Cs02_sample.qxd

CAPE: Parasitology 2 - Slide Seminar Series 2 CAPE: Parasitology 2 - Slide Seminar Series 2 CAPE: Parasitology 2 - Slide Seminar Series 2 CONTRIBUTOR’S DIAGNOSISOnchocerciasisNote the large number of adult female Filarial worms embedded in dense fibrous tissue. The worms are cut in transverse and in longitudinal section. Each worm contains a bi-lobed uterus which con- tains numerous microfilariae. The columns of nuclei in the microfilariae can be seen at higher magnifi-cation. Some of the worms have become degenerate and this has caused a brisk eosinophilia in the tissue.
Numerous microfilariae can be seen in the connective tissue. This feature distinguishes the Filarialworm - Onchocerca volvulus - from Wuchereria bancrofti, in which microfilariae are found circulating inthe peripheral blood.
In Onchocercal infections, microfilariae may be seen in smears made from fluid obtained by making a superficial nick in the skin. Microfilariae may infiltrate the tissues of the eye and cause blindness.
Slide 1 - the young lady had been working in Zambia, Africa, as a foreign correspondent. She devel- oped the lump a few months after returning to Australia. Slide 2 - a larger subcutaneous lump excised from an Australian man who had been working in Nigeria CAPE: Parasitology 2 - Slide Seminar Series 2 COMMENTARYThis disease is caused by the filarial nematode worm Onchocerca volvulus which occurs in Central Africa and Central to South America. The infection is transmitted from one person to another by a bit- ing black fly (Simulium) which lives in the vegetation beside fast flowing streams and rivers. The adultworms live in the dermis and subcutaneous tissue where they cause subcutaneous nodules. Microfilariaeare found in the dermis. The main clinical effects of Onchocerciasis are caused by the migrating micro-filariae. They cause severe itching and when they invade the eye they cause keratitis which leads toblindness. The diagnosis is confirmed by finding microfilariae in a sample of fluid extracted from a skinsnip. Alternatively, the diagnosis is made when the histopathologist examines a subcutaneous lump.
Figure 14.1 shows the cut surface of a subcuta- The morphology of these worms is similar to that neous nodule removed from the hip region of an of the Wuchereria bancrofti but the distinction is Australian male aged 30 years who had been work- made because the adult worms are found in a sub- ing in Nigeria. The microscopic section in Figure cutaneous nodule and not in a lymph node and the 14.2 shows a fibrotic nodule through which there microfilariae are non-sheathed and are present in are many adult Onchocerca worms cut in trans- the dermis, not in the blood (Figure 14.3).
CAPE: Parasitology 2 - Slide Seminar Series 2 Male - 34 yearsThis man presented to a family medicine doctor complaining of upper abdominal pain, anorexia, tired- ness and nausea for about a week. Prior to his present illness, he had been involved in a fight in which he had been kicked in the back. Investigations revealed mildly abnormal liver function tests and thepresence of a cystic lesion in the apical segment of the left lower lobe of his lung, with some collapse/con-solidation as well. A further space occupying lesion was found in the right lobe of his liver. He was treat-ed medically for three months, and then a left lower lobectomy was performed. The chest X-ray, CT andthe lobectomy specimen are illustrated. CAPE: Parasitology 2 - Slide Seminar Series 2 CAPE: Parasitology 2 - Slide Seminar Series 2 CONTRIBUTOR’S DIAGNOSISHydatid cyst of the lungThe patient is a casual employee of an abattoir in a country town in Australia. The serological test for Hydatid disease was positive, with a titre >1024. He was given a course of Albendazole before surgery was performed. It was decided to remove the lung cyst first and to perform a partial hepatectomy toremove the cyst in the liver at a later date. Before the pathologist opened the cyst, he aspirated fluid, centrifuged it and examined a wet prepara- tion (a drop of fluid on a microscope slide, with a coverslip placed on top of the fluid). A few hookletswere found, but no scolices. The hooklets are easier to see by using phase contrast illumination (Image6). Note the white laminated membrane filling the cyst. it has separated from the fibrous capsule in the lung. This capsule is the body’s response to the presence of the cyst. Microscopically it shows a foreignbody response. There are only occasional tiny fragments of laminated membrane attached to the liningof the capsule (Images 17-21). To properly identify the parasite, one must take sections of the white lam-inated membrane. (Images 25-32) In this case, no germinal layer can be seen on the inner lining of themembrane. It has been destroyed by the Albendazole. There are numerous hooklets in the cyst fluid, butno scolices or daughter cysts. Human infection is acquired by ingestion of dog tape worm eggs passed in the faeces of infected sheep Image 38 is a photograph of multiple, colourless, cystic structures vomited by a young child and sent to the laboratory for identification, by the Accident and Emergency doctor in a Children’s Hospital. Thequestion is: “Is this a parasite and if so, what is it? Because it looks rather like the membrane of hydatidcyst.” As you see in the gross picture these are semi-transparent cystic structures approximately 1cm indiameter. Microscopically, in the next three images they have no structure at all. These are gel cystswhich result from gastric digestion of various forms of jellied baby food. CAPE: Parasitology 2 - Slide Seminar Series 2 COMMENTARYThis occurs when man is infected with the larval stage of the dog tapeworm - Echinococcus granulosus.
Hydatid disease is prevalent in sheep raising countries throughout the world. In sheep raising com- munities there is a close working relationship between sheep, dogs and man. The adult tapeworm livesin the gut of the sheepdogs. Eggs contaminate the environment and man and sheep become infected anddevelop the larval stage of the parasite - hydatid cyst. Farmers kill some sheep for meat and the offal isfed to the dogs. Liver in particular contains hydatid cysts and when the dog eats the cysts, the cycle iscontinued. Hydatid cysts slowly enlarge and ultimately they cause symptoms resulting from pressureeffects.
Figure 2.1 is a dog tapeworm - E. granulosus. It is asmall worm, about 5mm long. It has a head (scolex)with suckers and hooklets. It has one mature and onegravid segment. In the gravid segment the uterus isfilled with eggs. The genital pore opens laterally inthe middle of the gravid segment. Figure 2.2 - the liver is the commonest organ in whichhydatid cysts develop. The cysts may produce palpa-ble enlargement of the liver. They show as a spaceoccupying lesion in the various techniques used forimaging the liver.(in this case an ultrasound) Figure 2.3 shows a hydatid cyst in a liver specimenfrom a fifty three year old sheep farmer. It was an inci-dental post mortem finding. The cyst is composed ofa thick white outer membrane one or two millimetresthick. Adjacent to the cyst there is a chronic inflam-matory cell reaction with fibrosis in the adjacent tis-sue. Within the cyst there are multiple daughter cysts of varying size. If the main cyst ruptures these daugh-ter cysts spill into other tissues and continue to grow. CAPE: Parasitology 2 - Slide Seminar Series 2 Figure 2.4 is a hydatid cyst being removed surgicallyfrom the liver of an eighteen year old female. Thewhite laminated membrane of the hydatid cyst can beclearly seen. There is usually a plane of separationbetween the laminated membrane of the cyst and theadjacent tissue. When such a cyst is being removed, itis important to be very careful not to spill any of thecontents of the cyst into the adjacent tissues or intothe peritoneal cavity. Otherwise, regrowth occurs. Figure 2.5 shows the inner lining of the laminatedmembrane. The laminated membrane is lined by asingle layer of germinal epithelium from which newdaughter cysts develop. The developing daughtercysts can be seen as granular projections on the innerlining of the cyst. As these daughter cysts grow, theybreak off from the germinal epithelium and floatfreely in the cyst as demonstrated in Figure 27.3. Figure 2.6 is a low power view of the laminated mem-brane lined by the germinal layer with daughter cystsdeveloping from it.

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