AMYLOIDOSIS

Amyloidosis is a group of diseases that result from the abnormal deposition of a particular protein, called amyloid, in various tissues of the body. Amyloid protein can be deposited in a localized area and may not be harmful or only affect a single tissue of the body. This form of amyloidosis is called localized amyloidosis. Amyloidosis that affects tissues throughout the body is referred to as systemic amyloidosis. Systemic amyloidosis can cause serious changes in virtually any organ of the body.

Amyloidosis can occur as its own entity or "secondarily" as a result of another illness, including multiple myeloma, chronic infections (such as tuberculosis or osteomyelitis), or chronic inflammatory diseases (such as rheumatoid arthritis and ankylosing spondylitis). Amyloidosis can also be localized to a specific body area from aging. This localized form of amyloidosis does not have systemic implications for the rest of the body. The protein that deposits in the brain of patients with Alzheimer's disease is a form of amyloid.

Systemic amyloidosis has been classified into three major types that are very different from each other. These are distinguished by a two-letter code that begins with an A (for amyloid). The second letter of the code stands for the protein that accumulates in the tissues in that particular type of amyloidosis. The types of systemic amyloidosis are currently categorized as primary (AL), secondary (AA), and hereditary (ATTR).

In addition, other forms of amyloidosis include beta-2 microglobulin amyloidosis and localized amyloidoses.

BLOOD PLASMA

Blood plasma is the yellow liquid component of blood, in which the blood cells in whole blood would normally be suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid. It is mostly water (90% by volume) and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide (plasma being the main medium for excretory product transportation). Blood plasma is prepared by spinning a tube of fresh blood containing an anti-coagulant in a centrifuge until the blood cells fall to the bottom of the tube. The blood plasma is then poured or drawn off. Blood plasma has a density of approximately 1025 kg/m3, or 1.025 kg/l. 

Blood serum is blood plasma without fibrinogen or the other clotting factors (i.e., whole blood minus both the cells and the clotting factors). 

Plasmapheresis is a medical therapy that involves blood plasma extraction, treatment, and reintegration.

FRESH FROZEN PLASMA AND OTHER TRANSFUSED PLASMAS

"Fresh frozen plasma" (FFP) is prepared from a single unit of blood or by apheresis, drawn from a single person. It is frozen to −40 °C (−40.0 °F) after collection and can be stored for ten years from date of collection. The term "FFP" is sometimes used informally to mean any frozen transfusable plasma product, including products which do not meet the standards for FFP. FFP contains all of the coagulation factors and proteins present in the original unit of blood. It is used to treat coagulopathies from warfarin overdose, liver disease, or dilutional coagulopathy. Other transfusable plasma is identical except that the coagulation factors are no longer considered completely viable. This is particularly important for Factor VIII and hemophilia, but these have been mostly replaced by more specific Factor VIII concentrates in the developed world and true FFP is rarely used for that indication.

Plasma used as a source of Cryoprecipitate (Plasma, Cryoprecipitate Reduced) cannot be used for treatment of some coagulation problems but is still acceptable for many uses.

DRIED PLASMA

"Dried plasma" was developed and first used in WWII. Prior to the United States' involvement in the war, liquid plasma and whole blood were used. The "Blood for Britain" program during the early 1940s was quite successful (and popular in the United States) based on Dr. Charles Drew's contribution. A large project was begun in August of the year 1940 to collect blood in New York City hospitals for the export of plasma toBritain. Dr. Drew was appointed medical supervisor of the "Plasma for Britain" project. His notable contribution at this time was to transform the test tube methods of many blood researchers, including himself, into the first successful mass productiontechniques.

Nonetheless, the decision was made to develop a dried plasma package for the armed forces as it would reduce breakage and make the transportation, packaging, and storage much simpler. 

The resulting Army-Navy dried plasma package came in two tin cans containing 400 ccbottles. One bottle contained enough distilled water to completely reconstitute the dried plasma contained within the other bottle. In about three minutes, the plasma would be ready to use and could stay fresh for around four hours. 

Following the "Plasma for Britain" invention, Dr. Drew was named director of the Red Cross blood bank and assistant director of the National Research Council, in charge of blood collection for the United States Army and Navy. Dr. Drew argued against the armed forces directive that blood/plasma was to be separated by the race of the donor. Dr. Drew argued that there was no racial difference in human blood and that the policywould lead to needless deaths as soldiers and sailors were required to wait for "same race" blood. 

By the end of the war the American Red Cross had provided enough blood for over six million plasma packages. Most of the surplus plasma was returned to the United States for civilian use. Serum albumin replaced dried plasma for combat use during theKorean War.

PLASMA SHIFT

Blood plasma volume may be expanded by or drained to extravascular fluid when there are changes in Starling forces across capillary walls. For example, when blood pressure drops in circulatory shock, Starling forces drive fluid into the blood vessels, causing autotransfusion.

Also prolonged still standing causes an increase in transcapillary hydrostatic pressure. As a result, approximately 12% of blood plasma volume crosses into the extravascular compartment. This causes and increase in hematocrit, serum total protein, blood viscosity and, as a result of increased concentration of coagulation factors, it causes orthostatic hypercoagulability. 

CHRONIC NASAL DISCHARGE IN THE CAT

Chronic upper respiratory tract (URT) disease is a relatively common problem in cats, and can have many causes. The most common form is termed chronic post viral or idiopathic rhinitis. In this condition viral infection (e.g. cat ‘flu - caused by feline herpesvirus or feline calicivirus) causes the initial mucosal damage; but the chronic signs relate to secondary bacterial infection of the damaged nasal passages. This may then lead on to chronic osteomyelitis of the turbinate bones (bacterial infection of the fine bones within the nose).  More unusual causes include:

•  Fungal infections which are very uncommon in the UK .

•  Inflammation which can result in polyps of inflammatory tissue.

•  Neoplasia (cancer) which can be localised within the nose, or be part of more widespread disease.

•  Physical damage which can result from foreign objects getting stuck up the nose, facial trauma (e.g. from cat bites or car accidents), or be associated with severe dental disease.

WHAT ARE THE CLINICAL SIGNS OF CHRONIC URT DISEASE ?

The main signs are nasal discharge and difficulty in breathing, ie chronic “snuffles”. The exact nature of the discharge, whether both sides of the nose are affected, and the presence of other clinical signs are dependent on the exact nature of the disease process occurring within the nose, and on the presence of any other illness the cat may have.

In order to determine the extent and nature of the disease it is important that the cat be given a thorough physical examination by a veterinary surgeon. Particular points that the vet will look for include:

•  The presence of nasal discharge, and whether it is bilateral (affecting both sides of the nose) or unilateral (affecting only one side of the nose). Some diseases tend to show unilateral signs (e.g. foreign bodies or cancer), while others more often cause bilateral signs (e.g. chronic post viral rhinitis). The type of discharge can also be important; whether it is clear, purulent (pus), or blood stained. Although the presence of a discharge can be helpful in making a diagnosis, it can on occasion be misleading.

•  Facial swelling may indicate a more serious underlying problem such as cancer or fungal infections arising within the nasal chambers. Although facial pain is seen rarely, resentment of facial examination is common among cats with URT obstruction, especially those with intranasal foreign bodies, or polyps.

•  Sneezing, difficulty in breathing, noisy breathing and mouth breathing may all be seen, but their presence is usually of little diagnostic value.

•  Examination of the eyes may reveal ocular discharge ‘runny eyes', usually resulting from tear duct damage associated with previous URT viral disease, but occasionally associated with cancer within the nose. Another legacy of URT viral infection can be the development of chronic inflammation of the cornea (the clear front part of the eye).

•  Evidence of painful or infected ears may be associated with inflammatory polyps. Cats with polyps may have problems eating if the polyps are large enough to cause obstruction at the back of the throat.

•  Cat's with URT obstruction often have a poor appetite and so experience a degree of weight loss. Marked weight loss is more suggestive of cancer, fungal disease or severe systemic disease.

•  The size and shape of the kidneys may be altered if certain cancers are present.

• Mild to moderate enlargement of the lymph nodes (glands) at the angle of the jaw is common, resulting from a local inflammatory response. If the lymph nodes become very large, or if lymph nodes elsewhere in the body are also affected, cancer or fungal infections are most likely to be the cause.

Over-interpretation of clinical signs can be very misleading since different diseases can give rise to similar signs. However, a few general rules do apply, e.g. facial deformity (changes in face shape) with associated pain, especially if accompanied by a unilateral nose bleed or marked lymph node swelling is suggestive of more serious underlying problems such as nasal cancer or fungal disease. Lack of these clinical signs does not rule out these diagnoses as some cases of nasal lymphosarcoma (a common type of cancer) can cause bilateral nasal obstruction and little nasal discharge of any kind. Although post viral rhinitis usually presents as chronic bilateral purulent discharge, it can also result in unilateral discharge, sometimes blood tinged and occasionally with severe nose bleeds.

 

HISTORY IS IMPORTANT TO HELP WITH DIAGNOSIS      

It is very important to know the answers to a number of questions relating to the cat's previous experiences, e.g.

•  Did the cat have an acute URT infection (cat ‘flu) as a kitten? This is the most common initiating cause of chronic rhinitis.

•  Is there any history of facial trauma, dental disease or ear infections?

•  At what age did the cat first develop the clinical signs? The age of onset and speed of onset of clinical signs can often be misleading, but can occasionally be of help in the diagnosis.

•  Has the nasal discharge always been of the same type, consistency and colour, and has it always been unilateral or bilateral? Are the signs progressing, is the cat systemically ill, and has the cat responded to any previous treatments? The answers to these questions may help determine the underlying cause of the problems.

 

My cat had ‘flu as a kitten and has had 'snuffles' ever since, although he is well in himself.  Should I ask the vet to find out what is wrong with him?

 

Arrange for your vet to examine your cat but if chronic post viral rhinitis is believed to be the most likely cause of the patient's clinical signs, and the cat is not too distressed by the nasal discharge, it is probably best not to put it through further examinations (except perhaps an FeLV test). Further investigations are generally best left for cats with severe or progressive clinical signs, or those with evidence of generalised disease.

When considering treating cats with severe chronic URT disease it is helpful, where possible, to differentiate between the possible underlying causes. This allows the correct treatment to be given and the probable outcome to be discussed. However, since most cases of URT disease will result from chronic post viral damage, it is important to remember that tests may give negative results and the likelihood for full recovery, even with treatment, may be poor.

TESTS TO FIND THE CAUSE   

•  Non-invasive tests, such as haematology, biochemistry and tests for FeLV and FIV may help to determine the extent of systemic disease.

 

•  Nose and throat swabs may be taken to look for the presence of bacteria, viruses or fungi.

 

•  For the best hope of finding a diagnosis it is necessary to give the cat a general anaesthetic in order to perform more extensive investigations. These include taking radiographs (X-rays) and examining the nose and mouth. Detailed examination includes looking up the cat's nose, and examining behind its soft palate (the flap of skin at the back of the throat). While examining the nose it is possible to take samples to look for bacteria, fungi, evidence of inflammation or cancer cells. These methods do not allow very good access to the nasal chambers, so it is possible that underlying disease may sometimes be missed.

 

•  If the less invasive methods of investigation are not successful in gaining a diagnosis it may be necessary to perform an exploratory rhinotomy under general anaesthesia. This involves surgically opening the nasal chambers via the front of the cat's face. This allows for the close inspection of the nasal chambers, the collection of material for biopsy, and the removal of diseased tissue. The procedure is not to be undertaken lightly since although it can be beneficial in some cases, for example where a foreign body, fungal infection or cancer is present, the procedure is traumatic for the cat, and should be reserved for patients with severe clinical signs or those which are already suspected of having nasal cancer or fungal disease. Surgical intervention is rarely curative in cases of chronic post viral rhinitis.

CAN CHRONIC URT DISEASE BE TREATED ?   

Yes, but in most cases treatment is unlikely to give a long term cure. In most cases the clinical signs can merely be controlled, since the chronically damaged bones cannot be repaired.

Antibiotics can be given to reduce secondary bacterial infection. It is usually necessary to give them for a long period or as repeated courses in order to control the clinical signs. Since extended courses of antibiotics are generally not advisable for the overall health of the cat, they are usually given only when the cat is severely affected. It is generally hoped that with time the cat, and its owners, will learn to live with the cat's disease, without the need for repeated courses of antibiotics.

Steam inhalation can help. Make a small room, such as the bathroom, steamy or construct a box or tent structure in which a bowl of boiling water can make the atmosphere steamy. Avoid any human proprietary decongestants as many of these are toxic to cats. If the cat is severely affected by ‘snuffles' and is undergoing further investigation, it is possible to therapeutically flush the pus from the nasal passages while the cat is under general anaesthetic. Although this procedure can occasionally give some degree of short term relief, the clinical signs usually return. The most essential aspect of treatment is good nursing care, keeping the cat's face clean and clear of discharge, and encouraging it to eat by feeding warmed up food that is strong smelling. Specific treatments can be given where specific causes have been found, e.g. polyps can be surgically removed, some cancers can be controlled with chemotherapy, and fungal disease can be treated with anti-fungal drugs.

DRUGS THAT DISRUPT MICROTUBULES

Colchicine, colcemid, and nocadazol inhibit polymerization by binding to tubulin and preventing its addition to the plus ends. The figure to the right shows this inhibition by colchicine (red). Vinblastine and vincristine aggregate tubulin and lead to microtubule depolymerization. Taxol stabilizes microtubules by binding to a polymer. 

MICROTUBULE MOTILITY: EXPERIMENTS IN VITRO

One can label beads with kinesin or dyneins and watch the direction of movement in a cell at the light microscopic level. What would happen if the beads were simply labeled with "cytoplasmic extract"? This cartoon shows the motility process in vitro. The tubule is moving along a negatively charged glass surface and the vesicle moves along the tubule. 

This electron micrograph shows microtubules in cross section with the MAP bridge. The arrows point to bridges between microtubules. The star points to a MAP bridge to the vesicle. In summary, MAPs accelerate polymerization, serve as "motors" for vesicles and granules, and essentially control cell compartmentation.

MICROTUBULE ASSOCIATED PROTEINS (MAPS) FUNCTION

Microtubule associated proteins (MAPs) are tissue and cell type specific. They are high molecular weight proteins (200-300 K) or the tau (20-60 k) proteins. One domain binds to tubulin polymers or unpolymerized tubulin. This speeds up polymerization, facilitates assembly and stabilizes the microtubules. The other end will bind to vesicles or granules. MAPs vary with the cell type. The best examples are found in neurons. 

Furthermore, it is believed that some of these MAPs may bind to special sites on the alpha tubulin that form after it is in the microtubule. These are sites where a specific molecule is acetylated or the tyrosine residue is removed from the carboxy terminal. These sites are important marker sites for stabilized microtubules, because they disappear when microtubules are depolymerized. 

This figure shows a 3-D view of a neuron with its processes containing microtubules. At higher magnifications, the vesicles are seen attached to MAPs and moving along the microtubule conveyer belt. The MAPs include kinesins and dynein which "walk" along the microtubules in opposite directions.The kinesins move the vesicle along towards the plus end and dynein walks towards the minus end. In neurons, as the microtubules grow from the cell body through the processes, the plus end is more peripheral. These proteins have head regions that bind to microtubules and also bind ATP. The head domains are thus ATPase motors. The tail domain binds to the organelle to be moved. It is not known how the energy from ATP breakdown is converted into vectorial transport. 

MICROTUBULE FORMATION

The first stage of formation is called "nucleation". The process requires tubulin, Mg++ and GTP and also proceeds at 37 C. This stage is relatively slow until the microtubule is initially formed. Then the second phase, called "elongation" proceeds much more rapidly. 

During "nucleation", an alpha and a beta tubulin molecule join to form a heterodimer. Then these attach to other dimers to form oligomers which elongate to form protofilaments. Each dimer carries two GTP molecules. However the GTP that appears to function binds to the beta tubulin molecules. When a tubulin molecule adds to the microtubule, the GTP is hydrolyzed to GDP. Eventually the oligomers will join to form the ringed microtubule. The hydrolysis of GTP of course is facilitated at a temperature of 37 C and stopped at temperatures of 4 C. 

This figure shows that, as the oligomers assemble, they form a series of rings, 25 nm in diameter. In cross section, each ring consists of 13 beads. The rows of beads in longitudinal section are called protofilaments.

In the cell itself, microtubules are formed in an area near the nucleus called the "aster". Microtubules are polar with a plus end (fast growing) and a minus end (slow growing). Usually the minus end is the anchor point. In this figure, the plus end is shown to the left by the numerous tubulin dimers. This is the end that carries the GTP molecules which may be hydrolyzed to GDP. Hydrolysis is not necessary, however (see p 810 in text and discussion below). 

Tests have shown that microtubules will form normally with nonhydrolyzable GTP analog molecules attached. However, they will not be able to depolymerize (see below). Thus, the normal role of GTP hydrolysis may be to promote the constant growth of microtubules as they are needed by a cell. 

DYNAMIC INSTABILITY

Microtubules may vary in their rate of assembly and disassembly. Tubulin half life is nearly a full day, however, the half life of a given microtubule may be only 10 minutes. Thus, they are in a continued state of flux. This is believed to respond to the needs of the cell and is called "dynamic instability". Furthermore, there are regulatory processes that appear to control this in a cell. Microtubule growth would be promoted in a dividing or moving cell. However, microtubule growth would be more controlled in a stable, polarized cell. 

As described in your text, the cell can provide a GTP cap on the growing end of a microtubule to regulate further growth. This happens when the tubulin molecules are added faster than the GTP can be hydrolyzed. Thus, the microtubule becomes stable and does not depolymerize. It may also be encouraged to continue growing. Once the GTP is hydrolyzed, it begins to shrink, however. Another way of capping a microtubule is to put a structure at its end, such as a cell membrane. 

MICROTUBULE STRUCTURE

Microtubules can be seen in a bundle in this negatively stained preparation to the left. Recall that negative staining starts by immobilizing the preparation on plastic on an electron microscopic grid. Then heavy metal stain is deposited around the structures, delineating their structure. This preparation may allow you to see the tubulin molecules in the protofilaments.

This transmission electron micrograph to the right shows the microtubules in longitudinal ultrathin section. Note, the tubulin molecules cannot be visualized in this preparation. 

Early electron microscopists found that in order to preserve microtubules, they had to fix the cells in glutaraldehyde at room temperature. Why do you think the temperature conditions were important? What might happen if they fixed the cells for 30 min in the cold? 

Sometimes, you can see collections of microtubules at the periphery of cells. They may be involved in both motility and cytoskeletal functions in this region. It is difficult to see the structure of separate microtubules. Also, microfilaments may also be accumulating in this region. 

The extensive distribution of microtubules can really be appreciated in the light microscope after immunolabeling for tubulin with fluorescein-labeled antibodies. This micrograph shows cells in culture labeled for tubulin. The labeling is so fine, the small microtubules can be delineated. 

ENCEPHALITIS

Encephalitis is an acute inflammation of the brain.

Encephalitis with meningitis is known as meningoencephalitis.

Causes

Viral

Viral encephalitis can be due either to the direct effects of an acute infection, or as one of the sequelae of a latent infection. A common cause of encephalitis in humans is herpes (HSE).

Bacterial and other

It can be caused by a bacterial infection such as bacterial meningitis spreading directly to the brain (primary encephalitis), or may be a complication of a current infectious disease syphilis (secondary encephalitis). Certain parasitic or protozoal infestations, such astoxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems.Lyme disease and/or Bartonella henselae may also cause encephalitis.

Another cause is granulomatous amoebic encephalitis.

Symptoms

Patients with encephalitis suffer from fever, headache and photophobia with weakness and seizures also common. Less commonly, stiffness of the neck (nuchal rigidity) can occur with rare cases of patients also suffering from stiffness of the limbs, slowness in movement and clumsiness depending on which specific part of the brain is involved. The symptoms of encephalitis are caused by the brain's defense mechanisms activating to get rid of the infection. Other symptoms can include drowsiness and coughing.

Diagnosis

Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present irritability, poor appetite and fever.

Neurological examinations usually reveal a drowsy or confused patient. Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningoncephalitis. Examination of the cerebrospinal fluid obtained by a lumbar punctureprocedure usually reveals increased amounts of protein and white blood cells with normal glucose, though in a significant percentage of patients, the cerebrospinal fluid may be normal. CT scan often is not helpful, as cerebral abscess is uncommon. Cerebral abscess is more common in patients with meningitis than encephalitis. Bleeding is also uncommon except in patients with herpes simplex type 1 encephalitis.Magnetic resonance imaging offers better resolution. In patients with herpes simplex encephalitis, electroencephalograph may show sharp waves in one or both of the temporal lobes. Lumbar puncture procedure is performed only after the possibility of prominent brain swelling is excluded by a CT scan examination. Diagnosis is often made with detection of antibodies in the cerebrospinal fluid against a specific viral agent (such as herpes simplex virus) or by polymerase chain reaction that amplifies the RNA or DNA of the virus responsible (such as varicella zoster virus).

Treatment

Treatment is usually symptomatic. Reliably tested specific antiviral agents are available only for a few viral agents (e.g. acyclovir for herpes simplex virus) and are used with limited success for most infection except herpes simplex encephalitis. In patients who are very sick, supportive treatment, such as mechanical ventilation, is equally important. Corticosteroids (e.g. methylprednisolone) are used to reduce brain swelling and inflammation. Sedatives may be needed for irritability or restlessness. Anticonvulsants are used to prevent and treat seizures.

Encephalitis lethargica

Encephalitis lethargica is an atypical form of encephalitis which caused an epidemic from 1917 to 1928, resulting in millions of deaths worldwide. Those who survived sank into a semi-conscious state that lasted for decades until the Parkinsons drug L-DOPA was used to revive those still alive in the late 1960s by Oliver Sacks.

There have been only a small number of isolated cases in the years since, though in recent years a few patients have shown very similar symptoms. The cause is now thought to be either a bacterial agent or an autoimmune response following infection.

Limbic system encephalitis

In a large number of cases, called limbic encephalitis, the pathogens responsible for encephalitis attack primarily the limbic system (a collection of structures at the base of the brain responsible for emotions and many other basic functions).

RABIES

Rabies is a disease that causes acute encephalitis (inflammation of the brain) in warm-blooded animals. It is zoonotic (i.e., transmitted by animals), most commonly by a bite from an infected animal but occasionally by other forms of contact. Rabies is almost invariably fatal if post-exposure prophylaxis is not administered prior to the onset of severe symptoms.

The rabies virus travels to the brain by following the peripheral nerves. The incubation period of the disease is usually a few months in humans, depending on the distance the virus must travel to reach the central nervous system. Once the rabies virus reaches the central nervous system and symptoms begin to show, the infection is effectively untreatable and usually fatal within days.

Early-stage symptoms of rabies are malaise, headache and fever, progressing to acute pain, violent movements, uncontrolled excitement, depression, and hydrophobia. Finally, the patient may experience periods of mania and lethargy, eventually leading to coma. The primary cause of death is usually respiratory insufficiency. Worldwide, the vast majority of human rabies cases (approximately 97%) come from dog bites. In the United States, however, animal control and vaccination programs have effectively eliminated domestic dogs as reservoirs of rabies. In several countries, including the United Kingdom, Australia and Japan, the virus has been eradicated entirely.

The economic impact is also significant, as rabies is a significant cause of death of livestock in some countries.