Trypanosoma theileri (Trypomastigote)

​Trypanosoma theileri is a non-pathogenic or mildly pathogenic trypanosome commonly found in cattle worldwide. It is typically transmitted by hematophagous insects such as tabanid flies. In most cases, infections are subclinical as observed in this calf and commonly detected incidentally during laboratory research.

Taxonomically, Trypanosoma theileri is classified under the subgenus Megatrypanum due to its large size compared with pathogenic trypanosomes, as well as its uniquely prominent distinct kinetoplast. In culture, Trypanosoma theileri is observed predominantly as replicative epimastigotes, with occasional differentiation into less abundant trypomastigote and amastigote‑like forms. The life cycle initiates when an infected tabanid fly deposits infective metacyclic trypomastigotes into a mammalian host during blood-feeding. Once in the bloodstream, the parasites transform into mature, extracellular trypomastigotes and multiply via binary fission. It is during this active phase that they become transiently detectable on peripheral blood smears.

​It’s very important to differentiate T. theileri from T. vivax, T. cruzi, T. congolense, T. brucei, and T. evansi because they are highly pathogenic, heavily regulated, and reportable to state veterinarians, the USDA, and international animal health organizations.

​The results from this case were molecularly confirmed by performing a PCR targeting the small subunit ribosomal RNA (SSU rRNA) gene that amplifies a ~556 bp fragment, and subsequently submitted for sequencing identification.

Cochliomyia hominivorax, (New World Screwworm-NWS)

​Is a parasitic fly attracted to open wounds, mucosal surfaces and the umbilical area in newborns, where female flies deposit eggs. These eggs hatch in approximately 24 hours and molt into larval instars 1 to 3 where they feed on healthy tissues (~ 1 week), causing extensive damage that requires prompt treatment. When the third larval instar is mature, it drops to the ground to pupate in the environment where depending on temperature and humidity, the fly emerges from the pupa after 7 to 54 days. The lifespan of the adult flies last between 2 and 4 weeks, with the males mating only once. This reproductive feature has been utilized to eradicate the NWS by the sterile insect technique.

​As this emerging pest has been recently detected in the USA, it is important to inspect animals, submit larvae for prompt identification, be in close contact with state veterinarians and insure that infested food animals properly treated are safe for consumption.

Image 3: Dorsal lesion with larvae.
Image 4: Larvae removed from dog. (Red arrows pointing  at dorsal pigmented tracheal trunks, blue arrows indicate posterior spiracles used for diagnosis, black circle indicates long mouth hooks)

Canine granulocytic anaplasmosis is caused by the intracellular bacterium Anaplasma phagocytophilum. In the US, it is transmitted by Ixodes scapularis and I. pacificus ticks. The active infection can be detected by PCR; additionally, though rarely, morulae can be seen in a blood smear within the granulocytes. Because A. phagocytophilum often occurs alongside other tick-borne pathogens, it is important to test for co-infections. A. phagocytophilum is zoonotic and can infect multiple domestic animals as well as humans.

​Strigiphilus syrnii are chewing lice found on owls, belonging to the order Psocodea. The genus is characterized by having a prominent dorso-anterior plate and relatively short, rounded abdomens approximately the same width as the temporal head width.  When infesting in high numbers they can cause feather damage.

Sarcoptes scabiei adult (Image 1) and egg (Image 2)

This parasitic mite causes sarcoptic mange or scabies in humans, dogs, horses, pigs and others, including foxes and bears.  Infestations commonly start on relatively hairless areas of skin and may later generalize. Bears can also get infested with the mite Ursicoptes sp. which appears morphologically similar to Sarcoptes scabiei, except for the anterior–ventral elongation (idiosoma elongate-ovoid in both sexes) and is primarily restricted to the hair follicles; while Sarcoptes scabiei have idiosoma ventrally flat and dorsally convex.

​Sarcoptes scabiei legs of both females and males are short and stubby.  Legs III and IV of both sexes do not extend beyond the lateral posterior margin of the idiosoma (Image 1). Legs have suckers or pads on long unsegmented stalks (Image 3; legs I and II in females and legs I, II an IV in males). The anal opening of females is terminal, and the dorsum of females have many pointed scales while the males have only a few.

Image 1: Adult, legs III and IV of both sexes do not extend beyond the lateral posterior margin of the idiosoma.
Image 2: Egg collected on skin scraping.
Image 3: Adult, legs have suckers or pads on long unsegmented stalks (legs I and II in females and legs I, II an IV in males).

Spirometra sp. plerocercoid. 

Spirometra spp. are cestodes that usually develop as adults in the small intestine of cats and dogs and release undeveloped eggs in the feces.  A larval stage (coracidia) grows within the egg for about 1 or 2 weeks and is released into the water. If copepods ingest this larva, an embryo called procercoid develops in the body cavity of the copepod. Typically, these copepods are ingested by various vertebrates (except fish) that act as second intermediate hosts where the final infective stage develops as plerocercoids.  Plerocercoids are in the subcutaneous tissues of these vertebrates and when ingested by a dog or cat they develop into adults. 

On some occasions dog or cats can develop plerocercoids (Sparagna) by 1)drinking water contaminated with infected copepods, 2) ingesting plerocercoid form vertebrate hosts or 3) direct infection of open wounds with plerocercoids.

​Sparganosis can be presented as non-proliferative or proliferative, in this case it was diagnosed as non-proliferative.  It is important to mention that sparganosis is a zoonosis, therefore preventive measures should be adopted to avoid consumption of contaminated water or food.