Case of mortality in lambs from a Colombian flock

Signalment

500 flock, cross-bred sheep, farm established 5 years ago with animals purchased from different locations.  No vaccines ever used (not available in the country).  Deworming has been done as a “blanket treatment to all animals” on a monthly basis with inyectable levamisole, ivermectin and albendazole.   Same farm has 40 beef creole cattle in different pastures never shared with sheep.

History

A total of 13 lambs between ages of 3 to 6 months died in August 2014, and according to the herdsman, with similar histories of eyelid paleness, bottle jaw, anorexia and severe weakness preceding death, or the animals were just found dead.  He states that many newborns tend to be very small, weak, have high mortality and require bottle feeding because the dam is not producing milk.  All the flock grazed together and spent 3-4 days in paddocks primarily comprised of Guinea grass (Panicum maximum), and were housed at night in sheds with dirt floor pens and where some supplemental concentrate was provided in communal open troughs.  Resting periods for grazed paddocks ranged between 30-40 days.

Physical Examination

About ¾ of the ewes have body condition scores of 1 or 2. Famacha scores are between 3-4 in most animals and a few with scores of 5.  Three lambs have submandibular subcutaneous swelling (on palpation it feels like edema).  No evidence of fecal soiling or nasal discharges. Occasional lameness.

Questions?

1. What does a body condition score of 1 indicate?

· It is an indication that the animal is emaciated (score 1) or very thin (score 2).  On a herd level, it is the best surrogate marker for assessing malnutrition.  A score of 2 is only considered optimum for ewes at weaning time, but for breeding and gestation an optimum score is 3-4.  Condition scores of ewes are directly correlated with lamb survival.  On average, a difference of one unit of condition score is equivalent to about 13% of the live weight of the ewe (Thompson and Meyer, 1994).

2. What is the Famacha score used for?

·  FAMACHA© – an acronym formed from FAffa MAlan CHArt – a system named in honor of one of its South African developers, Dr Francois “Faffa” Malan. This system uses a patented color chart against which the color of the inner surface of the lower eyelid is compared. The colors are 5 shades of red varying from red to very pale pink or flesh color, and they correspond to levels of circulating red blood cells. Bright red is correlated with normal red cell levels and the paler colors correlate with anemia or shortages of red blood cells. The GIN, Haemonchus contortus, is found in the abomasum of sheep and goats and feeds on blood. Large numbers of this worm cause anemia, poor performance, and even death. The FAMACHA© system is one method of targeted selective treatment and is applicable to Haemonchus contortus only. This is the most serious worm for sheep and goat producers across much of the United States.

Laboratory and necropsy findings:

Four month old lamb (photos a-d): Famacha score of 5 (a), bottle jaw (b), blood taken from lamb two hours prior to death was watery and produced a very small clot (c) with a PVC = 4.5% and total plasma protein = 2.5 g/dL.  On necropsy, thousands of thread-like white worms (identified as Haemonchus contortus) were retrieved from the abomasal fluid (d).  Fecal pellets were well formed in the distal rectum and had a FEC of 45,000 epg.  Apart from severe paleness of muscles and internal organs, no other gross abnormalities were observed.  Postpartum ewe with a body condition score of 1 (e), Famacha score of 5 (f), PCV =8%, TP = 4 g/dL, and a fecal egg count of 13,050 epg.  Fecal larval cultures confirmed Haemonchus to account for 97% of the total egg count. The animal had received fenbendazol and levamisol 2 weeks earlier and was found dead the day after the examination.      

1. List problems in order of importance:

• · Rapid death in lambs
• · Small newborns with high mortality
• · Anemia
• · Poor body condition
• · Edema
• · Heavy strongyle infection (FEC ≥8,000 epg)
• · Parasite resistance to anthelmintics highly suspected

2. What type of anemia would you suspect and what test would you do to further classify it?

• · Anemia due to blood loss. They are usually regenerative but given the malnutrition status it could be non-regenerative.  Test would be a Complete Blood Count.

3. How do you interpret FEC for strongyles, are there threshold levels that relate to clinical disease or specific production loses?

• · Just like counts for coccidial occysts, FEC for strongyles in general do not correlate well with clinical disease and/or production loses and you will not find specific cutoff points to establish the degree of infection or when to treat based on count numbers (Zajac, 2006).  They have to be interpreted in light of other findings (ie., Famacha score).   Typically, lambs and periparturient ewes are more susceptible and harbor greater number of strongyles; they would be the population at higher risk and the ones shedding the most eggs. 

4. What is your tentative diagnosis in order of decreased importance:

• · Clinical parasitism by the barber pole worm (confirmed by laboratory findings) associated with inadequate nutrition.
• · Other causes of anemia in sheep include: liver flukes (in adults), anaplasmosis, leptospirosis, copper toxicosis, Brassica ingestion.  

5. Therapeutic plan:

5.1. Immediate objective:

• Blood transfusions to the 3 clinically affected lambs.  This was performed to the 3 lambs with severe anemia and they responded favorably.  

• 5.2. Long-term objectives:  “control parasites” and “correct nutrition”

· What dewormer would you use?

• Asking the owner which one has not been used would not really tell you whether resistance has occurred to that drug.   He might have well imported the resistant worms when purchasing animals.  Ideally do a Fecal Egg Count Reduction Test (FECRT).  This was indeed performed and the results are below (See table 1).

Table 1. Results of the fecal egg count (mean epg, minimum-maximum) for Trichostrongylids at day 0 and 10 after treatment with several anthelmintics, and reduction (mean difference) and 95% confidence interval within each group.

Group (n=animals)	Mean epg (range)		Mean difference (95% CI)
	Day 0	Day 10
Control (n=13)	7027 (100-29000)	7473 (0-23050)	-446 [(-3660) – 2768]
Albendazol (n=14)	8768 (100-36600)	8071 (0-29100)	696 [(-953) – 2346]
Levamisol/triclabendazol (n=13)	5792 (100-22900)	6126 (0-29550)	-335 [(-3970) – 3301]
Ivermectin (n=13)	7381 (50-35700)	7153 (50-40150)	227 [(-4302) – 4756]
Moxidectin (n=12)	8320 (50-42250)	2062 (0-7300)	6258 [(-777) – 13293]
Trichlorfon(n=24)*	8437 (50-40150)	5181 (0-19750)	3256 [(-617) – 7130]

*The trichlorfon treatment was comprised of 24 animals from the ivermectin and albendazol groups, and was administered at time of fecal collection on day 10 of the latter groups, and repeated 6 days later.

Dosages: Control water; albendazole 3.5 mg/kg bw, sc; ivermectin 0.2 mg/kg bw, sc; moxidectin 0.2 mg/kg bw, sc;  Levamisol 5 mg/kg bw, sc plus triclabendazol 10 mg/kg bw, oral; Trichlorfon 50 mg/kg bw, oral.

5.2. What does having a large RANGE or a “STANDARD DEVIATION” greater than the MEAN for the group indicate?

· Some animals have cero counts and others extremely elevated counts.  In general, mature animals with a good plane of nutrition will develop acquired immunity with prolonged exposure and will be either resistant to infection (very low counts) or resilient (high counts with apparently no clinical consequence).  In this case, the animals were sorted into five treatment groups according to fecal egg counts that were done 2 days earlier.  The five animals with highest egg counts were placed randomly, one in each group, and so on until the formation of the five groups.  The same was repeated until all groups had been formed such that they all began the test with a very similar average number of egg counts. 

5.3. What drug/s still maintain efficacy?

· Moxidectin reduced FEC by about 75%, and trichlorfon only attained a 39% reduction.  According the FAO guidelines (FAO, 2004), when efficacy is below 90% there is resistance.  Moxidectin is the only drug that may reduce a clinically significant infection and at this point (because resistance is building up) it should be reserved as a rescue drug for heavily infected animals.      

5.4. List 3 general mechanisms of resistance that explain why antiparasitic drug lose their efficacy?

• · Inability to bind at the action site,
• · Increased metabolism,
• · Decreased penetration

5.5. Why is the oral route preferred over parenteral for most anthelmintics (ie., benzimidazoles)? Why should the drug be deposited with a balling gun in the back of the mouth? Or fast the animal overnight?

· All these questions are related to enhancing the efficacy of the anthelmintic.  Animals grazing lush green pasture with very high water content have much faster gastric transit of digesta (=quick flow) and this leads to lower drug availability and reduced efficacy against GI nematodes (Ali and Hennessy, 1993).  Fasting overnight will prolong residence in the GI and the overall bioavailibity of the drug.  Depositing the drug over the tongue prevents it from reflex closure of the esophageal groove that could dispense the drug into the abomasum and not the rumen (Zajac, 2006).  Going directly into the abomasum will significantly reduce both, the overall amount of drug that will be absorbed, and time present are therapeutic concentrations.   

5.6. How can you prolong the lifetime of dewormers?

· TST – “Targeted Selective Treatment” – Treatment of only those animals that will most benefit from treatment, leaving the rest of the flock or herd untreated. Worm numbers in sheep and goats are not uniform across members of the flock or herd with approximately 70-80% of the worms found in only 20–30% of the animals; the majority of the animals have relatively low worm burdens. TST strategies are directed toward the animals that are clinically affected by parasites, those animals most susceptible to disease, or those that are likely to contaminate the pasture the most. Examples of criteria that can be used to selectively choose animals for treatment include anemia (the FAMACHA© system); thin body condition; reduced live weight gains; elevated worm egg counts in feces; and below average milk production.

5.7. List some options to implement an Integrated Parasite Management

• ·Rotate with cattle or start grazing together.  
• ·Introduce new forages with activity against roundworms
• ·Use innate immunity: introduce resistant breeds in the flock (St Croix, Kathadin)
• · Resting periods that will break the cycle of the parasite.   

For further strategies to break the parasite cycle watch some webinars from University of Maryland at: http://www.sheepandgoat.com/recordings.html  on Integrated Parasite Management (by Susan Schoenian)

5.8. In this case, what recommendation would you provide to address the poor body conditions of the animals?

• · start by analyzing pasture for nutrients (TDN, protein, Ca, P),
• · separate animals according to nutritional needs
• · supplement to reach condition scores of 3-4, 
• · provide adequate feeder space.

References:

Ali DN and Hennessy DR (1993) The effect of feed intake on the rate of flow of digesta and the disposition and activity of oxfenbendazole in sheep. International Journal of Parasitology 23(4):477-484.

Thompson J, and Meyer H (1994) Body condition scoring of sheep. Extension Service, Oregon State University, Corvallis. (http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/14303/ec1433.pdf)

FAO 2004. Module 2. Helminths: Anthelmintic resistance, diagnosis, management and prevention. Guidelines Resistance Management and Integrated Parasite Control in Ruminants. FAO, Roma, p.78-118.

Shoenian Susan. University of Maryland.  http://es.slideshare.net/schoenian/integrated-parasite-management-ipm-in-small-ruminants

Zajac AM (2006)  Gastrointestinal nematodes of small ruminants: lifecyle, anthelmintics and diagnosis. Veterinary Clinics of North America. Food Animal Practice 22:529-541