62 Zoonotic hookworm infections

Hookworms on occasion cause creeping lesions in the superficial layers of the human skin that have been designated as cutaneous larva migrans for the purpose of contrasting the condition with visceral larva migrans. Currently, the disease is presenting most commonly to physicians specializing in tropical or travel medicine in patients who have just visited a tropical beach and are presenting with serpiginous tracks in their skin. The serpiginous tracts can persist for week, and are often pruritic, may be associated with accompanying bulla, and can rarely lead to secondary sequelae. The larval are likely to penetrate ultimately to deeper tissues, where they may be persisting in the tissues of humans in the same fashion as they would within the tissues of any other vertebrate paratenic host.

Most hookworm larvae are capable of penetrating the skin and causing lesions that are similar to cutaneous larvae migrans. However, the geographic distribution of cases still seems to suggest that only one species, A. braziliense, is the offending species. The other species appear to spend less time in the skin of the human host, and if they do cause lesions, they appear to produce lesions that are more vesicular or that cause disease of a markedly shorter duration. It seems that the development of improved molecular methods will ultimately lead to the means of more carefully discrimination the geographical location of the offending species and may someday be able to identify specific larvae from lesions.

There are other manifestations of zoonotic hookworm infection. These include the infection of the human intestinal tract with the adults of the canine/feline hookworm Ancylostoma ceylanicum; the induction of cases of eosinophilic colitis in people with the canine hookworm, Ancylostoma caninum; suspected cases of ocular larva migrans due to hookworm larvae, and the rare case of cutaneous larva migrans due to hookworm species that are only rarely associated with human infections.

The zoonotic hookworms typically associated with human disease are the common hookworm species of the dog and cat. Hookworm larvae are members of the superfamily Ancylostomatoidea. Therefore they are almost all capable of infecting the final host through skin penetration (Anderson 2000). Consequently it is likely that many of these larvae could cause skin penetration and infection in humans. However, most have been little studied in comparison to those of the dog and cat, and for the most part have not been of any reported significance in human zoonotic hookworm disease.

Zoonotic hookworm infections manifest in several different presentations. One species is responsible for hookworm infections of the small intestine in people and is similar to human hookworm species. In a second species, that infects dogs and cats, the larvae can cause significant human disease through the production of serpiginous pruritic tracts in the skin. A third form of infection is the development of canine hookworms to adulthood in people causing eosinophilic colitis. Hookworms that enter vertebrate paratenic hosts are capable of persisting in the tissues of these hosts for extended periods, and thus, after larvae penetrate the skin, they are capable of persisting in muscle and other tissues for very long times. There is some suggestion that the zoonotic hookworm infections are capable of causing ocular lesions, including retinochoroiditis. Finally, there have been skin lesions induced in people on rather rare occasions with the hookworms or ruminants or with other hookworm species of wildlife; these have typically presented as cutaneous lesions.

Looss was the first to show that hookworm larvae could penetrate the skin. First through the accidental spilling onto his own skin of a culture of third-stage larvae of the human hookworm, Ancylostoma duodenale, followed by careful work on the migratory behaviour of Ancylostoma caninum of the dog (Looss 1905). This led to the general elucidation of the hookworm life cycle. In hookworm endemic areas, the lesions induced in the skin of people by the penetrating human hookworm species, Ancylostoma duodenale and Necator americanus, was termed ground itch (Smith 1904). Working in Florida, USA, Kirby-Smith et al. (1926) recognized another condition wherein the larvae persisted in the skin for extended periods, and reported over 2,500 diagnosed cases that he distinguished from the ground itch of N. americanus. Not long afterward, it was shown in human volunteers that the larvae of the canine hookworm, Ancylostoma braziliense, caused lesions consistent with those of creeping eruption (cutaneous larva migrans) in human volunteers, while the larvae of the canine hookworm, Ancylostoma caninum, caused only transient papules, similar to that which occurred in ground itch (White and Dove 1928). Interestingly, there has only been one attempt to infect a person with the larvae of Ancylostoma tubaeforme, and this attempt proved unsuccessful (Kalkofen 1987).

Unfortunately, the two species, Ancylostoma braziliense and Ancylostoma ceylanicum, are very similar morphologically, and this caused significant confusion for a period. A. braziliense was described in 1910 by Gomes de Faria in Brazil from specimens recovered from cats and dogs. Looss (1911) described A. ceylanicum based on specimens recovered from a civet cat in Ceylon. Then, a few years later three human prisoners in India were found to have hookworms identified as A. ceylanicum (Grove 1990). The literature then became confused as to the existence and geographic distribution of the two species. Methods for distinguishing the two species were put forward by Biocca (1951), and single-sex cross-over experiments between the two species showed that fertile eggs were produced only when both sets of worms were either one species of the other. The distinction of the two species is also supported by the fact that human infections with A. braziliense have not been confirmed in areas where this is the only one of the two species present (Beaver 1956). A. ceylanicum is an important zoonotic agent in that it is capable of growing to adulthood in people, but it does not produce the same cutaneous larva migrans lesions as A. braziliense.

Cutaneous larva migrans in the south eastern USA has also been called ‘plumber’s itch’, because the lesions appear on plumbers and other labourers who have crawled under the typical coastal-style house with a raised floor. They lie on their backs in the moist shaded sand to do their work, and many of them subsequently develop cutaneous serpiginous lesions. An outbreak, with lesions appearing on arms, legs, or back, involved eight pipe fitters and a painter working in a three-foot crawl space under a new hospital being built at Patrick Air Force Base in Florida (Fuller 1966). An outbreak of cutaneous larva migrans occurred in 22 campers and staff at a children’s camp in the Miami area, attended by approximately 300 children (two to 15 years of age) and 80 staff members. Based on the higher proportion of infection among younger campers, the Miami-Dade County Health Department determined the outbreak was associated with a contaminated sandbox. Two feral cats had been observed at the camp and were removed from the premises (O’Connell et al. 2007).

The larvae of the zoonotic hookworms that succeed in penetrating the skin are likely to undergo a lung migration in the human host. Pneumonic radiographic lesions (Loeffler’s syndrome) has been diagnosed in patients after creeping eruption, 26 of 76 such patients (Wright and Gold 1946). Muhleisen (1953) found hookworm larvae in the sputum of a person 12 to 36 days following exposure to soil heavily contaminated with dog faeces, and on the basis of the minimal lesions associated with the sites of penetration, believed that the infection was due to A. caninum rather than A. braziliense. Recently, a case of Loeffler’s-like syndrome was reported in a person returning to France from Thailand with cutaneous larva migrans (Del Giudice et al. 2002).

The larvae in people who have suffered from cutaneous larva migrans and have not received treatment may possibly persist in muscle tissues as has been shown to occur in the paratenic hosts. In guinea pigs, larvae of A. caninum were recovered from skeletal muscle three years after infection, and larvae were recovered from swine belly fat 6 months after infection (Stone et al. 1979). In one human case where serial sections of a muscle biopsy was examined from a person three months after presenting with cutaneous larva migrans, a larva was found in the tissue (Little et al. 1983).

Human cases of cutaneous larva migrans are being reported most commonly at this time in travellers returning from areas where A. braziliense occurs. Thus, the cases are presented very typically to physicians specializing in tropical or traveller medicine. These cases are reported from around the world, but typically represent cases wherein people have returned home from an area where A. braziliense is known to be present (Biolcati and Alabiso 1997; Hochedez and Caumes 2007; Jensenius et al. 2008; Park et al. 2001; Prudhomme et al. 2002; Rivera-Roig et al. 2008; Senba et al. 2009; Veraldi and Arancio 2006). Fortunately, this is not a life threatening infection, but for a number of individuals, vacations are turned into tribulations. The problem is basically one of stray dogs and cats having access to beaches.

Treatment of cutaneous larva migrans can be quite successful. Cases are now treated with albendazole or ivermectin (Caumes et al. 1993; Hochedez and Caumes 2007; Senba et al. 2009), although thiabendazole is still used occasionally with very gratifying outcomes (Gourioto et al. 2001). In athletes, such as beach volleyball players, the concern is that the lesions can reduce performance and ability to enter competitions (Biolcati and Alabiso 1997).

It is the hookworms of the canine and feline companion animals that are most often associated with zoonotic hookworm disease. The hookworms commonly found in dogs are: Ancylostoma caninum, A. braziliense, A. ceylanicum, and Uncinaria stenocephala. The hookworms commonly found as adults in cats are: Ancylostoma tubaeforme, A. braziliense, A. ceylanicum, and U. stenocephala. However, U. stenocephlala rarely occurs in cats in the USA (Bowman et al. 2001). Except for A. ceylanicum, a species found in India and Southeast Asia, the parasites generally do not complete their life cycles in the human host (Beaver et al. 1984).

The life of a hookworm begins with first-stage larvae hatching from eggs passed in the host’s faeces. Eggs are not immediately infective but must first develop from the morula stage. There is then a period of development of the microbiverous larva in the soil to the infective, non-feeding third-stage larva. In the dog and cat hookworm larvae from the Ancylostomatidae branch enter the host mainly through skin penetration. However in the case of Uncinaria stenocephala and other members of the Bunostomidae the larvae are more likely to utilize oral infection of hosts (Anderson 2000).

After infective larvae enter the host, in adult dogs, a large proportion of A. caninum infective larvae undergo somatic migration and sequester in the tissues to be reactivated later, typically during lactation. Thus, puppies are often infected via the milk by the transmammary route. Transmammary infection does not routinely occur with other species such as U. stenocephala, A. tubaeforme, A. ceylanicum, and A. braziliense.

Hookworms of carnivores utilize paratenic hosts. The Ancylostoma spp. of dogs and cats are capable of being sequestered in the tissues of vertebrate paratenic hosts where they persist without any development, thus infection via hunting is a possibility with these species. It has also been shown that A. caninum is capable of persisting in the tissues of cockroaches and other insects, which probably aids in their reaching the tissues of paratenic hosts like rodents that are more likely to be eaten by the carnivorous final hosts.

Several species of the canine and feline hookworms cause significant blood loss into the intestine of the hosts, i.e. A. caninum, A. tubaeforme, A. ceylanicum. The blood loss due to the adult worms in the dog and cat (and people) can lead to hookworm associated disease related to anaemia. Peracute and acute disease from blood loss is particularly important and sometimes fatal in young puppies and kittens. Other hookworms such as Uncinaria and A. braziliense cause negligible blood loss (Miller 1971).

A. ceylanicum is an infection that humans can share with dogs and cats. The infection is induced by larvae penetrating the skin. The lesions that develop at the penetration site resemble those of ground itch rather than those of A. braziliense induced cutaneous larva migrans (Bearup 1967; Haydon and Bearup 1963; Maplestone 1933; Wijers and Smit 1966). There is pain associated with the infection during the period when the adults first appear in the intestinal tract following an infection (Carrol and Grove 1986; Wijers and Smit 1966). In most people infected with A. ceylanicum, the infections are short lived and produce few if any eggs after the worms develop to adulthood (Chowdhury and Schad 1972; Carroll and Grove 1986). However, in New Guinea, people are infected with large numbers of these worms and develop anaemia from the infections (Anten and Zuidema 1964). Treatment of these infections is the same as for other intestinal dwelling hookworms of people.

Several cases of eosinophilic enteritis have been attributed to infection with A. caninum, presumably following exposure to contaminated soil with infective larvae. Patients presented with mild to severe enteritis, abdominal pain, and peripheral eosinophilia as well as eosinophilic infiltration of the bowel wall. In some patients, immature adult A. caninum worms were found in the bowel lumen, indicating complete migration and attempted maturation within the gut (Croese et al. 1994a). Most reports of this infection have occurred in north-eastern Australia, where more than 200 cases were diagnosed clinically and serologically over a period of 4 years (Croese et al. 1994a, b). In these cases, solitary and immature adult hookworms were found in only 15 patients and identified as A. caninum in nine. Most of the cases had eosinophilic enteritis, but one was entirely asymptomatic.

In an attempt to reproduce the disease in a human volunteer, infections with A. caninum have been attempted (Langmann and Prociv 2003). In this study, a human volunteer was infected with small numbers of infective larvae that were administered orally and percutaneously to an informed healthy volunteer under medical supervision, over a period of a year. The volunteer was examined regularly for symptoms and weekly for blood eosinophil counts and the presence of eggs in the faeces by microscopy. The patient developed a marked blood eosinophilia followed a single oral exposure to 100 infective larvae, while faecal examination remained negative. Eosinophil counts then declined gradually, although a rapid, spontaneous rise several months later, at the beginning of the next spring did occur. Blood eosinophil numbers did not rise significantly after a secondary percutaneous infection with 200 larvae. However, a subsequent, smaller, oral inoculum of 20 larvae provoked an eosinophil response similar to that of the first oral infection. It was concluded that following ingestion of larvae that some developed directly into adult worms in the human gut (as they do in dogs) and that the percutaneous route of exposure, while being the most common means of human exposure, leads mainly to subclinical infections, and that oral exposure might be the means of the induction of the symptoms of eosinophilic enteritis. Other studies in people have utilized percutaneous infections with A. caninum, and in the case of heavy exposure, perhaps with thousands of larvae, there was the induction of numerous papules and pustules, with some being accompanied with short, migratory tracts that can recur at variable intervals and widely separated sites, for up to 7 months (Hunter and Worth 1945; Miller et al. 1991). The application of A. caninum larvae to human skin have thus routinely failed to induce lesions similar to the continuous, intermittently migratory creeping eruptions of A. braziliense.

With the experimental infection of a human with oral A. caninum larvae (Langmann and Prociv 2003), the presentation of eosinophil enteritis remains variable and difficult to impossible to diagnose. The typical manifestations include recurrent abdominal pain. Severe cases have presented with an acute abdomen, sometimes with distal small bowel obstruction, with little choice but surgical intervention. In most cases, there is peripheral blood eosinophilia, but it may be absent in the early acute phase (Croese et al. 1990). Also, high serum IgE levels are a common non-specific feature. Radiographs may reveal, with and without contrast studies, small bowel thickening and obstruction.

In cases where laparotomies have been performed, they have revealed inflamed segments of distal ileum, varying in length from 2 to 100 cm, with intense serositis and, sometimes, turbid (eosinophilic) ascites. Occasionally, the colon, caecum and appendix are involved. Other patients will develop milder, intermittent, or chronic patterns of illness, which can persist for years. Occult or frank intestinal blood loss can occur, and presentation in these cases may be precipitated by rectal bleeding. Colonoscopy often reveals focal inflammation and or ulceration of the terminal ileum and colon. In subclinical, or chronic cases, small aphthous-like ulcers of the ileal and caecal mucosa suggest hookworm attachment site lesions (Croese et al. 1996). In most cases, symptoms are not severe enough to justify surgery or colonoscopy, but blood eosinophilia does suggest the diagnosis.

The histopathology of canine hookworm enteritis is described in detail elsewhere (Walker et al. 1995). The ileal segment may appear grossly inflamed and oedematous, and all layers of its wall may be heavily infiltrated with eosinophils. This undoubtedly represents a true allergic response, in people sensitized to secretory products of developing third- or fourth-stage larvae or adult worms. It seems unrelated to the intensity of exposure, although eosinophil enteritis has not yet been diagnosed in a patient known to have been exposed to large numbers of third-stage larvae. In not one case has there been evidence of preceding cutaneous larva migrans of Loeffler’s syndrome.

Patent human infection with A. caninum has never been documented, making the diagnosis of eosinophilic enteritis very difficult, in the absence of a worm or a tissue specimen. Among patients with confirmed eosinophilic enteritis, or who have typical clinical features and blood eosinophilia, 70% have circulating IgG and IgE antibodies to adult A. caninum excretory-secretory antigens (ES Ags) demonstrable by ELISA. In the city of Townsville, 30% of patients who complain of non-specific, recurrent abdominal pain but do not have blood eosinophilia are seropositive, compared with 8% of healthy controls (Croese et al. 1994a). A Western blot using ES antigens of A. caninum is more sensitive and specific than the ELISA; more than 80% of patients with eosinophilic enteritis demonstrate antibodies to a protein fraction of molecular weight 68 kDa (Ac68). Detection of specific IgG4 antibodies by immunoblot may be even more sensitive and specific (Loukas et al. 1996). However it is premature to incriminate Ac68 as the putative allergen, for the correlation between disease severity and specific antibody levels is poor.

One of the strongest IgE responses, both in Elisa and immunoblot, was from an asymptomatic man with a solitary adult A. caninum, whereas a woman with florid eosinophilic enteritis and a worm in situ was seronegative (Croese et al. 1994b). Monoclonal antibody studies indicate that Ac68 originates from the excretory glands of adult A. caninum, whereas sera from patients often bind more strongly to amphidial gland cytoplasm, suggesting that another molecule is allergenic (Sawangjaroen et al. 1995).

Hookworm eosinophilic enteritis can be diagnosed only if clinicians are aware of the disease. The histopathological diagnosis is confirmed by examining biopsy material, but rarely is a worm found to establish the etiology. Furthermore, even experienced pathologists can overlook the small, inconspicuous parasite embedded between oedematous mucosal folds (Walker et al. 1995). Present serology is neither adequately sensitive not specific for diagnosis acute cases, and the surgeon may not be able to await test results. Nether the ELISA nor Western blot distinguishes infections with A. caninum from those with anthropophilic hookworms (which can be diagnosed coprologically).

Treatment is simple: a single 300 mg dose of mebendazole usually brings about a dramatic resolution of symptoms within 24 hours. In fact, failure of response suggests a mistaken diagnosis. A smaller dose, or another anthelminthic, such as pyrantel, may also prove to be effective, but has not been clinically trialled. Having anti-inflammatory and anti-eosinophil activity, corticosteroids also rapidly suppress the symptoms, but are less specific in their action than anthelminthics. Many patients relapse, weeks or months later, apparently without re-exposure, to infection. This, and the seasonal incidence of eosinophilic enteritis (Croese 1995) suggest that sporadic activation of dormant larvae underlies the intermittent appearance of immature adult worms in the gut, but currently available anthelminthics are unlikely to eradicate hypobiotic third-stage larvae sequestered within muscle fibres.

There are a few other reports from outside Australia where hookworms suspected of being A. caninum were associated with eosinophilic enteritis (Khooshoo et al. 1994, 1995; Bahgat et al. 1999). Two reports occurred in New Orleans, LA, USA, but there have since been no additional reports from the USA. In the one other report, out of 95 patients within Egypt with eosinophilic enteritis and unexplained abdominal pain with peripheral eosinophilia, 11 patients were considered as being potentially infected with A. caninum on the basis of serotesting by IgG ELISA to detect antibodies to excretory/secretory (ES) antigens of adult A. caninum and by IgG and IgG4 Western blot (W.B.) to detect antibodies to Ac68 antigen. The 11 patients presented with acute abdomen (5), appendicitis (3), or recurrent mild to moderate abdominal pain (3). In other patients in this study with human hookworms, there was cross reaction in the antibody tests used and the only differential for the A. caninum suspected cases was the lack of hookworm eggs present in the stools.

Hookworm larvae are suspected, along with Toxocara spp., Baylisascaris spp., and possibly some other yet unidentified small nematode larvae, as a possible cause diffuse unilateral sub-acute neuroretinitis, a form of ocular larva migrans, which can lead to loss of vision, inflammation in the posterior eye, and retinal lesions. Two different size ranges of nematode larvae have been observed in the affected eyes of patients with diffuse unilateral subacute neuroretinitis; based on the size of observed larvae in some cases, A. caninum is considered a likely cause, along with Toxocara spp. and Baylisascaris procyonis (Goldberg et al. 1993; Sabrosa et al. 2001). As of yet, such infections have not been demonstrated by larval isolation as specifically being due to the larvae of zoonotic hookworms.

There have been a number of reports of hookworms in people that have been due to hookworms that usually do not appear to cause disease in humans. These include Necator suillus, Cyclodontostomum purvisi, Ancylostoma malayanum, Bunostomum phlebotomum, and Uncinaria stenocephala.

Necator suillus Ackerrt and Payne, 1922, found in Trinidad and Central America, is a porcine hookworm very similar to N. americanus. While the latter does not develop in pigs, it probably evolved from N. suillus (Schad 1991) and its third-stage larvae can invade pig skin to cause ground itch (Ackert and Payne 1923). Buckley (1933) cultured eggs from adult N. suillus and infected himself percutaneously. Lesions developed at the entry site, and 54 days later, hookworm eggs appeared in his stools. Infection remained patent for four months, until treatment with oil of chenopodium expelled three adult N. suillus. He did not report abdominal symptoms, but speculated that this species may account for some presumed N. americanus infections in people living close to pigs.

Cylclodontostomum purvisi (Adams, 1933) is a parasite of the large intestine of rats in southeast Asia. Two adult specimens, a male and female, were found incidentally in the faeces of a 47 year old man in Thailand (Bhaibulaya and Indragarm 1975). No clinical significance could be attached to this case.

Ancylstoma malayanum (Alessandrini, 1905) infects bears in India and southeast Asia, and has a buccal capsule like that of A. duodenale. It is the largest member of the genus, with males growing to 15 mm and females to 19 mm. One case of human infection has been reported (Beaver et al. 1984).

Bunostomum phlebotomum occurs in cattle and related ungulates in most warm and temperate regions (Soulsby 1982; Anderson 2000), and can cause human cutaneous infection (Mayhew 1947).

Uncinaria stenocephala was reported as being able to cause percutaneous infection by Fülleborn in 1927 (Grove 1990).

Cases of cutaneous larva migrans have described in recent years from the UK, Germany, and Italy, but the agent(s) have not been clearly elucidated. One case in Great Britain was a 50 year old man who presented with a rash after paint-balling 3 weeks previously during the month of October (Diba et al. 2004). He had stored his fatigues in a shed where a dog was kept. Eight days after the event, there were approximately 40 lesions on the medial surface of his left forearm and his abdomen. He then noticed multiple itchy thread-like eruptions emanating from the marks, which also seemed to have shifted location. There was no recent history of travel abroad, but he had travelled to Sri Lanka 3 years previously. A biopsy did not reveal any hookworm larvae, but he did respond to treatment with oral albendazole at 400 mg twice a day for 5 days. It was assumed that the infection was due to U. stenocephala due to the lack of A. caninum in the area.

Two other cases of cutaneous larva migrans have been reported in the UK, both lesions appeared on the buttocks of individuals and have responded to therapy with either albendazole of ivermectin. There was also a report of cutaneous larva migrans acquired autochthonously in Germany (Klose et al. 1996) and cases from Italy (Albanese et al. 1995; Galanti et al. 2002) that included 6 persons that were infected with an association with potting soil used in flower arrangements. There have been 3 cases of autochthonous cutaneous larva migrans acquired in New Zealand, two in children in the northern town of Kaitaia and one in an 80 year old lady gardener in Christchurch (Bradley 1999; Manning et al. 2006). New Zealand is not known to have any A. braziliense, has only rare infections with A. caninum that was first observed in the country in 1976.

Hookworms have been introduced with pet dogs and cats into areas that span the globe along with their hosts. Thus, the most common canine and feline hookworms, A. caninum and A. tubaeforme, respectively, occur to some extent in most areas where cats are found. Interestingly, both A. braziliense and A. ceylanicum which are capable of infecting both dogs and cats have a more limited geographical distribution than A. caninum and A. tubaeforme. U. stenocephala has a range that extends into colder climates than the Ancylostoma species, appears capable of infecting cats and dogs, has an egg that is morphologically distinguishable from that of the members of the genus Ancylostoma, but has a distribution that is more poorly described than that of the Ancylostoma species.

This is a parasite of dogs and cats that also occurs is various wild canids and felids. The geographic distribution of this parasite was recently re-examined relative to its presence around the world with the application of both morphologic and genetic methods (Traub et al. 2007). This species has been reported along the eastern Atlantic and Gulf coast of the USA, through the Caribbean islands, and on the east coast of Mexico into Surinam, Brazil, and Uruguay. In Asia, A. braziliense appears restricted to the south below latitude 10°N, being reported from Malaysia and Indonesia. The number of cases of cutaneous larva migrans in vacationers from Thailand would indicate that this worm is also highly prevalent in this country.

Again, a recent re-examination of the geographical distribution of this parasite of dogs and cats and wild relatives is reported from India, Taiwan, central Thailand, Malaysia, Borneo, Indonesia, and Surinam in South America with older reports of this worm in Papua New Guinea (Traub et al. 2007).

This is a parasite of dogs and related canids and is present throughout most of the world where dogs are found. It is the most common of the canine parasites and also occurs frequently in wildlife species.

This is the common hookworm parasite of the cat and related felids around the world. This parasite has a worldwide distribution amongst felines around the world.

This parasite is common in dogs and foxes. It occurs in cats, but reports in naturally infected cats are fairly uncommon. It is considered to be a parasite that occurs in more temperature or cooler climates than the Ancylostoma species. It has been reported in the western hemisphere from Canada through Mexico into the northern countries in South America. It has been reported in northern Eurasia and around the Mediterranean (Bowman et al. 2001)

Control and prevention of the transfer of infections with these pathogens from dogs and cats to people requires diligence on three fronts: minimization of the reservoir populations, control of the parasites in the companion animal population, and sanitation to protect public areas from faecal contamination.

There are massive efforts around the world to now reduce the number of unwanted and stray dogs and cats through a multitude of programs that rely strongly on spay and neuter programs. In some cases more draconian programs are used.

Parasite control in companion animals is having a marked effect on the parasites in well-cared for pets relative to the parasites present in shelter animals. Examination of shelter animals in the USA has shown that there are very high numbers of parasites prevalent in these hosts with 19.19% of shelter dogs and 11% of shelter cats having Ancylostoma spp. infections and the current prevalence in shelter dogs remaining similar in a second survey 10 years later (Blagburn et al. 1996; Blagburn personal communication) based on results from about 2/3 of the 10,000 target animal faecal samples from around the USA. Similar numbers for dogs seeing veterinarians was 4.5% for animals on their first visit (Mohamed et al. 2009). Thus, routine veterinary care seems to be capable of minimizing the risk of parasites being present in pets.

Veterinarians are taking a more and more active role in reducing pet infections for the purpose of protecting health and protecting the human animal bond through the minimization of zoonotic risk to client’s from the pets under the veterinarian’s care. In the USA this program has been helped by an interest in the Centers of Disease Control and Prevention in by informing the public as to the risk that these infections may bring and means of their control through proper veterinary attention. It seems that this is making a difference in the number of parasites in pets, and this is a major means of preventing environmental contamination.

The control of faecal waste material and limiting access to pets where faecal deposition can affect public health varies with community interest. However, it is a program that is gaining in the public’s awareness. It is becoming more and more common for people to protect their own welfare and that of children through the proper management of dog and cat excrement. In the case of cutaneous larva migrans, a very large number of cases are associated with beaches, and this means that targeted control may be able to have a major positive outcome without the need to target the whole community.

Finally, there is the matter of wildlife. It seems highly unlikely that it will be possible to institute any significant control measures for wildlife reservoir hosts. However, it depends on the extent of the problem and the will of those involved. However, the process will probably involve the management of pets, then strays, and finally wildlife if the latter occurs at all.

People also need to have significant education as to how to protect themselves from these risks and to minimize the potential risks of others through the covering of sand filled play areas, laws limiting faecal deposition by pets, and the risk of contraction cutaneous larva migrans when on the beach. In discussions with Thai veterinarians, they feel that there are very few cases of cutaneous larva migrans in locals within Thailand while there are many in visitors to Thailand. This may be because local people are less likely to put themselves at risk lounging in areas where the larvae are liable to be prevalent.

Zoonotic hookworm infections appear to still be occurring throughout the world. Currently, the two major areas of increased incidence seems to be in cases amongst tourists from high income countries following visits to beach resorts that have A. braziliense present in the canine and feline population and in people who are somehow at risk of developing eosinophilic colitis due to A. caninum. It would seem that both these outcomes can be minimized through education, awareness, improved sanitation and targeted treatment of the animals that put people at risk.

The development of methods that will allow the determination of species present in a dog or cat through the characterization of faeces with molecular methods is going to provide a means of better delineating where the offending agents are in the world. Also, they may reach a point at sometime in the future where individual larvae if recovered in biopsies or biopsy sections will be able to be identified to actually verify the agents that are causing the observed lesions in people.