embryonic development of H. gallinarum and H. dispar nematodes obtained from domestic geese are established according to morphological and metrical characters. Of the two species, H. dispar is prevalent in domestic geese from Poltava, Kharkiv and Kyiv regions. Abundance index of this species is 9.8 specimens, and intensity of infection index is up to 62 specimens. H. gallinarum is rarer, its abundance index is 1.2 specimens and maximum intensity of infection is 30 specimens. Species-specific morphological differences are more distinct in male nematodes in the size and structure of the spicules, lateral wing-like protrusions of pseudobursas, numbers and position of tail papillae. Additional metrical characteristics differ between H. gallinarum and H. dispar nematodes, allowing us to identify not only adult specimens but also eggs. Embryonic development of both species occurs in four morphologically distinct stages: protoplast, blastomere cleavage, formation of first and second stage larvae. Eggs of H. gallinarum nematodes become infectious in eight days at 27 °С, eggs of H. dispar in four days, their viability in laboratory culture is 84.3 ± 0.58 and 91.3 ± 1.53% respectively.

In the present study, we observed in vitro the rate and stages of exogenous development of the nematode Trichuris sylvilagi Tiner, 1950 isolated from the European hare, Lepus europaeus. The viability of eggs and embryos at different temperatures was investigated. It was found that the most favorable temperature for embryonic development of the species was 30 °C, with the formation of 88.67 % of viable eggs with a motile larva in 20 days at laboratory conditions. With a decrease in temperature to 20 °C, the embryogenesis occurred in 32 days. The viability of eggs cultured at 20 °C decreased: 68.0 % of eggs reached larval stage, and 32.0 % of eggs died. At 10 °C eggs did not develop to infective stage. On the 32nd day of cultivation at 10 °C, 27.33 % of eggs remained at the zygote stage, 52.0 % at the stage of blastomere cleavage and formation, and 20.67 % died. Embryogenesis was characterized by metric changes in egg parameters. At optimal temperature, the growth and development of eggs was accompanied by an increase in the egg and plugs' width with a simultaneous decrease in their length, as well as with thinning of the shell

Passalurosis is a prevalent disease among helminthiases of domestic rabbits. This invasion is caused by the nematode Passalurus ambiguus (Nematoda, Oxyuroidae), which is cosmopolitan and localized in the cecum and colon of rabbits. Passalurosis is highly contagious and capable of unlimited spread, due to the biological characteristics of its pathogen, such as the conditions that ensure maximum preservation of parasites at exogenous stages of their development. Experimental research in the laboratory established the timing of development of P. ambiguus eggs isolated from the gonads of female helminths, depending on temperature regimes and features of their growth and development. According to the morphological features of Passalurus eggs, four stages were distinguished in their exogenous development: zygote, cleavage and formation of blastomeres, formation of larvae and motile larvae. Depending on the cultivation temperature, the duration of embryogenesis ranged from 4 to 9 days, and egg viability ranged from 59.3% to 72.7%. The most favourable temperature regime for the development of P. ambiguus eggs was the temperature of 35 °C, at which 72.7% of eggs with motile larvae were formed within 4 days. At this temperature, the zygote stage lasted for 1 day of cultivation, the stage of cleaving and formation of blastomeres occurred on days 1–2, the stage of larval formation on days 1–3, and the stage of formation of motile larva on days 3–4. At lower temperatures, the term of development of Passalurus eggs increased, and the number of viable eggs decreased. At temperatures of 30 °С and 25 °С, the development of Passalurus eggs took place during 5 and 7 days, respectively, and the viability was 66.7% and 62.7%. At these temperatures, the zygote stage lasted 1–2 and 1–3 days, the stage of cleaving and formation of blastomeres occurred on days 1–3 and 1–4, the stage of larval formation lasted from days 2–4 and 2–6, and the stage of formation of motile larvae took place on days 3–5 and 4–7, respectively. The least favourable temperature for the development of P. ambiguus eggs was the temperature of 20 °С, at which the formation of motile larvae occurred in 9 days, and their viability was only 59.3%. At this temperature, the zygote stage lasted 1–4 days, the stage of cleaving and blastomere formation occurred on days 2–6, and the larval formation stage on days 3–8, and the motile larval stage happened on days 5–9. The growth and development of P. ambiguus eggs was accompanied by significant changes in morphometric parameters, such as the increase in egg width and thinning of egg shell at the egg shell plug. The obtained data will allow preventive measures to be effectively implemented on rabbit farms that are susceptible to pinworms, taking into account the terms of exogenous development of pathogens in different seasons.

Trichostrongylus tenuis Mehlin, 1846 is a helminth species that parasitizes in the gastrointestinal tract of birds and causes trichostrongylosis. Research on the differential features of the pathogen at various stages of development facilitates timely finding of the foci of infection and providing recommendations for prevention and control. In the present study, the differential species traits of male and female Trichostrongylus nematodes parasitizing in the domestic goose were examined. The nematodes were obtained in helminthological dissection of the intestine of birds kept at farms and private households in Poltava region, Ukraine. It was revealed that the morphological features of T. tenuis females that should be considered in species identification include the structural specifics of the reproductive system and the tail end. 22 metric parameters were suggested for species identification, including the female body measurements for different parts, specifics of vulva and anus location, sizes of the ovijector, sphincter, ejector and vulval area. Differences were found in the metric parameters of the lateral crests of the cuticle in female nematodes in relation to the position of crests on the parasite’s bodies. The cuticular crests were absent at 0.1 mm from the head and tail ends, and the length of crests was 9.3 mm in total. The longest and widest crests were observed in the middle of the body, the shortest were found in the anus area, and the narrowest crests were from the anterior part of esophagus to its middle. The distance between crests varied 0.2–3.0 μm, the longest at the transition of esophagus into the intestine and the shortest in area between the vulva and the anus. The metric parameters of T. tenuis eggs obtained from bird feces and in the nematode uterus differed significantly by 5 characters. The collected data on the morphological and metric parameters of females and eggs of T. tenuis can be used in species identification and understanding of the taxonomic position of that species.

Dirofilariasis of animals and humans is a disease caused by nematodes of the genus Dirofilaria (Railliet et Henry, 1911). The role of wild predators, particularly the red fox (Vulpes vulpes) (Linnaeus, 1758) in the distribution of pathogen of the genus Dirofilaria in the world remains unclear. We studied the occurrence of Dirofilaria immitis (Leidy, 1856) in a population of the red fox. Twenty-seven foxes were examined during the winter hunting season of 2019–2020 in Dergachi district, Kharkiv region of Ukraine. All 27 examined foxes were older than 1.5–2 years old, 5 of them (18.5 %) were 4–5 years old. Dirofilaria immitis was found in 22.2 % of foxes. The intensity of infection ranged from 2 to 4 specimens of nematodes per host. In four foxes (66.7 % of infected hosts), the same number of male and female nematodes was detected, while two foxes (33.3 %) had each 1 male and 2 females of D. immitis. The length of D. immitis males (7 specimens) was 13.96 ± 0.29 cm and the length of females (9 specimens) was 19.58 ± 0.55 cm. Prevalence of infection of foxes with D. immitis presumably depends on their habitat and the presence of mosquitos (vectors of the nematode) in these areas.