3. Results and Discussion
Our report represents the first unequivocally autochthonous case ofO. lupi , an agent of zoonotic onchocerciasis, in Texas, near the
United States/Mexico border based on integrated histopathological,
parasitological and molecular data.
Histologically, the most significant finding was the presence of corneal
perforation with severe keratitis and anterior iris synechiae.
Additionally, two long, filarioid nematodes were discovered embedded in
the episcleral tissues. One of these parasites was degenerated and
surrounded by granulomatous inflammation, while the other was intact and
lacked surrounding inflammation. This specimen was a gravid, female
nematode, suggesting a patent infection. The pattern of cuticular ridges
of two inner striae within the space between two outer cuticular ridges
observed on the specimens were morphologically consistent with O.
lupi (Verocai et al., 2016) (Figure 1). Most likely, the dog was
co-infected with heartworm, D. immitis , as a recent study, has
shown that O. lupi infections are unlikely to generate
false-positive results in commercial heartworm antigen tests (Sobotyk
Oliveira, Savadelis, McLean, & Verocai, 2020).
The generated cox1 sequence was accessioned in GenBank
(MW577256), and showed 99.9 – 100% maximum identity with O.
lupi sequences available in GenBank. Phylogenetic analysis clustered
the Texas isolate with all previous isolates from North America, and
some European isolates, belonging to O. lupi “genotype 1” (99%
bootstrap support; Figure 2) (Rojas, Salant, Yasur-Landau, Tsarfati, &
Baneth, 2020).
Zoonotic onchocerciasis has been previously reported from a 10-year-old
boy from Mission, Texas also in the Hidalgo County, who traveled to
South Dakota, and slept in tents and cabins in New Mexico and Colorado,
reported fishing in fresh water lakes near home, and had a pet dog with
history of conjunctivitis and eye lesion of unknown etiology (Cantey et
al., 2016). Altogether, the present canine case may suggest that this
human infection may have been, in fact, acquired in Texas.
It is necessary to better understand the epidemiology of O. lupiin this newly recognized endemic area by screening dogs and cats from
shelters using classical and molecular methods. In addition to companion
animals and humans, coyotes (Canis latrans ) were reported
infected and may serve as wild reservoirs in the western United States
(Roe et al., 2020), and may also contribute to the epidemiology ofO. lupi in southern Texas, and neighboring Mexico. Other wild
carnivores that are known or have postulated as O. lupi hosts
such as wolves (Canis lupus ) and certain foxes (red fox,Vulpes vulpes ; swift fox, Vulpes velox ; kit fox,Vulpes macrotis ) are not present in southern Texas. However, the
widely distributed gray fox (Urocyon cinereoargenteus ), is
reported in this region, and across O. lupi endemic areas in
North America, and therefore, should be assessed as potential reservoir
host. Regarding the dipteran vectors, black flies (Simuliidae) have been
considered the putative intermediate host for O. lupi (Hassan et
al., 2015); however, biological confirmation remains necessary.
Therefore, xenomonitoring in Texas could also involve screening of other
dipterans, such as biting midges (Ceratopogonidae: Culicoides )
and sand flies (Psychodidae: Phlebotominae).
This unequivocal autochthonous O. lupi case in southern Texas
suggests that this parasite is endemic to the region, and transmission
may occur locally. In this case, it is postulated that O. lupicould have caused exophthalmos with secondary traumatic corneal
ulceration and subsequent perforation. There is a need for
epidemiological surveillance of companion animals, wildlife, and
dipteran vectors along the United States/Mexico border. It is important
to raise awareness of public health and medical specialists and
authorities as humans in this region might be at risk of infection.