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Zoonosis

Zoonosis is a disease or infection that is transmissible between humans and vertebrate animals. There are more than 200 zoonoses. 


Presentation

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. 

Cat Scratch
  • Cat scratch disease is the most common zoonotic infection caused by Bartonella bacteria.[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]
  • Direct contact transmission can occur through bites or scratches such as in the cases of rabies and cat scratch fever.[symptoma.com]
Fever of Unknown Origin
  • We also detected the presence of outer surface protein A gene of B. burgdorferi by PCR as well as anti-B. burgdorferi IgM by ELISA in human contacts who were suffering from fever of unknown origin.[ncbi.nlm.nih.gov]
Weakness
  • 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.[symptoma.com]
Neglect
  • This report represents the first systematic study on animals associated with patients suffering from febrile illness to confirm the emerging of such neglected zoonosis in Egypt.[ncbi.nlm.nih.gov]
  • This is the first reported Egyptian human case of trypanosomiasis evansi, a neglected zoonosis.[ncbi.nlm.nih.gov]
  • Among 868 reported zoonoses, echinococcosis (hydatid disease) is one of the most severe public health problems and listed as one of 17 neglected tropical diseases targeted for control by the World Health Organization.[ncbi.nlm.nih.gov]
  • This neglected disease has been shown through seroprevalence studies to be especially prevalent among children from socio-economically disadvantaged populations both in the tropics and sub-tropics and in industrialised nations.[ncbi.nlm.nih.gov]
  • PLOS Neglected Tropical Diseases . 9 (7): e0003919. doi : 10.1371/journal.pntd.0003919 . ISSN 1935-2735 . PMC 4493064 . PMID 26147942 . Taylor LH, Latham SM, Woolhouse ME (2001). "Risk factors for human disease emergence" .[en.wikipedia.org]
Burning Sensation
  • The authors present a case of human subconjunctival dirofilariosis in a 56-year-old man with mild itching and a burning sensation in his right eye. A slow-moving, whitish, thread-like worm was detected by slit-lamp examination.[ncbi.nlm.nih.gov]

Workup

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

In certain cases, biopsy is indicated for diagnosis. It can be obtained from infected lymph nodes, peripheral tissues or bone marrow. Liver biopsy is not helpful if the function tests are normal.

Slowing
  • A slow-moving, whitish, thread-like worm was detected by slit-lamp examination. The worm was surgically removed and parasitological examination identified it as an immature male Dirofilaria repens.[ncbi.nlm.nih.gov]
Dirofilaria Immitis
  • Dirofilaria immitis, the dog heartworm, is responsible for an endemic zoonosis in the Southeastern United States. The nematode is capable of infesting the lungs of man, causing pulmonary nodules.[ncbi.nlm.nih.gov]
  • Toxoplasmosis is a common infection of cats; in humans it is a mild disease although it can be dangerous to pregnant women. [16] Dirofilariasis is caused by Dirofilaria immitis through mosquitoes infected by mammals like dogs and cats.[en.wikipedia.org]
Trypanosoma Cruzi
  • cruzi armadillos , Triatominae (kissing bug) bite Clamydiosis / Enzootic abortion Chlamydophila abortus domestic livestock, particularly sheep close contact with postpartum ewes Variant Creutzfeldt–Jakob disease PrP vCJD cattle eating meat from animals[en.wikipedia.org]

Treatment

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. 

Prognosis

Since there are abundant zoonoses, the outcomes depend on the diseases. There are treatable infections with good prognosis and then there are those with lethal results (plague, dengue, and Hanta virus). Others like Lyme disease can result in morbidity. 

Etiology

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.

Fungal zoonosis include dermatophytoses, which are transmitted from animals. They infect human hair, nails, and skin. Additionally, sporotrihchosis is a fungal infection [5].

The etiology of bovine spongiform encephalopathy is the same as that of variant Creutzfeldt-Jakob Disease (vCJD) but these two are different diseases [6].

Epidemiology

Nearly 60% of human pathogens are zoonotic, including organisms such as viruses, parasites, bacteria and fungi [7]. 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 [8].

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

Sex distribution
Age distribution

Pathophysiology

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 salmonellaInhaling 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 diseasebabesiosis, 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

Prevention of many zoonotic diseases can be achieved through practicing good personal hygiene and applying safe work practices [9] [10] 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. 

Summary

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 [1] [2] [3] [4].

Patient Information

Zoonoses are infections that are transmitted from animals to humans or vice versa. Fleas, mosquitoes, and ticks can all transmit these infections. West Nile Virus and SARS-Corona virus are examples.  

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. 

References

Article

  1. Ganter M. Zoonotic risks from small ruminants. Veterinary Microbiology. 2015; pii: S0378-1135(15)00277-1.
  2. Ruiz-Fons F. A Review of the Current Status of Relevant Zoonotic Pathogens in Wild Swine (Sus scrofa) Populations: Changes Modulating the Risk of Transmission to Humans. Transboundary and Emerging Diseases. 2015 May 8.
  3. Chikeka I, Dumler JS. Neglected bacterial zoonoses. Clinical Microbiology and Infection. 2015;21(5):404-415
  4. Eremeeva ME, Dasch GA. Challenges posed by tick-borne rickettsiae: eco-epidemiology and public health implications. Frontiers in Public Health. 2015;3:55
  5. Welburn SC, Beange I, Ducrotoy MJ, Okello AL. The neglected zoonoses-the case for integrated control and advocacy. Clinical Microbiology and Infection. 2015;21(5):433-443
  6. Wiethoelter AK, Beltrán-Alcrudo D, Kock R, Mor SM. Global trends in infectious diseases at the wildlife-livestock interface. Proceedings of the National Academy of Sciences of the United States of America. 2015;112(31):9662-7.
  7. Seyedmousavi S, Guillot J, Tolooe A, Verweij PE, de Hoog GS. Neglected fungal zoonoses: hidden threats to man and animals. Clinical Microbiology and Infection. 2015;21(5):416-425.
  8. Mackenstedt U, Jenkins D, Romig T. The role of wildlife in the transmission of parasitic zoonoses in peri-urban and urban areas. International Journal for Parasitology: Parasites and Wildlife. 2015;4(1):71-9.
  9. Stull JW, Brophy J, Weese JS. Reducing the risk of pet-associated zoonotic infections. Canadian Medical Association Journal. 2015;187(10):736-43
  10. Denner J, Mueller NJ. Preventing transfer of infectious agents. International Journal of Surgery. 2015; pii: S1743-9191(15)01135-8.

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Last updated: 2017-08-09 18:05