A Threat to Wildlife

The study of diseases in wild animals is a relatively new scientific approach, when compared to study of disease in humans or domestic animals. While the first half of the twentieth century, a smaller number of researchers began instigating studies of diseases in Wildlife.

A Threat to Wildlife

International Wildlife Disease Association came into being in 1951 and started organization of studies on disease of Wildlife. Then researchers started work in different fields in which they were interested or where there was more need of research like Parasitology, Medicine, Pathology and many other fields.  In this article Emphasis is on parasites and how they have major impact on Wildlife population. Parasites are the organisms that live on or in another host organism and redirect its resources for themselves. They are as old as life itself.

Parasites effects on their host range from diminutive to lethal and they are the huge driving force in shaping the host populations, their impact on biosphere is colossal. The parasitism has been evolved dozen times in different clades. All known Wild animals carry parasites. Parasites split in further categories “Micro Parasites” can be seen by microscope like protozoa, bacteria, fungi and viruses etc. Macro parasites can be seen by naked eye.

Macro parasites are further divided into “Ectoparasites” which lives outside the host (e.g. ticks) and “Endo-parasites” which live inside the host (e.g. tapeworms) and the organism which kills the host, necessarily called “Parasitoid.” This discussion will be on parasite burden of wild animals and effects of parasites on wild animal adversity. Many animals are infected with at least one parasite at a time.

Parasites classification

                             Protozoa (unicellular) 


    Parasites       Helminths (Multicellular)     Trematodes      Endoparasites                            


                              Arthropods (Ectoparasites)


Protozoa are the unicellular organisms found worldwide in most of the habitats. Most species are free living. Almost every wild animal have infected with at least one protozoon at a given time. Infection ranges from symptomatic to life threatening, depending upon the specie or strain of parasite. Here are some examples of protozoa infecting wild animals


It belongs to genus trypanosoma. T. equinum in South America is a dyskinetoplastic variant of T. evansi and not a separate species. Transmitted mechanically from infected blood of animals, and is not capable of cyclical development in Tsetse Glossina spp., morphologically indistinguishable from T. brucei.

It is pathogenic in some wild and domestic animals. Wild animals include deer, capybara (reservoir host) and some other species. Organism is transmitted from animal to animal mechanically by hematophagous flies, including Tabanus spp. and Musca spp. Vampire bats in south and North America are the hosts as well.

Clinical signs include Anemia, weight loss, icterus, weakness, lethargy, edematous swelling of lower parts of body legs, brisket and abdomen, urticarial plaques on skin and ultimately lead to death. Post-mortem lesions include anemia, hemorrhages in internal organs, emaciated carcass, hydrothorax and ascites.  So it has greater impact on deer population and no vaccine develop yet because it changes its surface glycoprotein rapidly.

Babesia and Theileria

Babesia and Theileria are unicellular protozoa, transmitted by ticks, and they are intracellular. Babesia resides in RBCs and Theileria resides in WBCs. Old animals are more susceptible to infection. Wild animal host range includes Wild African Buffalo (B. occultans), White Tailed Deer (Odocoileus virginianus), Wild Boar (Sus scrofa), Yaks (Bos grunniens), Roe Deer (B. bigemina), Impala, Gazelles and some other species. In Babesiosis there is high fever, severe anemia, hemoglobinurea. Post-mortem lesions include intravascular hemolysis, pale mucus membranes, jaundice and dark colored enlarged spleen. Theileriosis is a lympho-proliferative disease. Lymphocytes are arrested in theileria attack.

List of some Protozoa infecting Wildlife



Wild Hosts


L. simondi, L. smithi

Geese, Swans


S. canis

Wild canines and felines


T. gondii

Wild dogs, cats and ruminants


L. donovani, L, tropica, L. braziliensis

Kangaroos, other macropods and variety of wild animals


E. invadens



G. simondi, G. microti

Bandicoot, microtine rodents

There are many other protozoan diseases having greater impact on wild animal’s populations.


  • Trematodes

Trematodes are the dorsoventrally flattened worms. Their size ranges from few millimeters to 7-8 cm. These are also known as flukes. Flukes possess an oral sucker around mouth and a ventral sucker or acetabulum. Suckers are used to adhere hosts. There is wide variety of wild animals infected by flukes. Alaria (A. alata) is a fluke, have wide range of hosts that includes Foxes, Minks and wild carnivores. Paragonimus westermanii, P. kellicotti known as lung worm, ectopic parasites involve intestine and cerebral involvement. Hosts include Wild boars, Cray fish and crustaceans.

Platynosomum fastosum commonly known as cat liver fluke disease known lizard poisoning which lead to hepatic dysfunction and jaundice, hosts include Wild and domestic cats. Fasciola hepatica known as common liver fluke and host includes wild ruminants. Liver is destructed due to juvenile migration of parasite and secondary infection accompanied by C. novyi, which cause Black disease.

Because migration lead to excessive hemorrhage and later fibrosis, then calcification of migratory ducts and liver become black in color known as pipe stem liver. Paramphistomum cervi known as conical flukes, migrating juveniles causes enteritis, severe hemorrhages, ulceration and bleeding for longer time lead to anemia. Mortality rate is up to 90%. Flukes severely damage the organs of their hosts and ultimately lead to death mostly in chronic infections. They are affecting wild life silently.

  • Cestodes

They all possess flat, ribbon like bodies and lack an alimentary track. Adult tapeworms usually inhabit the alimentary canal of their hosts (though they are occasionally found in the bile or pancreatic ducts) and attach themselves to the mucosa by means of a scolex. Despite the lack of a digestive system, they do absorb food from the hosts intestine; thereby providing the tapeworms a habitat that is associated with high nutritional levels.

Echinococcus granulosus and E. equinus (uniocular hydatid), if they are in the liver, may give rise to several hydatids which may result in to gross abdominal distention. If a cyst ruptures, there is risk of death from anaphylaxis. Hosts include wild carnivores (Red foxes). E. multiocularis, E. canadensis causes alveolar echinococcosis. Hosts include Foxes, Raccoons and dogs. Diphyllobothrium latum hosts include fish eating mammals (Bear).

Cestode absorbs large amount of Vitamin B12 and lead to impairment of Vitamin B12 absorption from intestine so lead to megaloblastic anemia. Macrocytic hypochromic anemia develops due to competition with host for vitamin B12. Death is rare. Davainea proglottina host range includes wild birds (fowl pigeon), other gallinaceous birds and gastropod mollusks. Highly pathogenic penetrate deep in villi and causes hemorrhages and severe enteritis and leads to death.

  • Nematodes

Nematodes are typically elongated, tapered at both ends, and bilaterally symmetrical. They vary in size from microscopic to nearly 1 m long. They have esophagus, mouth and anus. Mouth has lips and some species possess teeth. Adults feed on host tissues, fluids and gut content. Most parasitic nematodes are dioecious. Toxascaris leonina is an ascarid (round worm). Its final hosts are wild canines and felines.

Ancyclostoma caninum (hook worm) final hosts are wild canines commonly foxes, infection lead to bloody diarrhea, weight loss, and anemia and in chronic infestations lead to death of the host.  Toxocara cati is a round worm, hosts includes wild felines. Due to high infestation in kitten, there are more number of parasites which lead to intestinal blockage or intussusceptions and causes death. Angiostrongylus vesorum is French heart worm; hosts include wild canines, clinical signs include anemia, respiratory signs, sometimes coagulopathy and nervous signs.

Sudden death can occur even in the absence of respiratory signs. Capillaria philippinensis is a lung worm; hosts include dogs, foxes and cats. Heavy infection of C. hepatica can result in hepatic lesions and hepatic capillariosis is usually fatal.  Capillaria philippinensis in the small intestine can cause severe enteropathy and sometimes lead to death. There are many other species of nematodes that cause severe infections in wild animals which ultimately result in death of the animal.


Insects (flies, lice, fleas) are Ectoparasites. Adults are bilaterally symmetrical, segmented body (head, thorax and abdomen), 6 jointed appendages, eyes and antennae. They may or may not have wings. Arachnids include ticks (hard & soft) and mites having 2 segments of body. Some have sucking and some have chewing mouth parts. There are immense numbers of insects and arachnids which serve as vector for various other parasitic (protozoan) diseases. In Babesiosis Ixodid tick serve as vector, plasmodium’s vectors are mosquitoes.

Trypanosomiasis vector is Tsetse fly, leishmaniosis vector are sand flies (Phlebotomus) and Leucocytozoon vector are black flies (family simulidae). Fleas are significant vectors of various infections including pathogenic and zoonotic infections. It includes dog flea (ctenocephalides canis), cat flea (C. felis), oriental rat flea and poultry flea. Fleas were also responsible for transmission of yersenia pestis which causes bubonic plague.

The mites of cats and dogs are host specific with a few exceptions. The most prevalent significant mange mites are Demodex canis, found in wild canines and Demodex cati in wild felines. Among these arthropods many of them serve as vectors, as well as on their own they severely affect their hosts and causes annoyance to their host and heavy infestations of ticks and mites lead to death.

Now, we understand that parasites are affecting the wild animal populations in various forms either in form of vector or infecting directly and lead to fatal outcomes like death of host. So there are some wild animal species which are endangered due to disease problems either caused by micro or macro parasites and anthropogenic impact. It needs to pay attention that how to conserve them? Or let them extinct, Think……

Hammad ur Rehman Bajwa, Muhammad Kasib Khan,

Muhammad Adnan Sabir Mughal, Saad Salman

Department of Parasitology, University of Agriculture, Faisalabad

By Dr. Hammad Ur Rehman Bajwa

PhD Scholar, Department of Pathobiology, University of Illinois, Urnana-Champaign.