Like it or not, the local Lyme disease controversy refuses to lie down. Patients continue to ask their doctors if they could have it, and are not always satisfied with the answers they get. The argument has been going back and forth for several decades. Blow-by-blow accounts can be found elsewhere. Some of these have a polemic flavour, and don’t help advance the debate about whether or not we really do have classic Lyme disease in Australia.
Recognising Lyme Disease
The clinical features of Lyme disease, otherwise known as Lyme borreliosis occur in three distinct phases:
- early localised disease; typical rash known as erythema migrans (EM) or bull’s eye rash in majority of untreated patients after an average of one week (mx= 1 month), fatigue, muscle or joint ache, swollen lymph nodes
- early disseminated disease; EM distant to original location, chills, fever, headache, facial palsy, shooting pains, red & swollen large joints
- late persistent disease; joint pain and swelling (majority of untreated patients), neurological complications (small minority of untreated patients)
Who gets Lyme disease?
It takes a combination of events to lead to Lyme disease
- exposure to hard-bodied ticks (Ixodes species)
- one or more tick bites
- transmission of the causal bacteria during a tick bite (Borrelia burgerdorferi)
The majority of tick bites in Lyme disease endemic areas do not result in Lyme disease because the tick needs to be attached for more than a day before the bacteria can be transmitted. The larger adult ticks are more likely to be removed by then. That leaves the smaller stages in tick development, the nymphs. Particularly those in nooks and crannies where they can’t be seen as easily. The dominant tick species in parts of America where Lyme disease is common is Ixodes scapularis (black legged deer tick), and in Western Europe is Ixodes ricinus. In the Eastern United States the disease carrying vector is Ixodes pacificus. None of these tick species are present in Australia.
How is Lyme disease diagnosed?
- The mainstay of diagnosis is recognition of the clinical features, in the setting of a known tick bite.
- Laboratory tests can be used to confirm the initial clinical diagnosis, but these tests are only available in a limited number of reference centres.
- Antibody tests are prone to false positive results and need to be interpreted carefully.
- PCR (molecular) assays can be performed on skin biopsy material from EM lesions. The only PCR positive EM lesions to be Lyme disease so far in Australians have been associated with overseas travel.
Evidence for Lyme disease in Australia
There is little doubt that occasional cases of imported Lyme disease occur following exposure to Ixodes species ticks in endemic regions overseas. A careful travel history is therefore an important part of the assessment of any patient with clinical features suggesting Lyme disease.
None of the recognised tick vectors of Borrelia burgerdorferi are native to Australia.
None of the recognised reservoir hosts of Borrelia burgerdorferi (e.g deer) are native to Australia
One Ixodes species (I. holocyclus) is common in a narrow strip along the Eastern coast of Australia. Borrelia burgerdorferi has so far not been detected in many thousands of ticks sampled and tested in New South Wales.
If not Lyme disease, then what is it?
Several interpretations of the existing data are possible:
- Lyme disease is present in Australia but rare
- Non-Borrelia spirochaetes transmitted by tick bite may cause human infection
- Antibody test results overestimate the presence, area of distribution and prevalence of infection
- The initial reaction to I.holocyclus bites may be confused with the early stages of EM lesions
- A combination of two or more of the above
Sources of more detailed information: