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Archivos de medicina veterinaria

versión impresa ISSN 0301-732X

Arch. med. vet. vol.46 no.3 Valdivia  2014 



Maxillary osteomyelitis due to Halicephalobus gingivalis and fatal dissemination in a horse

Osteomielitis maxilar debido a Halicephalobus gingivalis y diseminación fatal en un caballo


LA Gracia-Calvo, M Martín-Cuervo, ME Durán, V Vieítez, F Serrano, J Jiménez, LJ Ezquerra*

Veterinary Teaching Hospital, Faculty of Veterinary, University of Extremadura, Caceres, Spain.
* Avenida Universidad s/n, 10003 Cáceres, España;


En la presente comunicación se expone un caso de infestación parasitaria poco habitual causada por Halicephalobus gingivalis, cuya manifestación principal fue osteomielitis del hueso maxilar. El caballo mostraba inicialmente inflamación y dolor en la región de la cresta facial derecha. Las radiografías demostraron la presencia de osteolisis y ensanchamiento de la cresta facial. La biopsia del hueso mostraba inflamación granulomatosa y un gran número de larvas del nematodo. El caballo fue tratado con ivermectina. Inicialmente mejoraron los signos clínicos, pero dos meses y medio después el caballo desarrolló uveítis y fallo renal, por lo que fue eutanasiado. El estudio anatomopatológico mostró múltiples granulomas parasitarios en los riñones y en la úvea. La infección por Halicephalobus gingivalis es poco frecuente en caballos y personas aunque presenta una distribución mundial. De acuerdo con los autores esta es la primera vez que se describe dicha infestación en un équido en España.

Palabras clave: Halicephalobus gingivalis, caballo.


This study reports a rare case of maxillary osteomyelitis in a horse caused by Halicephalobus gingivalis. The horse presented inflammation and pain in the region of the right facial crest and the radiographs detected osteolysis and widening of the facial crest. The biopsy revealed a granulomatous inflammation and a large amount of parasite larvae. The horse was treated with ivermectin but it developed uveitis and renal insufficiency 2.5 months later and was euthanised. The anatomopathological study found multiple parasitic granulomas in the kidneys and uveal tract. H. gingivalis is an infrequent infection in horses and people, and it has a worldwide distribution. To the best of our knowledge this is the first report of H. gingivalis infection in an equid to be diagnosed in Spain.

Key words: Halicephalobus gingivalis, horse.



Halicephalobus gingivalis is a panagrolaimid nematode from the order Tylenchida (formerly Rhabditida). They are free-living organisms with a wide geographic distribution (Anderson et al 1998) which are capable of facultative parasitism and can cause opportunistic infections in horses (Blunden et al 1987). The infection and life cycle are scarcely understood. Previous reports describe infection through wounds (Gardiner et al 1981, Eydal et al 2012), inhalation or ingestion (Blunden et al 1987), trans-mammary from dam to foal (Wilkins et al 2001) and posterior dissemination through the blood stream (Yoshihara et al 1985, Kinde et al 2000). After the nematodes enter a horse, they reproduce via parthenogenesis which causes granulomatous inflammation and destruction of host tissues (Ruggles et al 1983). They can cause meningoencephalitis (Bryant et al 2006), nephritis, gingivitis, osteomyelitis, posthitis, orchitis, papillitis, retinitis (Hermosilla et al 2011), uveitis, (Kinde et al 2000), ocular parasitism (Rames et al 1995), radiculomeningomyelitis (Johnson et al 2005) and arthritis (Simpson et al 1988). The condition is usually fatal and there are only three reports of successful treatment following the administration of ivermectin an antiparasitic drug, although the lesions did not affect the central nervous system (CNS) (Dunn et al 1993, Simon et al 2001, Schmitz and Chaffin 2004, Ferguson et al 2008).


An 11-year-old, crossbred gelding was referred to our institution with signs of enlargement of the retropharyngeal lymph nodes for 3 months, deformation of the facial crest, and sero-sanguinolent discharge from the right nostril during the previous 5 days. The suspected diagnosis was sinusitis.

On arrival, the physical examination detected inflammation, pain, and a small scar in the region of the right facial crest, enlargement of the right retropharyngeal lymph nodes and sero-sanguinolent discharge from the right nostril.

Radiographs were taken and the dorso-ventral view included an enlarged and osteolytic facial crest with a honeycomb-like appearance (figure 1). Fluid lines were not observed in the latero-lateral view of the maxillary or frontal sinuses.


Figure 1. Dorso-ventral view of the skull showing the
osteolytic facial crest with a honey-comb-like appearance.
X-ray parameters:
80 mAs, 90 kV.
Proyección dorsoventral de la cabeza donde se aprecia
la cresta facial con osteolisis y apariencia de panal de miel.
Exposición radiológica: 80 mAs, 90 kV.


Ultrasonographic examination of the facial crest detected discontinuation of the bone in an area of at least 10 cm, which was compatible with microfractures and osteolysis.

Endoscopic examination of the nasal passages did not detect discharge from the naso-maxillary opening.

The hematological and biochemical parameters were within the normal range (table 1).


Table 1. Hematological and biochemical parameters.
Valores hematológicos y bioquímicos.


A bone biopsy was conducted under local anesthesia. One sample was cultured for microbiologic identification. Candida spp. was isolated but it did not correlate with the histopathological findings. Histopathological analysis was performed using paraffin sections, which were stained routinely with hematoxylin and eosin. The light microscopic examination detected high-cellularity tissue and a granulomatous inflammation with giant multinucleated cells, lymphocytes, plasmatic cells, eosinophils and large amounts of parasite larvae (figure 2). In other sections, the bone tissue had normal characteristics. The cytological study of the right retropharyngeal lymph-node after fine needle aspiration found necrosis, cell degeneration, and a few lymphocytes.


Figure 2. Granulomatous inflammation with lymphocytes,
plasma cells, macrophages, fibroblasts and a large
amount of Halicephalobus gingivalis larvae. Biopsy
of the facial crest. H-E (x20).
Inflamación granulomatosa con linfocitos, células plasmáticas,
macrófagaos, fibroblastos y una gran cantidad de larvas de
Halicephalobus gingivalis.
Biopsia de la cresta facial. H-E (x20).


The distinctive morphology of these larvae allowed the identification of H. gingivalis nematodes. The treatment comprised ivermectin, ketoconazol (for 2 months) and phenylbutazone. The clinical signs of pain and inflammation improved almost completely.


The horse returned to our facilities 2.5 months later for follow-up control and the radiological and ultrasonography findings were similar to those during the first visit.

During the control visit, the horse had right unilateral uveitis. The surface of the left kidney was irregular on rectal palpation. The horse also presented pigmenturia and the urine analysis detected hematuria (200 cells/µL), proteinuria (0.3 g/L), 70 leukocytes per μL, and a urinary density of 1008 mg/mL. The hematology results indicated an elevated total protein level (9.8 g/dl), eosinophilia (11%) and an elevated platelet count (1,161x103 /μl) (table 1). The biochemistry findings indicated chronic renal failure; thus the horse was euthanized because of the poor prognosis. A subsequent anatomopathological study found multiple nodules measuring 1-6 cm in diameter in both kidneys, which were pale, rounded and solid in appearance (figure 3), and distributed in the cortical and medular areas. The histopathological analysis of the kidney demonstrated a loss of the renal parenchyma architecture and a granulomatous inflammation with lymphocytes, plasma cells, macrophages, eosinophils, and H. gingivalis larvae (figure 4). Several larvae and a lower level inflammatory reaction were found in the uveal tract (figure 5). Some nematodes were also observed within the vascular lumens.


Figure 3. Granulomatous inflammation with lymphocytes,
plasma cells, macrophages, eosinophils, and Halicephalobus
larvae in the kidney. H-E (x20).
Inflamación granulomatosa con linfocitos, células plasmáticas,
macrófagos, eosinófilos y larvas de Halicephalobus gingivalis
en el riñón. H-E (x20).


Figure 4. Parasitic Halicephalobus gingivalis larvae in
the uveal
tract. H-E (x40).
Larvas parasitarias de Halicephalobus gingivalis en la
H-E (x40).


Figure 5. Pale, rounded and solid parasitic granulomas
in the kidney.
Granulomas parasitarios pálidos, redondeados y sólidos
el riñón.


All of the parasites found in the different anatomical locations shared the same morphological characteristics but were at different stages of the life cycle. They were mainly larvae and only female nematodes were seen among the adult forms. The size of the larvae varied between 75 and 250 μm in length and 7.5 μm in width. The adult female width reached 15-19 μm. The length/width ratio ranged from 11/1 in the larvae to 15/1 in the adult nematodes.

The adult forms had a smooth cuticle, a cylindrical body, and a slightly conical anterior end, which had an extended cylindrical mouth with dimensions of 6-2 μm. The characteristic rhabditiform esophagus occupied the first third of the body. The esophagus had a corpus, an isthmus, and a valve bulb with a relative length ratio of 16/12/6. These morphological features confirmed the diagnosis of H. gingivalis infection (figure 6).


Figure 6. Image of Halicephalobus gingivalis showing
the characteristic anterior end.
H-E (x100). Halicephalobus gingivalis mostrando su
característica terminación anterior. H-E (x100).


H. gingivalis is a rare infection in horses and people. This facultative parasite has a worldwide distribution but this case is the first to be diagnosed in Spain. The mode of infection, pathogenesis, distribution, and prevalence of this parasite are all enigmatic and they require further study. In this case, we suspect that the infection may have entered via a wound over the facial crest. The wound had already healed but the clinical signs appeared much later, which was similar to the report by Eydal et al (2012).

As mentioned earlier, the organs that are affected most frequently in the horse include the brain, kidneys, oral and nasal cavities (Blunden et al 1987), lymph nodes, spinal cord and adrenal glands. Other tissues affected may include the heart, stomach, liver, ganglia and bone (mandible, maxilla, femur, and nasal bones) (Spalding et al 1990). In the current case, we confirmed lesions in the maxilla, kidneys, uveal tract, and lymph nodes, which were sampled for microscopic evaluation. The only exception was the central nervous system. Despite the lethargic behaviour of the horse we did not observe any macroscopic lesions so further examinations were not performed. It would have been beneficial to make a more detailed examination of the brain but due to the lack of other neurological signs, we assumed that the general condition of the horse and renal failure were responsible for the lethargy. Lethargy has been described as one of the symptoms in the four previously reported medical cases, altough other remarkable CNS-related symptoms were also present, such as neck pain, headache, confusion, and convulsions (Ondrejka et al 2010).It should also be noted that in people and horses, the clinical signs progress very rapidly when the brain is affected by the parasite. These symptoms/signs are related to the tropism for the CNS. After reaching the brain, damage is produced by the inflammatory reaction of the host which usually involves the infiltration of mononuclear cells (including macrophages, plasma cells and neutrophils) and multinucleated inflammatory cells. These inflammatory cells can also form micro-abscesses and granulomas (Pearce et al 2001, Johnson et al 2001, Ondrejka et al 2010, Eydal et al 2012). Other organs lacked macroscopic lesions or clinical findings that suggested lesions on them.

The dissemination route within the host is unknown in the present case. However, we consider that the parasite spread via the blood-stream because some nematodes were observed within the blood vessels of the kidney (Yoshihara et al 1985, Kinde et al 2000).

There is agreement regarding the poor prognosis for this condition. It has been hypothesized that the inability of antihelmintics to cross the blood-brain barrier (Plumb 2002), the lack of sensitivity to ivermectin therapy in H. gingivalis, the difficulty of obtaining an appropriate antemortem diagnosis in the absence of visible granulomatous lesions and the rapid evolution of the condition - especially when the nervous system is involved - may contribute to the poor prognosis (Ferguson et al 2008, Hermosilla et al 2011). In this particular case, we speculate that the prognosis for recovery was poor due because the nematode was protected from high concentrations of the drug by bone sequestration (Bröjer et al 2000), as well as the severe and rapid progression of the insult to the kidneys.

We conclude that H. gingivalis infection should be included in the differential diagnosis of osteolytic lesions of the head. Cutaneous lesions may be the site of entry and a guarded to bad prognosis is anticipated.



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Accepted: 19.12.2013


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