Diagnosic Dilemma No. 4 


Contributor: Emeritus Professor John Goldsmid, University of Tasmania

 
A 19 year old soldier was admitted to hospital with suspected meningitis after a tour of duty in a remote game reserve in the Zambezi Valley area of Zimbabwe. He was fit and well until he suddenly became ill, with headache, dizziness vomiting and neck stiffness. He became stupose, had difficulty in urination and generally had symptoms suggestive of uraemia. He had been bitten by Tsetse flies while in the Zambezi Valley and had been taking Deltaprim (pyremethamine+dapsone) as an antimalarial. Initially, it was thought he might have acute renal failure following malignant tertian malaria (Plasmodium falciparum), but repeat blood slides were negative. Blood slides were also negative for Tryopanosoma brucei var rhodesiense – East African Sleeping Sickness also having been considered a possibility. Although no malaria parasites had been detected, he did show some improvement when treated with quinine, but the very severe headaches continued. To rule out meningitis as a possibility, a lumbar puncture was performed. The CSF was clear but had a moderate increase in lymphocytes. What was found, however, was that numerous filarial microfilariae were present in the CSF. There was no indication of a bloody tap and no microfilariae had been found in the blood smears. The recovered microfilariae were all dead and partly autolysed (Fig 4.1).The mean size of the microfilariae was 172.3um x 4.6um. One microfilarial worm was still enveloped in it’s egg membrane (Fig 4.2).
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Fig. 4.1 - Microfilaria recovered from the CSF (phase contrast microscopy)
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Fig. 4.2 - Microfilaria within the egg membrane (phase contrast microscopy)

What is your diagnosis?



 


This is a difficult but fascinating case. Only two microfilarial worms have been described from humans in Rhodesia (now Zimbabwe) – Mansonella (= Acanthocheilonema = Dipetalonema) perstans and Wuchereria bancrofti – both of which occur in the Zambezi Valley where the patient had been. Of these two worms, M. perstans have microfilariae that are unsheathed and have a blunt tail with nuclei extending to the tip. W. bancrofti has sheathed microfilariae with a pointed tail and nuclei not extending to the tip. All the microfilariae seen in the CSF were dead and autolysed. There had thus been what appeared to be shrinkage of the nuclear column away from the body wall at the two ends of the microfilariae (see Fig. 1) Superficially, this gave the microfilariae the appearance of being unsheathed (the concept of it being sheathed being discounted as the covering seemed to be too short and tight-fitting for a sheath and appeared rather to be body wall ) and having a nuclear column which thus did not seem to extend to the tip of the blunt tail. The fact that the one larva was still in it’s egg membrane (Fig.2) suggested that the adult worms were established in the CNS.
The diagnosis made at the time and based on the morphology of the microfilariae, was cerebral filariasis due to Acanthocheilonema (= Mansonella) perstans and with the adult worms taking up an ectopic site within the CNS (Dukes et al, 1968).
Five years after this case was published, Orihel and Esslinger (1973) described a species of filarial nematode from the CNS of Cercopithecus monkeys from Guinea in tropical Africa. This species of nematode was identified as Meningonema peruzzi. Orihel (1973) then went on to make the fascinating observation that the microfilariae of M. peruzzi matched exactly the description and pictures of the earlier case from the soldier in Rhodesia. He thus suggested that the Rhodesian case was a case of zoonotic filariasis (Beaver, Jung and Cupp, 1984). This too was interesting as some three years previous to that, Condy and Hill (1970) writing about animal filariasis in Rhodesia had stated: “Microfilariae of animal origin could well play a significant part in filarial infestations of humans in Rhodesia”.
 
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