Studies On The Entozoa Of Man In New Zealand*
A Note On The Incidence Of Enterobius Vermiculis (Linn.).
The larger entozoa of man held a prominent place in medicine prior to the demonstration of the pathological nature of some bacteria. The development of bacteriology directed attention away from the entozoa, and their study was largely neglected for many years. The past twenty years has seen a revival of researches on the entozoa. This work is showing that the long neglect of these animals has in no way impaired their success. Dr. Norman Stoll has recently brought together available data on the incidence of helminth infestation. In his address, “This Wormy World” (J. Parasit., 33 , 1–18), he estimates the world incidence for several species as follows: 39 million infested with Taenia, saginata; 457 million infested with hookworm; 355 million infested with Ascaris; and, tentatively, 209 million infested with Enterobius, the common pinworm of man.
[Footnote] * This work has been carried out with grants in aid of research from the-National Medical Research Council.
It is clear that there is need of a proper evaluation of the entozoa. They cannot be disregarded in the light of these figures. Infestations may not in all cases have the dramatic results of some bacterial or virus infections. The clinical entities of helminthiases range from patent and serious disease, as in trichinosis and ancylostomiasis, through a series of diminishing intensity to the apparent complete tolerance of seemingly non-pathogenic species such as Trichuris and Enterobius. The clinical significance of the latter species is not clear; but studies on them can contribute much to our understanding of helminthiases in general.
The development of the N.I.H. swab by Hall and his Institute has given a technique for the detection of Enterobius infestation with a high degree of certainty and with reasonable facility. The swab consists of a one-inch square of waterproof cellophane wrapped over the tip of a length of four millimeter glass rod. The rod is passed through a stopper and carried in a test-tube. The cellophane is lightly rubbed over the perianal region collecting any eggs which may be present on the mucous membrane. Six swabs are supplied for each individual, and used one swab on each of six successive days.
In the present study, so far a total of 852 swabs have been distributed to 142 individuals, and 521 swabs have been examined. The majority of these individuals have been contacted through the services of the Royal New Zealand Society for the Health of Women and Children. They are, for the most part, members of young families. The age range within the group is from three weeks to 42 years, with virtually a complete gap in the 16 to 20-year range.
The gross infestation rate is 55%, ranging from 45.5% for children of 0 to 3 years, up to 80% for children of 11 to 15 years of age. There is no indication of acquired immunity to the pinworm. Adults, 20 years to 40 years in age, are commonly infested. Swabs from 40 adults have shown 50% infested, with no indication of any distinction in incidence between the sexes. In gross consideration, the infestation rates of parents are on par with those of children. Juveniles from 0 years to 15 years show an overall infestation rate of 57%. Both parents are as prone to infestation as are children, and the parental group must be regarded as proven potential reservoirs.
Enterobius infestation in this group is familial in nature, and of the thirty-one families so far studied, 74% were found to be infested. Six of the eight negative families have less than four children. Completely negative families as a rule have children all under school age, while families containing children of school age have one or more members infested. An incidence increasing from 47% in families of three individuals to 73% in families of seven individuals is correlated with increasing infestation from the 0 to 3-year group, to the 11 to 15-year group, where in the latter infestation reaches an incidence of 86%, although the number in this group is still small.
The data accumulating in this study must be correlated with our knowledge of the biology of this worm for a clearer understanding of its success in the face of what is considered a reasonably hygienic mode of life such as is followed in modern urban surroundings.
It is essential to keep in mind that there is no evidence of multiplication of this worm within the host. The life-span of the adult is still unknown, but oviposition commences two to four weeks after initial infection. Reardon (U.S. Publ. Health Rept., 53 , 978–983) has shown that the gravid worm carries 4,672 to 16,888 eggs. These are deposited chiefly on the perinaeum, develop to infectivity in six hours in this location, and transferred to clothing are widely distributed. The infective egg contains a larval stage. Eclosion of the larva has so far not been found possible until the egg has been exposed to air. In infested houses, 90% of dust samples from all rooms, taken from the floor, from furniture, and from ledges up to 9 ft. from the floor, contain ova. Under ordinary conditions, 30% survive at least six days. Ova resist fumigation even with hydrocyanic gas, but are remarkably susceptible to heat and low humidity.
Enterobius is a worm having a simple direct life-cycle coupled with a high rate of production of moderately resistant eggs. The eggs are distributed by the actions of the host. Each worm in the host intestine has been released from an ingested egg. Auto-infection is not only possible, but a prominent feature in prolonging infestation. After a latent period, the infested individual is a persistent source of infective eggs. The spread of infestation within the family group is linked with the continuance of infestation through reinfections and the absence of acquired immunity. These are important factors which contribute to the worm's success in maintaining its position even under present urban
ways of life. So far as present data slows, there is an increased incidence in families as the age of the children passes the school-entry level. School contact seems an important factor in the spread of infestation among family groups. This may have further significance.
Shope has shown (J. Exp. Med., 73, 74, 77) that swine influenza is a combination of influenza bacteria and virus, that the virus is harboured in the larvae of lung-worms, where it can survive even up to three years, and can be perpetuated in this way from outbreak to outbreak. This can be coupled with the demonstrated transmission of the virus of equine swamp fever through strongylids, as an indication that there is room to consider helminths generally and nematodes in particular as potential vectors of virus and bacteria.
These findings apparently have not yet been carried over in the investigation of human diseases; but having in mind the variety of “children's diseases,” their seasonal occurrence and other features in their epidemiology such as acquired immunity, it is clear that this is a field deserving of careful research. In such studies, Enterobius should be given careful consideration as a potential vector. It provides, with other entozoa, a potential pathway particularly suited to the transmission of virus from host to host. Whether important in that respect of not, Enterobius is of value in demonstrating the ease with which the intestinal fauna and flora can be transmitted from person to person. It demonstrates the inadequacy of our ordinary hygiene, and in its success shows the need for the encouragement of a very high order of individual hygiene. It is, in fact, a worm worthy of meticulous researches for its own sake and as a study in some aspects of the biology of man.