Über die Autorin bzw. den Autor

J. Scott Weese, DVM, DVSc, DipACVIM, is a zoonotic disease microbiologist at the Ontario Veterinary College and Chief of Infection Control at the Ontario Veterinary College Teaching Hospital.
 
Martha Fulford, MD, FRCPC, is an infectious diseases physician at McMaster University Medical Centre, Hamilton Health Sciences, and medical coordinator for the Waterloo Wellington Infection Control Network.

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Companion Animal Zoonoses is a comprehensive resource on diseases transmissible between animals and humans. Presenting detailed prevention and control strategies for zoonotic diseases, the book is an in-depth guide to practical information on the spread of disease between pet animals and humans. Companion Animal Zoonoses provides up-to-date information on emerging issues, disease incidence and risk, and management measures.

Covering the complete range of companion animal zoonoses, each topic begins with information on etiology, geographic distribution, epidemiology, and pathophysiology and moves into clinical presentation, diagnosis, management, and prevention information for both animals and humans. Companion Animal Zoonoses is an essential reference for practicing veterinarians, public health veterinarians, and veterinary students, and will also appeal to physicians wishing to better understand zoonotic diseases.

Key features

• Comprehensive resource on diseases transmitted between companion animals and humans
• Emphasizes prevention and control strategies for zoonotic diseases
• Provides practical information on preventing the spread of disease between pets and owners or veterinary staff
• Offers an in-depth, current guide with coverage of emerging issues, disease incidence and risk, and management measures

Aus dem Klappentext

Companion Animal Zoonoses is a comprehensive resource on diseases transmissible between animals and humans. Presenting detailed prevention and control strategies for zoonotic diseases, the book is an in-depth guide to practical information on the spread of disease between pet animals and humans. Companion Animal Zoonoses provides up-to-date information on emerging issues, disease incidence and risk, and management measures.
 
Covering the complete range of companion animal zoonoses, each topic begins with information on etiology, geographic distribution, epidemiology, and pathophysiology and moves into clinical presentation, diagnosis, management, and prevention information for both animals and humans. Companion Animal Zoonoses is an essential reference for practicing veterinarians, public health veterinarians, and veterinary students, and will also appeal to physicians wishing to better understand zoonotic diseases.
 
Key features
* Comprehensive resource on diseases transmitted between companion animals and humans
* Emphasizes prevention and control strategies for zoonotic diseases
* Provides practical information on preventing the spread of disease between pets and owners or veterinary staff
* Offers an in-depth, current guide with coverage of emerging issues, disease incidence and risk, and management measures

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Companion Animal Zoonoses

John Wiley & Sons

Chapter One

J. Scott Weese, Andrew S. Peregrine, Maureen E.C. Anderson, and Martha B. Fulford

Introduction

Companion animals can harbor a wide range of parasites, some of which are transmissible to humans. The overall burden of human diseases attributable to companion animal-associated parasites is unknown and varies greatly between regions. The risks associated with some are often overstated while others are largely ignored, and the range of illness can extend from mild and self-limited to fatal.

Ascaris lumbricoides

Introduction

A. lumbricoides is a roundworm that has typically been considered host specific to humans; however, there is evidence of infection of dogs and the potential for dogs to be an uncommon source of human infection.

Etiology

As with other intestinal nematodes, A. lumbricoides is a nonsegmented, elongated, cylindrical parasite that undergoes sexual reproduction. Like other ascarids, as well as hookworms and Trichuris, A. lumbricoides undergoes a maturation stage in soil and is therefore sometimes referred to as a geohelminth. Female worms are larger than males and can reach 40cm in length and 6mm in diameter.

Life cycle

Adult worms live within the small intestinal lumen of humans and excrete massive numbers of eggs per day. As with other ascarids, eggs are not immediately infective and must mature to infective third-stage larvae in the environment over a period of days. After embryonated eggs are ingested by a human, larvae hatch, penetrate the intestinal mucosa, and reach the liver via portal circulation. After migrating through the liver, the larvae eventually reach the lungs, penetrate the airways, ascend the tracheobronchial tree, and are coughed up and swallowed. They mature into adults in the small intestinal lumen and complete the life cycle. The time from ingestion of infective eggs to development of adults is approximately 8 weeks.

Geographic distribution/epidemiology

A. lumbricoides is one of the most prevalent nematodes in humans and is most common in tropical and subtropical regions, infecting approximately 25% of the world's population. Up to 80% of people can be infected in some areas. The regional prevalence varies depending on factors such as climate, sanitation, socioeconomic status, and human behavior. Areas with warm, humid climates facilitate maturation and survival of infective eggs. Poor sanitation leads to an increased risk of contamination of the environment with human feces. Outdoor defecation similarly results in increased likelihood of contamination, and outdoor activities in contaminated areas that are accompanied by suboptimal hand hygiene increase the risk of fecaloral infection. A. lumbricoides eggs can be found in the soil in public places such as parks and can survive outdoors for years in favorable environmental conditions. Infections are more common in children.

Some older studies reported the presence of ascarid eggs that could have been A. lumbricoides in canine feces. More recently, convincing evidence of the presence of A. lumbricoides in dogs has been reported. A study of dogs in tea-growing communities in northern India identified A. lumbricoides eggs in 18–37% of dogs. In that study, dogs were at increased risk of shedding A. lumbricoides if one or more household members regularly defecated outdoors. Simply finding eggs in feces, particularly in an environment where dogs may ingest human feces, does not necessarily indicate that dogs are involved in the biological cycle of the organism. Indeed, there has been some thought that dogs only act as mechanical vectors and that eggs passed in feces simply moved passively through the intestinal tract. However, a recent study of dogs in an area in Egypt where outdoor defecation by humans is common reported detection of adult A. lumbricoides in 8% of dogs. Furthermore, viable eggs were detected, suggesting that dogs can truly be infected and could potentially play a role in the life cycle of this human parasite. It has also been suggested that the dog's coat could be a source of exposure since the eggs are "sticky" and highly tolerant of environmental effects, and could potentially adhere and mature to the infective stage on the animal.

A study of young Nigerian children indicated that children whose families owned dogs were 3.5 times as likely to be shedding A. lumbricoides compared with non-dog-owning families. In contrast, contact with dogs was not a risk factor in a study of adult humans in northern India. Whether there truly is a risk from dogs is unclear, but the limited data indicate that consideration of the role of pets, particularly dogs, in the transmission of this predominantly human-associated parasite is required.

Animals

Clinical presentation

Little is known about A. lumbricoides in dogs. While it was previously thought that dogs shedding the parasite represented a mechanical, not biological, vector, there is now evidence that adult worms can grow in the canine intestinal tract. It is not known whether this can result in disease.

Diagnosis

Diagnosis is based on the detection of eggs in feces using fecal flotation and subsequent speciation of the parasite by evaluation of micromorphological features or using molecular methods such as PCR-RFLP.

Management

No specific data are present, but presumably, any prophylactic or therapeutic agent that is used for the treatment of Toxocara in dogs would be effective against A. lumbricoides. These include milbemycin oxime, moxidectin, fenbendazole, and pyrantel.

Humans

Clinical presentation

Various presentations can occur, but most infections are asymptomatic. Large worm burdens can result in malnutrition, nonspecific gastrointestinal signs, or, in rare cases, intestinal obstruction. Obstruction of the bile duct can result in cholangitis, biliary colic, or pancreatitis. Chronic infections can produce insidious disease, with growth retardation and negative effects on cognitive function in children. During larval migration, acute pulmonary signs (Loeffler's syndrome), fever, and marked eosinophilia can occur. There is also increasing concern about the broad effects of ascarid infection on the immune system, something that may be particularly important with concurrent infections such as malaria or for the development of allergic diseases, though more research needs to be performed in this area.

Diagnosis

Eggs are usually easily detectable in stool because of the large numbers that are shed by adult worms. Rarely, adult worms will be passed in stool or vomitus. Adult worms may also be identified ultrasonographically as an incidental finding or during investigation of gastrointestinal complaints.

Management

A single dose of albendazole, mebendazole, or pyrantel pamoate has high cure rates (88–95%).18 Three days of mebendazole or a single dose of ivermectin has also been recommended in people over 2 years of age. Nitazoxanide is also effective. Retesting of stool 2 weeks after treatment has been recommended. Most drugs are only effective against adult parasites, so repeated treatment may be needed.

Prevention

Prevention of zoonotic transmission of A. lumbricoides, should it occur, involves basic measures to reduce the incidence of exposure of dogs, to reduce...