It's possible that co-infections are more common in the U.S. than Europe, but I'd have to take a closer look. I've done a bit of research, and it seems that co-infections are becoming more frequent in both the U.S. and Europe. This may be due to increased awareness and better testing methods, as well as other factors I can't think of right now. One reason for the increased survival of the ticks themselves (at least in cold weather conditions) is the tick "antifreeze" associated with one possible co-infection. I posted about this on another forum, but you might find this interesting as well:
J Clin Invest. 2010 Sep 1;120(9):3179-90. doi: 10.1172/JCI42868. Epub 2010 Aug 25.
Anaplasma phagocytophilum induces Ixodes scapularis ticks to express an antifreeze glycoprotein gene that enhances their survival in the cold.
Neelakanta G, Sultana H, Fish D, Anderson JF, Fikrig E.
Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8022, USA.
In the United States, Ixodes scapularis ticks overwinter in the Northeast and Upper Midwest and transmit the agent of human granulocytic anaplasmosis, Anaplasma phagocytophilum, among other pathogens. We now show that the presence of A. phagocytophilum in I. scapularis ticks increases their ability to survive in the cold. We identified an I. scapularis antifreeze glycoprotein, designated IAFGP, and demonstrated via RNAi knockdown studies the importance of IAFGP for the survival of I. scapularis ticks in a cold environment. Transfection studies also show that IAFGP increased the viability of yeast cells subjected to cold temperature. Remarkably, A. phagocytophilum induced the expression of iafgp, thereby increasing the cold tolerance and survival of I. scapularis. These data define a molecular basis for symbiosis between a human pathogenic bacterium and its arthropod vector and delineate what we believe to be a new pathway that may be targeted to alter the life cycle of this microbe and its invertebrate host.
J Clin Invest. 2010 Sep 1;120(9):3087-90.
PMID: 20739755 [PubMed - indexed for MEDLINE] PMCID: PMC2929727 Free PMC Article
The tick "antifreeze" is associated with Anaplasma phagocytophilum
, which has also been found in Europe, as shown here:
Curr Probl Dermatol. 2009;37:130-54. Epub 2009 Apr 8.
Other tick-borne diseases in Europe.
Bitam I, Raoult D.
Unité des Rickettsies CNRS-IRD UMR 6236, Faculté de Médecine, Université de la Méditerranée, Marseille , France.
Ticks are obligate blood-sucking arthropods that transmit pathogens while feeding, and in Europe, more vector-borne diseases are transmitted to humans by ticks than by any other agent. In addition to neurotoxins, ticks can transmit bacteria (e.g. rickettsiae, spirochetes) viruses and protozoa. Some tick-borne diseases, such as Lyme disease and ehrlichiosis, can cause severe or fatal illnesses. Here, we examine tick-borne diseases other than Lyme disease that are found in Europe; namely: anaplasmosis, relapsing fever, tularemia, tick-borne encephalitis, tick-borne babesiosis and tick-borne rickettsiosis. Each disease is broken down into a description, epidemiology, signs and symptoms, diagnosis and treatment, providing clear overviews of each disease course and the interventions required. Furthermore, in the section concerning tick-borne rickettsiosis, a clear summary of the Rickettsia conorii complex and its role in the disease is provided.
Copyright 2009 S. Karger AG, Basel.
PMID: 19367099 [PubMed - indexed for MEDLINE]
Wiad Parazytol. 2009;55(4):341-7.
[Effect of coinfections in Ixodidae ticks on transmission of blood microparasites].
[Article in Polish]
Zakład Parazytologii, Instytut Zoologii, Wydział Biologii, Uniwersytet Warszawski, ul. Ilji Miecznikowa 1, 02-096 Warszawa. email@example.com
The purpose of this review was to describe and discuss the current spectrum of coinfections in Ixodidae ticks and their effects on the transmission of blood microparasites. Coinfections with Borrelia burgdorferi s. l. and Anaplasma phagocytophilum and/or Babesia sp. in ticks from Poland appear to be common, however, the potential influence on transmission dynamics, the mechanism of genetic variation and the ecology of interactions between pathogens remain poorly understood compared with infections by single pathogen.
PMID: 20209806 [PubMed - indexed for MEDLINE]
Edited to add: I probably should have started a new thread, but I might forget the possible connection to late complicated Lyme disease if I do. Here are more articles related to co-infections in Europe. Keep in mind, these are about infections found in ticks -- not rates of human infection:
Acta Vet Scand. 2009 Nov 27;51:47.
Prevalence of Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum in questing Ixodes ricinus ticks in relation to the density of wild cervids.
Rosef O, Paulauskas A, Radzijevskaja J.
Telemark University College, Bø i Telemark, Norway. firstname.lastname@example.org
PMID: 19943915 [PubMed - indexed for MEDLINE] PMCID: PMC2788566 Free PMC Article
cervid = any member of the deer family, Cervidae, comprising deer, caribou, elk, and moose, characterized by the bearing of antlers in the male or in both sexes
Vector Borne Zoonotic Dis. 2011 Dec;11(12):1595-7. Epub 2011 Sep 15.
Prevalence of Anaplasma phagocytophilum and Coinfection with Borrelia burgdorferi Sensu Lato in the Hard Tick Ixodes ricinus in the City of Hanover (Germany).
Schicht S, Junge S, Schnieder T, Strube C.
Institute for Parasitology, University of Veterinary Medicine Hannover , Hannover, Germany .
Abstract The castor bean tick Ixodes ricinus has been found to be the main vector for Lyme borreliosis spirochetes and Anaplasma phagocytophilum in Central Europe. 1646 I. ricinus ticks from Hanover, a city located in Northern Germany, were examined for infection with A. phagocytophilum and coinfection with Borrelia burgdorferi sensu lato (sl) to obtain so far missing prevalence data for this region. The total A. phagocytophilum infection rate was 3.2% (52/1646 ticks), divided into 4.1% (32/777) adults and 2.3% (20/869) nymphs. Coinfections with B. burgdorferi sl were found in 0.9% of all tick stages. The detected genospecies were B. afzelii, B. garinii, B. burgdorferi sensu stricto (ss), and B. garinii, which was the most frequent species in coinfected ticks.
PMID: 21919727 [PubMed - in process]