Pathology Case of the Month - Raccoon

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Case History: An adult male 4.04-kg raccoon (Procyon lotor) was found dead near a campground in Arizona, US.  Three raccoons and a gray fox (Urocyon cinereoargenteus) were observed panting, staggering with glazed eyes, seizing and exhibiting no fear of humans. 

Gross Findings: On external examination, conjunctivae and oral mucosa were pale pink.  On internal examination, there was minimal subcutaneous, visceral, peri-renal and epicardial fat.  Pectoral muscle was atrophied.  Large tan nematodes were present within the subcutaneous tissue and muscle fascia in all distal limbs.  On the epicardium, a 3.5 x 2 cm tan focus extended from the mid-left ventricle to the apex of the heart.  Tracheobronchial lymph nodes were enlarged.  Bronchi contained red mucousy fluid.  The esophagus was empty.  The stomach contained thick tan pasty material.  The wall of the stomach was expanded by edema.  The mesenteric lymph node was black and measured 5 x 2 x 0.6 cm.  Intestines contained scant tan to yellow digesta. 

Photographs from raccoon tissue showing long tan nematodes.

Figure 1. Photographs from a raccoon (Procyon lotor) from Arizona, US.  (A) Large tan nematodes (arrowheads) are present within the subcutaneous tissue and muscle fascia in the distal right forelimb. (B) Closer view of the distal right forelimb showing the large tan nematodes (arrowheads). (Credit: Susan Knowles, National Wildlife Health Center. Public domain.)

Diagnostic Test Results:

  • Feline panleukopenia positive (PCR)
  • Canine distemper virus negative (PCR)
  • Rabies negative (direct fluorescent antibody test)

Conditions:

  1. Feline distemper (cause of death)
  2. Dracunculiasis

Etiology: Dracunculus insignis, a subcutaneous nematode of the Family Dracunculidae.  There are 14 valid species of Dracunculus which occur in mammals, including humans, and reptiles.

Geographic distribution: North America (United States and Canada).

Host range: Dracunculus insignis primarily infects raccoons (Procyon lotor), but also mink (Mustela vison), fisher, (Martes pennanti), Virginia opossum (Didelphis virginiana), North American river otter (Lontra canadensis), and domestic dogs, cats, and ferrets.

Life cycle: Adult female nematodes develop in the subcutaneous tissue of the hosts, penetrate through the host skin, and when in contact with water release first-stage larvae into the water.  Larvae infect copepods (Acanthocyclops vernali and Cyclops bicuspidatus) where they develop into third-stage larvae.  Transmission occurs when the host ingests infected copepods or consumes frog or paratenic hosts.  Larvae migrate to the subcutaneous and intramuscular tissues of the thorax and abdomen and undergo two molts.  After maturation, male and female worms mate, and females migrate primarily to the subcutaneous tissues of the distal extremities.  There, the nematode penetrates the dermis and epidermis, exposing the most anterior portion of its body which contains the uterus full of first-stage larvae.  When the host comes into contact with water, the worm ruptures and releases first-stage larvae.  After female worms senesce, they may be removed by the host or calcify in the host’s subcutaneous tissues. 

Clinical signs: Lethargy or scratching of skin overlying the nematodes.

Pathology: Gross lesions may include swelling of the lower portion of the limbs and ulceration or scarring if the female has emerged through the skin.  Females of Dracunculus spp. can measure up to 100 cm; males are rarely observed.  Microscopic lesions include edema and inflammation in the subcutaneous tissues and muscle fascia with intralesional nematodes.  Dracunculus insignis, like other species of Dracunculus, is characterized by flat lateral chords, coelomyarian polymyarian muscles, a reduced intestine and a large larvae-filled uterus.

Diagnosis: Histopathology; dissection scope examination; PCR.

Public health concerns: None.

Wildlife population impacts: Wildlife population impacts are not significant as infection does not usually result in morbidity.

References:

  • Bowman DD. 1999. Diagnostic Parasitology. In: Georgis’ Parasitology for Veterinarians, 7th Ed., W.B. Saunders Company, Philadelphia, Pennsylvania pp. 285–396.
  • Cleveland CA, Garrett KB, Cozad RA, Williams BM, Murray MH, Yabsley MJ. 2018. The wild world of Guinea Worms: A review of the genus Dracunculus in wildlife. Int J Parasitol Parasites Wildl: 7:289–300. doi:10.1016/j.ijppaw.2018.07.002.
  • Davidson WR, Nettles VF. Racoon (Procyon lotor). 1997. In: Field Manual of Wildlife Diseases in the Southeastern United States, 2nd Ed., University of Georgia, Athens, Georgia pp. 139–164.

 

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