Transmission and epidemiology of scabies

1
Transmission and epidemiology of scabies

• Ian F Burgess
• Medical Entomology Centre
• Insect Research Development Limited

2
Transmission of scabies An infestation almost as
difficult to catch as Hansens disease
3
How transmissible is scabies?

• Scabies is very contagious and spreads very
  quickly and easily from person to person..
  (http//www.all4naturalhealth.com/scabies-causes.h
  tml)
• Whats the evidence?

4
How transmissible is scabies?

• Scabies IS transmitted from one person to another
  during prolonged skin to skin contact
• Hand holding
• Supporting or handling someone with skin contact
• Sexual contacts

5
How transmissible is scabies?

• Scabies is NOT transmitted through
• Hugging, embracing, etc.
• Sharing items of clothing or other household
  articles
• Just being in the vicinity of an infected person
  (see other silly comments on http//www.all4natura
  lhealth.com/scabies-causes.html)

6
How is scabies transmitted?

• Juvenile mites run around on the skin surface
• Able to transfer
• Short-lived 3 days per stage
• Can mature on new host females and males
• Male mites run around on the skin surface
• Able to transfer
• Not able to reproduce
• Female mites in burrows
• Long lived cannot leave burrow
• Not able to transfer

7
How is scabies transmitted?

• Mellanby 1940s
• Dug out female mites with a needle could then
  burrow in to give new infection
• Transferred juvenile stages no infections
• Shared beds (25 experiments) no infections
• Underclothing swap (38 experiments) 2
  infections
• Munro 1910
• Transferred juvenile stages obtained infections

8
Factors affecting transmission

• Scabies is transmitted during skin to skin
  contact
• The transmissible forms are
• Larvae and nymphs can develop to adults
• Unmated females must find a mate
• Males are a dead end
• Contact must be relatively prolonged
• To allow tiny creatures to cross over
• To allow enough parasites to cross over

9
Risk of transmission

• The risk of mortality of juvenile forms is high
• Dehydration
• Not being able to establish/develop
• Being washed off
• Not finding a mate
• Evidence from community studies in rural India
  suggest each index leads to 1.9 new cases

10
Risk of transmission

• In British urban communities where
• Smaller families
• Less crowding
• Fewer physical contacts
• Transmission risk would be a lot lower not a
  lot greater than currently found for Hansens
  disease (leprosy) of about 0.6 cases per index
  case
• Conclusion It is difficult to contract scabies

11
Epidemiology of scabies
12
Scabies epidemiology

• Historical data give a good indication of
  epidemiology
• Denmark scabies was notifiable from 1881 to
  mid-1980s
• Various increases and reductions on a roughly 20
  year cycle
• Differences in age group risks
• Seasonal variations in prevalence

13
Scabies in Denmark 1900-1975
14
Scabies in Czech Republic

• Palicka in Prague (1960s) looked at gt11000 cases
  in 6000 families with history of scabies
• 63 of households only one person infested
• Incidence within family up to 22
• Incidence in general population only 1.3

15
Scabies Sheffield

• Church Knowelden in Sheffield (1978) 1482
  cases in 609 families
• 38 of households more than one case
• Index case
• 15-20 years old in 60 of households
• Child at school in 30 of households
• Pre-school child in 10 of households
• Proportionate risk relative to representation in
  the population
• Late teens 8 times more frequently infested
• Schoolchildren twice as often infested

16
Scabies Sheffield
17
Scabies epidemiology

• Sheffield, and India in the 1960s and 70s
  found
• Each index case led to approx 2.6 cases
• Mostly intra-family transmission
• Inter-family transmission mainly by teenagers
• In Sheffield found many more cases in community
  than reported to health workers
• Over 60s extremely low risk

18
Scabies data for the UK

• What data are there for the UK?
• Some hospital dermatology departments have long
  series of data like the Edinburgh Dispensary for
  Diseases of the Skin (ESD) and the Royal
  Infirmary Edinburgh (RIE)

19
Recent scabies epidemiology

• The most useful recent data come from the RCGP
  sentinel scheme
• Approximately 100 GP practices around England and
  Wales
• Provide weekly returns of consultations resulting
  in prescriptions

20
Recent scabies epidemiology
21
Regional incidence by year
22
Seasonal incidence by year
23
Seasonal incidence by region
24
Seasonal incidence by age
25
Influence of age on risk

• Data from Denmark showed extremely low incidence
  in the elderly
• Historical data from RIE also show low incidence
  in over 50s

26
Recent incidence by age
27
Recent incidence by age
28
Recent incidence by age

• Why is the incidence of scabies increasing in
  older people?
• More people living longer
• Older people have less effective immune systems
• Many older people with scabies are in care
• Older people harder to diagnose so may infect
  more contacts