Animal and Plant Health Inspection Service | Veterinary Services | 1

1. Disease Information

1.1 General Disease and Pathogen Information: Acarapisosis or acariosis or acarine 

disease is a disease of the adult honey bee (Apis mellifera) and other Apis species. It 

is caused by infestation with the Tarsonemid mite (tracheal mite) Acarapis woodi. The 

tracheal mite is an internal parasite of the respiratory system that lives and reproduces 

in the prothoracic trachea of the honeybee, where it feeds on the host’s hemolymph. 

They may also be found in the head, thoracic, and abdominal air sacs. Mites are 

spread among nestmates through direct contact with infested individuals. A. woodi has 

a nearly cosmopolitan distribution, likely being found where A. mellifera colonies are 

managed. Two additional Acarapis species found in the U.S., A. externus and A. 

dorsalis, are confined to the exterior of honey bees and are thought not to have severe 

impacts on honey bee health.

1.2 Clinical Signs: Clinical signs are nonspecific and resemble those of other diseases. 

Common clinical signs include a distended abdomen, disjointed wings, and an inability 

of infected bees to fly leading to a tendency for them to crawl in front of the hive or 

climb nearby blades of grass. Dysentery may also be present in infected bees. As the 

infection severity is correlated with the parasitic load present, clinical signs of disease 

may go undetected in less severe cases and only become apparent when infection 

worsens. High parasitic loads can lead to obstructed air ducts, lesions in the tracheal 

walls, and depletion of hemolymph. With increasing parasite infestation, the tracheal 

walls become opaque and discolored with blotchy black areas. Tracheal mite 

infections can peak in winter through early spring in the Northern hemisphere. Mortality 

of infected bees ranges from moderate to high.

2. Laboratory Criteria

2.1 Agent Isolation and Identification: Parasites can be visualized by dissection of 

individual bees to isolate the trachea, or by grinding of whole bodies minus wings and 

legs, followed by microscopic inspection. Inspection of bulk samples is quicker but less 

accurate than dissection of individuals. Staining is also available for visualization of 

mites. A direct enzyme-linked immunosorbent assay (ELISA) is available; however, it 

is prone to false-positives. A specific polymerase chain reaction (PCR)-based assay is 

also available for detection in honey bees and hive debris.

2.2 Agent Characterization: Detection of A. woodi in samples using PCR methods is 

faster, more efficient and may be more sensitive than using microscopy. However, 

care must be taken when interpreting results from PCR tests due to genetic similarities 

between A. woodi and closely related species, A. dorsalis and A. externus, to avoid 

false positives. Positive detections with PCR should be confirmed with microscopy.

Case Definition

Acarapisosis of honey bees (Acariosis, Acarine)

(Monitored) December 2023
Animal and Plant Health Inspection Service | Veterinary Services | 2

2.3 Serology: NA.

3. Case Classification

3.1 Suspect Case: Honey bees or other Apis species with compatible clinical signs OR an 

epidemiologic link to a confirmed case.

3.2 Presumptive Positive Case: A suspect case with a positive ELISA or PCR test.

3.3 Confirmed Positive Case: A suspect case with positive visualization of mites via

microscopic techniques.

4. Reporting Criteria: Acarapisosis is a U.S. monitored condition that is reportable monthly 

under the APHIS National List of Reportable Animal Diseases (NLRAD).

4.1 NLRAD reporting in accordance with the NLRAD Standards for monitored diseases; 

and by APHIS to the World Organisation for Animal Health (WOAH).