Tick-borne pathogens in a nature reserve area in the Netherlands: serological and molecular assessments in large herbivores and Ixodes ricinus ticks.

Research Overview

• This study investigated the presence and prevalence of various tick-borne pathogens in large herbivores and questing ticks (Ixodes ricinus) in the Oostvaardersplassen nature reserve in the Netherlands.
• It combined serological and molecular methods to assess infection rates, providing insight into pathogen circulation and potential risks to animal and human health.

Background and Rationale

• Ticks act as vectors for multiple pathogens that can affect both animals and humans, making them a public and veterinary health concern.
• While tick monitoring occurs in the Netherlands, less is known about tick-borne pathogens in wild, free-living large herbivores such as red deer, cattle, and horses.
• Understanding pathogen prevalence in these animals can help assess impacts on animal health and the risk of transmission to humans.
• The Oostvaardersplassen reserve, a key natural habitat with large herbivore populations, was chosen due to its ecological relevance and potential as a pathogen reservoir area.

Study Design and Methods

• Sampling Period: September 2023 to December 2024.
• Samples Collected:
  • Blood from Heck cattle, Konik horses, and red deer culled as part of population control.
  • Questing ticks collected from vegetation in the reserve.
• Testing Approaches:
  • Serological tests on serum samples to detect antibodies indicating past or current infection.
  • Molecular tests (likely PCR-based) on blood and pooled tick samples to detect pathogen DNA or RNA, indicating active infection.
• Pathogens Assessed:
  • Tick-borne encephalitis virus (TBEV)
  • Anaplasma spp., especially Anaplasma phagocytophilum
  • Babesia spp. including Babesia microti, B. caballi, and Theileria equi
  • Borrelia burgdorferi sensu lato and B. miyamotoi

Key Findings

• Ticks:
  • A total of 2,617 questing Ixodes ricinus ticks were collected and tested.
  • Detected tick-borne pathogens in ticks included:
    • TBEV at very low prevalence (0.04%).
    • Babesia spp. at 1.5%, mainly B. venatorum and B. cf. odocoilei, excluding B. microti.
    • B. microti at 1.9%.
    • B. burgdorferi s.l. at 8.5%, indicating the Lyme disease group bacteria.
    • B. miyamotoi at 1.8%, a relapsing fever Borrelia species.
    • A. phagocytophilum at 1.1%.
• Red Deer (177 animals):
  • TBEV seropositivity: 6.2%, showing past exposure to the virus.
  • A. phagocytophilum prevalence: 58.9%, a very high rate indicating active infection circulation.
  • Babesia spp. prevalence: 53.4%, predominantly B. divergens and B. cf. odocoilei species.
• Cattle (36 animals):
  • No TBEV seropositivity detected (0%).
  • A. phagocytophilum prevalence: 14.3%.
  • Babesia spp. prevalence: 3.6%.
• Horses (89 animals):
  • No TBEV seropositivity detected (0%).
  • A. phagocytophilum prevalence: 1.2% (very low).
  • Babesia spp. prevalence: 0%.

Interpretation and Significance

• Confirmed active transmission of multiple tick-borne pathogens, including tick-borne encephalitis virus, in this Dutch nature reserve.
• Red deer appear to be significant reservoirs or indicators of pathogen circulation, given their high infection rates compared to cattle and horses.
• Low prevalence of TBEV in ticks but notable seropositivity in red deer suggests ongoing but limited virus circulation.
• Detection of diverse Babesia species and Borrelia species illustrates a complex pathogen ecology involving multiple pathogens.
• Findings highlight the importance of monitoring wildlife and vectors to understand disease ecology and potential transmission to domestic animals and humans.

Recommendations and Future Directions

• Integrate systematic tick and pathogen surveillance into existing wildlife and nature reserve management programs.
• Use a One Health framework that links veterinary, ecological, and public health perspectives to monitor and mitigate tick-borne disease risks.
• Expand surveillance to include more extensive temporal and spatial sampling to track trends and emergence of pathogens.
• Further study the health impacts of these pathogens on wild herbivore populations and potential spillover into livestock and humans.
• Public health agencies may consider these data to assess human risk and inform awareness or preventive measures in the region.