Zoonotic Diseases

 

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Definition/Description

A zoonotic disease is any disease or infection that is transmissible from vertebrate animals to humans. ,

Classes of Zoonoses

1. Viral Zoonoses

     Most Common Viral Zoonoses

     Ehrlichiosis

Please see below under Bacterial Zoonoses.  Noted here due to diagnostic techniques used.

     Rickettsia (Rocky Mountain Spotted Fever)

Please see below under Bacterial Zoonoses.  Noted here due to diagnostic techniques used.

     Rabies

A viral disease associated with mammals, including dogs, cats, horses, and wildlife. Rabies can be transmitted through bites, scratches, aerosolized respiratory secretions, and saliva. It may take several weeks or even a few years for people to show symptoms after getting infected with rabies, but usually people start to show signs of the disease 1 to 3 months after the virus infects them. The early signs of rabies can be fever or headache, but this changes quickly to nervous system signs, such as confusion, sleepiness, or agitation. Once someone with rabies infection starts having these symptoms, that person usually does not survive. For this reason, all animal health care workers should be vaccinated against rabies and should have their titers checked every other year. Many kinds of animal can pass rabies to people. Wild animals are much more likely to carry rabies, especially raccoons, skunks, bats, foxes, and coyotes. However, dogs, cats, cattle, or any warm-blooded animal can pass rabies to people.

     West Nile Virus

A viral disease spread by mosquitoes which can affect birds, horses, and other mammals Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite. About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent. Up to 20 percent of the people who become infected have symptoms such as fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks. Approximately 80 percent of people (about 4 out of 5) who are infected with WNV will not show any symptoms at all. People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito. There is no specific treatment for WNV infection. In cases with milder symptoms, symptoms pass on their own. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing, and nursing care. Personal protective measures are the primary way to avoid contracting the virus.

     Equine Encephalitis

A mosquito borne infection normally maintained in nature by a cycle from an arthropod vector to a vertebrate reservoir host. Although some people experience it only as a mild illness, eastern equine encephalitis is fatal in about one-third of the cases. Symptoms of eastern equine encephalitis usually appear three to 10 days after a bite by an infected mosquito. A vaccine exists for horses but not for humans. Personal protective measures are the primary way to avoid contracting the virus.

     Diagnostic Tests/Lab Tests/Lab Values          

1. ELISA (Enzyme Lined Immuno-Sorbent Assay)- detects the actual disease. May not be sensitive enough to detect infection in the asymptomatic carrier.

2. PCR (Polymerase Chain Reaction)- amplifies minute quantites of microbial DNA or RNA allowing for recognition of latent phases of viral diseases. May yield false positive result for the disease but give a true positive for infection within the agent.

3. Serology (Indirect Fluorescent Antibody Testing)- used to detect Rickettsial organisms which cause Ehrlichiosis and Rickettsia

2. Bacterial Zoonoses

     Most Common Bacterial Zoonoses

     Anthrax

Anthrax is an acute infectious disease caused by the spore-forming bacterium Bacillus anthracis, a microbe that lives in the soil. Anthrax most commonly occurs in wild and domestic mammals (cattle, sheep, goats, camels, antelopes, and other herbivores), but it can also occur in humans when they are exposed to infected animals or to tissue from infected animals. Anthrax can occur in three forms: cutaneous, inhalation, and gastrointestinal.

     Bartonella (Cat Scratch Fever) 

Cat scratch disease (CSD) is a bacterial disease caused by Bartonella henselae. Most people with CSD have been bitten or scratched by a cat and developed a mild infection at the point of injury. Lymph nodes, especially those around the head, neck, and upper limbs, become swollen. Additionally, a person with CSD may experience fever, headache, fatigue, and a poor appetite. Bartonella will begin in the human as a pustule that will gradually progress to regional lymphadenopathy which can last for months (or become a systemic illness in immunocompromised patients).  In addition to the cat or dog scratch, bartonella can also be transmitted through the feces of fleas.

     Borrelia (Lyme Disease)

Lyme disease is a bacterial disease caused by Borrelia burgdorferi. People get lyme disease when they are bitten by ticks carrying this bacteria. Within 1 to 2 weeks of being infected, people may have a "bull's-eye" rash with fever, headache, and muscle or joint pain. Some people have Lyme disease and do not have any early symptoms. Other people have a fever and other "flu-like" symptoms without a rash. After several days or weeks, the bacteria may spread throughout the body of an infected person. These people can get symptoms such as rashes in other parts of the body, pain that seems to move from joint to joint, and signs of inflammation of the heart or nerves. If the disease is not treated, a few patients can get additional symptoms, such as swelling and pain in major joints or mental changes, months after getting infected.

     Brucellosis

a zoonotic infection transmitted from animals to humans by the ingestion of infected food products, direct contact with an infected animal or inhalation of aerosols. The timely and accurate diagnosis of human brucellosis continues to challenge clinicians because of its non-specific clinical features, slow growth rate in the blood culture, and the complexity of its serodiagnosis. Brucellosis in human beings is rarely fatal, but can lead to severe debilitation and disability Diagnostic methods for brucellosis are primarily based on serology, with the LPS smooth chains producing the greatest immunological responses in various hosts.

     Ehrlichia

Ehrlichiosis is the general name used to describe several bacterial diseases that affect animals and humans. Human ehrlichiosis is a disease caused by at least three different ehrlichial species in the United States: Ehrlichia chaffeensis, Ehrlichia ewingii, and a third Ehrlichia species provisionally called Ehrlichia muris-like (EML). Ehrlichiae are transmitted to humans by the bite of an infected tick. Symptoms usually occur within 1-2 weeks following a tick bite and include fever, headache, fatigue, and muscle aches. Ehrlichios is is diagnosed based on symptoms, clinical presentation, and later confirmed with specialized laboratory tests. Treatment for adults and children of all ages is doxycycline. Same diagnositc techniques are used as with viruses

     Leptospirosis

is caused by many different species of the spirochete Leptospira.  Dogs can be a vector for human disease, and humans are infected by exposure to urine, blood, or tissue from an infected dog.  If shed in urine, the organism can survive in an environment between 0°-25°C.  Prevention can be improved by good sanitation practices and vaccination of dogs.  The most common means of transmission is through water contact with skin wounds or mucous membranes.  Leptospires invade organs including the kidneys, liver, spleen, central nervous system, eyes, and genital tract.  Any dogs which are suspected of shedding leptospira should be treated with doxycycline.

     Plague (Yersinia enterocolitica, Yersinia pestis) 

A rare bacterial disease associated with wild rodents, cats, and fleas.Yersiniosis is a disease caused by the bacterium Yersinia enterocolitica, or yersinia pestis (a gram negative coccobacillus). People with yersiniosis can have different symptoms depending on how old they are. People can start to get sick 4 to 7 days after infection and can be sick for 1 to 3 weeks. Young children usually have fever, stomach pain, and diarrhea. Adults do not get sick with yersiniosis as often, but they can feel pain on their right side and may have a fever. Usually, these signs go away after about 3 weeks but sometimes pain in joints, such as knees or wrists, can start after that and last for several months. Animals can pass Yersinia enterocolitica in their stool, and people can get sick from contact with infected feces. Several kinds of animals can carry this disease, but usually people get sick from pigs that are sick with yersiniosis. Other animals that can carry this disease include cats, dogs, horses, cows, rodents, and rabbits. The pulmonary form is spread by airborne or droplet infection. Human infections from nonrodent species usually result from direct contact with infected tissues, by scratch or bite injuries, and handling of infected animals.

     Rickettsia (Rocky Mountain Spotted Fever)

A disease caused by the bacterium Rickettsia rickettsii, which is carried by ticks. People usually start having fevers and feeling nauseous about a week after being bitten by a tick. A few days after the fever begins people will often have a rash, usually on the arms or ankles. They also may have pain in their joints, stomach pain, and diarrhea. People get this disease when they are bitten by a tick that is carrying the bacterium R. rickettsia. Because ticks on dogs can be infected with R. rickettsii, dogs and people can get Rocky Mountain spotted fever from the same ticks. These ticks can also bite other animals and pass Rocky Mountain spotted fever to them. When you remove ticks from any animal, the crushed tick or its parts can also pass this disease through any cuts or scrapes on your skin. Same diagnositc techniques are used as with viruses

     Methicillin Resistant Staphylococcus Aureus (MRSA)

The most common MRSA infections between pets and humans are 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-associated infections in pets are typically acquired from their owners and can potentially cycle between pets and humans. 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. CA-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 invasive infections, such as bloodstream infections or pneumonia, leading to a variety of 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.

     Streptococcus suis

Streptococcus suis is a zoonotic pathogen that infects pigs and can occasionally cause serious infections in humans. S. suis infections occur sporadically in humans throughout Europe and North America, but a recent major outbreak has been described in China with high levels of mortality. The mechanisms of S. suis pathogenesis in humans and pigs are poorly understood.

     Diagnostic Tests/Lab Tests/Lab Values

1. Blood Culture is the gold standard in the diagnosis of bacterial infections including brucellosis

3. Fungal Zoonoses

     Most Common Fungal Zoonoses

     Dermatomycoses

Dermatomycoses are caused by fungal spores which remain viable for long periods on carrier animals. Exposure to reservoir hosts harboring different dermatophytes determines the type and incidence of infection in humans. Pets may also acquire disease from humans. Dermatomycoses can be transmitted directly or indirectly through contact with asymptomatic animals or skin lesions on infected animials, contaminated bedding or equipment, fungi in the air, in dust, or on surfaces of the room. The disease in rodents or in cats is often asymptomatic and not recognized until people are affected, but dogs will often show classic skin lesions. Varying severity of dermatitis occurs with local loss of hair. Deeper invasion produces a mild inflammatory reaction which increases in severity with the development of hypersensitivity. In humans, the disease is often mild and self limiting. Scaling, redness, and occasionally vesicles or fissures will be present with thickening and discoloring of nails. A circular lesion with a clear center may also be present.

     Systemic Fungal Diseases (indirect zoonoses)

     Blastomycosis

Blastomycosis generally results from inhalation of Blastomyces dermatitidis conidia following exposure to contaminated soil in an endemic area. Primary infections commonly involve the lungs, although secondary dissemination to other body sites may occur.

     Coccidioidomycosis

Coccidioidomycosis is an infection with the spores of the fungus Coccidioides immitis. It is most commonly seen in the desert regions of the southwestern United States and in Central and South America. The infection starts in the lungs and is contracted by breathing in fungal particles from soil. Most people with this infection do not have symptoms. Some may have cold or flu-like symptoms or symptoms of pneumonia. If symptoms occur, they typically start 5 to 21 days after being exposed to the fungus. Symptoms include, change in mental status, chest pain, cough (possibly hemoptysis, fever, headache, joint stiffness/pain, loss of appetite, muscle aches, neck stiffness, night sweats, painful red lumps on lower legs (erythema nodosum), sensitivity to light, weight loss, and wheezing.

Prevention

The best way to protect oneself from many of these zoonotic diseases is to practice good hygiene after handling animals or their waste. Washing hands thoroughly with hot, soapy water after any contact will help prevention contraction of zoonotic diseases.   In addition screening newly received animals, conducting a routine sanitization of the contaminated environment, equipment, and caging, wearing gloves and protective clothing will help decrease the possiblity of contracting a zoonotic disease.

Recent Related Research (from Pubmed)

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== Recent Related Research (from Pubmed)

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References

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