Lyme borreliosis, or Lyme disease, is the most commonly reported tick-borne disease in Europe and North America.  The disease is caused by infection with the arthropod-borne gram-negative-like spirochete, Borrelia burgdorferi sensu lato (B. burgdorferi s.l.),  and can involve multiple organs or tissues, resulting in skin, cardiac, musculoskeletal and neurological disorders.  In most countries, Lyme borreliosis is not a notifiable disease; therefore, exact data regarding annual incident rates are not available.  In the United States, the causative agent is B. burgdorferi sensu stricto (B. burgdorferi s.s.)  and Lyme borreliosis is localized to north-eastern, mid-Atlantic and upper north-central states.  In 2010, a total of about 30,000 cases of Lyme borreliosis were reported to the US to the Centers for Disease Control and Prevention (CDC).  An updated report by the CDC in 2013, which takes into account diagnostic data from other sources, estimates that the actual number of new cases per year in the United States is closer to 300,000 (http://www.cdc.gov/media/releases/2013/p0819-lyme-disease.html).  In Europe, B. afzelii and B. garinii are the main causative agents of Lyme borreliosis, as well as B. burgdorferi s.s.  and B. bavariensis, which contribute to a lesser extent depending on the geographic location.  The prevalence of Lyme borreliosis varies considerably in different European countries with an overall increased prevalence from west to east.  In much of Europe, the number of reported cases of Lyme borreliosis has increased since the early 1990s (e.g., the Czech Republic, Estonia, Lithuania; see Lyme borreliosis in Europe, WHO report of 2006), and the geographic distribution of cases has also expanded. 
Borrelia belongs to the family Spirochaetaceae, which is subdivided into the medically important genera Treponema, Leptospira and Borrelia.  B. burgdorferi s.l.  is a spiral-shaped, vigorously motile gram-negative bacterium, about 10-20 μm long and 0.2-0.5 μm wide, that grows under microaerophilic conditions.  The spirochetal cell wall consists of a cytoplasmic membrane surrounded by peptidoglycan and several flagella and then by a loosely-associated outer membrane. 
Lyme borreliosis generally occurs in stages characterized by different clinical manifestations, with remissions and exacerbations.  Stage 1, early infection, consists of a localized infection of the skin, followed within days or weeks by stage 2, disseminated infection, and months to years later by stage 3, persistent infection.  However, the infection is variable; some patients have only localized infections of the skin, while others display only later manifestations of the illness, such as arthritis.  Different clinical syndromes of Lyme borreliosis are also caused by infection with diverse B. burgdorferi s.l.  species.  B. burgdorferi s.s.  more often causes joint manifestations (arthritis) and heart problems, B. afzelii causes mainly dermal symptoms (erythema migrans; EM and acrodermatitis chronica atrophicans; ACA), whereas B. garinii is implicated in most cases of neuroborreliosis. 
Localized infection—The most common symptom of stage 1 of an infection is erythema migrans, which occurs in 70-80% of infected people.  This skin lesion is often followed by flu-like symptoms, such as myalgia, arthralgia, headache and fever.  These non-specific symptoms occur in 50% of patients with erythema migrans. 
Disseminated infection—During stage 2, the bacteria move into the blood stream from the site of infection to distal tissues and organs.  Neurological, cardiovascular and arthritic symptoms that occur in this stage include meningitis, cranial neuropathy and intermittent inflammatory arthritis. 
Persistent infection—Stage 3 of the infection is chronic and occurs from months to years after the tick bite.  The most common symptom in North America is rheumatoid arthritis, caused by an infection with B. burgdorferi s.s.  Persistent infection of the central nervous system with B. garinii causes more severe neurological symptoms during stage 3, and a persistent infection of the skin with B. afzelii results in acrodermatitis chronica atrophicans. 
In some risk groups, such as farmers, forestry workers, hikers, runners or vacationers, seroprevalence and disease incidence rates have increased, as well as in children under 15 years of age and adults between 39 and 59, without gender preference.  This increased incidence of Lyme borreliosis is linked to changes in forest habitats as well as social factors.  Environmental changes, such as forest fragmentation, have led to a sharp reduction of rodent predators such as foxes and birds of prey, which in turn has led to an increase in the mouse population, with a subsequent increase in the tick population.  More recently, patchy reforestation has increased the number of deer and thus the number of ticks.  Suburban sprawl and the increasing use of woodland areas for recreation such as camping and hiking has brought humans into greater contact with the larger number of tick Borrelia vectors.  All of these factors together have contributed to a wider distribution of Borrelia and a higher incidence of Lyme borreliosis. 
Antimicrobial agents are the principle method of treatment of Borrelia infection.  The antibiotic used depends on the stage of the disease, symptoms, and the patient's allergies to medication.  The length of the antibiotic course also depends on the stage of the disease and the severity of symptoms.  Early Lyme borreliosis is typically treated with oral tetracyclines, such as doxycycline, and semi-synthetic penicillins, such as amoxicillin or penicillin V. Arthritic and neurological disorders are treated with high-dose intravenous penicillin G or ceftriaxone.  Up to 30% of Lyme borreliosis patients do not display the early characteristic symptoms of infection with Borrelia, making diagnosis and treatment problematic.  The antibiotic course can be long (up to several months) and sometimes ineffective and is thus debated in the Borrelia field, especially during later-stage disease.  Even in the case of effective treatment of Borrelia, patients can be left with debilitating fatigue, pain, or neurological symptoms for years afterwards, which is referred to as post-treatment Lyme disease syndrome.  In general, the use of antibiotics can have undesirable consequences, such as the development of resistance by the target micro-organisms.  Finally, antibiotic therapy may effectively cure Lyme borreliosis, but provides no protection against subsequent infections. 
A monovalent serotype 1-OspA-based vaccine (LYMErix™) was approved and marketed in the USA for the prevention of Lyme disease caused by Borrelia burgdorferi s.s.,  but the vaccine is no longer available.  Furthermore, heterogeneity in OspA sequences across different serotypes in Europe and elsewhere precludes efficient protection with a vaccine based on OspA from only a single serotype. 
Chimeric OspA molecules comprising the proximal portion from one OspA serotype, together with the distal portion form another OspA serotype, while retaining antigenic properties of both of the parent polypeptides, may be used in the prevention and treatment of Lyme disease or borreliosis (WO2011/143617, WO2011/143623). 
Currently, there is no preventative medicament for Lyme borreliosis on the market and thus there is a need in the art for the development of such a medicament that can provide effective protection against Borrelia that are present in the USA, Europe and elsewhere, especially for the development of a medicament that can provide effective protection against several Borrelia serotypes simultaneously.  The serotype 3 OspA-containing heterodimer, Lip-S4D1-S3hybD1, of the current invention improves on our previously-disclosed heterodimer, Lip-S4D1-S3D1 (see WO2014/006226) with regard to both ease of production and stimulation of specific antibodies as measured by antibody surface binding to serotype 3 Borrelia spirochetes.  Additionally, the more specific quality of the immune response to the new heterodimer indicates that the potency is also superior in comparison to the previously-disclosed heterodimer.