Pathology of Haemonchus contortus in New World camelids in the southeastern United States

Introduction

Haemonchus contortus is a gastrointestinal nematode that attaches to the abomasum of small ruminants (sheep and goats) and feeds on whole blood.^1,4,11,13 Additional blood is lost into the gastric lumen because of mucosal irritation, resulting in clinical anemia. Adult worms are 2–3 cm long and can easily be observed at autopsy. The female worm is identified by the twisting of the white reproductive tract with the red, blood-filled intestinal tract, giving this parasite the nickname “barber pole worm.”

Clinical signs of infection include weight loss, exercise intolerance, submandibular edema (“bottle jaw”), and mucous membrane pallor. ¹ Severity of antemortem infection is primarily measured in 2 ways: fecal egg count (FEC) and the FAMACHA system (FAffa MAlan CHArts). In the former, the total number of eggs per gram (EPG) is calculated by counting trichostrongylid eggs, which are ellipsoidal with a thin, smooth wall and contain a morula. ¹ The eggs of trichostrongyle nematodes (e.g., genera Haemonchus, Trichostrongylus, Teladorsagia, Ostertagia, Oesophagostomum) are all very similar in size and shape and cannot be accurately differentiated on FEC. A coproculture, polymerase chain reaction (PCR) assay, or lectin staining is required to confirm the presence of Haemonchus spp. antemortem. ³ FECs are typically used in a herd setting to monitor anthelmintic efficacy through the use of FEC reduction tests. They can also be used to diagnose trichostrongylids postmortem, if no worms are noted grossly at autopsy. The FAMACHA system is an inexpensive, rapid method used to categorize the level of antemortem anemia based on conjunctival mucous membrane color.^13,18 The chart contains a color scale of 1–5, with 1 being red and 5 pale white. The chart is held next to the conjunctiva, and a score is assigned based on the closest matching color (Fig. 1).

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Figure 1.

Demonstration of the FAMACHA (FAffa MAlan CHArts) technique in a llama (Llama glama).

The small ruminant industry is a major sector of livestock agriculture with ~2 billion sheep and goats worldwide. ⁵ Developing countries depend heavily on small ruminants for sustenance and income; therefore, H. contortus is considered a major economic problem for small ruminant farms worldwide, particularly those in warm, moist environments where the parasite thrives. Prevalence can reach as high as 80% in the summer, ⁴ and in severe infections, lambs can lose an estimated one-fifth of their circulating red blood cell mass volume in a single day.^7,8

Like goats and sheep, camelid species (henceforth referring to llamas and alpacas only) are susceptible to H. contortus.^9,12,15 Furthermore, North American camelids are commonly co-grazed with small ruminants, increasing the likelihood of infection.^10,12,15,17 In camelids, H. contortus resides in the third gastric compartment (C3) and has become a major health issue for camelid farms in the southeastern United States. ⁹ H. contortus has been well studied in small ruminants, but primary literature on this infection in New World camelids remains sparse. As camelids are becoming more popular in the United States, parasite control should be emphasized. The objective of our review was to characterize the clinical and anatomic pathology of H. contortus infection in llamas and alpacas in the southeastern United States, in order to determine whether disease differed from that observed in small ruminants.

Materials and methods

Results

Antemortem clinicopathology

Average erythron parameters, TP, and FECs are reported in Table 1. Student t-tests revealed that FEC estimates were significantly higher in anemic animals than nonanemic animals ( p = 0.0143). Anemic animals had an average FEC estimate of 441 ± 591.1, whereas nonanemic animals had an average FEC estimate of 85 ± 113.9. Pearson correlation analysis revealed that FEC estimates were negatively correlated with HCT (r = −0.75, p < 0.0001), RBC (r = −0.67, p = 0.0002), and HGB (r = −0.76, p < 0.0001). FEC was not significantly correlated with MCV, MCH, MCHC, or TP ( p = 0.1552, 0.5319, 0.7909, and 0.9418, respectively).

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Table 1.

Clinicopathologic values for camelids at The University of Georgia Veterinary Teaching Hospital (Athens, Georgia) with Haemonchus contortus infections between the years 2002–2013.*

Parameter	n	Mean	Standard deviation	Normal llama reference interval†	Normal alpaca reference interval‡
HCT	30	18.63	6.12	25.0–45.0	22.5–39.0
RBC count (×106 cells/μl)	25	8.32	2.52	10.1–17.3	10.2–18.4
HGB (g/dl)	30	8.03	2.81	11.3–19.0	10.9–18.4
MCV (fl)	25	23.94	2.95	22.0–29.5	15.2–25
MCH (pg)	25	10.56	0.93	9.6–12.0	8.4–11.6
MCHC (g/dl)	25	43.14	7.24	38.9–46.2	39.4–55
TP (mg/dl)	22	5.35	0.87	4.7–7.3	5.2–7.1
FEC (eggs/g)	31	325.00	515.37

*

HCT = hematocrit; RBC = red blood cell; HGB = hemoglobin; MCV = mean corpuscular volume; MCH = mean corpuscular hemoglobin; MCHC = mean corpuscular hemoglobin concentration; TP = total protein; FEC = fecal egg count.

†

Published data (Fowler and Zinkle, 2009).

‡

Established on 2 commercial systems^c,e at The University of Georgia College of Veterinary Medicine (unpublished data).

Postmortem study

Of the 198 camelids that were autopsied (144 alpacas, 54 llamas), 55 showed evidence of H. contortus infections (32 alpacas, 23 llamas), either through the presence of nematodes within C3 (Fig. 2) or trichostrongylid eggs in the feces. The rate of infection was significantly higher in llamas (42.6%) than alpacas (22.2%; p = 0.004). Of all camelids, 28.4% of females and 26.7% of males were infected. There was no association between sex and infection among camelids as a group ( p = 0.913), nor among individual alpaca ( p = 0.391) and llama groups ( p = 0.695). Infected animals ranged from 2.5 months to 17 years old. H. contortus was considered the major cause of death in 31 cases (17 alpacas, 14 llamas) as a result of a significant worm burden, FEC, and the lack of other diseases. These animals were categorized as “severely infected” (Table 2). In 8 of the H. contortus–infected cases (14.5%), H. contortus nematodes were identified; however, another major cause of death was designated at autopsy. In these cases, H. contortus was often considered a key secondary player, and these cases were categorized as “moderate.” The final 16 cases of H. contortus infections (29.1%) were incidental findings characterized by the presence of low numbers of eggs on fecal flotation. These cases were categorized as “mildly infected.” Other frequent causes of death in adult camelids included infection with Parelaphostrongylus tenuis, hepatic lipidosis, trauma, and gastrointestinal perforation secondary to ulceration.

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Figure 2.

Haemonchus spp. nematodes in the third gastric compartment of a llama (Llama glama). Females are identified by the twisted “barber pole” appearance. Photo by Dr. Corrie Brown.

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Table 2.

Prevalence of Haemonchus contortus infections on postmortem examination of camelid species.*

Level of infection	Alpacas (n = 144)		Llamas (n = 54)		All camelids (n = 198)
	Number	%	Number	%	Number	%
Severe	17	11.8	14	25.9	31	15.7
Moderate	4	2.8	4	7.4	8	4.0
Mild	11	7.6	5	9.3	16	8.1
Total	32	22.2	23	42.6	55	27.8

*

Severe indicates that H. contortus was the major cause of death. Moderate indicates that H. contortus was a secondary cause of death. Mild indicates that H. contortus eggs were incidentally present in the feces.

On external examination, H. contortus–infected animals were frequently in poor body condition and had pale mucous membranes. Gross anatomic lesions were generally more striking in the severely infected group. At autopsy, on opening the carcasses, prominent findings included subcutaneous edema and decreased viscosity of blood. The edema was most commonly located in the intermandibular area, with fewer cases having ventral edema. Abdominal, thoracic, and/or pericardial effusions were common. Overall, individuals had serous atrophy of fat and muscular and visceral pallor, particularly in the liver. If present, H. contortus nematodes were identified on the C3 mucosa and also within the C3 ingesta. The C3 mucosa was sometimes reddened, but generally there were no other gross mucosal lesions.

Samples were evaluated histologically for severely and moderately infected cases, excluding those tissues that were too autolyzed for histologic evaluation. Common histologic findings in the liver included hepatocellular atrophy, centrilobular necrosis, and extramedullary hematopoiesis (commonly present in the spleen). There was often lymphoplasmacytic inflammation of the lamina propria in C3. H. contortus larvae were deep within the C3 mucosa of 6 severely infected cases and were characterized by a thin-walled digestive tract and longitudinal cuticular ridges (Fig. 3).

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Figure 3.

Cross-sectional (A) and longitudinal (B) photomicrographs of Haemonchus spp. in the third gastric compartment of a llama (Llama glama). Hematoxylin and eosin.

Discussion

Our review confirms the high prevalence of H. contortus infections in New World camelids. The occurrence of infection, however, is likely higher than this review represents because of the rapid decomposition of nematodes postmortem. Autopsies should ideally be performed as quickly as possible after death, yet many camelids are not brought to the diagnostic laboratory in a timely manner, either because of delays in discovery of the carcass or in transport. Additionally, as a result of the retrospective nature of this review, a FEC was not collected on every autopsied animal, again lowering the level of H. contortus detection.

The finding that llamas have higher infection rates than alpacas is interesting. One possible reason for this difference could be differences in immunity and stress levels between the 2 species. It is possible that the llamas in our study were either exposed to more stressful scenarios, such as show events or other travel, or that they had a lower capacity to handle these stressful scenarios; either scenarios could lead to immunosuppression and exacerbation of infection. Additionally, alpacas are generally more highly regarded as pets and better cared for than llamas. As a result, owner care and dewormer administration could be a reason for variations in the degree of parasitic infection. A clinical comparison study is indicated to determine if there are differing rates of infection in living camelids under the same living and treatment conditions.

As expected, anemic animals were more likely to have a higher FEC, and FEC was negatively correlated with anemia parameters including HCT, RBC, and HGB. Interestingly, however, TP was not negatively correlated with FEC. H. contortus adults feed on whole blood, so TP and HCT would both be expected to decrease. Although clinical dehydration may elevate both HCT and TP, additional factors may have affected TP and prevented a clear correlation with FEC. Inflammation, protein-losing enteropathies and nephropathies, as well as liver disease, could all have altered the TP concentration. Comparison studies of TP in H. contortus–infected small ruminants would be useful. Although studies have shown a decreasing TP associated with H. contortus infection in sheep and goats, values have not been compared to corresponding FECs.^2,14,16 Even though TP was not significantly correlated with FEC, infected individuals were debilitated by both anemia and hypoproteinemia, to which the majority of the gross and histological findings could be attributed.

Because of its retrospective design, our study presented many challenges. Sample size was limited due to the requirement of having a CBC count, chemistry, and FEC performed during the same hospital visit. Future prospective studies would allow for greater consistency and sample size. Regardless, the highlights of this review include how important hematologic and pathologic effects of H. contortus in camelid species can be. H. contortus should be a top differential for recumbent camelids. Finally, clinicians and producers should monitor camelids showing poor body condition or exhibiting signs of weakness, pale mucous membranes, or dependent edema. Routinely monitoring camelids with FAMACHA checks and FEC should aid in diagnosing and preventing loss caused by parasitism.