Calcium Oxalate Nephrosis - what does that mean?!

Approximately 35% of the koalas seen at the Adelaide koala and wildlife hospital are diagnosed with calcium oxalate nephrosis. Unfortunately we are yet to find a cure or a cause to this terrible condition that causes calcium oxalate crystals to be deposited into the kidney tubules, which eventually leads to kidney failure. In the blog I'll attempt to simplify the inner workings of the kidney and explain some of the potential causes for oxalate nephrosis in koala.

How does the kidney work?

The kidney is a complex organ which filters the blood to remove waste products, produces hormones that aid in normal body function and maintains electrolyte and water balances with in the body. I will be focusing on the kidneys ability to maintain water balance and filter waste in this blog.

The kidney is composed of many tiny filtering units called nephrons - each nephron contains a glomerulus which acts as a filter and a tubule which helps maintain water and electrolyte balances.

Blood flows through the glomerulus, and it filters out the waste products and water while allowing blood cells and other large molecules to continue on in the blood stream. This water filled with waste products then passes through the tubules, which actively pump the water and electrolytes we need back into the blood stream while allowing waste products to pass into the collecting duct and urine.

The concentration of the urine is mainly determined by the tubules, a low concentration of urine means there is more water and fewer waste products passed. A higher concentration of urine means water is being kept in the body and there are more waste products exiting.

The kidney, a nephron and the labelled anatomy.

What happens in calcium oxalate nephrosis?

Calcium oxalate crystals can be produced from a number of causes which I will discuss soon. These tiny crystals make their way from the blood stream, through the glomerulus and into the tubules causing blocking of the tubules. As the crystals are deposited they also cause local inflammation which then damages the kidney further.

As the tubule becomes damaged its ability to keep waste products inside it, and filter water back to the body slowly gets worse. When we test the urine of koalas with oxalate nephrosis we get a low urine concentration reading (USG below 1.035) - this is because water is essentially slipping through the kidney with out being taken back to the body so the urine is more watered down. This means the koala slowly gets dehydrated because the tubule can not effectively pump water back into the blood stream.

Because the waste products are not being filtered effectively we also get a build up of the products in the blood stream which can be tested using blood biochemistry machines. We look at the blood urea nitrogen (over 9mmol/l) and creatinine (over 250mmol/l)  in particular as indicators of poor kidney health.

In many cases the crystals can also be seen in the urine and on post mortem in the kidney as can be seen in the photos. Unfortunately once a koala has crystals deposited in the kidneys they eventually will succumb to renal failure, and die.

The yellow particles visible in the kidney are calcium oxalate crystals, depositing in the nephrons causing inflammation, blockage and destruction of the normal architecture

This a photograph of a microscopic view of the calcium oxalate crystals excreted in the urine

What are some potential causes?

Humans and other animals can also suffer from calcium oxalate nephrosis, so much of the research into causes in koalas follows what we already know in other mammals.

One potential cause is high oxalate or calcium content in diets. Studies have shown that South Australian gum contains around 4% more oxalate then Queensland gum, but researchers don't think that is enough on its own to be causing the high numbers of renal failure we see.

In humans common causes include a lack of enzymes in the liver to degrade oxalate, an excessive production of oxalate and a lack of certain gut bacteria which help degrade oxalate. Another common cause in humans is gastrointestinal problems such as Chron's disease and pancreatitis.

Researchers are yet to determine the cause in koalas, or why South Australian koalas are so heavily affected compared to the other states. The treatment methods I have trialed are based around helping the degradation of oxalate in the gastrointestinal system and in encouraging water intake to help flush out crystals and allow the waste products to be flushed out with out causing as much dehydration.

Current research and treatment efforts

The Adelaide Koala and Wildlife Hospital have started trialing some treatments used in humans for calcium oxalate nephrosis such as probiotic supplementation and increased water intake. Unfortunately due to low sample size, inability to follow a koala for its whole life in the wild and other external factors it is hard to gauge how successful these treatments are, but we have seen an improvement in life span.

The University of Adelaide, in particular Dr Natasha Speight, are studying the potential causes, pathology and epidemiology of oxalate nephrosis in South Australian Koalas.

Here is LINK to Dr Speight's thesis for those wanting more information.

To donate to the Adelaide Koala and Wildlife Hospital to help us save more koalas click HERE.

Kidneys and renal failure are difficult topics to explain and understand. If you have further questions please don't hesitate to message the Vettails page on facebook or comment below!