Bacterial, Viral and Fungal Zoonoses Acquired from Pets
Pets provide many benefits to humans. They comfort us and they give us companionship. However, they can also pass some zoonotic diseases to people. Zoonoses can be transmitted either through direct contact with the infected animal or indirectly via exposure in our shared surroundings.Many diseases spread by touching a contaminated hand to the mouth or to the delicate mucosal tissues of the nose. Some zoonoses rely on the infectious agent sitting dormant in the environment until the appropriate conditions of temperature, moisture and host vulnerability allow it to reach and infect the new host. Anyone exposed to a zoonotic agent can become a victim, but children, elderly and other immunocompromised individuals do have a higher potential of becoming infected. Rabies, salmonella, and toxoplasmosis are among the most commonly known zoonoses that can be transmitted between pets and pet owners. Many infectious diseases in humans can be acquired through contact with pets. Dogs and cats may be the most frequent household pets around the world, but there are also many other vertebrates that share our household environment. Some zoonoses are quite common as salmonellosis or campylobacteriosis but are usually not life-threatening. On the other hand some zoonoses are rather uncommon but can be particularly severe for infected persons, such as lymphocytic choriomeningitis (LCM) or rabies.
Bacterial zoonoses acquired from pets:
In India, human brucellosis cases have been reported from almost all the parts. Majority of the human cases are found to be due to Brucella melitensis though B. abortus and B.canis have also been isolated. Dog can act as mechanical or biological vetor of B.abortus, B. suis and B. melitensis.human beings get the infection by means of ingestion, inhalation, direct or indirect contact with infected material, accidental inoculation in conjunctiva or skin and even through intact skin.
Confirmatory diagnosis of brucellosis can only be made by isolation of pathogens from the patient. Various serological tests like standard tube agglutination tets, 2-mercaptoethanol test (2-MET), Coobs antiglobulin test (AGT), CFT, ELISA have been developed for prompt diagnosis.
Campylobacteriosis is mainly caused by Campylobacter jejuni, C.fetus and C. coli. It causes diarrhoea in human beings and as per the regional estimetes, the annual number of patients developed Campylobater diarrhoea worldwide is a staggering 400 million. The food and companion animals, birds and wild animals act as reservoir host for this disease. Direct transmission of the disease occures from kittens or pups to man. Dogs are mainly affected with the disease and exihibits signs like mucoid diarrhoea with or without blood followed by vomition, fever and anorexia. In mans, signs are dirrhoea to dysentry with fever and abdominal cramps and some patients experience malaise, headachae, nausia and vomiting. The disaese can be diagnosed by direct demonstartion of ‘S’ or coma shaped pathogen from fresh stool through dark field microscopy or by isolation of organism from faeces and rectal swab of patients by culture method. In serodiagnosis techniques we can use CFT and ELISA. Personal and environmental hygiene should be maintained for prevention of disaese.
Cat Scratch Disease:
Cat Scratch Fever is a clinical syndrome that has been reported in humans for nearly a hundred years however the etiological agent Bartonella henslae was only identified in 1992. Case control studies of human CSD have confirmed the epidemiological association of cats with disease in human. The outbreaks of CSD in families have also been recorded from kitten. Most of the cases of CSD appear to occur from direct cat exposure (scratch or bite). In initial stage of the disease papules and pustules form around the site of infection which progresses to failure of the wound healing. In later stage regional lymph nodes swells and forms abscess. Those people with close contact with large numbers of cats such as veterinarians are most at risk. The disease can be diagnosed on the basis of primary lesions, regional lymph adenopathy, demonstration of bacilli from capillaries walls and macrophages with Wartin-Starry silver stain. The recent techniques like PCR, ELISA, hanger-Rose skin test can also serve the purpose. For the prevention of disease avoids rough handling of cat or kittens, avoid wound licking by cats and maintenance of personal hygiene are the way.
Leptospirosis is also known as canicola fever, it is widely spread disease in southern states and some western states like Gujarat and Rajasthan of India. The disease is prevalent in almost all domestic animals and in rodents. The common serotypes distributed among domestic animals L. icterohaemorrhagae, L. canocola, L. pomona, L. grippotyphosa and L. hardjo. Dogs are commonly infected with icterohaemorrhagoae and canicola serotypes. Carrier animals shed the organisms in their urine. Leptospires can survive for week in soil and water particularly if pH is alkaline. Human being contracts the disease through indirect contact with contaminated water and soil.Affected people generally suffer an acute onset of headache, fever and occasionally conjunctivitis, vomiting or abdominal pain. For the confirmatory diagnosis of the disease, direct microscopic examination of samples after treatment with certain chemicals (0.25% trypsin for tissues, 40% formaline for urine, and 10% acetic acid for impression smears) can be examined by dark field microscopy. Bacterial isolation in this disease is very much useful because leptospires takes several weeks to grow and isolation rate is also low. Microscopic agglutination test (MAT) is a most widely used method for this disease diagnosis because it is fast and specific. It is also known as WHO standard reference test in which serial dilutions filtered and heated (56º C for 20 min.) serum is reacted with same amount of either live or formalized Leptospira culture. In this test dilution at which at least 50% agglutination occurs on examination under dark field microscope is considered as positive and a titre 1:100 or more indicates a present or past infection. Personal hygiene, protection and sanitation are the best ways for its prevention.
Lyme disease is caused by Borrelia burgdorferi. The disease is widespread in America, Australia, China, Japan and Russia while in India, status of disease needs to be ascertained. The pathogen of disease is transmitted to man through bite of infected tick vector and pet dogs and cats are thought to be an introducer of ticks in human habitats. The disease in human beings starts from a macule or papule followed by fever, chills, fatigues, headache, myalgia and stiff neck leads to dizziness, weakness and cardiac symptoms after weeks or months. In later stage it involves large joints. For diagnosis of disease clinical signs may serve some purpose but detection of monoclonal antibodies for borrelial antigen, use of DNA probes and PCR methods are the reliable methods. Personal protective measures should be adopted for prevention.
Plague is caused by Yersinia pestis and in India its seropositive cases in rodents and dogs were found in Maharastra. In human beings, it is a worldwide disease and first pandemic of this disease was reported in 542 AD at Egypt. In India, plague is a disease of antiquity and find place in Bhagwat Purana. The main route of transmission of this disease to humans is by fleas bites but it may be transmitted through bites and scratches of infected cats. The signs of this disease in humans is swelling in groins in bubonic form while cough, haemoptysis and other respiratory symptoms in septicaemic form. For the diagnosis of disease clinical features are suggestive of plague while demonstration of bacilli with characteristic safety pin appearance in smears of sputum, CSF and throat specimens may serve the purpose. Isolation of organism in CIN agar, laboratory animal (guinea pig) inoculation, serodiagnosis by PHA, CFT and IgM capture ELISA, bacteriophage analysis and PCR techniques gives confirmatory diagnosis.
Salmonellosis is caused by different servers of genus Salmonella and in India, human salminellosis is endemic and one of the most widespread zoonoses. For human infections, eggs have been positively identified as the chief vehicle of transmission but disease may also transmit directly from animal to man through pets. Infected persons with salmonellosis usually have diarrhoea, abdominal pain, nausea and sometimes vomiting and complicated cases leads to dehydration, sepsis, meningitis and osteomyelitis. For the diagnosis of disease clinical symptoms and history of the case is important factor which may be confirmed with isolation and identification of pathogens from stool, vomitus and foods. For further confirmation ELISA, PCR may be used. Cases of salmonellosis may be reduced by personal hygiene and managemental practices.
Viral zoonoses acquired from pets:
Rabies is a viral infection spread through saliva e.g. via biting or by saliva entering an open wound. It attacks the central nervous system causing a variety of symptoms including behaviour changes and is almost always fatal. Documented cases of human recovery are extremely rare. Carriers do exist but are uncommon. The cases of rabies occur in many countries and on many continents throughout the world. Currently Japan, New Zealand, Great Britain, a number of island nations and Australia are the only countries considered to be free of the virus. In India rabies mainly spreads by the dog bites. Heavy economic losses occur in our country due to this deadly disease. About 3 to 3.5 million people undergo post- exposure antirabies treatment. Nearly 30,000 human deaths occur every year in India. The diagnosis of rabies is based on clinical signs, demonstration of negribodies in the impression smears of brain by Seller’s stain. Fluorescent antibody technique (FAT) is highly specific test and can provide results within few hours. Another method of diagnosis the case is Immunoperoxidase reaction test; it is a staining method in which we detect rabies antigen in brain tissues. Virus isolation is the most confirmatory technique in which suckling mice are inoculated intracerebrally with suspected tissue suspension and than it is coupled with FA test or microscopic examination of infected mouse brain tissue. For prevention and control of rabies prophylactic vaccination of pets especially dogs, cats and humans is one of the most important method.
Fungal Zoonoses acquired from pets:
It’s a systemic fungal disease caused by Histoplasma capsulatum. Dogs are most commonly affected with this disease. The disease usually occurs through inhalation of fungal spores and spores may also get entry through injuries or broken skin. In man, most of the cases (about 90%) are asymptomatic but in some cases it shows flu like symptoms and in case of organs other lungs involvement it depicts hepatomegaly, spleenomagaly, anaemia, leukopenia and weight loss. For the diagnosis of disease CFT and immunodiffusion test can be used for detection of fungus in tissues and isolation of causative agents. The histoplasmin skin test and radioimmuno assay for histoplasma antigen can be used for detection of fungal agent in human urine. For the prevention of disease exposure to dust and direct contact with pets should be avoided.
Ringworm is a generic term used to describe a number of fungal skin infections in animals and man. They are called “ringworm” due to the characteristic red ringed appearance of the infection in humans. Several fungal species belonging to genera Trichophyton and Microsporum are known to cause ringworm which is zoonotic in nature. Infected pets such as dogs, cats and rabbits may transmit the infection to pet owners. M. canis most frequently associated from dogs and cats causes microsporia in man, a special form of dermatophytosis which is characterized by the development of single or multiple, round, oval or polycyclic reddened scaly lesions, primarily on face, neck and arms. Children are particularly susceptible and often attacked due to their frequent contact with cats and dogs. For the diagnosis of disease skin scrapings are examined for presence of spores and mycelia. In this method skin scrapings are first treated with 20% KOH solution to dissolve the keratin and when examined under ultraviolet light M. canis produces greenish fluorescence. However, false positive fluorescence may also be observed. The cultural examination of clinical samples is very specific to give a definitive diagnosis. Prevention of infection can be achieved by careful handling of pets with skin lesions and by good personal hygiene.
The diseases which are transmitted from pets to human beings and vice –versa is of great concern to the pet owners as well as the veterinarians who regularly come in contact of them. It is also important for children to get away from these diseases. Therefore, emphasis should be given to the personal hygiene, environmental sanitation, health education, regular deworming and vaccination of pets and their owners.
- Colville,J.L. and Berryhill, D.L. (2007).Hanbook of Zoonoses Identification and Prevention. Mosby Elsevier, USA.
- Krauss, H., Weber, A., Appel, M., Enders, B., Isenberg, H.D., Schiefer, H.G., Slenczka,W., Graevenitz, A.V. and Zahner, H. (2003). Zoonoses Infectious diseases Transmissible from Animals to Humans. IIIrd Edn. ASM Press Washington, D.C.
- Sherikar,A.T., Bachhil, V.N. and Thapaliyal, D.C.(2004). Textbook of Elements of Veterinary Public Health. 1st Edn. Vol.II Indian Council of Agriculture Research .New Delhi.