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Table 2 Notation, definition and values of model parameters

From: Modelling Neglected Tropical Diseases diagnostics: the sensitivity of skin snips for Onchocerca volvulus in near elimination and surveillance settings

Symbol

Definition

Value and units

References

x ij

Number of microfilariae in the ith skin snip biopsy from body site j (shoulder, hip or calf)

Data from each participant

[24, 3034]

d ij

Weight of the i th skin snip biopsy from body site j (shoulder, hip or calf)

See Table 1, in mg

[24, 3033]

ε*

Rate of production of microfilariae per (mated) fertile worm per mg of skin

1.1538 year-1

[41]

m * ij

Mean number of microfilariae per skin snip at baseline

For the mean number of mf/mg for each site and setting see Table 1

 

k m

Aggregation (overdispersion) parameter of skin microfilariae

Estimated by fitting the model, see Table 3

 

μ m

Per capita rate of microfilarial mortality

0.8 year-1

[38, 39]

w

Number of adult (mated) fertile female worms harboured by the host

Unobserved, assumed to be linearly related to microfilarial load

[39]

θ W

Mean number of adult (mated) fertile female worms per host

Unobserved, estimated by fitting the model, see Table 3

 

k W

Aggregation (overdispersion) parameter of adult female worms

Estimated by fitting the model, see Table 3

 

α = ε *1 /ε *2

Ratio of the rate of microfilarial arrival in a shoulder or calf skin snip to the rate in a snip from the iliac crest

Estimated by fitting the model, see Table 3

 

ρ

Rate of resumption of microfilarial production

0.29 year-1

[40, 42]

t

Time since last ivermectin treatment

1, 3, 5 years

 

ζ

The per dose reduction in female worm fertility caused by ivermectin treatment

0

[43]

0.07

[54]

0.35

[55]

n

No. of (annual) ivermectin rounds to which a surviving (mated) female worm has been exposed

10

 

x +

The event that any of the skin snips taken from a host are positive