PATHOLOGICAL EFFECT OF THE PARASITE UPON THE HOSTthat the host tissue adjacent to the cyst usually consists of nothing more than layers of
fibres. The cellular nature of the tissue becomes more apparent as the histological sec-
tion moves into the actual lung tissue. Where the hydatid membrane is adjacent to the
fibrous tissue, the lamination is more intense and there is some evidence that keratin-
like material is deposited.
n E. granulosuscysts are unilocular whereas the cysts of E. multilocularisare alveolar —
formed by series of cysts that have budded off from the original mother cyst.
n An alveolar cyst can cause far more pathological damage to the host, particularly if it
becomes established in the brain tissues.7.6.3.1 Diagnosis
Detecting the presence of a hydatid cyst in the intermediate host and in particular in humans
can be done in one of the following ways:
n Infected lungs are detected by radiography and examination of the sputum for proto-
scoleces or hooklets.
n Ultrasound scanning of the liver (now one of the most widely used methods of
diagnosis).
n Immunodiagnosis using a variation of the ELISA (enzyme linked immunosorbent
assay) technique. There is evidence to indicate that in older infections the concentra-
tions of IgG 4 antibodies increase with the age of infection.7.6.3.2 Strains of E. granulosus
Chemical analysis has been carried out on E. granulosusobtained from different geo-
graphical locations. Differences in DNA and enzymes have been detected in different
isolates and a pattern has emerged which suggests that there are different strains of
E. granulosus. In Britain there appears to be both a sheep/dog and a horse/dog strain, which
are morphologically different. The Swiss cattle/dog strain also appears to be a distinct
strain. Not all strains are infective to humans.
Knowing that strain differences do occur may have important consequences from the
point of chemotherapy, potential vaccine development and serodiagnosis.
n BOX 7.6 DISTRIBUTION
Hydatid disease or hydatidosis is a zoonotic disease which occurs thoughout the world,
especially among communities where sheep and goat rearing is an occupation, using dogs
to herd the flocks. This is reflected in differences in the disease occurrence between urban
and rural populations. In Uruguay between 1962 and 1971 the incidence of hydatidosis in
the urban populations was 10 cases for every 100,000 persons; however, in the rural areas
it was 123 per 100,000. Similarly in Argentina the urban incidence of the disease was
2 per 100,000; and in the rural areas 150 per 100,000.
Another very endemic area is the Turkana region of Northern Kenya, with 15,000 diag-
nosed cases in a population of 143,000. The reason for the high incidence in that area is
partly due to the fact that humans are not buried below ground and the villagers have a
close association with domestic dogs.