complex and meaning that the antigen is now




Diseases Caused due to Fungi in Animals

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5 Differences between Ectoparasites and Endoparasites – Explained!          










































Tonsils/ thymus- Make antibodies
Lymph nodes-
Lymph vessels- Carry lymph fluid around the body, one of three types of blood

As each pathogen is specific to a particular victim and therefore not
all organisms are susceptible to the same pathogens. For example, humans can
not catch the viruses that cause canine distemper, feline leukemia, and mouse
pox. Similarly, the virus that causes AIDS in humans does not infect animals
such as cats and dogs.


immune system is a composite arrangement of organs, containing cells that
recognise foreign pathogens entering the body and destroy them, via the
process of phagocytosis (the engulfment of foreign pathogens). Phagocytosis

Sometimes the immune system can malfunction. It may react to the wrong
thing (autoimmunity), overreact (hypersensitivity), and in some cases it may
not react at all (immunosuppression and immunodeficiency).



Natural immunity is where you become immune to a disease
once you have already caught it. For example, if you catch chicken pox as a
young child, the risk of catching it again as an adult is minimal.

B lymphocytes are activated, resultantly secreting antibodies,
which move through the blood stream, binding it to the foreign antigen and
deactivating it, forming an antigen-antibody complex and meaning that the
antigen is now unable to bind to the host cell. T lymphocytes


Adaptive immunity is the third line of defence and refers to
the type of immunity in which mechanisms have become specialised to respond to
a specific pathogen. This type of immunity is often developed after the first
exposure to a disease, remaining ‘on standby’ in case of further infection. Adaptive
immunity involves two types of response (cell mediated and humoral). In cell
mediated response, T helper cells are produced in the thymus and have
antibodies on their surface which are specific to a certain antigen which bind
together, forming an antigen-antibody complex via a process known as clonal
selection and therefore activating the T helper cell. After this, clonal
expansion will occur, a process whereby the T lymphocyte will divide mitotically
to produce clones of itself, causing the activation of T regulatory cells, T
killer cells and macrophages. T regulatory cells suppress immune response and T
killer cells attack their own cells when they have been antigenically altered
as well as unicellular parasites. They do this by severing their cell membranes,
causing the contents to overspill.



The second line of defence is referred to as innate immunity and is the
next step to prevent disease, should the first line of defence have been
ineffective. Innate immunity is immunity which is non- specific and present
from birth, effective against a wide variety of pathogens and foreign
substances via physical, chemical and cellular defences. It provides a quick
response, however it does not distinguish between different pathogens so is only
a basic defence mechanism. Macrophages carry out a process called phagocytosis
which is essentially the engulfment of pathogens. Each pathogen will have an
antigen on its surface which is specific to that particular pathogen. During
the phagocytic process, the phagocyte will recognise the pathogen, prompting
the cytoplasm of the phagocyte to enclose itself around the pathogen, assisted
by opsonins in engulfing it.  As a result
of this, the pathogen will now be contained within a phagosome (a type of vesicle
which is a fluid filled sac, found within the cytoplasm of a cell and responsible
for the transportation of substances into and out of the cell). The phagosome
will then fuse with a lysosome, the digestive enzymes within, breaking down the
pathogen. Lastly, the macrophage will become an antigen-presenting cell,
meaning that it will present the antigens of the pathogen which will stick to
its surface which then will activate other cells found within the immune system.


Blood clotting is also part of the first line of defence. It works by
host cells releasing histamine which increases the permeability of the blood
vessels at the site of damaged tissue, causing acute inflammation. Inflammation
causes an increase in blood flow to the affected area due to vasodilation so
there will be an increased concentration of white blood cells which will help
expel pathogens from the infected site. Signs of inflammation include pain,
redness, heat and swelling. A blood clot will form to prevent continued
bleeding; this occurs due to the damage to blood vessels exposing collagen
fibres which activate platelets and therefore start the blood clotting cascade
reaction, resultantly forming a temporary plug. The platelets activate the
soluble enzyme, fibrogen in the presence of vitamin K and calcium ions and are
reinforced by substances known as clotting factors. This causes the formation
of fibrin (a soluble protein produced by the liver and found within blood
plasma at the wound due to the action of the clotting enzyme, thrombin) which
forms a platelet plug at the site of the damaged tissue, holding platelets and
clotting factors together.


Within the body, there are three lines of response to pathogens, the
first of these being physical and chemical barriers. The skin is the largest organ
in the barrier and provides a physical barrier which pathogenic microorganisms
are unable to penetrate. Tears, mucus and saliva contain lysozyme, an enzyme
which destroys bacteria via the destruction of their cell walls by breaking
down the bonds holding together the peptidoglycans that the cell wall is
composed of. Cilia, lining the trachea and the lungs move mucus and other
particles which may become trapped away from the lungs, pushing them back out
and urinary flow flushes pathogens out of the bladder area. The acidic nature
of the stomach ensures that any bacteria and parasites which may have been
ingested are destroyed.

























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that are required to exploit more than one host species for the completion of
their life cycle are referred to as having an indirect lifecycle, whereas those
infecting only one species are said to have a direct life cycle.


parasite is an organism which obtains its nutrients from a ‘host’organism.
Parasites can be classified into the categories of endoparasites and ectoparasites
as well as protozoa. There are several defining characteristics of the two
types of parasites; endoparasites live within the host’s own body and are
usually permanent, respiring anaerobically. They are also usually obligate
parasites, meaning that they are unable to complete their entire life cycle
without the exploitation of a host organism. On the other hand, an ectoparasite
lives on the surface of the host and has the capacity to be either temporary,
intermittent or permanent. Some are also obligate parasites, however some are
facultative (does not depend upon its host for continuation of life cycle).
Ectoparasites also respire aerobically, which occurs within the mitochondria of
its cells where adenosine triphosphate is broken down in to adenosine
diphosphate by breaking the bond connecting one of the phosphate groups to the
rest of the molecule, therefore releasing energy.  Protozoa are unicellular, eukaryotic organisms

Rabies is an example of a viral
infection that can be contracted in animals and is neurotropic, (attacks the
body’s nerve cells). It is of lyssavirus genus, meaning that it is of
icosahedral shape, approximately 180 nanometres in length and of the
rhabdoviridae family, meaning that it consists of a helical ribonucleoprotein
core situated within a surrounding lipoprotein envelope. Five proteins are
encoded by the rabies genome- nucleoprotein (N), phosphoprotein (P), matrix
protein (M), glycoprotein (G) and polymerase (L). In order to infect its host,
the rabies virus first binds to the receptor before entering the host cell via
the endosomal transport pathway via a process called endocytic recycling, which
regulates the composition of the proteins found within the plasma membrane. The
disease is usually passed on when an infected animal bites another infected
animal, as the virus is carried in saliva. Rabies has a relatively long
incubation period, with symptoms usually taking approximately three- eight
weeks to present in dogs and two to six weeks to present in cats. Clinical signs
of the disease vary, however there are three main stages which may occur,
although not every infected animal will necessarily present with every stage.
The first stage is called the ‘prodomal phase’ and lasts for approximately two-
three days in dogs and a day or two in cats. Signs that they are within this
phase include repetitive licking of the site of infection and a fever. Erratic
behaviour often occurs, with otherwise friendly animals becoming shy or
irritable whilst unaffectionate animals may become affectionate and docile.
They may also display signs of nervousness, anxiety, isolation and trepidation.
The second stage is known as the ‘furious phase’, which cats are more prone to
developing than dogs and lasts approximately one- seven days. Restlessness and
irritability occurs, followed by hyperresponsiveness to both visual and
auditory stimuli. Animals within the furious phase become highly agitated,
becoming more and more vicious and irritable, potentially biting and attacking
people/ other animals around them and their surrounding environment.
Disorientation sits in and seizures occur, resulting in death of the animal.
Lastly, the paralytic phase (which occurs after either the prodromal or furious
phase) affects the nerves in the head and throat, causing salivation and
difficulty swallowing. There is potential for facial paralysation due deep,
laboured breathing and a dropped jaw. A choking sound will occur, as though
there is something lodged in the animal’s throat, proceeded by the occurrence
of respiratory failure and eventually death.


The optimum temperature range for
the growth of viruses is around 37 degrees Celsius, with the ideal pH range
being a neutral condition of around 7-7.4. In order for viruses to grow, Oxygen
is not needed and they reproduce within the body’s own cells; therefore
antibiotics are ineffective on viruses.


Complex: Structures
are formed from a combination of helical and icosahedral shapes and they often
have a complicated outer wall, incorporating head-tail morphology in certain
viruses and usually only affect bacteria.

Helical: Consist of
proteins forming a circle around a capsid with a cavity in the middle which is
filled with nucleic acid. 15-19nm is the standard width, with 300-500nm being
the general range of length.


Envelope: Surrounded by
a lipid bilayer membrane, encasing the virus. As the virus exits the cell via
budding, the envelope is formed. Examples of these include hepatitis C and


Icosahedral: At a
distance, icosahedral viruses appear spherical to the naked eye, however upon
closer inspection they are not strictly spherical- they are composed of
equilateral triangles, fused together to form a sphere. Icosahedral viruses are
released into the atmosphere when the cell dies, breaks down and lyses, thus
causing viral diseases at this point.


Viruses are extremely small
organisms, ranging from just 20-750 nanometres, composed of a capsid (protein
coat) surrounding a coiled up strand of nucleic acid. There are four different
shapes of which a virus can take form:

Aspergillosis is a fungal disease
which is prevalent in mammals and birds. The respiratory tract is the most
commonly affected area (nasal aspergillosis); however it has also been known to
affect the ears, mouth, liver and throat (systemic aspergillosis). The nasal
form of aspergillosis is contracted via airborne transmission as aspergillus
fungi shed conidia (microscopic spores) which are very easily inhaled as they
float around the air. A healthy immune system will prevent these spores from
entering the body, however if the immune system is compromised, it will be able
to find a way in so some animals are more vulnerable to the disease than
others. It is not yet known how the systemic strain of the disease is
contracted. In both forms of the disease, the fungus aspergillus causes
necrosis and the formation of small abscesses which grow out spore producing
hyphae, thus causing the further spread of infection. Symptoms are different,
dependent upon which organs and species of animal is affected, varying between
nasal and systemic. Chronic nasal discharge with a strong odour is usually
prevalent in the nasal strain of the disease and will not subside with
antibiotics, as it is not a bacterial infection. Intermittent nosebleeds and ulcers
around the nostrils are also often common. Systemic aspergillosis symptoms
depend upon which organs are affected however may include lameness, weakness,
lack of appetite, weight loss and lack of coordination. It can also lead to the
development of uveitis and holes with pus or bloody discharge may be present,
however most animals with systemic aspergillosis will not show any nasal
symptoms. Aspergillosis is a nasty disease with reference to the fact that
clinical signs take a long time to present themselves so it is usually at a
critical stage before diagnosis.


There are several fungal routes
of transmission, one of these being via direct contact (tactile) transmission
which is how lymphangitis is contracted. Epizootic lymphangitis is a fungal
disease which is most common in equine organisms, however can also occur within
cattle. It is caused by the fungus Histoplasma farciminosus and causes chronic
inflammation and suppuration of both the cutaneous and the subcutaneous
lymphatic vessels and glands. It enters the body via a wound or an abrasion on
the skin or of a mucous surface and is usually spread via fomites such as tack
or grooming brushes which have come into contact with an already infected
animal. The incubation period of lymphangitis is relatively long (on average 6-
8 weeks) and the disease’s spread is slow and subtle, causing gradually increasing


The function of fungi is to
survive and reproduce and they have several methods of reproduction and may be
classified according to how they reproduce. There are two asexual methods of
reproduction and one sexual method of reproduction. Zygomycota reproduce
asexually when nuclei fuse within a thick-walled zygospore when certain hyphae
grow towards each other and join together. The second asexual method of
reproduction within fungi produces a group called ascomycota. These organisms
can produce asexually or sexually, taking their name from the sac-like ascus
formed during sexual reproduction, however also reproducing asexually via
fission, spores or budding. Lastly, basidiomycota reproduce solely sexually via
spores, for example mushrooms and toadstalls. They produce basidia upon a
fruiting body and develop basidiospores, enabling them to reproduce.


Fungi are multicellular,
eukaryotic organisms. The main body of fungi is composed of a fine, branched
structure called hyphae which intertwine to form mycelium. Generally the cell
wall is composed of chitin, however a few types of fungi have cellulose cell
walls, in the way that plants do. Fungi are heterotrophic organisms, absorbing
nutrients from living or dead organic matter on which they grow. They thrive
within a slightly acidic environment and require very little moisture for their
growth. The optimal conditions for growth of fungi vary, with most surviving
best in a temperature range of 21- 32°C, however some
species of fungi can be found below freezing and above 65°C, so it is largely

Another species of bacteria which
can have a negative effect upon animalistic organisms is bacillus anthracis,
which causes a disease called anthrax, carried by both wild and domestic
animals in Africa, Asia and certain parts of Europe. There are three types of
anthrax- cutaneous anthrax begins as a bump on the skin and gradually expands,
ulcerating and is not a serious illness. On the other hand, inhalational
anthrax is far more severe and can even be fatal. Far less common, the victim
will start out with flu-like symptoms which gradually progress to pneumonia,
respiratory failure and eventually septicaemia, ultimately leading to shock and
in some cases, death. The rarest form of anthrax is intestinal anthrax,
resulting in fever and severe gut disease.

There are four types of reproduction within bacteria. Firstly, binary fission
is a type of asexual reproduction, based around cell division. During the
process of binary fission, the cell will grow to a point where it appears to be
double its initial size, before splitting. Conjugation is a form of sexual reproduction within bacteria. In order
for it to occur, direct cell-to-cell contact must occur and genetic material is
exchanged between cells. Another type of bacterial reproduction
is transformation, where a homologous gene from the environment binds to and
replaces the matching gene in the bacteria, resultantly meaning that one type
of bacteria is transformed into a different type of bacteria. Lastly,
transduction is where DNA from one bacterial cell is transferred into another
bacterial cell, with the help of a bacteriophage- a virus which parasitizes a
bacterium by infecting it and reproducing inside it.


Although there are many types of
bacteria which are beneficial towards animals, there are also many types which
may cause illness and disease. For example, E. Coli is a type of bacteria which
is usually found within the intestine of animals and is usually harmless,
however certain types of E. Coli easily cause intestinal infection within
organisms. For example E. Coli 0157:H7 causes symptoms such as diarrhoea,
abdominal pain and fever. In severe cases, it can cause dehydration or
potentially even kidney failure, affecting the very young, the elderly and
people with weakened immune systems the most severely.


There are three main shapes which
bacteria may form. The first of these is called the bacillus (rod) and can be
either obligate aerobes (require oxygen for respiration) or facultative
anaerobes (do not require oxygen for respiration) and have the ability to
reduce themselves and lie dormant for an extremely long period of time. The
second of these is the coccus (sphere) and this refers to any bacteria with a
spherical, oval or generally round shape, however they can appear flattened
when viewed next to one another. Last but not least, spirilla (twisted)
bacteria are curved bacteria which can range anywhere from a gentle curve to a
tight, corkskrew-like spiral, many of which possess the ability to move.

Bacteria may be classified according to how they obtain their nutrients.
Autrophic bacteria gain their nutrients by building their own organic food via
photosynthesis and turning it into organic nourishment. The opposite of an
autrophic organism is a heterotrophic organism; this means that they use
organic carbon as food, in the same way as fungi and animals (including


In order for bacteria to thrive,
the conditions must be just right. Warm, moist conditions are essential for
bacterial growth, with the optimum temperature range being from 15-20°c for psychrophilic
bacteria, 30-37°c for mesophilic bacteria and 50-60°c for thermophilic
bacteria. The ideal pH range for most bacteria is in neutral conditions of
around 6.5-7; however some types of bacteria can withstand extreme values,
although it may not be the optimum conditions for growth.


Bacteria are prokaryotic,
unicellular photosynthetic organisms which are generally only a few micrometres
in length. They do not contain a nucleus or other membrane-bound organelles;
however they do contain a cell wall which provides rigidity to the cell.