Ascaris suum
A parasite of swine with a worldwide distribution that can infect humans as well. The pigs get infected when ingesting infective eggs from the environment.  The larval stage 3, hatches in the small intestine and stomach, enters the wall of cecum and colon and migrates to the liver via portal vein. After a few days the larvae arrive to the pulmonary capillaries, proceed to the bronchial tree ant trachea and then swallowed.  Once they arrive to the small intestine, they mature with eggs being detected in feces between 6 and 8 weeks. Pathologic effects are associated with larvae migration, while adults can cause reduce growth and sometimes diarrhea. 

​The economic impact of this parasite is relevant in pig production, where prevention efforts are continuously monitored.

Musca domestica

The common housefly deposits eggs on decaying organic material and rarely can cause secondary myasis. Females live about 6 to 7 weeks and when the egg hatches, the larval stage 1 emerges, molts twice, and pupate during 2 to 3 weeks.

Adults feed on feces, decaying fruits or other soluble materials. They transport bacteria and other organisms; in horses they act as vectors of the nematode parasites Draschia megastoma and Habronema muscae. 

Raccoons are considered the primary host for this ectoparasite, recognized as the only chewing louse reported from raccoons. Trichodectes octomaculatus is an ischnoceran louse that feeds mainly on skin debris and dried blood.

It can be morphologically identified by the broad head with eight dark circular spots, which helps distinguish it from other lice. Additional features include 3-segmented antennae, a single claw on each tarsus, and prominent abdominal setae.

​Like other lice, the entire life cycle of T. octomaculatus occurs on the host, with development proceeding through three molts. Heavy infestations may lead to irritation, pruritus, feeding marks in the coat, and hair loss. This louse is common in wild raccoons.

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.