Symptoms of Lyme Disease Overview
Lyme disease symptoms are associated with three developmental stages of the condition; the early localized stage (acute) , early disseminated stage, and late stage Lyme disease sometimes referred to as late persistent infection. The severity of Lyme disease symptoms tends to increase over time, as does the difficulty of Lyme disease treatment, although all stages of infection appear to respond well to short-term antibiotic treatment. The spirochaetal agent that causes Lyme disease is the Borrelia genus of bacteria, with Borrelia burgdorferi sensu lato (s.l.) the broad categorization of bacteria related to the condition. Specific strains of Borrelia bacteria within this category are prevalent in different geographical locations. B. burgdorferi sensu stricto (s.s) is held responsible for all cases of Lyme disease in North America and some cases in Europe. The B. afzelii and B. bavariensis spirochaetes are found in Europe along with B. garinii, which is also prevalent in Asia. There are a number of other strains which have an association with Lyme disease although infectious cases are rare and unconfirmed for most of these. Hybridization has been found in Borrelia bacteria and a large volume of research has already accumulated documenting the presence and prevalence of new variations of the genus in varying locations around the world.
The importance of the particular bacterial strain that is responsible for the infection is only just being revealed with researchers observing patterns of Lyme disease symptoms associated with each type of Borrelia bacteria. In Europe, where the B. afzelii bacteria is the common cause of infection, arthritis as a symptom of Lyme disease is much less likely to develop than in the USA where B. burgdorferi s.s. often leads to this symptom. B. afzelii is more often associated with the development of the chronic skin condition acrodermatitis chronica atrophicans (ACA) and B. garinii with neurological symptoms. Thus, knowing the prevalent strains of spirochaete in an area can allow the population to be on the lookout for specific symptoms in order to catch Lyme disease in its localized early (acute) stage rather than as it disseminates and becomes harder to treat. Early Lyme disease symptoms can be easily overlooked and those who are aware of the risk of Lyme disease in their communities are usually more likely to seek early medical attention after observing more subtle symptoms of infection.
Symptoms Reported by Lyme Disease Cases, Ontario Canada 1999-2004
When to Watch for Lyme Disease Symptoms
Asymptomatic Lyme disease infection does occur but is thought quite rare, occurring in an estimated 7% of diagnosed cases in the USA. Infection without Lyme disease symptoms may be more common in Europe although there are no official estimates of such cases. In most areas symptoms are more likely to arise in the period between May and September due to the time delay between tick-bite and infection incubation and the spreading of the infection from the bite of a nymphal tick rather than an adult tick. The tick’s tendency to bite humans does vary between different regions, and the type of tick hosts, such as deer, cattle, or sheep. Ticks prevalent in Europe, for example, may be more likely to bite humans and spread infection in the adult stage rather than the nymphal stage which is thought responsible for most cases of Lyme disease in the USA. Where adult ticks spread the infection the onset of symptoms will usually be felt in late Summer, Autumn, or even Winter as opposed to Spring and early Summer where nymphs are the main cause of tick bites and Lyme disease.
Lyme Disease Tick Lifecycle
The tick lifecycle takes around three years to complete, with each stage (larva, nymph, and adult) lasting around a year. There is some variation with some ticks living only two years and some up to six years. Feeding on a host animal, either human or non-human, lasts only a few days in each stage of the tick’s life but is sufficient to spread infection and maintain a ‘reservoir’ of infected host animals. The Ixodes ricinus tick species feeds on animals from March until October, although there is some variation in this pattern due to climatic differences. Where the I. ricinus tick exists, around 80% of Lyme disease infections are thought attributable to the nymphs due to their higher inclination to bite humans and their relative predominance compared to adult ticks. The Ixodes persulcatus tick which spreads the Borrelia afzelii and B. garinii spirochaetes is thought more likely to bite humans in its adult stage, with the I. persulcatus nymphs seemingly reluctant to bite humans. The larvae is usually infected (<5%) and is unlikely to either feed on humans or transmit infection to humans.