On the invasion of the central nervous system by nematodes. I. The incidence and pathological significance of nematodes in the central nervous system

A wide variety of nematode species have been observed to invade the central nervous system. They may be located in the meningeal spaces or may penetrate into the tissues of the brain and spinal cord.

The pathological changes resulting from invasion of the central nervous system are influenced by the route of entry, the size and the mobility of the parasite. They may be diffuse or focal and may include haemorrhage, degenerative changes, cellular infiltration and glial proliferation. Such changes may or may not be observed in close association with the parasite.

Symptoms indicating involvement of the central nervous system have long been associated with nematode infections outside the central nervous system. The pathogenesis of these symptoms is obscure, but they may possibly be of allergic origin.

The direct pathological effects on the central nervous system are mainly the result of trauma and are directly proportional to the size and activity of the parasite. The possibility that nematodes may transport viruses into the central nervous system is briefly discussed.

On the invasion of the central nervous system by nematodes. II. Invasion of the nervous system in ascariasis

1. Experimental infections in mice showed that the larvae of Toxocara canis, T. mystax, Ascaris devosi, A. columnaris and Toxascaris transfuga reached the brain of mice; the larvae of Ascaris lumbricoides, A. suum, Parascaris equorum and Toxascaris leonina were not recovered from the brain. The larvae of T. canis, T. mystax, T. transfuga and A. columnaris remained hi the brain of mice for several months.

2. Larvae reaching the brain produced characteristic haemorrhages on the surface of the cerebral hemispheres in the early stages of infection. It was concluded that the larvae reach the brain via the arterial blood stream, leave the arteries at the point where their diameter approximates that of the larvae, i.e. mostly on the surface of the brain, and penetrate into the brain from the subarachnoid space and chorioidal tissues.

3. The larvae of T. canis were found to occur in the brain of mice in relatively greater numbers than the larvae of other species, but only very rarely caused nervous symptoms. The larvae of T. canis and T. mystax showed no growth in the brain.

4. The larvae of A. columnaris (skunk) frequently caused nervous symptoms in mice, the effect appeared to result from traumatic damage due to the relatively large size attained by these larvae about 3 weeks after infection.

5. The brain of infected mice showed very slight changes consequent upon infection with larvae of T. canis. These larvae moved actively through the tissues; they incited little or no cellular reaction, but left haemorrhagic tracks. The larvae of A. columnaris also moved actively; when in the extended state they were usually found in normal tissue; when coiled, they were often associated with a necrotic focus infiltrated with leucocytes.

6. After experimental infections of dogs with larvae of T. canis, two out of twelve infected animals harboured larvae in the brain. No natural infections with these larvae were found in the brains of dogs and cats. After experimental infection, larvae of T. canis were found in the brain of mice, rats and guinea-pigs, but not of rabbits.

7. Larvae of A. suum were recovered from the cerebrum of one pig suffering from posterior paralysis, but not in an experimentally infected pig.

8. No larvae of P. equorum were found in the brain of foals in natural and experimental infections.