Biology Reference
In-Depth Information
Newly emerged ticks: Adults molted between December 1963 and May 1964
remained dormant during the entire dry season under the litter. Clusters of two to
ten individuals were observed under individual leaves in the litter. However, a
minor activity was observed during summer showers: ticks resting under deeper
layers of litter and humus crawled up to the superficial layers. No significant lateral
dispersal or emergence from the litter was observed. Similarly, adults from nymphs
released from November 1964 to March 1965 spend the entire dry period in a state
of dormancy under the litter. However, two to five individuals from each batch
emerged from the litter and climbed on the plants after a heavy pre-monsoon
shower. Adults that molted from June to mid-November invariably dispersed and
climbed on the plants immediately after molting.
Dormant ticks spent the dry months in a state of repose with the legs folded and
clinging to the undersurface of the litter leaves. When the leaves were turned
upside down and exposed to light they became active within 1
3 min, crawled
toward the undersurface, and again came to rest. Under direct sunlight, activation
was immediate and the ticks immediately rushed toward darker places.
Invariably the dormant ticks became active after the first few monsoon rains.
Ticks lying under thick forest canopy became active a few days earlier than those
lying under thin canopy or under direct sunlight. Gradually they emerged from the
litter and settled on the undergrowth vegetation. Total displacement was observed
10
40 days after the onset of activity. Initially ticks were found on plants of all
heights up to 150 cm, but later the ticks settled on smaller plants (2
15 cm), des-
cended, spread out, and settled on larger plants.
H. spinigera as a Reservoir of KFD
46,115
H. spinigera is the principal vector of KFD, the nymphal stage being the one biting
the humans and transmitting the virus. Both epizootics and epidemics coincide
with the nymphal prevalence and activity. Studies have shown that virus can persist
in the unfed stages through rainy seasons under the natural conditions. Survival of
the nymphs through rainy season suggests the carryover of the virus by the infected
nymphs through the rainy season, enabling the virus to start a new cycle in the fol-
lowing season. Field studies have shown that unfed ticks can carry the virus from
one year to the next. Viral persistence in ticks suggests that the virus can be held in
an unapparent state by infected ticks, a significant aspect of their role as reservoir
of vertebrate infection.
Human Infestation with H. spinigera
15,46,128,129
In KFD area, 95% of the isolations are from Haemaphysalis (see
Table 2.3
). H. spi-
nigera is the most predominant species and has also yielded the maximum number
of isolates. This species is considered to be the chief vector of the disease. A year-
long study, in which 4,668 persons were examined, had revealed that H. spinigera
was the predominant species infecting man. There was an average of 2.5 ticks per
infected person.
