Schistosoma Nasale

Also known as

Shistosoma nasalis, nasal schistosomiasis, snoring disease

Description

Nasal schistosomiasis (snoring disease) is caused by the blood fluke Schistosoma nasale, a snail-borne trematode (flatworm). It infects humans, domestic animals and wild animals in different parts of Asia, India and Africa. Species commonly occurring in India are Schistosoma nasale and S. spindale in cattle, S. indicum in equines and sheep and S. incognitum in pigs.

These parasitic flatworms (flukes) reside in the nasal veins of cattle, buffalo and other animals. The infection and clinical signs are usually less severe in buffalo than in cattle. Affected cattle shows rhinitis (inflammation of the mucous membranes inside the nose), profuse thick nasal discharge, sneezing, difficult breathing and snoring sounds.

Chronic infections cause outgrowths in the lining of the nasal passages, creating small nodules and abscesses containing eggs of the fluke. Buffaloes are not affected as much, and generally just have pin-head sized eruptions in the membranes. The fluke passes its eggs out into the nasal discharges.

Clinical signs in cattle include cauliflower-like growths in the nasal cavity that create partial obstruction of the passage and snoring sounds, and profuse nasal discharge that is often thick and bloody. In endemic areas, some of the local cattle remain negative for S. nasale eggs, while others excrete eggs but without showing signs of the disease.

Most infected cattle, however, exhibit signs along with the presence of eggs in nasal discharge.

A different form of nasal schistosomiasis exists in some regions where local cattle are negative for S. nasale but local buffalo carry it without showing any signs, and cross-bred cattle exhibit snoring disease and eggs in their nasal discharges. The eggs are boomerang or oval shaped.

Schistosomiasis is a common parasitic infection in cattle and rarely in other domestic animals in Africa and Asia. Most infections in endemic areas are subclinical, but high prevalence rates of subclinical infections cause economic losses due to long-term effects on growth and productivity of the animals, and increased susceptibility to other parasitic or bacterial diseases.

Signs

• Growths inside the nose
• Snoring sounds when breathing
• Nasal discharge

Cause

S. nasale is a species of trematode (parasitic flatworm) in the family Schistosomatidae. It was identified first in India in 1933. The freshwater snail Indoplanorbis exustus acts as intermediate host. This blood fluke adversely affects health and production of cattle and some serious outbreaks of disease caused by this species have been reported.

Adult worms are parasites in the blood vessels of animals (feeding on blood) and cannot complete their life cycle outside the host. The mature female is more slender than the male and normally is carried in a groove along the underside of the male body.

Of the 19 species reported to infect animals, 8 of them are parasites of ruminants. Most of them reside in blood vessels in other parts of the body (such as those that serve the intestines and liver), but S. nasale lives in the nasal veins.

Eggs pass into the nasal mucous and are swallowed, then passed in the feces. They must be deposited in water if they are to hatch and release miracidia, which invade the water snails that serve as intermediate hosts.

The immature flukes develop within the snail--becoming primary and secondary sporocysts and then cercariae. When fully mature, the cercariae leave the snail and swim freely in the water, where they remain viable for several hours. Ruminants are usually infected with cercariae when the tiny flukes penetration the skin, or when drinking water containing them.

At that point, the cercariae develop into schistosomula, which are transported via the lymph and blood to their preferred sites in the host’s body. The prepatent period (between acquiring the immature flukes and the egg-laying adults) varies with the species of fluke but is generally 45 to 70 days.

The occurrence of cattle schistosomes depends on the presence of intermediate snail hosts, their level of infection, and frequency of water contacts. In areas where conditions are favorable, prevalence rates of infections in cattle may be 40% to 70% or higher.

There is evidence that cattle can acquire some immunity to schistosome infection, which mainly suppresses fertility of the flukes. Examination of naturally infected animals has shown that partial protection against reinfection also occurs, and acquired resistance to schistosomes is of major importance in slowing infection intensity in endemic areas.

Adult flukes in the blood vessels of the nasal mucosa don’t seem to cause as much problem as the growths they create for passing their eggs, which cause abscesses in the lining inside the nose. The abscesses rupture and release eggs and pus into the nasal cavity, which eventually leads to extensive fibrosis.

Large granulomatous growths are common on the nasal mucosa, which block the nasal passages and cause difficult breathing.

Prevention

The most effective way to control cattle schistosomiasis in endemic areas is to prevent contact between cattle and the parasite by fencing off wet areas where snails reside and supplying an uncontaminated water source for drinking. This is not always possible in parts of the world where cattle herds are nomadic.

Other methods of control include destruction of the snail population at transmission sites, either by chemical or biologic methods, or removal with or snail traps. Draining their swampy habitat, removal of water weeds, or increased water flow can also make these areas unsuitable for snails.

These measures not only help reduce the transmission of schistosomiasis but also help control other parasitic trematodes such as liver flukes and rumen flukes which also depend on water snails as intermediate hosts and frequently are found in the same localities as schistosomes.

Treatment

Anthiomaline was originally the drug of choice, but often led to relapse after treatment. Praziquantel is now more commonly used, though recently some cases have been successfully treated by administering triclabendazole. In treated herds, there may be some issues of drug resistance developing in future populations of fluke.

Praziquantel at proper dosage is highly effective, although two treatments 3 to 5 weeks apart may be required. For practical and economic reasons, schistosomiasis in domestic stock is rarely treated, however.