Are animals friends or foes?

Are animals friends or foes?

The article below appeared in the July 21st  issue of Health with Perdana, a regular column in The Star by Perdana University faculty members. This week’s article is contributed by Dr. Mohammad Nazmul Hasan Maziz, Lecturer in Microbiology at the Perdana University Graduate School of Medicine (PUGSOM).

Animals are integral part of the nature. As we all know that there are many animals surrounding us, how many of us really consider them as friends? Animals help humans in many ways: Animals help fertilize plants; they are part of the food chain and keep ecosystems in balance; they serve as companion animals like helping reduce depression, loneliness etc. Do we know that even the good animals can be harmful to us? We all know the beneficiary effects of the animals but in this article, we can see a highlight on the hidden harmful effects of animals on humans that we should be aware of.

Zoonoses are infectious diseases in animals caused by bacteria, viruses and parasites which are transmitted to human by direct contact with infected animals or their products or through any vector (insects, mosquitoes etc.). The natural reservoir for these infectious agents are animals. These infectious diseases normally affect animals, but can be transmitted to humans. Certain individuals may be at greater risk for contracting zoonoses. These include people with occupational exposure, such as veterinarians, farmers and slaughterhouse workers or individuals who participate in outdoor recreational activities, such as hunters.

There are a number of different types of microbial agents that cause zoonotic diseases and various ways humans can become infected with these agents. These may best be explained by a few examples. We can look at some common zoonoses like:  Rabies, Brucellosis, Plague, Lyme disease, Relapsing fever, Cat scratch disease, Leptospirosis, Pasteurellosis, Rat bite fever, Scrub typhus, Yellow fever, Ebola and Toxoplasmosis.

  • Rabies is a deadly disease caused by rabies virus which spread to people from the saliva, bite or scratch of infected animals. Dogs, foxes, raccoons, wolves, jackals, bats etc. are some of the main reservoirs of rabies virus.  Hydrophobia, irritability, confusion, hallucinations and convulsions are some of the important symptoms seen in human. By the time the symptoms appear, it is generally too late to save the patient.
  • Brucellosis is an infectious disease caused by a type of bacteria called Brucella. It is a highly contagious disease which is transmitted to human from cows, dogs, pigs, sheep, goats, and camels. Human acquire this disease by ingestion of unpasteurized milk or undercooked meat from infected animals or close contact with their secretions. Symptoms include fever, back pain body-wide aches and pains, poor appetite and weight loss, headache, night sweats, weakness and abdominal pain.
  • Bubonic plague is an acute febrile, infectious, highly fatal disease caused by the bacterium Yersinia pestis. It is primarily a disease of rats, dogs and cats and is usually spread to humans by fleas. Symptoms include abdominal pain, diarrhea, nausea, vomiting, fever, chills, extreme weakness, bleeding and shock.
  • Lyme disease is caused by the bacterium Borrelia burgdorferi and is transmitted to humans from mouse or squirrel through the bite of infected blacklegged ticks. Typical symptoms include fever, headache, fatigue and a characteristic skin rash called erythema migrans.
  • Relapsing fever is a recurring febrile disease caused by several species of the spirochete Borrelia.  It is an arthropod-borne infection spread by lice and ticks. Symptoms include sudden high fever, headache, bleeding, muscle aches, joint aches, stiff neck, nausea and vomiting.
  • Cat-scratch disease is an infectious disease caused by the bacterium Bartonella henselae.  It results from licks, scratch or bite of an infected cat. Symptoms typically include a non-painful bump or blister at the site of injury and painful and swollen lymph nodes. People may feel tired, headache or fever.
  • Leptospirosis is an infection caused by corkscrew-shaped bacteria called Leptospira interogans. It is usually transmitted to humans through contact with urine from infected animals such as rats, cats, dogs, mice, deer, rabbits, cow etc. Symptoms are usually headaches, muscle pains, fever, bleeding from the lungs or meningitis.
  • Pasteurellosis is infection caused by the bacterium Pasteurella multocida.  It is transmitted to humans by contact with infected animals, usually following bites or scratches from cats or dogs. It most commonly causes skin and soft tissue infections. Pain, tenderness, swelling, and erythema often develop and progress rapidly.
  • Ratbite fever is caused by the bacterium Streptobacillus moniliformis. It is a disease that occurs in humans who have been bitten by an infected rat or, in some cases, squirrels, mice, cats, and weasels. It is a systemic illness and the symptoms include fever, rigors, and polyarthralgias. 
  • Scrub typhus is an acute febrile illness caused by the bacterium Orientia tsutsugamushi, transmitted to humans by the bite of the larva of trombiculid mites. Symptoms include swollen lymph nodes, tiredness, red lesion or sore on the skin at the site of the bite, cough and rash.
  • Yellow fever is a serious, potentially deadly flu like disease spread by mosquitoes. It’s characterized by a high fever and jaundice. Mosquitoes acquire the virus by feeding on infected primates (human or non-human) and then can transmit the virus to other primates (human or non-human). 
  • Ebola virus disease, formerly known as Ebola hemorrhagic fever, is a rare but severe, often fatal illness in humans.  This viral disease spread to people by infected blood, tissues, secretions, or excretions of wild animals. Symptoms include fever, severe headache, muscle pain, weakness, fatigue, diarrhea, vomiting, stomach pain
  • Toxoplasmosis is a disease caused by the parasite Toxoplasma gondii, one of the world’s most common parasites. Infection usually occurs by eating undercooked contaminated meat, exposure from infected cat feces. Cats play an important role in the spread of toxoplasmosis. They become infected by eating infected rodents, birds, or other small animals. The parasite is then passed in the cat’s feces. Symptoms include swollen lymph glands, muscle aches, headache, fever and inflammation of the heart muscle, lungs and eyes.


Factors involved in increase of zoonosis

There has been a disturbing trend of reemergence of previously recognized zoonoses that were believed to be under control. This has been coupled with the emergence of new zoonotic diseases. Numerous factors may account for this, including:

  1. Alteration of the environment, affecting the size and distribution of certain animal species, vectors, and transmitters of infectious agents to humans.
  2. Increasing human populations causing an increased level of contact between humans and infected animals.
  • Increased industrialization of foods of animal origin.
  1. Increasing movements of people, as well as an increased trade in animals and animal products.
  2. Decreasing surveillance and control of some of the major zoonoses.



The best defense against contracting zoonoses is education. People should be aware of the respective zoonoses that may be circulating in their environment and the times of year of greatest risk for contracting these zoonoses. This type of information is generally available from public health departments and veterinarians, and can also be found on the Internet. Vaccines are available for the general public for a small number of zoonoses, such as Japanese encephalitis and yellow fever, and on a limited basis for individuals perceived to be at occupational or recreational risk. In addition, chemoprophylactic regimens such as antimalarial drugs are recommended for travelers to high disease-risk areas. The risk of contracting vector-borne diseases can be reduced by avoidance of areas infested by arthropods, use of insect repellents, and appropriate clothing (the less skin exposed the better). Occasionally it is possible to reduce zoonotic disease risks by decreasing the abundance of certain reservoir hosts such as rodents. Individuals should also not drink untreated water or unpasteurized milk. Areas containing potentially contaminated animal material such as rodent excreta should be cleaned using appropriate disinfectants. Patients with diseases such as Ebola virus should be kept in strict isolation. Diseases such as leptospirosis may be contracted by handling infected animal tissue, so trappers should use gloves when handling dead animals. We should increase our personal hygiene and wash hands after handling animals. Domestic pets should be vaccinated and kept clean at all time.  We should avoid contact with wild animals. Children should not be allowed to play with animals an if bitten by animals with unknown vaccine status, child should receive post-exposure medications.

Preventing zoonotic diseases requires coordinated actions by government authorities responsible for human and animal health. Rapid detection, response, and control of public health emergencies, including outbreaks of zoonotic diseases, can prevent the international spread of diseases and ensure global health security.

The human-animal bond is a mutually beneficial. Although animals are a source of many diseases, but due to their huge beneficial roles, animals should be considered as Friends, not Enemies!!!


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