Pelodera Dermatitis Flashcards
Pelodera dermatitis (rhabditic dermatitis) basics
Local erythematous, nonseasonal pruritic dermatitis caused by a cutaneous infestation with the larvae of Pelodera strongyloides
Larvae of free-living nematode P. Strongyloides invade skin of dogs under filthy conditions
Adult parasites have a direct life cycle and live in damp soil or decaying organic material (rice hulls, straw, marsh hay stored in contact with the ground for months).
Found in skin scrapings or associated bedding, in histologic sections larvae and some parthenogenetic female nematodes may be found in hair follicles and with typical folliculitis
Causes of human skin infections with larval nematodes contracted from dogs
A. Braziliense, A. Caninum, U. Stenocephala, Gnathostoma spinigerum, and Strongyloides stercoralis, Pelodera Strongyloides
Pelodera dermatitis Clinical signs and Diagnosis
Clinical signs: distribution of skin lesions at contact surfaces (feet, legs, perineum, lower abdomen and chest, and tail), skin erythematous and partially to completely alopecic, multiple papules later develop to crusts, scales, and secondary infection from pruritus which varies from mild to intense
Dx: skin scrapings (small, motile nematode larvae 625-650 um), larvae and adults in litter using Baermann, history
DDx: hookworm dermatitis, dirofilariasis, strongyloidiasis (based on larval findings), grossly skin lesions resemble contact dermatitis, bacterial folliculitis, demodicosis, or scabies
Pelodera dermatitis Histopath and Treatment
Histo: varying degrees of perifolliculitis, folliculitis, and furunculosis, nematode segments within hair follicles and dermal pyogranulomas, numerous eosinophils
Treatment: complete removal and destruction of bedding, insecticide application to environment, bedding replaced with cedar/wood shavings, cloth, or shredded paper; bathe patient with warm water shampoo to soften and remove crusts then with parasiticidal dip as for scabies, typically results in prompt relief of pruritus and rapid healing, unlikely repeated dips are necessary, steroids short term (few days) for pruritus, systemic antibiotics for secondary pyoderma; infestation is self-limited and resolves spontaneously after removal from contaminated environment
Strongyloides stercoralis-like infection
Boston Terriers in a kennel: 3 weeks after new pup 6 mo old puppies had mucous, blood-flecked feces, anemia, general lymphadenopathy, and focal dermatitis; rough, dull, and dry hair with crusted lesions of 1cm diameter on tail, distal hind legs, ventral trunk, and other areas of ground contact; some with severe, hemorrhagic pododermatitis. Environment was outdoor pens with concrete and shaded grass. Fecal samples had large embryo aged and unembryonated ova (80x35um) and L1 larvae (200um), ova larger than S. Stercoralis (normally 55x32um) and S. Stercoralis usually sheds only L1 larvae in feces, in this case when feces were cultured for 18 hours, free-living adults and L3 larvae were produced
Thiabendazole 11.4mg/kg PO q24 x 5d or Ivermectin 200-500ug/kg PO, retreatments may be necessary
Anatrichosomiasis - larval migrans by nematode Anatrichosoma cutaneum
Monkeys and humans in Africa with blisters on the hands and feet
Case of 13 yo South African cat with lameness with necrosis, sloughing, and ulceration of the footpads of all 4 feet
Histopath: superficial perivascular dermatitis with numerous worms and bioperculate eggs in necrotic migratory tracts within the epidermis, female worms avg 42mm in length
Case of female 5mo old Boxer with double-operculate eggs in feces, similar eggs from skin scrapings from raised, flaking, erythematous nodule on dorsal midline lumbar, on surgical removal eggs and nematode segments ID as Anatrichosoma on Histopath
Schistosoma dermatitis
Schistosoma cercariae of ducks, shore birds, voles, mice, or muskrat (natural hosts) penetrate the skin of warm-blooded animals that are abnormal hosts causing pruritic dermatitis
Schistosoma life cycle
Trematodes: Trichobilharzia ocellata, T. Stagnicolae, and T physellae infest waterfowl of Great Lakes; Austrobilharzia variglandis infests ducks and terns in FL and HI
Eggs shed in feces of natural host, miracidia hatch within 20 minutes and must either find a mollusk (snail) host within 12 hours or die, they form sporocysts in the mollusk and hatch in 4 weeks as cercaria, which are shed in water but die in 24 hours unless they reach a warm-blooded natural host. In the natural host they go to the liver and intestinal wall where eggs are laid and passed in feces.
Human infection called swimmers’ itch, clam diggers’ itch, and rice paddy itch - cercariae penetrate the skin of abnormal host and cause clinical disease, spring to fall infection possible but more likely on bright warm days of midsummer due to increase of both animals swimming and and cercariae
Schistosomiasis clinical signs, diagnosis, and treatment
At penetration the cercariae produce macules and wheals that last 15 to 20 hours, later develop into papules and after 2-4 days into vesicles, these stages all intensely pruritic
DDX: mosquito, chigger, or flea bites
Healing in 5-7 days, cercariae walled off by acute inflammatory reaction with infiltration of neutrophils, lymphocytes, and eosinophils (some people have one strong reaction and subsequently seem immune, but most have increasingly severe reactions on each re-exposure
Local treatment of skin not effective except palliative anti pruritic lotions, controlled by staying out of water.
Limited value: removing water vegetation that encourages snail populations, killing mollusks by adding dilute copper sulfate to small ponds
Pelodera dermatitis, numerous nematodes within the hair follicles
Dracunculiasis species and geographic distribution
Dracunculus insignis: parasite of dogs and wild carnivores of North America (reported in dog, raccoon, mink, fox, otter, and skunk)
Dracunculus medinensis (guinea worm):P affects humans, cats, and other animals in Asia and Africa
Dracunculus life cycle and infection
Intermediate host is a Cyclops (crustacean) ingested from contaminated water by host, larvae develop in the host during a period of 8-12 months, adults develop in SQ tissues of abdomen and limbs
Typically a nodule forms and eventually a fistula develops, just before the fistula opens the host may show urticaria, itching, and a slight fever. The host enters cool water and the female worm is stimulated to release larvae which escape through the cutaneous fistula. Some larvae may enter the blood but are distinguished from Dirofilaria and Dipetalonema by their long tapered tails.
Application of cold water to the fistula stimulates the female worm to make a smear of the exudate and ID larvae.
Dracunculiasis clinical signs, diagnosis, and treatment
Chronic, single to multiple nodules on the limbs, head, or abdomen that eventually ulcerate and do not heal, lesions often painful and pruritic.
Adult parasites occasionally seen in fistulae.
Exfoliative cytology: neutrophils, eosinophils, and macrophages as well as larvae (500um length).
Histology: nodular to diffuse dermatitis containing adult and larval nematodes surrounded by fibrosis and eosinophilic pyogranulomatous inflammation.
Lesions may be removed surgically, or worm removed gently by carefully winding it up on a stick during a period of several days. Multiple lesions make treatment more difficult and may not be effective. Diethylcarabmazine, thiabendazole, metronidazole, niridazole, and ivermectin are not uniformly successful.
Control by decontaminating water supplies or drinking only finely filtered water.
Dirofilariasis
Dirofilaria immitis adults found in heart, larvae in blood and occasionally SQ tissues, but adults rarely found in abscess-like lesions in the skin especially on the legs. Microfilaria rarely cause skin disease.
Larvae can cause hypersensitivity resulting in pruritic papulonodular dermatitis.
Dogs with cutaneous dirofilariasis (heartworm dermatitis): chronic, pruritic dermatitis with ulcerated papules, nodules, and plaques. Most commonly on head or limbs but may be anywhere.
Poor response to antibiotics, topical agents, sedatives, and glucocorticoids is poor.
Dirofilariasis Diagnosis and Treatment
Other findings: peripheral eosinophilia, + Knott’s test for microfilaria, or lesions with occult filariasis
Histopath: varying degrees of angiocentric pyogranulomatous dermatitis, microfilarial segments present intravascularly and extra vascular lay within the granulomatous dermal nodules, few to numerous eosinophils, many of the blood vessels in the central areas of the lesions contained microfilariae but none of the deep dermal or SQ vessels outside the lesions had cellular infiltrates or microfilariae.
IHC: + immune reaction of microfilaria with anti-immunoglobulin G (IgG) serum
With standard heartworm treatments lesions become non-pruritic within 2 weeks and completely heal within 8 weeks
