ONE HEALTH AND EMERGING ZOONOTIC DISEASES OF CANINES
Dr. Asmita Narang
Dogs have been our companions for more than 10,000 years. They share our environment and have gained a major status as pets, especially in our urbanized society. Although, the man-dog friendship has proven to be beneficial for physical and psychological well beings of humans but there is dearth of awareness among the owners about the zoonotic diseases that could transmit from dogs to human. A zoonotic disease is a disease that can be passed from animals to humans. Around 60% of all human diseases are zoonotic and 75% of all emerging diseases are considered zoonoses. These diseases can be caused by viruses, bacteria, parasites, and fungi. Humans can contract zoonotic or vector-borne diseases through
- contact with an animal
- contact with its bodily fluids, its infected waste or its living environment
- contact with water or soil contaminated by infected animal waste
- eating meat from infected animals
- eating food such as fruits and vegetables that have been contaminated by infected animal waste;
- vectors from infected animals to humans via mosquitoes, fleas or ticks
Dogs closely share the domestic environment with humans and are potential reservoir of many zoonotic diseases. The infection can spread to human through the faeces, urine, saliva, nasal discharge, nails etc. Therefore it becomes important for the dog owners to be informed about canine zoonoses, their possible ways of transmission and measures that can help prevent the diseases. The present manuscript highlights the emerging and re-emerging zoonotic diseases our companion animals which are important in Indian context.
Rabies
Rabies is one of the deadliest and oldest zoonoses in India. It is an infectious viral disease that affects the nervous system. Human contracts rabies either through the direct contact with the saliva or through the bites of rabid dog. It is 100% fatal but easily preventable. It may take one week to one year to become clinically manifested in human patients depending upon the site of bite and the amount of inoculated virus. Rabies typically manifests two forms depending upon the route virus takes to reach the brain. Classical signs of “furious rabies” comprise anxiety, hypersensitivity, hydrophobia and aerophobia leading to death within two to three days. The other form is “paralytic/ dumb rabies” which terminates into death due to muscular paralysis. Public education, dog vaccination and correct WHO recommended pre and post-bite measures can prevent the incidences of rabies deaths worldwide. Vaccinating pets not only protects them but it provides a “buffer zone” between humans and rabid wild animals. Immediate wound washing with soap under running water can reduce the viral load and prevent subsequent possibility of rabies infection.
Leptospirosis
Leptospirosis is caused by a spirochete excreted in the urine of an infected animal. Disease is caused by pathogenic strains of Leptospira species harbored in the rodents (primary reservoir host). However, dogs spread the infection as secondary hosts.Major public health concern arises during natural disasters when cases of leptospirosis may peak owing to the poor sanitary conditions. Transmission to dogs is either through direct contact with infected urine, or indirectly through drinking, swimming in contaminated water bodies. Man contracts infection through broken skin contact with water or soil and consumption of food/water contaminated with infected urine. It has non-specific influenza like clinical symptoms in man. Dogs manifest the signs of fatigue and depression, colic, liver damage and even death. Infected dogs acquire the carrier stage and continue to shed the spirochetes in urinefor months to several years. Leptospirosis can be treated with antibiotics. Occupational risk to human can be prevented by protective clothing and avoidance of swimming in contaminated water bodies. Dog drinking water from marshy areas or slow-moving or stagnant water should be prevented. Control in animal population can be achieved by vaccination of pet animals and by a testing a culling programme for rodent control.
Methicillin-Resistant Staphylococcus Aureus (MRSA)
MRSA-associated infections in pets are typically acquired from their owners and can potentially cycle between pets and their human acquaintances. Transmission of MRSA infections between pets and humans are increasing, with the most common being infections of the skin, soft-tissue and surgical infections. Dog or cat bites can result in infection, caused by bacteria from the animal’s mouth and on the patients’ body. Animals are potential reservoirs of MSRA infection due to increasing prevalence of community-acquired MRSA (CA-MRSA) in humans and domestic animals such as dogs, cats and horses. MRSA most often enters the body through a cut or scrape and appears in the form of a skin or soft tissue infection, such as a boil or abscess. The involved site is red, swollen, and painful and is often mistaken for a spider bite. Though rare, CA-MRSA can develop into more serious blood infections or pneumonia, leading to other symptoms including shortness of breath, fever, chills, and death. CA-MRSA can be particularly dangerous in children because their immune systems are not fully developed. Therefore, minor skin problems such as pimples, insect bites, cuts, and scrapes should not be neglected, especially in children.Treatment of MRSA infections in pets is similar to that used in humans. Resistant to penicillin and methicillin, CA-MRSA infections can still be treated with other common-use antibiotics.
Lyme Disease
It is a bacterial disease caused by Borrelia burgdorferi. Disease spreads through the bite of an infected Ioxides ticks. In India, Lyme disease is highly underreported due to its non-specific symptoms, non-availability of reliable diagnostic testing facility and unawareness among the medical practitioners and pet owners. The dogs are ‘the sentinels’ for the risk of disease transmission to humans as the ticks feeding on dog blood can transmit Borrelia spirochetes to human through bite. Common clinical manifestations include a “bull’s-eye” rash with fever, headache, and muscle or joint pain.After hikes or other outdoor activities in high-risk areas, dogs and humans should be checked for ticks and their removal promptly. Specific insect repellants such as containing deetand permethrin can be effective. Pets should be regularly treated with flea and tick prevention medication.
Salmonellosis
Salmonellosis can cause diarrhoea, fever and abdominal cramps 12 to 72 hours after infection. The illness usually lasts four to seven days, and most people recover without treatment, although it can be fatal to those with fragile immune systems. Dogs with Salmonella infections may be lethargic and have diarrhea or bloody diarrhea, fever, and vomiting. Some pets will have only decreased appetite, fever and abdominal pain. Well animals can be carriers and infect other animals or humans. It is possible to contract Samonella from handling contaminated pet food or treats. This infection can be prevented by few measures, like washing hands after touching sickdogs and/or handling their waste, cleaning pet food bowls, feeding areas, litter boxes and habitats routinely. Children younger than age 5 should be kept away from pet food and feeding areas. Pets’ food and water dishes should be cleaned in a separate sink or tub, not in the kitchen or bathtub.
Kennel Cough (Bordetella bronchiseptica)
Several human cases of Bordetella bronchiseptica infections have been reported in immunocompromised individuals, especially organ transplant recipients and cancer patients who had been exposed either to dogs or cats that can be healthy carriers of this emerging zoonotic pathogen. Symptoms can range from being asymptomatic to severe pneumonic signs. Although B. bronchiseptica infection remains a rare clinical condition among humans, it should be considered as potentially pathogenic when found in airways of immunocompromised patients.
Echinococcosis
The disease is caused by the dog tapeworm of genus Echinococcus and its larval stage (hydatid cyst). Carnivores, especially dogs are the definitive host harboring a mature tapeworm of Echinococcus in their intestine. Parasite eggs are shed in the environment, contaminating fruits, vegetables or water bodies, and can stick to the fur of animals and can transfer on hands to the mouth of human handlers. Wide range of herbivorous and omnivorous species acts as intermediate hosts of Echinococcus. Intermediate hosts become infected while grazing on the pasture contaminated with dog feces laden with parasite eggs. Humans are accidental intermediate hosts, acquire infection by ingestion of the parasite eggs in contaminated food and water. Exposure to the eggs of this tapeworm can cause damaging cysts (hydatid cysts) to form in the liver and other parts of the human body.
Cryptosporidosis
Cryptosporidium canis is specifically a canine pathogen causing severe diarrhoea, malabsorption and weight loss. Among the other species, Cryptosporidium parvum, is zoonotically important due to its potential to cause serious human health complications. As in dogs, the infection in humans is mostly found in children and the symptoms are similar. Symptoms include watery diarrhea, fever, abdominal cramps, nausea, and vomiting. Infection in immunosuppressed individuals such as the very young, the elderly or those with HIV/AIDS may be life threatening. It can lead to acute dehydration and weight loss, possibly aggravating any existing health issues and leading to a serious combination of problems. Cryptosporidiosis has been found in people, cats and dogs living in the same environment, suggesting the potential for zoonotic transfer between species. Contaminated water and pet waste are the risk factors. No effective medical treatment has been found. In normally developing cases (both in humans and animals) the condition lasts for up to three or four weeks and developing immunity has been reported. This can be prevented by good personal hygiene and proper hygienic preparation of food and drinking water.
Ancylostomiasis
Dog harboring hookworm parasite Ancylostoma can pass on the infection to the people dwelling in their surroundings. Dogs carrying adult parasite, excrete the eggs in the faeces which hatch to larvae in environment. Hookworms cause haemorrhagic diarrhoea in puppies and chronic microcytic hypochromic anaemia in adult dogs. The place where dogs defecate get contaminated with eggs and larvae voided in the faeces. Human may acquire an infection by touching or walking barefoot on contaminated soil and by accidental ingestion of contaminated soil or water. This soil transmitted hookworm infection is one of the most common roundworm of humans. Infected human develop a skin condition called Cutaneous Larva Migrans (CLM). Control measures need to be implemented to prevent shedding of infected parasite eggs in dog faeces.
Toxocariasis
Canines are the definitive host for Toxocara canis. The puppies less than one year old are often affected. The incidence tends to decrease with advancing age of the dog and among well domesticated pet dogs.Evidence of high prevalence in stray dogs raised health risks to people visiting public places contaminated with dog faeces. Human toxocariasis, primarily is a soil-transmitted zoonosis acquired from contaminated grounds. Geophagia, poor personal hygiene, playing with non-dewormed puppies and consumption of raw contaminated vegetables increases the risk of toxocariasis in Human. There could be low infection that is asymptomatic. In ‘visceral’ form juvenile stages (larvae) of the worm migrate to organs, such as the liver causing severe clinical manifestations. In the ‘ocular’ form the larvae migrates to the eye. Theeggs are shed through a pet’s feces and, while fresh feces are not infectious, the eggs become infectious over time as they sit in grass, soil or sand. This is why picking up pet waste promptly is important. Human disease flared up as visceral larva migrans (VLM) due to migration of larvae through the liver, heart, lung, muscle, eye, and brain. The conditions are treatable but there is a risk of long-term organ damage and blindness.Simple hygienic measures are the main line of defence against an infection. Gardeners should wear gloves and wash hands after working outside.Dogs should be regularly dewormed.
Giardiasis
Giardia is an intestinal parasite of domestic animals including dogs that can be transmitted to the susceptible hosts by drinking water contaminated with infected feces. Giardiasis has got the public health importance due to its potential to infect millions of people worldwide. Illness in humans is usually self-limited characterized by diarrhea, abdominal cramps, bloating, weight loss, and malabsorption, however, in infected children it disturbs the growth and cognitive functions. Dogs pick them up from the environment, usually from something they eat, or from standing water they drink when outside. In humans, poor levels of hygiene are usually implicated, picking up the infection from handling contaminated animals, food, objects or being in close contact with infected people. Treatment consists of a dewormer and medication depending on the presentation of the individual case.
Companionship with dogs brings benefits, but they represent excellent sentinels for pathogens that can infect humans. Improved diagnostic tools and techniques have increased our knowledge about the zoonotic potential of canine pathogens present in our direct environment. The risk of zoonoses can be limited with good animal care and application of appropriate preventive measures in the human environment. To conclude, simple hygienic measures can drastically reduce the risk of zoonotic spread of disease from dog to people. For this, regular veterinary care is important for the health of every animal. Because any dog at any age can become infected with parasites, an annual exam with a fecal exam is important. One of the best ways to prevent zoonotic diseases is to promptly clean up pet waste. Many parasites or bacteria are not infectious in fresh pet waste, but become infectious over time and can contaminate the soil, sand or grass if allowed to sit. Washing hands thoroughly with hot, soapy water after playing with dog or handling its waste is also important preventive measure.
