| Pachysentis | |
|---|---|
 | |
| Proboscis ofP. lenti[2] | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Acanthocephala |
| Class: | Archiacanthocephala |
| Order: | Oligacanthorhynchida |
| Family: | Oligacanthorhynchidae |
| Genus: | Pachysentis Meyer, 1931[1] |
| Type species | |
| Pachysentis canicola Meyer, 1931 | |
| Otherspecies | |
| |
Pachysentis is agenus inAcanthocephala (thorny-headed worms, also known as spiny-headed worms) thatparasitizeprimates andcarnivorans. They are distributed across Africa, the Middle East, and the Americas.Pachysentis species attach themselves to the inner lining of the gastrointestinal tract of their hosts using their hook-coveredproboscis. Their life cycle includes an egg stage found in host feces, a cystacanth (larval) stage in anintermediate host such as theEgyptian cobra, and an adult stage where cystacanths mature in the intestines of the host. This genus appears identical to the closely relatedOncicola apart from a greater number of hooks on the proboscis. There are eleven species assigned to this genus, althoughP. septemserialis is of uncertain taxonomic status. The female worms range from 12 millimetres (0.47 in) long and 1.6 millimetres (0.063 in) wide inP. lauroi to 50 millimetres (2.0 in) long and 4 millimetres (0.16 in) wide inP. dollfusi. Virtually all of the length is the trunk, with a short proboscis. There is pronouncedsexual dimorphism in this species as females are around twice the size of the males.
Phylogenetic analysis has been conducted on one of the eleven species in the genus,P. canicola.[3] Sequences of the molecular marker [[18S rDNA]] gene were compared to the same sequences in related species and it was concluded thatP. canicola samples formed a well-supported group with other species in the familyOligacanthorhynchidae.[3] Phylogenetic analyses have also been conducted onOncicola, a genus morphologically nearly identical toPachysentis apart from the number of hooks on the proboscis, and have also placed it in the family Oligacanthorhynchidae.[4] Thetype species forPachysentis isP. canicola.[5][2] In 1972, Schmidt reclassified six species from theProsthenorchis genus and one species from theOncicola genus into the genusPachysentis.[6]
| Archiacanthocephala |
| Phylogenetic reconstruction for select species in the class Archiacanthocephala based on a28S rRNA gene comparison from Gomeset. al (2019) and a 18S rDNA gene comparison from Amin and colleagues (2020).[2][7] Amin and colleagues (2022) used the 18S rDNA gene to addP. canicola phylogenetically to the family Oligacanthorhynchidae.[3] |
| Number of proboscis hooks[2] | Barbs in hooks | |
|---|---|---|
| P. angolensis | 42 | No barbs |
| P. canicola | 72 | No barbs |
| P. dollfusi | 48 | Barbs |
| P. ehrenbergi | 102 | Barbs[a] |
| P. gethi | 42 | No barbs |
| P. lauroi | 48 | Barbs |
| P. lenti | 48 | No barbs |
| P. procumbens | 90 | No barbs |
| P. procyonis | 42 | No barbs |
| P. rugosus | 42 | No barbs |
Pachysentis looks identical to the closely relatedOncicola apart from the number of hooks on the proboscis. Species ofOncicola have 36 or fewer hooks whereas species ofPachysentis have more. Theprobosces ofPachysentis species are not quite spherical and contain 42 to 102 hooks arranged into 12 longitudinal rows of 3 to 12 hooks each. Depending on the species, the rows may be regularly or irregularly alternating and straight or crooked. Hooks have tips with or without barbs, and the larger hooks with complex heads (manubria) and roots with the remaining spines being rootless. The trunk is around twice as long as wide with the anterior half usually wider than the posterior half. The testes are in tandem with at least one located before the middle of the worm. There are eightcement glands compactly arranged each with a single giant nucleus used to temporarily close the posterior end of the female after copulation.[8][9] The eggs have a sculptured outer membrane. Species can be distinguished based on the number and arrangements of proboscis hooks, whether these hooks are barbed, the arrangement of the cement glands, host, and the length oflemnisci (bundles of sensory nerve fibers).[2]
| Female measurements (mm)[2] | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Measurements[b] | P. angolensis | P. canicola | P. dollfusi | P. ehrenbergi | P. gethi | P. lauroi | P. lenti | P. procumbens[c] | P. procyonis | P. rugosus | |
| Length ofproboscis | 0.55-0.63 | 0.57-0.80 | ? | 0.8 | 0.583 | 0.68 | 0.63 | 0.55 | 0.697 | 0.564 | |
| Width of proboscis | 0.70–0.82 | 0.57–0.85 | ? | 0.9 | 0.794 | 0.76 | 0.664 | 0.55 | 0.716 | 0.694 | |
| Length of proboscis receptacle | 1.5 | 2 | ? | 1.3 | 1.07 | 1.16 | 1.32 | 1.2 | 1.37 | 1.24 | |
| Width of proboscis receptacle | ? | ? | ? | ? | 0.498 | 0.47 | ? | ? | 0.531 | 0.481 | |
| Length of trunk | 34–48 | 20–26 | 50 | 26–29 | 15–25 | 12.07 | 20–25 | 6 | 25-35 | 32 | |
| Width of trunk | 4.8–5.5 | 5-11 | 4 | 6 | 1.5–3 | 1.62 | 2–2.5 | 1.25 | 2–3 | 3 | |
| Length oflemnisci | 5.8–6 | 7 | 4.3–6.6 | 7 | 3.48 | 4.45 | 3.15 | ? | 3.64 | 4.64 | |
| Width of lemnisci | ? | ? | ? | 0.8 | ? | ? | ? | ? | ? | ? | |
| Uterine bell[d] | ? | 3.15–8.15 | ? | ? | 5.56 | 1.19 | 1.41 | ? | 4.64 | 5.86 | |
| Size of eggs | 0.09 × 0.043 | 0.07 × 0.045 | 0.08 × 0.05 | 0.07 × 0.05 | 0.084 × 0.054 | 0.073 × 0.045 | ? | ? | 0.071 × 0.042 | ? | |
| Male measurements (mm)[2] | |||||||||||
| Length of proboscis | 0.55-0.63 | 0.57-0.80 | ? | 0.8 | 0.583 | 0.68 | 0.63 | 0.55 | 0.697 | 0.564 | |
| Width of proboscis | 0.70–0.82 | 0.57–0.85 | ? | 0.9 | 0.794 | 0.76 | 0.664 | 0.55 | 0.716 | 0.694 | |
| Length of proboscis receptacle | 1.5 | 2 | ? | 1.3 | 1.07 | 1.16 | 1.32 | 1.2 | 1.37 | 1.24 | |
| Width of proboscis receptacle | ? | ? | ? | ? | 0.498 | 0.47 | ? | ? | 0.531 | 0.481 | |
| Length of trunk | 17-23 | 15-28 | 50 | 25 | 10–15 × 1.0–2.5 | 9.63 | 15–20 | 6 | 20-30 | 25 | |
| Width of trunk | 3.5–4 | 4-8 | 4 | 4 | 1.0–2.5 | 1.91 | 1.0–2.5 | 1.25 | 2–3 | 3.5 | |
| Length of lemnisci | 5.8–6 | 7 | 4.3–6.6 | 7 | 3.48 | 4.45 | 3.15 | ? | 3.64 | 4.64 | |
| Width of lemnisci | ? | ? | ? | 0.8 | ? | ? | ? | ? | ? | ? | |
| Size of anteriortestis | 2–3 × 0.9 | 2 | ? | 3 | 1.40 × 0.581 | 1.15 × 0.48 | 1.76 × 0.51 | ? | 3.01 × 1.24 | 1.57 × 0.697 | |
| Size of posterior testis | 2–4.3 × 1.0 | 2 | ? | 3 | 1.40 × 0.581 | 1.27 × 0.55 | 1.82 × 0.547 | ? | 3.15 × 1.07 | 1.69 × 0.664 | |
| Dimension of group ofcement glands | 3 | 3 | ? | 7 | 1.54 | 0.86 × 0.56 | 2.98 | ? | 3.56 | 2.02 | |
| Ejaculatory duct length | 2.3 | ? | ? | ? | 4.64 | 1.42 | ? | ? | 3.53 | 1.68 | |
The genusPachysentisMeyer, 1931 contains eleven species, althoughP. septemserialis is of uncertain taxonomic status.[2][10][e]
P. angolensis was found infesting theside-striped jackal (Canis adustus). The proboscis has a total of 42 hooks without barbs in 12 regularly alternating rows of three and four hooks (six rows of each).[11] The eight cement glands are organized in pairs.[2] This species is named afterAngola, the country where it was first discovered.[11]
P. canicola was found infesting thered fox (Vulpes vulpes) inBushehr,Bushehr Province, Iran,[12] thegolden jackal (Canis aureus) also in Iran,[13] captivemaned wolves (Chrysocyon brachyurus) in a zoo inTexas, and thestriped skunk (Mephitis mephitis) found nearby.[3] It was also found infesting thewestern diamondback rattlesnake (Crotalus atrox).[14][15] It is thetype species of the genusPachysentis.[1] The species namecanicola is derived from the Latin word for canine which is the type of creature (familyCanidae) that this species infests.[1]
P. dollfusi was found infesting the intestines of thecommon brown lemur (Eulemur fulvus) in a Brazilian zoo but originally from the island ofMadagascar.[16] It is thus unknown if the worm originates from Brazil or Madagascar.[2] The proboscis has 48 barbed hooks arranged into six rows of four hooks each followed by another six rows of four hooks each. The cement glands are in uniform pairs.[2] It is synonymous withProsthenorchis spirulaTravassos 1917.[17] It is named after the parasitologistRobert-Philippe Dollfus.[16]
P. ehrenbergi was found infesting the red fox (Vulpes vulpes) in Egypt and in anintermediate host, theEgyptian cobra (Naja haje). The proboscis is armed with 102 barbed hooks arranged into six rows of nine each followed by six rows of eight hooks each.[2]P. ehrenbergi was reported infesting the body cavity of 5.4% of a sample ofAfrican five-lined skinks (Trachylepis quinquetaeniata) in theQena Governorate of Egypt, however the measurements and morphological description do not match either the original description by Meyer in 1931[1] or the reexamination of original specimens by Gomes and colleagues in 2019.[2] JuvenileP. ehrenbergi have been reported infesting thelong-eared hedgehog (Hemiechinus auritus) in the Faran Oasis,South Sinai, Egypt. Juvenile trunk length is reported to be 3.22–4.16 mm by 0.87–1.04 mm, the proboscis length to be 0.42–0.60 mm in length by 0.45–0.68 mm in width, the proboscis sheath to be 0.79–1.0 mm by 0.37–0.52 mm (whereas the measurements given by Meyer in the original 1931 description is larger, at 1.3 mm in length and the proboscis measuring 0.8 mm in length by 0.9 mm in width). The anterior proboscis hooks in the juveniles are reported to be large, from 0.078–0.086 mm long, and the posterior hooks smaller, from 0.052–0.062 mm.[18]
P. gethi was originally described in 1950 by Machado-Filho infestingtayra (Eira barbara) inPará andRio de Janeiro, Brazil but this remained the only record until it was rediscovered in 2016 infesting the wildlesser grison (Galictis cuja), also in Rio de Janeiro, with different measurements.[19] The proboscis has 42 hooks without barbs arranged into six rows of four hooks followed by six rows of three hooks. The eight cement glands occur in pairs.[2] The species is named after Dr. Geth Jansen.[16]
P. lauroi has been found infesting theSouth American coati (Nasua nasua) inMato Grosso do Sul, Brazil. The proboscis has 48 barbed hooks arranged into six rows of four hooks followed by six rows of four hooks. The eight cement glands are clustered. It was found in thesmall intestine.[2] The species is named afterLauro Travassos [pt], a parasitologist who studied Brazilian Acanthocephala.[2]
P. lenti has been found infesting thewhite-headed marmoset (Callithrix geoffroyi) inEspírito Santo, Brazil. The proboscis has 48 hooks without barbs arranged into six rows of four hooks followed by six rows of four hooks.[2] It is named afterHerman Lent [pt], a Brazilian parasitologist.[16]
P. procumbens has been found infesting the red fox (Vulpes vulpes)inArgo, Egypt. The proboscis has 90 hooks without barbs arranged into six rows of seven hooks followed by six rows of eight hooks.[2] The species name is from the Latinprocumbent, meaning "lying prostrate".[20]
P. procyonis was found infesting the intestines of acrab-eating raccoon (Procyon cancrivorus) in Rio de Janeiro, Brazil.[21] The proboscis has 42 hooks without barbs arranged into six rows of four hooks followed by six rows of three hooks. Distinguishing features include eight clustered cement glands and very short lemnisci that do not reach the anterior testis.[2] The species is named after the genus of the host (Procyon) it was found infesting.[16] It is the only known parasite of the crab-eating racoon in Brazil.[22]
P. rugosus has been found to infest the large intestine ofAzaras's capuchin (Sapajus cay) in Rio de Janeiro, Brazil, and thetufted capuchin (Sapajus apella), also in Brazil.[23] The proboscis is armed with 42 hooks without barbs arranged into six rows of four hooks each followed by six rows of three hooks each. This species can be identified by its clustered cement glands and long leminisci that reach the anterior testis.[2] The species namerugosus is Latin for 'wrinkled'.
P. septemserialis is considered by Gomeset al. in 2019 to have an uncertain taxonomic status due to differences between theparatypes morphological characteristics and the original description, the similarity in hosts (primates of the familyCallitrichidae including theblack tamarin (Saguinus niger),[24] and the absence of samples or measurements of adult males. Morphologically, new observations by Gomeset al. in 2019 suggest it is synonymous withP. lenti.[2] Specifically, the original description of one paratype described the lack of a collar at the base of the proboscis whereas a collar was observed in the paratype by Gomeset al. in 2019 (suggesting affiliation with the genusProsthenorchis). A second discrepancy from another paratype is the number of hooks; 12 longitudinal rows of four hooks with total of 48 hooks were observed by Gomeset al. in 2019 but contradicts the seven rows of seven hooks with a total of 49 hooks given in the original description by Machado-Filho in 1950. The nameseptemserialis refers to the seven rows in series.[16]
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The nearlycosmopolitan distribution ofPachysentis species is determined by that of its many hosts.Pachysentis species have been found in South America (Brazil), Africa (Egypt and Angola), and Asia (Egypt and Iran).[2]
The life cycle of an acanthocephalan consists of three stages beginning when an infective acanthor (development of an egg) is released from the intestines of thedefinitive host and then ingested by an arthropod, theintermediate host. The intermediate hosts of mostPachysentis species are not known. When the acanthormolts, the second stage called the acanthella begins. This stage involves penetrating the wall of themesenteron or the intestine of the intermediate host and growing. The final stage is the infective cystacanth which is thelarval or juvenile state of an Acanthocephalan, differing from the adult only in size and stage of sexual development. The cystacanths within the intermediate hosts are consumed by the definitive host, usually attaching to the walls of the intestines, and as adults they reproduce sexually in the intestines. The acanthor is passed in thefeces of the definitive host and the cycle repeats.[27]
Pachysentis species exclusively parasitize primates and carnivorans as their primary host.[2]Paratenic hosts (hosts where parasites infest but do not undergo larval development or sexual reproduction) forPachysentis have been found forP. ehrenbergi (Egyptian cobra,Naja haje)[18] andP. canicola (western diamondback rattlesnake,Crotalus atrox).[15] There are no reported cases of anyPachysentis species infesting humans in the English language medical literature.[26]
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