First clinico-pathological investigation of nasal adenocarcinoma in sheep of semi-arid Rajasthan

In the vast, dry landscapes where sheep and goats graze, the animals are constantly exposed to a world of invisible threats. Among the many challenges they face, respiratory diseases are common, but a specific type of illness involving tumors in the nose and lungs is exceptionally rare. These tumors, known as adenocarcinomas, are abnormal growths of tissue that start in the glands lining the airways. In some parts of the world, a virus is known to cause these tumors to spread through flocks of sheep and goats, creating a condition that slowly destroys the animal's ability to breathe and see. While this disease has been documented in many countries, it has remained a mystery in large parts of India, where farmers rely heavily on their flocks for their livelihood. Understanding how this disease behaves in new environments is crucial, not just for the health of the animals, but for the economic stability of the communities that depend on them.

Researchers from the Central Sheep and Wool Research Institute recently turned their attention to the semi-arid regions of Rajasthan, India, where a troubling pattern began to emerge in sheep flocks. Starting in 2019, farmers reported that adult sheep were becoming sick with strange symptoms, while the younger lambs remained healthy. The illness appeared to be spreading through the herds, causing significant numbers of animals to die. To understand what was happening, the scientists conducted a detailed investigation, examining the sick animals, studying the fluids from their noses, and looking closely at the internal organs of those that had passed away. Their goal was to determine the nature of the disease, how it affected the sheep, and whether it matched known patterns of respiratory tumors found elsewhere in the world.

The investigation revealed a grim picture for the affected flocks. In the villages where the disease struck, between 15 and 16 percent of the adult sheep showed signs of illness, and between 9 and 15 percent of the flock eventually died. The disease did not spare the animals' ability to see or breathe. When the researchers examined the sick sheep, they found that the tumors growing inside the nasal cavity were pushing outward, causing the eyeballs to bulge. In severe cases, this pressure damaged the cornea, the clear front part of the eye, leading to a total loss of vision. The animals struggled to breathe, often making coarse, snoring noises, and many were seen breathing with their mouths open or panting with their bellies heaving. They became thin and weak, losing weight steadily despite still eating some food. A key observation was that the nasal discharge was often mixed with blood, a sign that the delicate tissues inside the nose were being eroded by the growing mass.

To confirm what was causing these symptoms, the team collected fluid from the noses of seven sick sheep and spread it on glass slides to look at the cells under a microscope. They found a high number of abnormal cells that looked like the kind that form tumors, confirming a diagnosis of nasal cancer. They also took blood samples from these animals and compared them to healthy sheep from a different area. The sick animals were found to be anemic, meaning they had significantly lower levels of red blood cells and hemoglobin, which carry oxygen through the body. They also had an unusually high number of a specific type of white blood cell called eosinophils, which often rise when the body is fighting a parasite or a chronic infection. These blood changes suggested that the animals were under severe physical stress from the disease.

When the researchers performed autopsies on the animals that had died, the internal damage was clear. The bodies were emaciated, with very little fat or muscle left. Inside the head, they found a soft, greyish-white mass of tumor tissue filling the back part of the nasal cavity. This mass was attached to the bony structures of the nose and had grown into the sinuses, but it had not yet invaded the brain. The tumor was irregular and had areas where the tissue had died and turned into debris. In one of the sheep, the researchers made a startling discovery: the lungs also contained tumor masses. These lung tumors looked similar to the ones in the nose, appearing as solid, greyish nodules that had replaced the normal air sacs. This finding was particularly significant because, while the disease is known to stay in the nose, finding it in the lungs suggested a more aggressive spread than usually seen in sheep.

Under the microscope, the tissue from the nasal tumors showed a slow-growing cancer that was forming gland-like structures, typical of adenocarcinoma. The cells were relatively uniform, dividing slowly, and were surrounded by signs of long-term inflammation. The lung tissue showed similar patterns, with the air sacs being filled with these abnormal, finger-like growths. Importantly, the researchers checked the liver, kidneys, heart, and brain of the dead animals and found no signs that the cancer had spread to these distant organs. The disease seemed to be confined to the respiratory system, yet its local growth was severe enough to cause death through respiratory failure or secondary infections.

This study marks the first time this specific type of nasal adenocarcinoma has been reported in sheep in the semi-arid region of Rajasthan. The findings suggest that the disease is likely caused by a virus that spreads easily when sheep from different farms mix, a common practice in the region where farmers share breeding males and graze their flocks on common land. The high rates of sickness and death observed in these flocks are concerning, as they represent a significant loss for the farmers. The researchers noted that without effective vaccines or treatments, the only way to manage the disease is to identify and remove the sick animals early, a difficult task without better diagnostic tools. This outbreak highlights a gap in disease monitoring in extensive grazing systems and underscores the need for better awareness and control strategies to protect the health of the flocks and the people who rely on them.