A study on the occurrence of pinworms in the hindgut of Periplaneta americana

Abstract

American cockroach, Periplaneta americana harbours pinworms in their gut. In the present study, 88 host cockroaches were dissected and the number of adult females of each pinworm species was recorded from Barasat, North 24 Parganas, West Bengal. Three species of Oxyurid nematodes were found: Hammerschmidtiella diesingi (Hammerschmidt, Helminthologische Beiträge. Isis (oken), Leipz 5:351–358, 1838), Leidynema appendiculatum (Leidy in Proc Acad Natl Sci Phila 5:100–102, 1850) and Thelastoma sp. (Leidy in Proc Nat Acad Sci Phila 4:30, 1849). At a time two nematode infections (double infection) were also found. H. diesingi and L. appendiculatum mixed infection being more common than H. diesingi and Thelastoma sp. infection. Ed the H. diesingi shown highest prevalence (40.90%) and abundance pattern (1.227). It was the dominant species in most cases. Lowest prevalence (7.95%) and abundance pattern (0.272) was found in Thelastoma sp. Thelastoma sp. has the highest mean density (3.428) followed by Hammerschmidtiella diesingi (3) and Leidynema appendiculatum (2.368). Three species were never found in the same host. This study suggests that host sex had no noticeable impact on the occurrence of pinworms.

Introduction

Cockroaches constitute one of the most diverse groups of insects with about 4500 species that inhabit the most varied environments on Earth (Rentz 2014). They belong to the order Blattodea and preferentially inhabit tropical and temperate forests (Beccaloni and Eggleton 2013). The animal parasitic nematodes belonging to Order–Oxyurida, constitute two super-families–Oxyuroidea (nematode parasitising vertebrates) and Thelastomatoidea (the nematode parasites of invertebrates essentially arthropods). The Thelastomatides are parasitic (or commensal) in the hind gut of most saprophytic insect and other arthropod hosts and feed on bacterial fauna (Jex et al. 2005). Oxyurid nematodes (commonly known as pinworms) are ubiquitous and abundant in Periplaneta americana, often occurring in 80% of laboratory populations (Tsai and Cahill 1970). It is still poorly understood how these worms affect their host. One of the genera of pinworm is Leidynema, which was first described by Schwenk 1926 (in Travassos 1929), with L. appendiculatum (Leidy 1850) as type species (Leidy 1850). Several parasitic nematode species like Thelastoma bulhoesi, T. periplaneticola, Hammerschmidtiella diesingi, Leidynema appendiculata sometimes co-infect American cockroaches (Dobrovolny and Ackert 1934; Chitwood 1932; Adamson and Noble 1993). In India, many authors have reported different species of nematodes of cockroach (Periplaneta americana L.) from different parts of India at different times (Basir 1940; Parveen and Jairajpuri 1980; Singh and Kaur 1988; Mathur and Khera 1989; Majumder and Khan 1992). However, detailed information on the occurrence and density of these parasites in P. americana is still limited in India. Thus the main objective of this study was to compare the prevalence, abundance and mean density of these closely related nematode species in P. americana collected from Barasat, North 24 Parganas, West Bengal, India.

Materials and methods

Collection of cockroach host (Periplaneta americana) and isolation of parasitic nematodes

P. americana were collected from different regions of Barasat, West Bengal which is a suburb in the outskirts of Kolkata, West Bengal, India and the district headquarter of the district North 24 Parganas. The city is located at latitude 22.72 North and longitude 88.48 East.

Eighty-eight live cockroach specimens were collected and dissected between September 2016 and December 2016 and the number of adult females of each pinworm species was recorded. After collection, nematodes were dehydrated by slow dehydration process in alcohol glycerin mixture. After that the dehydrated nematodes were mounted on glass slides. Observations were made using an optical microscope equipped with an ocular micrometer. Photographs of the specimens were taken using Carl Zeiss Axio Scope A1microscope. Taxonomic identifications were made following Chitwood (1932).

Estimation of parasites

Prevalence, abundance and mean density of the pinworms were estimated through the following formula proposed by Margolis et al. (1982) as: Prevalence of Infection = Total number of infected cockroach/Total number of cockroach host examined × 100. Parasite Abundance = Total number of parasites recovered/Total number of cockroach host examined. Mean Density = Total number of parasite recovered/Total number of infected cockroach host.

Statistical methods

The effect of sex on prevalence and mean density was assessed and compared in all the isolated nematode species. Average (mean value) was calculated using the relation. Average = mean value of individual observation/Total no. of observations. Mean value of individual observation = Total no. of parasites found/No. of host dissected on a particular day (Shah et al. 2005). Tests of significance were determined at the probability level of p < 0.05 i.e. the differences were considered to be significant when the p value obtained was less than 0.05.

Results

Three species of Oxyurid nematodes were found in the gut of American cockroach. These are Hammerschmidtiella diesingi (Hammerschmidt 1838) and Leidynema appendiculatum (Leidy 1850) and Thelastoma sp. (Leidy 1849) (Figs. 1, 2, 3). Single species infections were more common in nymphal stages of the hosts and double species infections are common in the adults. In the adult cockroach at a time two nematode species infections were found. Double infection of H. diesingi and Thelastoma sp. were less frequent than H. diesingi and L. appendiculatum infection. Co infection of Leidynema appendiculatum and Thelastoma sp. was never found. H. diesingi showed the highest prevalence (40.90%) and abundance pattern (1.227). It was the dominant species in most of the cases. Lowest prevalence (7.95%) and abundance pattern (0.272) was found in Thelastoma sp. (Table 1) Thelastoma sp. has the highest mean density (3.428) followed by Hammerschmidtiella diesingi (3) and Leidynema appendiculatum (2.368). These three species were never found in the same host.

Fig. 1.

Photomicrographic details of Hammerschmidtiella diesingi. a Adult female head with pseudo bulb. b Egg filled Uterus. c Egg. Scale bars. a 100 μm; b 100 μm; c 40 μm

Fig. 2.

Photomicrographic details of Leidynema appendicultum. a Adult female head with end bulb. b Egg. c Adult female tail with lateral alae (arrow) Scale bars, a 100 μm; b 40 μm; c 150 μm

Fig. 3.

Photomicrographic details of Thelastoma sp. a Adult female head with end bulb. b Egg filled Uterus. c Egg. Scale bars. a 100 μm; b 100 μm; c 40 μm

Table 1.

Average prevalence (%), abundance and mean densities of nematodes from the hind gut of P. americana collected from Barasat, Noth 24 Parganas, West Bengal

No. of hosts examined	No. of host infected	No. of parasites recovered	Parasite species	Prevalence (%)	Abundance	Mean density
88	36	108	Hammerschmidtiella Diesingi	40.90	1.227	3
	19	45	Leidynema appendiculatum	21.59	0.511	2.368
	07	24	Thelastoma sp.	7.95	0.272	3.428

Sex wise prevalence: The prevalence of pinworm infection in the two sexes was also calculated separately. The available data also showed that there is no significant difference in prevalence (p > 0.05) between male and female P. americana (Table 2) for the three types of nematodes. So, probably, the prevalence of infection by these nematodes may have no sex-linked preference.

Table 2.

Sex wise prevalence of nematodes from the hind gut of P. americana collected from Barasat, North 24 Parganas, West Bengal

	No. of cockroach examined	No. of cockroach infected	Prevalence (%)	No. of observation	Average (±SD)
Hammerschmidtiella diesingi
Male	44	17	38.63	4	0.372 ± 0.21
Female	44	19	43.18	4	0.427 ± 0.19
Leidynema appendiculatum
Male	44	09	20.45	4	0.211 ± 0.15
Female	44	10	22.73	4	0.235 ± 0.49
Thelastoma sp.
Male	44	03	6.818	4	0.230 ± 0.1
Female	44	04	9.09	4	0.307 ± 0.27

Mean densities of Hammerschmidtiella diesingi and Leidynema appendiculatum and Thelastoma sp. in male P. americana were 3.647, 2.777 and 5.333 respectively (Table 3). Mean densities of Hammerschmidtiella diesingi and Leidynema appendiculatum and Thelastoma sp. in female P. americana were 2.421, 2 and 2 respectively (Table 2). As both male and female cockroaches were infected with three species of nematodes the mean number per host of each species was compared by means of a Student’s t test for males versus females (Table 3). All tests of significance were determined at the probability level of p < 0.05. The results showed that there is no significant difference in mean densities between male and female pinworm infections.

Table 3.

Sex wise mean densities of nematodes from the hind gut of P. americana collected from Barasat, North 24 Parganas, West Bengal

Isolated parasites	No. of male cockroach infected	No. of parasites	Mean density	No. of female cockroach infected	No. of parasites	Mean density	Male (SD)	Female (SD)
Hammerschmidtiella diesingi	17	62	3.647	19	46	2.421	±3.185	±2.116
Leidynema appendiculatum	09	25	2.777	10	20	2	±2.439	±1.414
Thelastoma sp.	03	16	5.333	04	08	2	± 2.08	±1.4

Discussion

P. americana is infected by several pinworm species which also infects other host species (Ozawa et al. 2014) indicates that pinworms are less host specific.

In India, Basir (1940) described three species of Thelastomatidae in the gut of Periplaneta americana viz Hammerschmidtiella diesingi, Thelastoma aligarhica and Periplaneticola mirzaia from Aligarh (Northern India). Only in one case, a single cockroach harboured all the three different species of nematodes. Subsequently, Parveen and Jairajpuri described a new species Schwenkiella atheri sp. from P. americana in 1980. Farooqui (1970) described for the first time Thelastoma alli from intestine of Spirostreptus species at Aurangabad, Maharashtra. Later it was redescribed by Singh and Malti (2003) from P. americana at Meerut (Utter Pradesh). Shah et al. (2005) recovered a new species of the genus Protrellus from P. americana in Manipur, North East India. However, most of the previous studies were limited to morphological study and taxonomic identification.

Thelastomatid nematode parasitism was studied in the hindgut of P. americana by Majumder and Khan (1992). Effects of multiple species infection of nematodes in P. americana were reported by Renapurkar and Gosavi (1992). Shah and Jairajpuri (2000) showed the prevalence of some parasitic nematodes of insects in different season from Manipur, India. But, till date there is no comparative prevalence, mean density data of three species of gut nematodes of P. americana from West Bengal, India. The present study showed that Hammerschmidtiella diesingi are most prevalent (40.9%) in adult cockroach among the three species of nematodes. On the other hand, Thelastoma sp. had lowest prevalence (7.95) but highest mean density (3.428) in P. americana. Interestingly, Leidynema appendiculatum were mostly found in juvenile cockroach. It is important to note that the population of nematodes was found to be dependent on the co-infected Nyctotherus ovalis in P. americana. Nematode population was usually less in protozoan infected hosts. The prevalence of nematode infection did not differ significantly between the two sexes. These data corroborated well with the observation of Yu and Crites (1990). Therefore, it can be concluded that host sex had no noticeable impact on the occurrence of the nematodes in P. americana.

It is important to note that the co-occurrence of H. diesingi-Thelastoma sp. were less than H. diesingi-L. appendiculatum. So it would be interesting to study in future the individual role played by these species in nematode-host interaction and nematode–nematode interaction. Another interesting observation of the present study was that L. appendiculatum and Thelastoma sp. never coexisted in the same host. Thus, it raises the question whether any species antagonism between L. appendiculatum and Thelastoma sp. exist or not. The present study has generated several questions regarding species interaction which needs further investigation.