Zoonosis is a disease or infection that is transmissible between humans and vertebrate animals. There are more than 200 zoonoses.
A wide range of zoonoses usually manifest in nonspecific symptoms including fever, malaise, arthralgia and myalgia. Achieving the correct diagnosis can be challenging as more common infectious diseases are implicated while many go undiagnosed. Thus the lack of recognition and reporting does not accurately depict the incidence of zoonotic diseases. Challenges with diagnosing animal infections also exist as these animals may not display clinical signs. In those who do manifest with signs, identification and reporting of disease in livestock is less than that of humans. This poses challenges in terms of communicating about prevalent diseases between animal healthcare professionals and the medical community.
Shared features and presentations among zoonotic diseases can overshadow the true diagnosis. Note that among many others, brucellosis, Q fever, bartonellosis and leptospirosis may present similarly. However, more specific presentations associated with specific diseases can also cloud the diagnosis as they lack sensitivity and or/specificity and can vary in different populations. Examples of this include varied presentations of hepatosplenomegaly in brucellosis or pneumonia in Q fever.
One of the profound presentations observed in many zoonoses is central nervous systems (CNS) involvement. Seizures are frequently observed in Africa with 4.4 million affected. Neurocysticercosis, caused by T. solium, accounts for 30% of epilepsy in India, sub-Saharan Africa, and Latin America. Echinococcosis and trichinosis are other examples of parasitic diseases that may present with CNS disease. Furthermore, toxoplasmosis, caused by Trypanosoma brucei rhodesiense, is attributed to neurologic manifestations in HIV patients. In conclusion, neurologic sequelae can be devastating in endemic areas.
Entire Body System
If AIDS were a zoonosis that is capable of significant human-to-human spread, there would be a plethora of founder subtypes and groups. (iii) Human exposure to SIV is thousands of years old, but AIDS emerged only in the 20th century. [ncbi.nlm.nih.gov]
If AIDS were a zoonosis that is capable of significant human‐to‐human spread, there would be a plethora of founder subtypes and groups. (iii) Human exposure to SIV is thousands of years old, but AIDS emerged only in the 20th century. [doi.org]
While many zoonotic disease present similarly, a detailed history is warranted to streamline the differential diagnoses. It is important to inquire about all potential contaminants (food, water, etc), bites or scratches, and exposure to animals. Also, ascertain the length of illness, symtoms, and whether others in the household are experiencing symptoms. A full exam should include inspection of body for bites, ticks, scratches, etc. To aid in establishing the diagnosis, studies such as imaging and/or laboratory tests are crucial. Consultation with infectious disease experts can help throughout the workup (and treatment) process.
Generally routine laboratory studies include complete blood count, electrolytes (especially if emesis or diarrhea are present), urinalysis, blood cultures, liver and renal function tests, and coagulation profile. Additionally, blood, sputum, and stool smears are helpful. Serology for differential diagnoses (if available) are important. Finally, lumbar puncture is useful especially in neurologic signs.
With regards to imaging, chest X-rays are performed if a pneumonia like picture is observed. Ultrasonography and CT imaging are useful to assess size of liver and spleen. Another mode of imaging is echocardiography which can diagnose endocarditis.
- Bartonella Henselae
cats represent a large reservoir for human infection, as they are the main reservoir for Bartonella henselae, Bartonella clarridgeiae and Bartonella koehlerae. [ncbi.nlm.nih.gov]
Cat-scratch disease is caused by Bartonella henselae and Bartonella quintana from fleas which are endemic in cats. [en.wikipedia.org]
Bartonellosis Cat scratch disease and other zoonotic Bartonella infections Highlights: • Primary agent: Bartonella henselae bacterium • Cats are main reservoir; also rodents • B berkhoffii a cause of endocarditis in dogs Suspect B berkhoffii in dogs with [web.archive.org]
This occurs when a cat contaminated with the bacterium Bartonella henselae transmits it through a bite or scratch. The patient can have swollen lymph nodes, fever, headache, and skin sores. This infection should should be treated with antibiotics. [symptoma.com]
- Rickettsia Rickettsii
Rocky Mountain spotted fever Rocky Mountain spotted fever Highlights: • Rickettsia rickettsii an intracellular bacterium • Dogs and humans have clinical illness • Rickettsiae induce vasculitis, thrombosis Prompt removal of ticks, early diagnosis important [web.archive.org]
rickettsii dogs, rodents tick bite Ross River fever Ross River virus kangaroos, wallabies, horses, opossums, birds, flying foxes mosquito bite Saint Louis encephalitis Saint Louis encephalitis virus birds mosquito bite Severe acute respiratory syndrome [en.wikipedia.org]
- Plasmodium Falciparum
Similarly to Plasmodium falciparum, P. knowlesi can reach high parasitaemia in the human host and both species cause severe and fatal illness. [ncbi.nlm.nih.gov]
- Erysipelothrix Rhusiopathiae
Erysipelothrix rhusiopathiae is an important animal pathogen with a worldwide distribution, yet this zoonotic infection is rarely reported in humans. [ncbi.nlm.nih.gov]
If the diagnosis is undetermined or if cultures are still pending, empiric therapy is warranted. Treatment is initiated after diagnosis is established unless 1) the patient satisfies the criteria for culture negative endocarditis, 2) the clinical picture is indicative of cryptic disseminated tuberculosis, or 3) CNS manifestations are present.
Stable patients without worrisome findings should be managed in the outpatient setting with close follow up. In cases where the facility cannot adequately manage the patient in terms of worsening clinical picture or tests are unavailable, patient transfer is necessary.
Consultation with infectious disease experts can help elucidate the best regimen. Additionally, pulmonology, gastroenetrology, interventional radiology, and other specialists should be consulted as needed. Close follow up and surveillance are important.
Bacteria account for a myriad of infections. Foodborne illnesses include salmonellosis and campylobacteriosis which produce diarrhea, abdominal pain, fever, and malaise. Additionally, the following infections are resultant of bacterial infections: Brucellosis, anthrax, leptospirosis, shigellosis, and plenty others as well.
Parasites contribute to zoonosis especially in cysticercosis and taeniasis, which are resultant of Taenia solium infection. This organism undergoes a lifecycle using humans and pigs. Cysticercosis affects approximately 1 in 1000 in Latin America. Parasites are also responsible for toxoplasmosis, trematodosis, and trichinellosis.
An example of a viral zoonosis, rabies, is transmitted to humans by bats and humans (and others) through bites. This infection is life threatening. Further diseases that fall into the viral category include Ebola virus disease, avian influenza, and Crimean-Congo hemorrhagic fever.
Nearly 60% of human pathogens are zoonotic, including organisms such as viruses, parasites, bacteria and fungi . Additionally, 75% of recent infectious diseases are arising from animals. Arthropods comprise a significant proportion of zoonotic vectors. These exhibit adaptability, diverse host range, challenges with control, etc .
Mosquitoes are important vectors for human infections while ticks are chief vectors for animals. Other vectors include flies, bugs, and fleas. There have been increased occurrences of mosquito transmission of West Nile disease, malaria, and equine encephalitis in tropical regions in recent years. Next to mosquitoes, tick borne diseases are also gaining attention.
When considering the implications of zoonoses, geographical location plays a role in the management and outcome of the infectious disease. For example, Chagas disease can be controlled, treated, and prevented yet has a marked occurrence in South America. Plenty of diseases demonstrate a profound effect in developing regions such as leishmaniasis in Africa and Asia.
In addition to vector borne transmission, zoonoses are also spread through vertebrates such as in cases with rabies.
The pathogenesis of zoonotic infections is initiated through the mode of contact. Direct contact transmission can occur through bites or scratches such as in the cases of rabies and cat scratch fever. Additionally, handling infected animals with salmonellosis, anthrax, tinea corpora, avian flu, and others are examples of direct contact. Consumption of animal product is also direct infection. Examples include Creutzfeldt-Jakob disease and cystercercosis.
Indirect infection occurs through exposure, ingestion, and inhalation of contaminants. Exposure to water or soil containing pathogens can cause leptospirosis or schistosomiasis while consumption of unsanitary food and water results in diseases such as giardiasis and salmonella. Inhaling contaminated feces, amniotic or other body fluids, and milk can also produce zoonotic infections. Some examples are brucellosis, psittacosis, and Hanta virus.
Vector borne infectious diseases transmitted by mosquitoes include malaria, dengue, and Japanese encephalitis. Lice are vectors for typhus while ticks are responsible for Lyme disease, babesiosis, ehrlichiosis, and rickettsiosis. Fleas transmit pathogenic organisms that result in the plague and endemic typhus while flies account for leishmaniasis, onchocerciasis and African trypanosomiasis.
Prevention of many zoonotic diseases can be achieved through practicing good personal hygiene and applying safe work practices   according to guidelines. Frequent hand washing is essential especially after using restroom, before/after changing diapers, before/after food preparation, before/after eating, after handling animals, and after touching contaminated objects. For laboratory personnel, it is necessary to wear personal protective equipment according to guidelines. These include gowns, scrubs, gloves, shields, masks, etc.
Zoonosis is a disease or infection resulting from transmission from animals to humans or vice versa. Bacteria, parasites, viruses, and fungi all contribute to over 200 zoonotic diseases. West Nile Virus, SARS-Coronavirus, and others that have emerged recently are zoonoses. Currently, animals are the source for 75% of emerging infectious diseases. Vectors that play a main role in transmitting these pathogens are mosquitoes, ticks flies, bugs, and fleas. In addition to vectors, transmission of zoonotic infections occurs through bites, scratches, contaminated food and water, inhalation, and handing of animals.
The clinical pictures in most endemic zoonotic diseases resemble each other, hence it is usually challenging to differentiate them clinically. This results in underdiagnosing and underreporting of disease, thus the exact burden of these endemic diseases tends to be overlooked.
The workup consists of a through history, physical exam, laboratory tests, imaging, and/or tissue biopsy. The latter three will depend on the differential diagnoses and clinical manifestations. Expert consultation is prudent in decision making during the workup and treatment stages.
Preventative measures are important to limit epidemics. Individuals handling animals or contaminants should be trained and vigilant regarding pathogens of specific animals and the regions that they originate from    .
Other ways of contracting these diseases are eating/drinking contaminated substances (water, food, milk, bodily fluids, stool), handling infected animals or pets, scratches or bites from animals or insects, contact with animal feces or urine by mouth or breathing, and eating infected meat.
An example of a zoonotic disease is cat scatch disease. This occurs when a cat contaminated with the bacterium Bartonella henselae transmits it through a bite or scratch. The patient can have swollen lymph nodes, fever, headache, and skin sores. This infection should should be treated with antibiotics. The cat itself does not have symptoms.
The doctor determines the diagnosis of zoonitic infections by obtaining a comprehensive history and physical exam. Depending on this, a series of laboratory tests and imaging may be necessary to make the diagnosis. Generally, zoonotic infections are treated according to the diseases they produce.
Preventing these diseases can be accomplished by exercising some precautions such as:
- Washing hands thoroughly with warm water and soap after using restroom, after changing diapers, before and after eating, before and after cooking food, and after handling animals.
- Vaccinating pets and maintaining their health.
- Avoiding stray or unknown animals.
- Keeping the litter boxes and cages clean.
- Pregnant women and those with weak immune systems should avoid litter boxes or unclean animal cages, etc.
- Cooking meat well and adequately.
- Storing food and trash away from locations that attract animals.
- Wearing protective clothing when gardening or landscaping. This includes, gloves, long sleeves, and boots.
- Using insect and mosquito repellents and netting.
- If you are in areas where ticks are common, inspect the body thoroughly.
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