Stuart E. Knapp

Biology of Nanophyetus salmincola and 'salmon poisoning' disease.

Publisher Summary The digenetic trematode Nanophyetus salmincola (Chapin) is the vector for Neorickettsia helminthoeca, a rickettsia-like organism that causes “salmon poisoning” disease (SPD). The disease is usually fatal for dogs, foxes, and coyotes. Nanophyetus s. salmincola ( N.s. salmincola ) requires multiple hosts for completion of its life cycle. The first intermediate host is the pleurocerid stream snail, Oxytrema silicula. The second intermediate hosts are salmonid and some non-salmonid fishes and the Pacific giant salamander in which the cercariae encyst. The definitive hosts are fish-eating birds and mammals. The chapter reviews several aspects of SPD. Some of them are (1) geographical distribution, (2) etiology, (3) transmission, (4) symptoms, and (5) pathogenesis and pathology. The treatment of SPD is also reviewed. Various sulfanilamides given orally or parenterally have been successful in the treatment. Dosage at therapeutic blood levels should be maintained for at least 3 days. Effective results have also been obtained with penicillin, chlortetracycline, chloramphenicol, and oxytetracycline. The best results follow administration of large divided doses. If the animal is dehydrated, intravenous fluid therapy is essential to avoid nephrotoxic effects. Treatment in the late stages of the disease may not be successful.

Detection of Fasciola hepatica in infected intermediate hosts using RT-PCR.

Fasciola hepatica, the common bile duct fluke, is an economically important parasite of domestic livestock. Current research interest is directed toward an understanding of the parasites biology at the intermediate host level. To permit study of seasonal transmission patterns and parasite/intermediate host interactions, a fasciolid-specific assay has been developed to detect infected snail vectors. This assay uses the reverse transcriptase-polymerase chain reaction (RT-PCR) to amplify specifically a region of F. hepatica small-subunit rRNA, followed by hybridization to an F. hepatica-specific probe. The assay does not cross-react with 2 trematodes outside of the Fasciolidae but does detect Fascioloides magna rRNA. Sequence alignment with additional small-subunit rRNAs shows Fasciolopsis buski would also cross-react with the assay. The detection limit of the assay is 10 fg of fluke total RNA with 5 micrograms of snail RNA added as background. Additionally, the assay detects individual infected snails immediately after miracidial exposure and throughout the parasites development period.

A NUCLEIC ACID-BASED TEST FOR DETECTION OF FASCIOLA HEPATICA

The use of nucleic acid techniques in the diagnosis of parasitic infection has become increasingly widespread. An oligonucleotide probe derived from a rRNA sequence was developed for the detection of Fasciola hepatica in its intermediate snail host Pseudosuccinea columella. Total RNA obtained from whole adult liver flukes was used in a polymerase chain reaction to isolate and amplify a region of approximately 650 base pairs in the small subunit rRNA. This portion of the ribosomal cDNA, which contains highly conserved regions as well as variable regions, was subcloned and sequenced. In comparison to known small subunit rRNA sequences, a sequence unique to F. hepatica was identified and an oligonucleotide probe (CS4) for detection of F. hepatica was developed. A northern blot analysis using CS4 successfully identified small subunit rRNA from F. hepatica. Slot-blot analysis determined that RNA derived from 5 miracidia can be detected with CS4. Moreover, a slot blot utilizing CS4 distinguished RNA derived from snails infected with F. hepatica from RNA of uninfected snails.

RELATIONSHIP OF DIFFERENT SPECIES OF FORAGE TO THE SURVIVAL AND INFECTIVITY OF HAEMONCHUS CONTORTUS IN LAMBS.

Third-stage Haemonchus contortus larvae that had been placed on outdoor forage plots in December survived overwinter and were ineffective for lambs the following May. The plots were 8 ft square and each consisted of one of the following species of forage: perennial ryegrass, velvetgrass, red clover, alsike clover, subterranean clover, and white clover. Four replicates of each forage species were used in the first experiment and six in the second. One helminth-free lamb grazed each plot for 18 consecutive days. All lambs contained adult Haemonchus at necropsy except the controls which had grazed on noninfested plots. Enough parasites were present in some animals to produce a significant decrease in their packed cell volume. Highest numbers (means) of adult worms were recovered from lambs which grazed white clover and subterranean clover.. The grass groups contained the lowest numbers of parasites. These results suggest that greater numbers of third-stage H. contortus larvae will overwinter and retain their infectivity if they are on forage species which have heavy dense growth characteristics rather than on forages which have an open, sparse type of growth. Larval behavior on different plant species is discussed. A comprehensive review on the survival of free-living stages of Haemonchus contortus by Kates (1950) indicates that freezing temperatures and desiccation are primary factors in the survival of free-living stages of this parasite. Only a few studies have indicated the influence different species of forage might have on survival of preparasitic nematode larvae. Furman (1944) found that free-living Ostertagia circumcincta larvae could survive the entire summer on irrigated pasture in northern California. He also reported that in the summer months, irrigated ladino clover was more favorable to nematode survival than irrigated alfalfa or ryegrass. A report by Pullar (1953) indicated that development of free-living larvae may be aided by pasture plants with broad horizontal leaves which conserve surface

Fascioloidiasis in Game-ranched Elk from Montana

The distribution of Fascioloides magna in game-ranched elk and the potential for spread of the parasite through movement of infected animals was examined in Montana (USA). Fecal samples (n = 448) collected from captive elk on 29 game ranches were examined for eggs of F. magna by fecal sedimentation. Eggs were detected in elk on 5 ranches. This suggests that F. magna has been translocated by infected game-ranched elk. The wide distribution of snail intermediate hosts for F. magna in Montana indicates a potential to spread the parasite to other captive cervids, domestic livestock or free-ranging wildlife.

Prevalence of Eyeworm in Three Populations of Columbian Black-Tailed Deer in Northwestern Oregon

ABSTRACr: Populations of black-tailed deer (Odocoileus hemionus columbianus) from 3 geographic locations representative of habitat types in northwestern Oregon were sampled in fall, 1971, to determine the presence of the nematode eyeworm (Thelazia californiensis). Geographic locations included were the Willamette Valley floor, foothills bordering the valley, and within the Coast Range. Only individuals within the population inhabiting the valley floor were infected with eyeworm. Eyeworms were found in 21 of 64 (32.8%) deer examined. Prevalence of infection was proportional to increased age of individual deer examined. Among mature deer, females were more frequently infected than males (P < 0.05). No adverse effects related to eyeworms were observed in any of the infected animals.

Range of heartworm (Dirofilaria immitis) infection in Montana dogs

The serological presence of heartworm in dogs of Montana was studied in a 3-yr survey. Serum samples were provided by veterinary practitioners throughout Montana or were submitted to the state diagnostic laboratory. Sera from 3,490 dogs were tested using an enzyme-linked immunosorbent assay (ELISA) for circulating adult heartworm antigen. Twenty-four serum samples were positive for heartworm antigen. Two were from dogs that had never been outside the state. Nineteen additional positive dogs, 7 of which presumably had never been out of the state, were reported through correspondence with veterinary practitioners. Because suitable vectors for Dirofilaria immitis exist in Montana, there is potential for propagation of heartworm.

SUSCEPTIBILITY OF CATTLE TO AN ISOLATE OF Dictyocaulus viviparus FROM BLACK-TAILED DEER*

Patent infections did not develop in calves after inoculation with Dictyocaulus viviparus infective larvae isolated from black-tailed deer (Odocoileus hemionus columbianus). One calf died of bacterial pneumonia on postinoculation day 21. Two calves coughed and had elevated respiratory rates and dyspnea between days 14 and 21. Respiration was normal for these calves on day 25. A calf and a susceptible black-tailed deer were placed on contaminated grass pasture with eight deer infected naturally with D. viviparus. Patent infection did not develop in the calf but larvae of D. viviparus were recovered in feces from the deer on post-exposure day 30.

TREATMENT AND CONTROL OF Dictyocaulus viviparus IN CAPTIVE BLACK-TAILED DEER*

An outbreak of dictyocauliasis among a captive herd of black-tailed deer fawns (Odocoileus hemionus columbianus) occurred in January, 1971. A transient decrease in output of Dictyocaulus viviparus larvae in feces occurred after treatment with levamisole hydrochloride given as a drench at the rate of 16 mg/kg of body weight. Lungworm larvae were not recovered in feces 6 days after cambendazole, 2-(4-thiazolyl)-5-isopropoxycarbonylaminobenzimidazole, was given as a drench at 40 and 50 mg/kg of body weight. Larvae were again recovered in feces from these fawns between post-treatment days 15 and 23. Output of larvae in feces increased when fawns were confined on a contaminated grass pasture that was intensively grazed. Deteriorating physical condition of the fawns necessitated additional treatment with cambendazole and movement to a woodlot where reinfection by ingestion of larvae was probably minimized. A noninfected deer was placed on the contaminated pasture 75 days after the infected herd was removed. After 55 days, lungworm larvae were recovered in feces from this deer. Then 29 days later, 20 fawns were placed on this pasture. Four of six of these fawns that were subsequently necropsied harbored light burdens of D. viviparus. Small numbers of lungworm larvae were recovered in feces from five of eight remaining fawns.